400E ‘92 400E ECU Help

[brann]

Hello everyone!

I purchased a ‘92 400E with 192k miles on it 4 or 5 months ago. I am fairly young and it’s the first car I’ve ever owned that’s older than I am. I have virtually zero mechanical experience but bought the car because I love how it looks but also with the intention of teaching myself how to work on it, since I also have a w204 C63.

I have lurked here for a while and have a million different questions but am going to try to keep this as short, on topic, and simple as possible. I purchased the car for about $1500 and have driven it something like 2000mi without any significant issue. While it’s been good to me, I feel that I can tell something is about to slip and am trying to prevent that from happening. It’s running differently than before and leaking too much oil/power steering fluid.

When I purchased the car, it came with a spare ECU not installed, I was told it is the OEM Bosch ECU (part # 012 545 30 32). I just removed the black ECU cover for the first time and it appears all 4 different modules are also OEM as they all say Bosch and/or have Mercedes logos. From what I have gathered here and elsewhere, the bottom or innermost module is the one that was replaced for the sake of ‘tuning’. The part number on the installed module is (014 545 15 32). I have attached a picture of this and the one in my hand is the spare one I was provided.

Essentially, my question is: which ECU I should be running to ensure optimal engine performance? The car currently runs but does not sound or feel super healthy. The engine bay has been caked in oil and power steering fluid since I purchased the car and I am just trying to take preventative measures to ensure it remains running as long as possible. I will get to correcting the leaks as quickly as possible.

All help and advice is very much appreciated. I am not mechanically inclined but I am eager to learn and will do my best to understand everything to the fullest extent.

Thank you all for your time!

 

[gsxr]

Congrats on the new car!

012-545-30-32 and 014-545-15-32 are functionally equivalent, both are correct for your 1992 400E. The later (014-) part number replaced the earlier (012-) module. There's a decent chance one or both of those need the capacitors inside replaced. If the fuel pump relay clicks rapidly at idle, that means the capacitors have definitely failed. Click here for details on a forum member that offers a capacitor replacement service that is very reasonably priced. No "tuning" of any kind is possible for these ECU's. There's an EPROM available that increases the redline slightly along with increased top speed limiter, but neither are useful for USA street-legal speeds.

You should really pressure wash the front of the engine to remove as much of the caked oil & grime as possible. If you are leaking power steering fluid, the most common leaks are the short hose below the reservoir to the pump, and the low pressure S-shaped return hose to the frame rail. Sometimes the front shaft seal on the pump leaks. All are DIY repairs, not a big deal, just messy and time consuming. Search the forum for details on these jobs.

Engine oil leaks are often from the cam advance solenoids (click here) and that's another item to add to your list. The P/S reservoir has to come off to remove the driver side solenoid, so you can bundle the jobs together if you can afford to have the car out of service for a few days to a week.

I assume there were no service records and you have no maintenance history. If so, eventually you should pull the valve covers to inspect the chain rails... expect to find several broken. It's a BIG job to replace the chain rails. Not a lot of cost in parts, but a ton of hours (like, 10-20 hours for a 1st-time DIY'er). Search the forum for info on this as well. The chain itself (and tensioner) almost never need replacement.

You'll need to provide more info about what you mean, "runs but does not sound or feel super healthy". Check the caps & rotors, and cut the extra vent slots as shown in this thread. And, learn how to check fault codes... get a hand-held blink code reader if you don't already have one. Details are in the sticky threads of this subforum.

Welcome to the forum!

 

[brann]

Congrats on the new car!

012-545-30-32 and 014-545-15-32 are functionally equivalent, both are correct for your 1992 400E. The later (014-) part number replaced the earlier (012-) module. There's a decent chance one or both of those need the capacitors inside replaced. If the fuel pump relay clicks rapidly at idle, that means the capacitors have definitely failed. Click here for details on a forum member that offers a capacitor replacement service that is very reasonably priced. No "tuning" of any kind is possible for these ECU's. There's an EPROM available that increases the redline slightly along with increased top speed limiter, but neither are useful for USA street-legal speeds.

You should really pressure wash the front of the engine to remove as much of the caked oil & grime as possible. If you are leaking power steering fluid, the most common leaks are the short hose below the reservoir to the pump, and the low pressure S-shaped return hose to the frame rail. Sometimes the front shaft seal on the pump leaks. All are DIY repairs, not a big deal, just messy and time consuming. Search the forum for details on these jobs.

Engine oil leaks are often from the cam advance solenoids (click here) and that's another item to add to your list. The P/S reservoir has to come off to remove the driver side solenoid, so you can bundle the jobs together if you can afford to have the car out of service for a few days to a week.

I assume there were no service records and you have no maintenance history. If so, eventually you should pull the valve covers to inspect the chain rails... expect to find several broken. It's a BIG job to replace the chain rails. Not a lot of cost in parts, but a ton of hours (like, 10-20 hours for a 1st-time DIY'er). Search the forum for info on this as well. The chain itself (and tensioner) almost never need replacement.

You'll need to provide more info about what you mean, "runs but does not sound or feel super healthy". Check the caps & rotors, and cut the extra vent slots as shown in this thread. And, learn how to check fault codes... get a hand-held blink code reader if you don't already have one. Details are in the sticky threads of this subforum.

Welcome to the forum!

Thanks so much for the very thorough response, I have spent months reading your replies/threads and am honored! I’m relieved to hear the two ECUs are practically interchangeable as I was led to believe it had some sort of aftermarket ECU. I will absolutely start with everything you listed, thank you again.

Funny enough, I just finished pressure washing/scrubbing the front and bottom of the engine last night and it’s looking much better. Took me a full week to get it in clean, manageable shape. I did that with the intention of pinpointing the source of the oil leak but haven’t been able to thus far today. In full transparency, I also don’t exactly know what I’m looking at when inspecting the various hoses and rubber lines, much less everything else. The terminology is something I’m still working on so forgive me.

I could tell something was wrong and it “does not sound or feel super healthy” a few weeks ago when my radar detector powered down due to “low power” and the blinker indicator started to flicker while the car was being driven. This led to me inspecting the alternator (still OEM it appears) and finding it caked in oil/black gunk. It also stutters quite a bit at high RPM before shifting when I put the accelerator on the floor, even before the pedal clicks.

The serpentine belt appears to be getting coated in P/S fluid as well as oil from an undiscovered location and it flings both fluids everywhere, resulting in everything along the front of the engine being covered in a mixture of the two. The oil leak seems to originate from the bottom half of the engine or the timing covers, I’m not exactly sure. The top of the oil pan had something like a 1/2” of gunk build-up before I washed it.

When I started the car to move it after cleaning the engine bay last night the P/S wasn’t working very well and the battery light was on, which I’ve never seen before. I’ve been letting the engine bay dry ever since and have been too scared to start it today. Is it possible I got water into the electrical system? That’s what I’m most worried about at the moment.

Apologies for the information dump. I love this car and only want to drive it mildly with confidence.

Edit: Attached a photo for added context!

Edit 2: I also do have the original service manual which is dated to the first 100,000mi, signed from the ‘90s. I have nothing from that point to now however, unfortunately.

 

[gsxr]

Water won't hurt anything, EXCEPT if you got the ignition system wet (distributors, spark plug wires, etc). This will eventually dry out. Once dry, it should be back to normal (where "normal" is, what it was doing before it got wet).

The battery light on the cluster indicates the alternator isn't charging. If everything has dried out and you still have this problem, first remove the voltage regulator (make sure to disconnect the battery first!). If you are lucky, just the regulator is worn out and a new one will cure it. I *think* you can do this without pulling the alternator off the engine, but I forget... haven't done this in forever.

Removing the alternator is a bit of a PITA, you may need to remove the sway bar (not fun), and miiiight need to pull the fan clutch / fan shroud (even less fun, special tools needed). Definitely get the charging system sorted out first. Should be right around 14.0 volts at the battery with the engine running. If the slip rings inside the alternator are excessively worn, or if you have a failed diode or bearing, you'll need to replace the alternator. If that's the case I'd consider looking for a good used 143A-150A unit as an upgrade (or rebuilt, if your budget allows). The stock 110A unit was kinda borderline for this application.

Monitor the P/S fluid level in the reservoir. It should never drop. If the level drops, you definitely have a P/S leak somewhere (and, it's very likely you do). As mentioned above, it's not expensive to fix, just messy. Also take a look at the steering box output shaft, it should be 100% dry. If not, you may have a P/S leak from the output shaft seal - again, not expensive to fix. The HOW-TO thread has all the info you need.

Now that the engine is clean(er), you may be able to figure out what engine oil leaks you have. There may be several. The front crankshaft seal is another common leak. The seal isn't expensive, but once again, it's a lot of work - and, some special tools are needed. Lots of info in this thread.

If you don't already have a link to the factory service manuals (FSM)... click here.

 

[brann]

Water won't hurt anything, EXCEPT if you got the ignition system wet (distributors, spark plug wires, etc). This will eventually dry out. Once dry, it should be back to normal (where "normal" is, what it was doing before it got wet).

The battery light on the cluster indicates the alternator isn't charging. If everything has dried out and you still have this problem, first remove the voltage regulator (make sure to disconnect the battery first!). If you are lucky, just the regulator is worn out and a new one will cure it. I *think* you can do this without pulling the alternator off the engine, but I forget... haven't done this in forever.

Removing the alternator is a bit of a PITA, you may need to remove the sway bar (not fun), and miiiight need to pull the fan clutch / fan shroud (even less fun, special tools needed). Definitely get the charging system sorted out first. Should be right around 14.0 volts at the battery with the engine running. If the slip rings inside the alternator are excessively worn, or if you have a failed diode or bearing, you'll need to replace the alternator. If that's the case I'd consider looking for a good used 143A-150A unit as an upgrade (or rebuilt, if your budget allows). The stock 110A unit was kinda borderline for this application.

Monitor the P/S fluid level in the reservoir. It should never drop. If the level drops, you definitely have a P/S leak somewhere (and, it's very likely you do). As mentioned above, it's not expensive to fix, just messy. Also take a look at the steering box output shaft, it should be 100% dry. If not, you may have a P/S leak from the output shaft seal - again, not expensive to fix. The HOW-TO thread has all the info you need.

Now that the engine is clean(er), you may be able to figure out what engine oil leaks you have. There may be several. The front crankshaft seal is another common leak. The seal isn't expensive, but once again, it's a lot of work - and, some special tools are needed. Lots of info in this thread.

If you don't already have a link to the factory service manuals (FSM)... click here.

You’re the man dude, thank you.

It’s definitely leaking a bunch of P/S fluid. Before I topped the reservoir off (when it was empty/low on fluid) I would hear the P/S pump struggling when I turned the wheel but now I seem to hear it the whole time the car is running, regardless of touching the wheel. The leak drips onto the belt and onto some hoses below before dripping onto the floor. Directly beneath the P/S reservoir.

I’ve been worried the constant noise I’m hearing is actually the oil pump since the oil pressure gauge has been behaving abnormally ever since I cleaned the engine bay the first time, but it certainly sounds just like the P/S pump in noise and location (not sure where the oil pump is). Given my lack of education I’m not exactly sure how the pressure gauge should be behaving and finding that out here and elsewhere has been a bit difficult. My urge to think wishfully just points to the change in temperature versus the Summer, I live in the desert about 100mi outside of Vegas. I think it used to be pegged at 3 the whole time it was running and now it mostly sits around 0 once the engine is warm and being driven, but 3 for a while after a cold start. Might bounce up to 2 on the occasional acceleration.

I started the car yesterday after letting it dry for about 2 days and the battery light was off and everything seemed fine aside from some scentless ‘smoke’ emitting from the engine bay which I hope was just steam. It went away after 10mins or so.

The battery is practically brand new. It measures 12.54V while the car isn’t running and ~12.29V while it is. To my knowledge this almost definitely implicates the alternator but I’ve also seen some threads about the voltage regulator you mentioned, so I’m hoping that is the issue. Despite the measurement on my multimeter the battery dash light has remained off.

Would the lack of dash light point more to the regulator than the alternator by chance? Thanks for all your time.

 

[gsxr]

You should fix the PS leak ASAP. It's not particularly difficult and not expensive, just VERY dirty / messy, and tedious. Very, very likely that most of your leak is from the short hose between reservoir and pump. You'll need to clean this up and see if the pump front seal is leaking or not - if so, do everything at the same time. Note that your 1992 engine has a manual belt tensioner... this is a bit tricky to R&R. Take pictures of the position of the linkage rod & washer if you remove it or you'll have fun figuring out how to put it back. Also, DO NOT overtighten it when installing. Err on the looser side (2nd mark, not between 2nd and 3rd). FSM docs are here.

The oil pressure gauge should be at zero with engine off. On cold start it will go up to 3 and stay there. As the oil reaches operating temp (which takes longer than coolant reaching operating temp), the gauge should be around 1.0-1.5 at hot idle. But it should never be at zero. 95% of the time, the sending unit has failed. Replace with OE/Genuine, or OEM Hella/VDO, only. Something like $75 and not too difficult to replace. There's a slight chance the gauge reading could be wonky if your lower harness is failing, but that's a big job to repair. Replace the sender first and see what happens. Click here for the HOW-TO writeup.

And yep, 12.3v with the engine running indicates the alternator not charging. This is PROBABLY because the alternator failed (specifically, the voltage regulator probably died). There's a slight chance a failing lower harness could be causing a problem. Unfortunately, there's no way to verify without removing the alternator. Get the alternator out and take it to your local McParts/FLAPS, they will test it for free. If it tests good, then I would dig into the lower harness repair. If it tests bad, you can either replace with a standard rebuilt unit (110A), or upgrade to a 143A-150A unit. Click here for the HOW-TO writeup on the alternator R&R.

 

[brann]

You should fix the PS leak ASAP. It's not particularly difficult and not expensive, just VERY dirty / messy, and tedious. Very, very likely that most of your leak is from the short hose between reservoir and pump. You'll need to clean this up and see if the pump front seal is leaking or not - if so, do everything at the same time. Note that your 1992 engine has a manual belt tensioner... this is a bit tricky to R&R. Take pictures of the position of the linkage rod & washer if you remove it or you'll have fun figuring out how to put it back. Also, DO NOT overtighten it when installing. Err on the looser side (2nd mark, not between 2nd and 3rd). FSM docs are here.

The oil pressure gauge should be at zero with engine off. On cold start it will go up to 3 and stay there. As the oil reaches operating temp (which takes longer than coolant reaching operating temp), the gauge should be around 1.0-1.5 at hot idle. But it should never be at zero. 95% of the time, the sending unit has failed. Replace with OE/Genuine, or OEM Hella/VDO, only. Something like $75 and not too difficult to replace. There's a slight chance the gauge reading could be wonky if your lower harness is failing, but that's a big job to repair. Replace the sender first and see what happens. Click here for the HOW-TO writeup.

And yep, 12.3v with the engine running indicates the alternator not charging. This is PROBABLY because the alternator failed (specifically, the voltage regulator probably died). There's a slight chance a failing lower harness could be causing a problem. Unfortunately, there's no way to verify without removing the alternator. Get the alternator out and take it to your local McParts/FLAPS, they will test it for free. If it tests good, then I would dig into the lower harness repair. If it tests bad, you can either replace with a standard rebuilt unit (110A), or upgrade to a 143A-150A unit. Click here for the HOW-TO writeup on the alternator R&R.

Hey @gsxr hope you’re doing well. I’m just now getting to the things we discussed in this thread and was hoping you can provide a bit of further direction. I am going to attempt to replace the voltage regulator and fix the P/S leak as I believe the car will become drivable once again if I do both correctly. I understand I may need to replace the whole alternator but will cross that bridge when I get there.

The P/S leak is so severe that the reservoir is now completely empty after letting the car sit for a few months. I understand you believe the leak is likely to be stemming from the short hose between pump and reservoir but I cannot seem to figure out how to definitively pinpoint this. I plan to just replace as many gaskets and seals as possible without dropping the motor or disconnecting the radiator hose but I can’t seem to pinpoint the location of the leak or a tutorial on how to access these locations without some serious engine bay digging.

My questions are basically:

Does fixing the P/S leak necessitate the removal of the belt? If so, how do I make sure I don’t somehow mess up the tensioner? I know you mentioned marking the tensioner in a specific way to alleviate possible difficulty in reassembling it but I don’t really have a full understanding of this. I need a new belt anyway and imagine I’ll have to do this belt removal again if the alternator does indeed need to be replaced.

Given that replacing the alternator is a possibility, should I try replacing the voltage regulator before I dig into the P/S problem? To pinpoint whether or not a new alternator is needed?

I found a video on replacing the P/S reservoir-to-pump hose, reservoir filter, reservoir gasket, and skinny silver (return?) pipe O-ring (not sure what this pipe is called/for). This was helpful to visualize possible locations of the leak but I’m not sure how to proceed with the motor and entire P/S system still in the engine bay. Is it even possible for me to do so?

Any help or input you’re willing to provide would be endlessly appreciated. In investigating this P/S area, I also saw a small bit of oil, which you can see in the attached photo. I’m unsure from where this might implicate an oil leak but figured I’d include the photo as you’ll certainly know much better than me. Checking the dipstick, the oil level still seems to be great despite there being at least 12 months since the last oil change, likely quite a bit longer.

Thank you again for all your time.

Edit: attached another photo showing the bottom of the P/S system where it is leaking the green P/S fluid.

 

[gsxr]

My questions are basically:

Does fixing the P/S leak necessitate the removal of the belt? If so, how do I make sure I don’t somehow mess up the tensioner? I know you mentioned marking the tensioner in a specific way to alleviate possible difficulty in reassembling it but I don’t really have a full understanding of this. I need a new belt anyway and imagine I’ll have to do this belt removal again if the alternator does indeed need to be replaced.

Sorry for the late reply! I was out of town most of the past 2 weeks and got behind on, well, everything.

Fixing the P/S leak does require belt removal. Take some pictures of the tensioner assembly before you touch anything, follow the FSM procedure, and when you remove it pay CLOSE attention to the position / location of the spacer behind the tensioner. Reassemble in the same way. Make sure to set belt tension before tightening the large center bolt which locks the tensioner in place (and, loosen before making any adjustments, then re-tighten, etc.)

Given that replacing the alternator is a possibility, should I try replacing the voltage regulator before I dig into the P/S problem? To pinpoint whether or not a new alternator is needed?

Pretty likely the alternator is bad, however, a defective lower wire harness could potentially cause a good alternator to not charge. Best option here is to remove the alternator and bring it to your local McParts/FLAPS where they will test it for freeeeee, and try to sell you a new alternator. If the alternator tests OK, your lower harness is the next suspect to investigate. If the alternator fails the test, you can bring it home, swap the VR, bring it back and test again. Alternator R&R isn't fun and also requires belt removal. Sway bar removal provides easier access to drop the alternator out the bottom. This is a good time to replace worn sway bar bushings (get OE/Genuine bushings only, not aftermarket).

I found a video on replacing the P/S reservoir-to-pump hose, reservoir filter, reservoir gasket, and skinny silver (return?) pipe O-ring (not sure what this pipe is called/for). This was helpful to visualize possible locations of the leak but I’m not sure how to proceed with the motor and entire P/S system still in the engine bay. Is it even possible for me to do so?

That video showed how to do it on the workbench, but the same applies on the car. You only need to remove the reservoir. Then remove the pipe nipple from above. Space is tight, I'd also drain the radiator so you can remove the upper radiator hose to make more room to work. However, if the pump is leaking from the front shaft radial seal, you should reseal the entire pump. The front seal is pretty much the ONLY place the pump will leak from, although in rare cases the top plate O-ring can leak (usually on Vickers/LUK pumps, not ZF, due to the design differences). If the front shaft seal is totally dry you can probably leave it alone.

Any help or input you’re willing to provide would be endlessly appreciated. In investigating this P/S area, I also saw a small bit of oil, which you can see in the attached photo. I’m unsure from where this might implicate an oil leak but figured I’d include the photo as you’ll certainly know much better than me. Checking the dipstick, the oil level still seems to be great despite there being at least 12 months since the last oil change, likely quite a bit longer.

Oil at the lower edge of the valve cover as shown in your photo is most likely from the valve cover gasket itself... however, it could possibly be from leaking cam advance solenoids? You'll need to de-oil the area completely (ideally, remove the plastic shrouds, carefully - those are all NLA). Then drive the car and watch where the oil appears from.

Edit: attached another photo showing the bottom of the P/S system where it is leaking the green P/S fluid.

Green oil is almost always from the PAG oil in the air conditioning system, usually indicating a leak from the AC compressor front seal. Do you have any other green fluids? Factory P/S fluid is gold/light-brown color, although red ATF can also be used in the P/S system. Antifreeze should be yellow/gold if it's the original G-05 (blue G-48 is also ok). Hopefully you don't have green antifreeze, if so, flush the entire system (remove both block drains) and flush/refill with G-05 or G-48.

 

[brann]

Sorry for the late reply! I was out of town most of the past 2 weeks and got behind on, well, everything.

Fixing the P/S leak does require belt removal. Take some pictures of the tensioner assembly before you touch anything, follow the FSM procedure, and when you remove it pay CLOSE attention to the position / location of the spacer behind the tensioner. Reassemble in the same way. Make sure to set belt tension before tightening the large center bolt which locks the tensioner in place (and, loosen before making any adjustments, then re-tighten, etc.)




Pretty likely the alternator is bad, however, a defective lower wire harness could potentially cause a good alternator to not charge. Best option here is to remove the alternator and bring it to your local McParts/FLAPS where they will test it for freeeeee, and try to sell you a new alternator. If the alternator tests OK, your lower harness is the next suspect to investigate. If the alternator fails the test, you can bring it home, swap the VR, bring it back and test again. Alternator R&R isn't fun and also requires belt removal. Sway bar removal provides easier access to drop the alternator out the bottom. This is a good time to replace worn sway bar bushings (get OE/Genuine bushings only, not aftermarket).




That video showed how to do it on the workbench, but the same applies on the car. You only need to remove the reservoir. Then remove the pipe nipple from above. Space is tight, I'd also drain the radiator so you can remove the upper radiator hose to make more room to work. However, if the pump is leaking from the front shaft radial seal, you should reseal the entire pump. The front seal is pretty much the ONLY place the pump will leak from, although in rare cases the top plate O-ring can leak (usually on Vickers/LUK pumps, not ZF, due to the design differences). If the front shaft seal is totally dry you can probably leave it alone.




Oil at the lower edge of the valve cover as shown in your photo is most likely from the valve cover gasket itself... however, it could possibly be from leaking cam advance solenoids? You'll need to de-oil the area completely (ideally, remove the plastic shrouds, carefully - those are all NLA). Then drive the car and watch where the oil appears from.



Green oil is almost always from the PAG oil in the air conditioning system, usually indicating a leak from the AC compressor front seal. Do you have any other green fluids? Factory P/S fluid is gold/light-brown color, although red ATF can also be used in the P/S system. Antifreeze should be yellow/gold if it's the original G-05 (blue G-48 is also ok). Hopefully you don't have green antifreeze, if so, flush the entire system (remove both block drains) and flush/refill with G-05 or G-48.

No worries whatsoever, I appreciate you replying at all! Hope your time out of town was well spent.

From your previous comments and other examples of general consensus on here, I’ve been assuming (also wishfully hoping) that the voltage regulator is most likely the source of the electrical issue as opposed to the alternator itself. Have you changed your mind regarding this for some reason? I was told by the previous owner that the wiring harness had been replaced but I wouldn’t be entirely surprised if that was not true. It’s also possible he was talking about the upper as opposed to the lower.

I am using this very helpful thread to guide me through the power steering issue regarding the process and the parts to order. I’m not sure if @RicardoD ‘s vehicle is directly comparable to mine in parts, model year, etc. but I’ve been relying on AutohauzAZ’s internal system to verify if the parts will work for me and it hasn’t indicated otherwise thus far (not sure how much faith to put in them). I do now definitely know my PS pump is ZF.

Regarding the green fluid, that is just the color of the Prestone Power Steering fluid I’ve been adding to keep the car halfway drivable. I had to add it in a pinch as it was the only recommended fluid available at my local Autozone and the car was completely dry. The reservoir is now completely empty as the car has been sitting for several months, leaking in my garage.

I think I am going to order all the P/S reservoir seals and gaskets as well as a new voltage regulator and am going to lead with replacing the latter first since, as I understand, the alternator does not need to be removed in order to do so. I’ll see if this corrects the electrical issue but am going to assume it will not. In either case, I will then dig into the PS leak, draining the coolant and removing + replacing the serp. belt in the process as the current one is definitely on its last leg. During this, if replacing the VR failed to fix the issue, I’ll remove the alternator and have it tested in order to determine whether or not the wiring harness is the issue. Replacing the alternator if the test puts it at fault.

I only outline this with such detail to see if you believe there is any flaw in the efficiency of my approach. I’d also be open to replacing other components if I’m already doing half the work in getting there, I’m just not sure what those components might be (water pump?). I know you mentioned sway bar bushings so I will definitely add this to the list, I am just curious if there are any others off the top of your head, so long as they don’t require above average understanding.

Thanks as always.

 

[gsxr]

From your previous comments and other examples of general consensus on here, I’ve been assuming (also wishfully hoping) that the voltage regulator is most likely the source of the electrical issue as opposed to the alternator itself. Have you changed your mind regarding this for some reason? I was told by the previous owner that the wiring harness had been replaced but I wouldn’t be entirely surprised if that was not true. It’s also possible he was talking about the upper as opposed to the lower.

Almost everyone only inspects / replaces the upper harness. The lower harness is ignored / never noticed, as it doesn't affect engine running most of the time. I'm still suspecting the VR as the top candidate, but the lower harness is a possibility too. If the upper harness has been done, that's great, one less thing to worry about.

I am using this very helpful thread to guide me through the power steering issue regarding the process and the parts to order. I’m not sure if @RicardoD ‘s vehicle is directly comparable to mine in parts, model year, etc. but I’ve been relying on AutohauzAZ’s internal system to verify if the parts will work for me and it hasn’t indicated otherwise thus far (not sure how much faith to put in them). I do now definitely know my PS pump is ZF.

E500E's have tandem pumps - different part numbers, different seal kits, vs the 400E P/S pump. Otherwise much of the work is the same. ZF P/S pumps uses seal kit 000-460-47-80, which is NLA from MB, but there are aftermarket kits available.

Regarding the green fluid, that is just the color of the Prestone Power Steering fluid I’ve been adding to keep the car halfway drivable. I had to add it in a pinch as it was the only recommended fluid available at my local Autozone and the car was completely dry. The reservoir is now completely empty as the car has been sitting for several months, leaking in my garage.

Ah, got it. After you get the system leak free you might want to change that out for the original stuff which is light brown in color, although the Prestone may be cromulent.

I think I am going to order all the P/S reservoir seals and gaskets as well as a new voltage regulator and am going to lead with replacing the latter first since, as I understand, the alternator does not need to be removed in order to do so. I’ll see if this corrects the electrical issue but am going to assume it will not. In either case, I will then dig into the PS leak, draining the coolant and removing + replacing the serp. belt in the process as the current one is definitely on its last leg. During this, if replacing the VR failed to fix the issue, I’ll remove the alternator and have it tested in order to determine whether or not the wiring harness is the issue. Replacing the alternator if the test puts it at fault.

I only outline this with such detail to see if you believe there is any flaw in the efficiency of my approach. I’d also be open to replacing other components if I’m already doing half the work in getting there, I’m just not sure what those components might be (water pump?). I know you mentioned sway bar bushings so I will definitely add this to the list, I am just curious if there are any others off the top of your head, so long as they don’t require above average understanding.

Sounds like a good plan! Water pumps generally last the life of the car - they'll usually start to leak when they fail. If the t-stat is old or of unknown age, replacing with a new OEM Behr/Mahle is a good idea. Pics here. Make sure to get the 116- part number, the 119- number is used on later engines.

The P/S reservoir has to come off for the cam solenoid reseal project - while this is a lot of work, I'd consider bundling those jobs together so you never have to pull the reservoir again. Details in this thread.

 

[brann]

Hey @gsxr and others, hope you all are well!

I started writing a brand new thread but it very quickly became wordy and probably a bit overwhelming to read. I think I’ll end up writing a couple threads or one big one to help anyone else who is in a similar position to myself but I’d rather not post in the wrong place or provide information that could be deemed redundant. Everything is brand new to me but these things may be obvious to everyone else.

My current issue is fairly straightforward: removing the alternator led to me disconnecting the lower radiator hose, which completely drained the radiator. Despite making a huge mess, I caught a decent amount of the liquid that came out in a bucket and it is a yellow/gold color that looks a bit lime green under the right lighting.

Since this coolant is what was in the car when I bought it, I have no idea which brand or type it is. I at least figured out it’s the same color as Zerex G05 so I bought 2 gallons of it. It was only afterwards that I realized it being yellow does not guarantee it is the same and I became worried about mixing it in with the coolant that is still in the car as I read about the dangers of mixing two different coolants.

I poured a small amount of the new G05 into my drainage bucket and could discern no visible or chemical changes to the contents of the bucket—this is what the below photo shows. It looks to me like I added in more of the same stuff but I’m also not sure what it would look like if it were not more of the same stuff. Hope that makes sense.



I’ve been reading on here about what a pain and mess it is to drain coolant from the block of these older ‘92 year cars so I’m trying to avoid doing so if possible. Not only that, but I’m having a very difficult time figuring out where the two drain plugs even are. I know their general vicinity but am not quite sure what I’m looking at once I’m actually underneath the car. I assume I’ll need to order and replace the two crush washers in order to do so as well, which means more days spent waiting for them to arrive, unless it’s possible they’re available at Mercedes or a local parts store.

Do you guys think I should just add the G05 to the expansion tank until it’s full and call it good? Or is this too risky and the only wise move is to completely drain and flush the system? As always, I greatly appreciate the help and input.

 

[gsxr]

Photo below shows 1992 block drain location on passenger side. Looks the same on the driver side. Flat-head plug with hex/Allen socket head, I think 6mm IIRC?

If you don't know when the coolant was last replaced, it would be a good idea to drain the block and flush both the radiator and block with a garden hose to rinse everything out. Then refill with a 50/50 mix of G-05 (premix before you refill). System capacity is ~13 quarts total but you may only get 9-10 quarts in, the rest is hiding in the heater core and hoses. Fill the block via the upper radiator hose first (about 4 quarts) then connect the hose to the radiator, and fill the radiator via the expansion tank. A new OEM thermostat (Behr/Mahle) is a good idea as well if the age is unknown.

If you don't want to do this now, you can refill with water temporarily and wait a few weeks / months, just make sure you are back to 50/50 mix before Utah winter and freezing temps.

 

[brann]

Photo below shows 1992 block drain location on passenger side. Looks the same on the driver side. Flat-head plug with hex/Allen socket head, I think 6mm IIRC?

If you don't know when the coolant was last replaced, it would be a good idea to drain the block and flush both the radiator and block with a garden hose to rinse everything out. Then refill with a 50/50 mix of G-05 (premix before you refill). System capacity is ~13 quarts total but you may only get 9-10 quarts in, the rest is hiding in the heater core and hoses. Fill the block via the upper radiator hose first (about 4 quarts) then connect the hose to the radiator, and fill the radiator via the expansion tank. A new OEM thermostat (Behr/Mahle) is a good idea as well if the age is unknown.

If you don't want to do this now, you can refill with water temporarily and wait a few weeks / months, just make sure you are back to 50/50 mix before Utah winter and freezing temps.

View attachment 239066

Thank you for the very quick reply! I think I am almost certainly missing something here but I just can’t seem to locate the drain plug as it’s shown in your photo, unless I need to remove components in order to see or access it. They seem much higher up on the engine block than how it appears to me but I just took some photos of the two areas to show you what I’m seeing.

I circled the only two 6mm hex bolts that I can find, but they seem much too low to correspond to your reference photo. Do I need to look higher up?

 

[gsxr]

Yup, you need to look higher up, and further back! They are behind the engine mount brackets.

 

[brann]

Yup, you need to look higher up, and further back! They are behind the engine mount brackets.

View attachment 239069 View attachment 239070

Roger that, I will do some more digging and may opt to go the distilled water route in the meantime as I need to start the car in order to test my previous work.

I wound up having to completely remove the sway bar and the alternator in order to access the voltage regulator. I tested the alternator before and after replacing the regulator and it passed the test both times, doing only marginally better after replacement.

I’m embarrassed it took me this long to realize, but a couple weeks prior to when my electrical issue started I had swapped out the old Interstate H8 battery for an unused battery my father happened to have sitting in his garage for a couple months. This new battery was a NAPA AGM battery rated at 800CCA, 80Ah and 140RC. It never occurred to me this battery may be too small and could be the actual source of my electrical issues.

Could a battery of this size be the culprit of low running voltage and surging RPMs when idling? Or should I now focus my attention on the lower harness? The car would always run fine for a bit after charging the battery in my garage but this would be short-lived. I will likely replace the battery for an H8 either way.

 

[gsxr]

Battery size should not be an issue, although a proper Group 49/H8 is preferred. If the battery has enough power to start the car, it won't affect running or charging while the engine is running.