400E Mysterious rough running

[400Benz]

Hello all,

As of the past two weeks i have been chasing this issue on my daily driver 92’ 400E to no avail and would greatly appreciate some support. So far it seems nobody has been curse with this problem on this forum(hopefully)



Problem:

only under warm conditions my idle is unstable but not hunting, smell of unburnt fuel apparent it is running rich and until anything more than a tap of the throttle it stutters and nearly/does stall. Yet reads about ~600 from the gauge cluster. This happens Typically after about 10 mins or so, not necessarily when it hits 84C. It also has the same but worse effects of stutters and stalling when in gear, over about 1700 the running seems normal and smooth but in gear at roadspeed can bog under more than light throttle.



So far i have installed: New Coils, New Distributors, New CKP, New FPR, Newer CTS(from November), Spare EZL(ran the same) My wiring harness is rebuilt, and has been running since a year ago last week when i finished my engine rebuild.

I have unplugged the MAF, Unplugged FPR, unplugged EGR, do not hear any vacuum lines undone. Fuses in the module box are good, everything is seated. Connector for ETA vacuum set.

My timing is not hitting the marker is needs to be out additionally, about a few degrees to the driver fender when its having its issues.
Currently i am suspecting i will need a replacement ETA as mine is original, but i am suspecting maybe it is the vacuum lines i believe 8mm running under the driverside distributors as i read in another forum.

Additionally attempting to reset the ETA seems promising, albeit not sure if it will provide a difference. I am in college so saving money so i can eat is nice. The past year with this 034 has been very cheap as opposed to a lease on a newer car.

Here are some codes i reset I assume come from this issue, since have been reset and have not returned yet issue remains. Other additional codes are from past repairs I didn’t wipe(cam sensor)
I also have running data stream numbers if that could help. Currently waiting on confirmation for a rebuilt eta on ebay 000 141 78 25

 

[400Benz]

 

[gsxr]

Problem:

only under warm conditions my idle is unstable but not hunting, smell of unburnt fuel apparent it is running rich and until anything more than a tap of the throttle it stutters and nearly/does stall. Yet reads about ~600 from the gauge cluster. This happens Typically after about 10 mins or so, not necessarily when it hits 84C. It also has the same but worse effects of stutters and stalling when in gear, over about 1700 the running seems normal and smooth but in gear at roadspeed can bog under more than light throttle.

What you describe are 100% classic symptoms of misfiring under load, due to moisture in the distributor caps AND/OR engine oil at the lower edge of the caps causing problems with the high voltage spark an inch or two away. First thing to do is cut extra vent slots into your new caps as shown here. Second thing is to remove both intake cam advance solenoids, and either replace them, or re-seal them as shown here.

So far i have installed: New Coils, New Distributors, New CKP, New FPR, Newer CTS(from November), Spare EZL(ran the same) My wiring harness is rebuilt, and has been running since a year ago last week when i finished my engine rebuild.

It's also possible you MAY have a defective new cap and/or rotor. This is not common, but can cause a lot of headaches when you assume the new parts are good. More than 1 person on the forum has reported new-in-box parts that ended up being defective and causing misfires. It happened to me.

My timing is not hitting the marker is needs to be out additionally, about a few degrees to the driver fender when its having its issues.

Not sure what you are indicating here. The crank position indicator is only used to check if the camshafts are out of time, which requires pulling both valve covers. That won't help with your misfire. Since you mentioned an engine rebuild, I assume you already have new chain rails installed AND verified the cam timing is ok.

Currently i am suspecting i will need a replacement ETA as mine is original....

The ETA cannot cause misfiring. Full stop. A bad ETA will cause dead cruise control, low idle speed, and on cars with ASR it will cause limp mode and other issues.

but i am suspecting maybe it is the vacuum lines i believe 8mm running under the driverside distributors as i read in another forum.

Make sure the 8mm tube is not leaking anywhere, AND also make sure the purge "MOT" valve is not stuck open. If so, disconnect the tube and plug it, otherwise you end up with a large vacuum leak that will cause other issues (but, will not cause misfiring under load as you describe).

Additionally attempting to reset the ETA seems promising, albeit not sure if it will provide a difference. I am in college so saving money so i can eat is nice. The past year with this 034 has been very cheap as opposed to a lease on a newer car.

There is no "reset" on the ETA, and it won't help your misfire. When a new/different ETA is installed, just leave the key on for about 1 minute to let the computer (T/LLR without ASR, E-GAS with ASR) recognize the different ETA.

Here are some codes i reset I assume come from this issue, since have been reset and have not returned yet issue remains. Other additional codes are from past repairs I didn’t wipe(cam sensor)

I'm not sure what scanner you are using, but I do not trust it. I'm not aware of any newfangled scanner that will properly show codes from these old OBD-1 cars. It could be displaying erroneous descriptions. Use a hand-held blink code reader to check / clear fault codes!! Details are in the sticky threads here. Wrong codes could send you chasing after all sorts of red herrings.

That said, if the "adaptation at limit" code is legit, you could have injection issues. Need to know what specific LH module is installed in your 400E, and if it has a non-stock EPROM / chip or not.

I also have running data stream numbers if that could help. Currently waiting on confirmation for a rebuilt eta on ebay 000 141 78 25

If that's your ETA part number, your 400E does not have ASR. Again, this won't help your misfire. If idle speed is normal (when not misfiring) and cruise control works ok, save your $$$ and skip the ETA replacement (for now).

Live data would help, again assuming it's accurate. Find the adaptation values for the LH and report what those are. See 2:08 in the video below for an example of what the values should look like (0.xxxx or 1.xxxx). If you have full live data including EZL, this will tell you which specific cylinders are misfiring (0:27in the video). I doubt your scanner will show EZL data.

 

[gsxr]

View attachment 231352

You have oil leaks that could be causing ignition problems. Near 100% probability the leak source is the intake cam advance solenoids.

 

[TerryA]

@400Benz,
To confirm what @gsxr said about the oil leaks take a look at the center electrode on your new distributor cap photo. It’s covered in oil!

Reseal or replace the cam advance solenoids and cut the additional slots in both distributor caps.

 

[400Benz]

What you describe are 100% classic symptoms of misfiring under load, due to moisture in the distributor caps AND/OR engine oil at the lower edge of the caps causing problems with the high voltage spark an inch or two away. First thing to do is cut extra vent slots into your new caps as shown here. Second thing is to remove both intake cam advance solenoids, and either replace them, or re-seal them as shown here.

I have overlooked the severity of even small amounts of oil, for in this picture it is after i wiped down the black plastic of the distributor housing underneath, that I thought “Okay maybe no evaporation under heat now”. Will test these two for certain, i swapped my distributors back and forth it no solution.

I was initially concerned about it but decided against when i saw my caps were dry plus my cam seal dry, especially since initially my passenger cam seal failed shortly after rebuilt due to my inexperience but second times the charm.

It's also possible you MAY have a defective new cap and/or rotor. This is not common, but can cause a lot of headaches when you assume the new parts are good. More than 1 person on the forum has reported new-in-box parts that ended up being defective and causing misfires. It happened to me.

This idea came to my head when my box of bosch distributors said “Made in Spain”. They seem to work great when cold but casting bubbles where they plug in and overall roughness on the rotor/action side

Not sure what you are indicating here. The crank position indicator is only used to check if the camshafts are out of time, which requires pulling both valve covers. That won't help with your misfire. Since you mentioned an engine rebuild, I assume you already have new chain rails installed AND verified the cam timing is ok.

By this i mean the photo of my timing mark was taken during the misfiring and under the light of a timing light and presented it out of place. Well to be frank i am sure it is supposed to be at the pin towards the left.

The ETA cannot cause misfiring. Full stop. A bad ETA will cause dead cruise control, low idle speed, and on cars with ASR it will cause limp mode and other issues.

Ok i hope to rule that out i will take it for a short drive and activate cruise control to test, it sounds/feels great normally in terms of operation.

I'm not sure what scanner you are using, but I do not trust it. I'm not aware of any newfangled scanner that will properly show codes from these old OBD-1 cars. It could be displaying erroneous descriptions. Use a hand-held blink code reader to check / clear fault codes!! Details are in the sticky threads here. Wrong codes could send you chasing after all sorts of red herrings.

That said, if the "adaptation at limit" code is legit, you could have injection issues. Need to know what specific LH module is installed in your 400E, and if it has a non-stock EPROM / chip or not.

Very true i borrowed it from a shop nearby that has a 38 pin attachment. Owner almost bought a Chinese replica of the Star software on a replica laptop but never went through with it. This shop scanner is definitely for newer toys for sure just what i have to use until i buy one of those laptops for Christmas. Yes i have put off buying/making a blink code reader, i really should not be disrespecting my car so much.

012 545 30 32 LH, I believe its a WOT unit as my car says its a 9/91 production date

If that's your ETA part number, your 400E does not have ASR. Again, this won't help your misfire. If idle speed is normal (when not misfiring) and cruise control works ok, save your $$$ and skip the ETA replacement (for now).

Live data would help, again assuming it's accurate. Find the adaptation values for the LH and report what those are. See 2:08 in the video below for an example of what the values should look like (0.xxxx or 1.xxxx). If you have full live data including EZL, this will tell you which specific cylinders are misfiring (0:27in the video). I doubt your scanner will show EZL data.

Okay thank you very much i was under the impression ETA but tbd when i test cruise control, revs great when warming anyways.

The scanner had a mention of adaptations i did not check as I assumed it was unrelated but i will check that and my scanner does not have EZL compatibility but i will see if maybe i missed that since I missed LH adaptation.

You have oil leaks that could be causing ignition problems. Near 100% probability the leak source is the intake cam advance solenoids.

Well thank you very very much for direction, ill try the Slots and check the Solenoids asap and report.

 

[gsxr]

This idea came to my head when my box of bosch distributors said “Made in Spain”. They seem to work great when cold but casting bubbles where they plug in and overall roughness on the rotor/action side

Bosch caps have been made in Spain for at least 10+ years. This is nothing to be worried about (and, Bosch caps are the preferred caps nowadays). Rotors should also be made in Spain.

By this i mean the photo of my timing mark was taken during the misfiring and under the light of a timing light and presented it out of place. Well to be frank i am sure it is supposed to be at the pin towards the left.

Forget the timing light, unless you have reference data from an engine running normally, you can't tell anything from this. And, nothing is adjustable for timing anyway.

Very true i borrowed it from a shop nearby that has a 38 pin attachment. Owner almost bought a Chinese replica of the Star software on a replica laptop but never went through with it. This shop scanner is definitely for newer toys for sure just what i have to use until i buy one of those laptops for Christmas. Yes i have put off buying/making a blink code reader, i really should not be disrespecting my car so much.

The nearby shop should have invested in the Star/SDS for use with Mercedes. All the aftermarket scanners have limitations, and on these early cars, make that severe limitations. I'm impressed it could pull any codes at all, but I still don't trust what it says. Shell out the $40 for the blink code reader and also get the breakout box that allows using numbered 4mm sockets. On a non-ASR 034, this gets you basically everything except live data.

012 545 30 32 LH, I believe its a WOT unit as my car says its a 9/91 production date

Yep, that is original / correct for a 1992 400E.

Well thank you very very much for direction, ill try the Slots and check the Solenoids asap and report.

Sounds good!

 

[400Benz]

Bosch caps have been made in Spain for at least 10+ years. This is nothing to be worried about (and, Bosch caps are the preferred caps nowadays). Rotors should also be made in Spain.




Forget the timing light, unless you have reference data from an engine running normally, you can't tell anything from this. And, nothing is adjustable for timing anyway.




The nearby shop should have invested in the Star/SDS for use with Mercedes. All the aftermarket scanners have limitations, and on these early cars, make that severe limitations. I'm impressed it could pull any codes at all, but I still don't trust what it says. Shell out the $40 for the blink code reader and also get the breakout box that allows using numbered 4mm sockets. On a non-ASR 034, this gets you basically everything except live data.




Yep, that is original / correct for a 1992 400E.




Sounds good!

Back to report!

Upon inspection I discovered this. Well well well, seems like exactly what you were speaking of @gsxr. I unfortunately did not have the time this weekend to do further diagnosis and pinpoint the leak to the actual magnets by removing the plastic covering, which is critical to actual progress! Nonetheless, i am looking into purchasing two new magnets as in the forum you attached it was advised to wait 48 for sealant drying for rebuilding and i would prefer to purchase a replacement and rebuild the originals as to add to my parts bin not to mention the issue of having my car immobilized for two days.


I did a “bandaid” test fix of installing my 1 year old distributor caps but now slotted and they solved my dying at idle as it seems it’s enough to let atomized moisture/oil to escape the caps.

Yes I intend on doing this to my new caps soon as these were for testing of my skills with a dremel.



Unfortunately I also discovered that my already totaled cats suffered from the rich running of my multiple diagnostic runs and are causing blockages where i can hear the sounds of it from underneath + different exhaust note and raspiness. I see magnaflow has a compatible California set for a small price of $1200… ouch. I am on fresh registration so i feel compelled to try and clear the blockage when i get access to a lift and use a hammer other tools for clearing the blockage for the time being until cough up the money.

 

[gsxr]

Bummer about the cats!

Remember that if you replace the cam solenoids with the new style, you also need to replace the armatures (they are slightly different), and the center bolt for the armature is a single-use that also needs replacement. The parts aren't expensive.