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LH Module?

kre8tive202

kre8tive202

E500E Enthusiast
Member
Hello everyone,

I apologize ahead of time if I am asking a question that has already been answered. So I have a 1992 Mercedes 500E, a couple weeks ago the car developed a weird knocking noise under the car centralized around the middle of the car. It sounded as something was getting knocked around under the floor board. Long story short, I thought it was my fuel pumps or fuel pump relay going bad. So I started out by changing the relay. I thought I fixed it but after letting the car sit, it started making that weird noise again. So I pull over get under the car and I hear a definite pulsating through the fuel lines under the driverside rear seat and I can hear a knocking inside the fuel tank if I go into the trunk. In the moring I have a hard time cranking the car to start. but once its started its fine through out the day. Is my LH module bad? if so where can I get one?

Thanks,
Mario
 
Are you sure it's not the fuel pump relay clicking? Remove the rear bottom seat cushion on the passenger side when the problem occurs, see if the green fuel pump relay is clicking. If so, your LH module is bad. If you need one, I may have a replacement, shoot me a PM with your current module number.

If the noise is occurring and it is NOT the relay clicking... you'll need to do some more diagnosis to figure out the source of the noise!

:detective:
 
kre8tive202 said:
It was clicking last night. But all day today I cant replicate the clickijg its running like a champ
Click to expand...
If the relay was clicking, the LH module is the cause of the problem. It seems to be worse when the car (actually, LH module) is cold, it may go away at higher RPM's and/or when warmed up. Pretty likely it will happen again at the next cold start. Keep an eye on it and see what happens.

:bbq:
 
Could the LH module going bad explain the hard starts in the mornings. I have to crank it two to three times before the car starts. but after teh morning start, its fine throughout the day. Oh how hard is it to R/R the LH module.
 
It's possible, but the hard start could also be related to the fuel pressure regulator, or fuel pump issues. With the relay clicking, I'd probably start with the LH and go from there...

:5150:
 
I had already ordered two fuel pumps, I will be replacing those tomorrow. I ordered them before I found out it could be a LH module issue.

gsxr said:
It's possible, but the hard start could also be related to the fuel pressure regulator, or fuel pump issues. With the relay clicking, I'd probably start with the LH and go from there...

:5150:
Click to expand...
 
If there's a fuel pressure issue, more likely to be regulator than pumps. Generally you can listen and hear if pumps are working OK. It's a whirring sound that emanates from behind the passenger side rear wheel.
 
I can definitely hear the pumps working, I thought maybe they were on the brink. Is there anyway to test the fuel pump regulator. Would a faulty regulator explain my hard starts in the morning.
 
After 20+ years, replacement fuel pumps are a good idea for preventive maintenance. At least then you shouldn't have to worry about them for another 20+ years. I've already had a couple go bad... the ethanol blend foisted upon us by EPA probably isn't helping any.

:wormhole:
 
You would need to stick a fuel pressure gauge on the fuel rail and start the engine, and then stop it and see how fuel pressure bleeds off compared to the MB spec.
 
I have seen pictures of where the regulator sits. How hard is it to get too. I am away from home and want to change it, the local auto parts store has it in stock but they want $85.00. Can I get to it without any tools?

gerryvz said:
You would need to stick a fuel pressure gauge on the fuel rail and start the engine, and then stop it and see how fuel pressure bleeds off compared to the MB spec.
Click to expand...
 
You need to remove the airbox on top of the engine to access the FPR. It's right there on top of the engine. You will need a pair of snap-ring pliers to get the circlip off, and then the regulator pulls right out with some effort. You will need a couple of rags handy to catch spilled fuel. It is best to do this job when the system is not pressurized, so in the morning or after the car has sat at least 4 hours.

Also this Bosch part is available for around $35-40 from online sources, such as AutohausAZ.com. I would order it through there (and orders above $75 have free shipping) so combine it with other things you need.
 
Ok guys so the car did it again after letting the car sit for 4 hours. The fuel pump relay is clicking (its brand new). I got looked under the car and the fuel rails under the driver side is pulsating making the thumping sound. So is this the FPR or LH. Module. Hey what does LH. Stand for
 
Clicking relay is the LH module.

The hard start could be totally unrelated - hard to say for sure. If a new LH module makes the clicking go away and you still have the hard start, then I'd replace the FPR next.

:watermelon:
 
Ok so I ordered a new FPR and should be here in a couple days. I am also working on buying an LH from one of the forum members. I am hoping that the FPR will solve my issue but its a long shot as i definitely hear my relay clicking. you guys think its safe to drive the car until then? The pulsating and clinking diminishes and goes away after the car warms up. Is R/R the LH module a DIY?
 
Replacing the FPR absolutely will not cure the clicking relay.

LH module is plug & play, just make sure the key is off when swapping, and make sure the module is FULLY seated when installing.

:mushroom1:
 
kre8tive202 said:
I am hoping that the FPR will solve my issue but its a long shot as i definitely hear my relay clicking. ?
Click to expand...

FPR and relay clicking are not related! As Dave said, clicking will stop if you replace LH module, FPR replacement should solve starting issue..

Oops! Dave beat me to it already .
 
Don't forget to clear codes on the replacement LH module, AND also reset the adaptation, after installing.

:matrix:
 
kre8tive202 said:
How do I do that? Help
Click to expand...
You need either a digital scanner that will communicate with LH systems, or you need a hand-held blink code reader. This has been discussed several times elsewhere on the forum...

:cel:
 
kre8tive202 said:
Does anyone know if the LH module can be repaired?
Click to expand...
There was a thread that described replacing all the capacitors on the circuit board. If you are handy with soldering components on circuit boards, it would be worth a try, just keep in mind that if you screw it up, you'll still need to buy a replacement module.

:jelmerian4:
 
I am handy but thats a repair that I would not feel comfortable doing myself

Sent from my SAMSUNG-SGH-I747 using Tapatalk
 
Ok so here is my dilemma keeping me from pulling thr trigger from buying the LH. The hard starts and click in of the relay started simultaneously. Are you guys sure that a clicking relay is due to a bad LH

Sent from my SAMSUNG-SGH-I747 using Tapatalk
 
Funny (well not really) that this is a current thread as I am pulling my hair out with my LH module right now too. The one that came in the car was bad and I have subsequently tried two now from an eBay seller with the 2nd being yesterday and sure enough as soon as the we started the car the fuel pump relay (which we already replaced) starts clicking profusely. So we pull it out and throw a spare LH out of a '93 we had lying around and problem solved (well except for it is a '93 LH). Anyways so I am really scratching my head at this point as in doing some research it sounds like the consensus is that the capacitors that were used to make these things were garbage and time / use is just finally catching up with them. Therefore rather than keep trying to find used ones that work I would like to try and find an outfit that can just repair mine. I found this website this morning ( http://mandbspecialist.com/mercedes-electronic-parts-repair.php ) and sent them an email. Hopefully they will respond to me Monday or Tuesday and can help but in the interim if anyone else has any luck with any specialist electronics repairs shops and could send me or post their info I would appreciate it. Lastly and this is probably a question best for Dave or Gerry but worst case scenario and I need to try to find another used one that works are there any compatibility issues between the various part numbers I need to be worried about? The one that came in the car has a Bosch part # 0 280 002 532 / MB A 014 54517 32 and when I checked EPC this morning I found that is lists A 014 54518 32. The two other ones I have purchased and tried are a Bosch # 0 280 002 512 / MB A 012 54562 32. Obviously given that my car is already a '92 I want to stick with one that has WOT enrichment but I just wanted to confirm the different part numbers were not contributing to the problem in any way.
 
Last edited:
Ok well being that my problems happened concurrently I am gonna hold off until I get that FPR in but I think my problems are far from over as I am still anticipating a clicking relay problem will continue. Can someone remind me again how much the horse power difference us between a wot vs non wot?

Sent from my SAMSUNG-SGH-I747 using Tapatalk
 
Ok so here is an update my thumping of the fuel lines goes away and so does the clicking. If anything it is so slight of a clicking but i need to pull the seat to hear it. So I am really wondering why the two issues are married to each other.

Sent from my SAMSUNG-SGH-I747 using Tapatalk
 
The relay clicking is turning the fuel pumps on/off/on/off rapidly, which is likely causing the thumping in the lines. Dyno graphs of the WOT module vs non-WOT (on 93-94 engines) are here.

Eric, a different part number won't cause clicking... the clicking is due to the failed module, which MAY be fixed by replacing the capacitors. I suspect any place that claims to "rebuild" them is simply replacing the electrolytics and then charging you a fortune for it.

:scratchchin:
 
Ok here is an update guys. I got my FPR regulator today. I didnt have to option of putting it in prior to having to use the car, but the R/R was very straight forward. I figured out though that the PO did not take much care in making sure that he didnt lose the clips that hold down the airbox. So I will be looking to make that a project soon.

I definitely took a gas bath did not anticpate that there would be that much pressure under the FPR. I no longer have a thumping sound coming from the fuel lines, and hot starts are very quick. I will hope that my cold start in the morning improve. The relay clicking is still there so I bought Patrick's LH module with out the WOT for now as money is tight. I hope to get the LH module and complete fixing my fuel delivery issues. You guys are definitely spot on with your diagnoses, thank you again. Just out of curiousity do they still sell LH modules with WOT new?
 
Well I think I spoke to soon. I got to work let the car sit for 5 hours, and when I went to go start her up....well it took three tries. The knocking is still gone which is a plus. Do you guys think that when I change out my LH module it will fix the cold start issues?
 
kre8tive202 said:
Just out of curiousity do they still sell LH modules with WOT new?
Click to expand...
Yes, about $3200 list, $2500 parts.com. Same price as the later modules without WOT enrichment. :spend:


kre8tive202 said:
Well I think I spoke to soon. I got to work let the car sit for 5 hours, and when I went to go start her up....well it took three tries. The knocking is still gone which is a plus. Do you guys think that when I change out my LH module it will fix the cold start issues?
Click to expand...
It is very unlikely that replacing the LH module will fix the cold start issue. If the cold start problem continues, the next thing I would do is connect a fuel pressure gauge, and verify you are getting proper pressure at the rail. If there is good pressure and the engine STILL doesn't want to start, it's not fuel pressure related...

:scratchchin:
 
kre8tive202 said:
I got new fuel pumps should I install them?

Sent from my SAMSUNG-SGH-I747 using Tapatalk
Click to expand...
Probably a good idea, yes, assuming you got new Bosch. If they are off-brand / no-name, I would not use them. Pinch off the supply hose from the tank or you could get a 20-gallon bath, which isn't the safest thing. Good time to replace the fuel filter as well.

:wormhole:
 
I had exactly the same problem 2 months ago. I felt "metal ticking noise" under the car + the relay.


I changed the LH module and solved the problem. Thanks to Gsxr and this forum.



Sent from my iPhone using Tapatalk
 
I am waiting for my LH module to arrive. As soon as it gets here, I will update everyone. I am also changing out my fuel pumps and fuel filter.

Sent from my SAMSUNG-SGH-I747 using Tapatalk
 
Patrick just got it. Thanks again. Now its time to get it into my car and get rid of that ticking .

Sent from my SAMSUNG-SGH-I747 using Tapatalk
 
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