Knocking sound fuel lines/jittering idle pressure in fuel rail/bad idle

[RobertK]

Hello I am Robert from Almere in the Netherlands and the new proud owner of an blue black metallic 500E of 1993 since 3 weeks. This car has been imported from Japan
On the odo: it has been run 98k kilometres.

I have (for me) a hard to solve issue with this car:
At idle, you hear a knocking sound from the back of the car. The engine runs bad at idling in that case. The engine is shaking a bit.
When driving everything is fine. It pulls very strong. Only at idling you notice this knocking sound etc.

The wiring loom in the engine has been replaced for a new one already.

The following actions has been already taken to examine/solve this:

-The fuel relay renewed
-The fuel pressure regulator has been renewed.
-Both fuel pumps and valves renewed.
-Examined the pressure in the fuel rail on top of the engine: It shows a jittering 3.6-4 bar pressure instead of a stable 4 bar constantly during idle.
-Exchanged the LH Module with an other 500E of 1992. With the LH module of mine the other car runs fine at idle. My car with the other module gives the same result.
The same issue persist.

Do anybody know what the cause is of this issue ?

 

[nocfn]

Welcome and congratulations. Did you check all the vacuum connections and lines from front right fender to the manifold and airpump, ezl to the manifold /eta and up under driver windscreen to the manifold.

 

[RobertK]

Thanks,
You mean all the positions (vacuum connections) here in this drawing ?
I have to investigate these connections.

 

[gsxr]

Is the fuel pump relay is clicking? Pull up the rear passenger seat cushion and check.

 

[RobertK]

Yes, it is clicking indeed.

 

[Eno]

That means your LH module is faulty if I am not mistaken, I had the same issue a few years ago.

 

[RobertK]

Could be, but strange that exchanging the module's with an other 500E showed the same issue,.though we had not cleared the faulty codes in the memory only exchanged the module. I do not know what reset is required when you exchange modules.

Revision of the module by ECU.de could be the solution.

 

[r44raven]

I had the same problem recently with a clicking fuel relay=faulty LH module, but as far as I recall it didn't cause rough running at idle.

 

[Kyiv]

Robert, could please be more specific as to how bad the isle is? Clicking relay under back seat is a consensus of a bad LH module. But you say when your LH module is put on a different car there is no issue, correct?

My 400e has had a slightly shaky idle for 4.5 years/14k miles on 2 different LH module. I've had plugs/wires (correct type, 1mm gap), upper and lower wiring harness, both ignition coils, both fuel pumps, fuel filter, fuel pressure regulator, oxygen sensor, and MAF done. Probably something else, but I can't remember now. Supposedly no vacuum leaks, tested twice, but I don't know how properly vacuum tests were done. Still issue is there. Seems to be better in colder weather (less shake, practically none). I have full power and idle is much better once the car is driven. Been told by mechanics it could be a leaking injector - for what it's worth. The issue doesn't seem to interfere with car's drivability in over 14k miles and almost 5 years.

Be mindful before you throw parts at it and please clarify how bad your idle is and whether it improves one the car is driven

 

[RobertK]

Yes, but clicking of the fuel relay also occured on the other car with its own LH module and also on my car. So exchanging did not solve any issue.
To become more clear: the other car runs well with its own module and my module but has also a clicking fuel relay.

If the bad LH module only fix the clicking relay then I have probably more other problems to solve:
Knocking sound in the fuel lines together with bad idle (some "puffing" sound from the exhaust and a shaky engine which like running on 7 cilinders for a short time) Engine will not stop in that cases. I have full power too and only at idling this issues shows up.

We have measured a jittering fuel pressure in the fuel rail during that bad idle. Related to the clicking fuel relay probably ?

To become more clear: Sometimes the bad idling, but also the knocking sound is gone after half an hour driving. But in most of the cases not.

I think I have to start with a revision LH module. Then I have to look which problems will left over.

 

[Hakie]

I did not read about distributor caps, rotors and insulators? Did you inspect those?

 

[RobertK]

That is a good one and also measuring the ignition wiring. 1-2k Ohm should be good.

I have also send my LH Module to a specialized firm to test and repair eventually.

The vacuum hoses on top of the engine looks well. This should be tested in an other way, smoketest or something.

 

[Hakie]

Best to check caps and rotors. Dutch weather eats them. I always keep a spare set on the shelf.

 

[RobertK]

Good plan I will do that too.

 

[TimL]

Since about two weeks I've had the exact same symptoms occur in the circumstances you describe in your post, Robert.

My car received brand new wiring harnesses, as well as an LH Module 5 months ago at Mercedes Benz in Lynnwood The only thing that wasn't done back then were the caps and rotors, so it's in the shop right now to get that done. If I were you, I'd just start out with the caps and rotors and go from there (it's the least expensive of the bunch of repairs that people have outlined in their reply to your posts). Will let you know if the issue is eliminated once I get the car back later this week.

 

[RobertK]

Allright, I am curious about the result of it. But I think you do not have that knocking sound in the fuel lines I suppose, you have only bad idling ?
I think I have two problems.
Which new caps and rotors do you use ? The OEM from Mercedes ? (Bosch)

 

[Hakie]

I always order a set by eBay. Normally I use Bosch but last time I ordered a Bremi set. I don’t think there is a “better” one. Just search for a good deal and try them. In any case they don’t last more then 10-15 miles in my experience.
But search the forum on this subject. You find lots and lots of info.
I did caps and rotors on my 400E recently. It is in a project topic.

 

[samiam44]

Bosch is not the OE supplier of caps and rotors according to GSXR. asking, but doesn't the coil voltages go out of range when missfiring? I know I've viewed them using HHT live data before. Dang, don't remember how I got there....

 

[195910]

Bosch is not the OE supplier of caps and rotors according to GSXR. asking, but doesn't the coil voltages go out of range when missfiring? I know I've viewed them using HHT live data before. Dang, don't remember how I got there....

Interesting point, this could help identify a caps&rotor issue if we can confirm that this can be seen in the live data.
Lower voltage will cause the combustion time in each cylinder to change as well. But can anyone confirm that they have seen this on star? I doubt the system is quick/sensitive enought to detect it.

 

[TimL]

Allright, I am curious about the result of it. But I think you do not have that knocking sound in the fuel lines I suppose, you have only bad idling ?
I think I have two problems.
Which new caps and rotors do you use ? The OEM from Mercedes ? (Bosch)

It's in the shop at Mercedes Benz , so I assume they will put in whatever is the OEM component.

 

[gsxr]

Bosch is not the OE supplier of caps and rotors according to GSXR.

Bosch is the OE supplier for dealer caps and insulators, but Doduco is the OE supplier for dealer rotors. Rumor was in the past, the dealer Bosch caps/insulators had a clear coating applied, while the aftermarket Bosch items did not. However, I thought people were reporting in the last couple of years that the OE/dealer items no longer had the clear coating anymore? I'm not certain about this, but if so, it likely means the OE stuff may not be worth paying 2x-3x more. There were also some threads discussing buying a specialty, high-voltage clear coat spray to treat the aftermarket Bosch items yourself. The Doduco / OE rotors have the clear coating, btw.

Bremi has never been the OE supplier of any M119 ignition components. There is lengthy discussion on ignition part brands in older threads.

asking, but doesn't the coil voltages go out of range when missfiring? I know I've viewed them using HHT live data before. Dang, don't remember how I got there....

If you have access to live data, this is correct... the EZL / DI voltages displayed will spike on the affected cylinder(s) when there is a misfire. This is generally helpful for pinpointing a problem cylinder, or left vs right distributor.

 

[RobertK]

Checked rotors, caps and insulators and they are fine.
Awaiting the testresults of the LH Module

 

[Sam SL]

My car, when cold and especially when it hasn't run for days, has a knocking sound in the vicinity of under the rear seat on the passenger side. The noise goes away once car nears the '80' mark on the temperature which is usually 3-5 minuets after startup. I have not fully delve into the symptom but this thread caught my attention.

 

[TimL]

Checked rotors, caps and insulators and they are fine.
Awaiting the testresults of the LH Module

Ok, thanks for the note. Got my car back two days ago with new caps and rotors and the problem of rough idle and not accepting gas has gone away. Good look with your trouble shooting. Be interested to know what you end up diagnosing

 

[RobertK]

That knocking sound symptom started by me at the same way you describe Sam SL. First only at startup and with the time it becomes more often and now it is continiously at idle and sometimes in very rare situations it disappear.

@TimL
Nice that your problem has been solved ! You can enjoy driving your car again !

 

[RobertK]

I have feedback form ECU.de about testing and repair of my LH Control unit.
The technician said as follows in answer on my question which test results he had and if the detected defect(s) has correlation with the knocking sound in the fuel lines:

"On the test bench we were able to determine that the KSP relay is not being controlled correctly. The reason for this was defective components in the control unit -> internal cause.
What that has to do with the knocking in the fuel lines, unfortunately, we can not say clearly"

Does anybody know what the KSP relay is ? Probably airpump related ?

 

[RobertK]

I found the answer myself ☺
KSP stands for "KraftStoffPumpe" in English that means: Fuel Pump
So it could be related I think.

 

[nocfn]

So the LH module controls the fuel pump relay. Spare LH available? New fuel pump relay?

 

[RobertK]

Yes, but my LH module has been repaired and they will send it back to me. Hopefully I will get it tomorrow.

Fuel pump relay has already been replaced but that was not the solution for my problem.

 

[nocfn]

I may have mentioned it on this thread, too lazy to check but a recent dead battery issue for my Dad's 94 e420 turned out to be a toasted fuel pump relay (read that the relay was malfunctioning) was because power distribution from the LH was operating at will. Replaced LH and relay, problem solved. (in his case)

 

[RobertK]

Mmm..interesting I had in the beginning also two times a dead battery issue because of leaking voltage from a bad radio/CD player.
I only do not understand why this results in a toasted fuel pump relay and a broken LH Module as you describe.

 

[nocfn]

I am suggesting only with the reason behind the dead battery in my Dad's car. His specific issues were LH sending power to the fuel pump overnight, due to an issue with the LH circuitry. The relay was bad as a over-voltage issue and the LH was determined the fault for passing the battery voltage to the relay when it was not supposed to when the car was sitting with no key. The issue I described is for my experience, not to diagnose your issue or the radio problem that you mention. Clearly there is an electrical issue that you are experiencing. ymmv

 

[RobertK]

Allright I understand but it gives me some information about possible faults and effects of a bad working LH module.

 

[northNH]

Strictly regarding the fuel pump relay, the LH module simply functions as an on-off switch for the fpr by grounding one side of the tiny coil in the fpr (which similarly simply functions as an on-off switch for the fuel pumps). The module also supplies the voltage for the other side of the control coil in the fpr.
The supply voltage from the battery for the pumps is always present at the fpr and flows to the pumps when the ground signal from the LH triggers the relay coil to engage.

If the always-present battery voltage that supplys the pumps is "shorted" to that control negative lead from the LHm (LH #25 via fpr #3) due to internal fpr failure, it will short term drain the battery and long-term fry the LHm.

BTW no electronic control system on these complx cars simpler to diagnose/work-around than the one that controls the fuel pumps...
An on-off switch with alligator leads connected between terms 1 and 3 of the fpr receptacle will eliminate the need for the fpr and for LHm control, and allow entirely manual control of the fuel pumps.

Long enough leads on the switch and one doesn't need the fpr at all.
Or even a functioning part of the LHm that controls it...

 

[RobertK]

Thanks for the extended info about all the electrical concerning fuel pump, relay and LH module northNH.

Good news yesterday my repaired LH module has been back from Germany. I put it in and startup the engine.
The issue has gone, no bad idling or knocking sound anymore.

Everybody thanks for your info and help related to this issue.
500Eboard.com is a great forum !!

 

[nocfn]

Excellent news, and thank you for reporting.

 

[gerryvz]

We do appreciate the follow-up. Indeed, 99% of the time when there is a knocking sound, it has been a bad LH unit.

 

[RobertK]

Unfortunately I thought that I had found the voltage leakage by puting a new radio in the car. but I was two days away from home (with another car) and had parked the 500 E in my garage with the central doorlocking system on. I came back and the battery is dead ☹
I assume that there is only voltage leaking when the doors are (centrally) locked.

 

[gsxr]

You'll need to trace the source of the power drain using an ammeter. A clamp-type meter is easier but not required. Don't forget that a faulty 38-pin connector can cause a rapid power drain... there's a detailed thread on this.

 

[RobertK]

Thanks Dave for the attention to that thread. I recognize some symptoms which are mentioned: i.e. some weird behaviour of the fuel pumps when the ignition is off.
Examination of the connector and connectors and replacement should be neccessary by my car I think.

I will give feedback about the follow up.

 

[RobertK]

Added a photo of the connector.
Looks not good in my opinion. Pin 3 is very corroded.

 

[RobertK]

I think that 38-pin connector was the cause of the power drain. I have installed a new one and soldered a few new pins.
The pin connector was also very brittle.
Weird behaviour of the fuel pump has gone and I have no fast power drain anymore.

Thanks for your help guys !