Can someone help with "Christine"? At wits end

[jondoel]

Desperately need some help from somebody who knows something about 500SLs.

Car:- 1994 500SL with 62,000 on the clock.

Problem:-

 Once warmed up (about 15 – 20 mins) car starts to cough and splutter, shudder, misfire, lose power and engine dies. Then it won’t start (only backfires if you try) until 30 – 40 minutes have passed, then it’s perfect for the rest of the day.
 Doesn’t matter what time of day
 This problem has been ongoing since March 2004

Work done to in connection with problem.

 Distributor caps and rotor arms replaced 18/03/04
 Crank position sensor replaced 07/03/06
 Coolant sensor replaced 06/04/06

OK for a couple of weeks then problem resumed.

 Ignition switch replaced 25/09/06
 Ignition module fitted 18/12/06 (second hand from S Class saloon)
 Throttle actuator function checked in December result 80% OK.

Ran OK for one trip to Yorkshire then back to the same old problem.

13/2/07 Mercedes Bromley ran a diagnosis but it showed there was no problem.

It broke down on the way home.

 

[AlisonH]

You could be describing the problem I had some years ago - but it wasn't a Merc that I had then. Mine finally turned out to be the coil, but by the time that was changed just about everything else had been, too!

 

[jibcl500]

ignition module £1000 from MB dealers, hard to find second hand and if you do find one £500-600

jib

 

[jondoel]

that's already been replaced...

 

[Parrot of Doom]

Sounds like too much fuel to me.

 

[jibcl500]

with a used part!!!! how longs a bit of string, ignition module common failure.

jib

 

[Uncle Benz]

First I will admit I am no expert on these, but the small experience I have of ignition modules on this model is that they operate as two seperate systems; each coil is run independently. ie. if a failure occurs, the car will run on one bank. Since he says the car dies completely, I would feel that the module is not the problem.

As I say, I am not an expert on this system, and I am sure someone else on here can throw more light on it....

 

[jondoel]

jib, the part checked out OK and the diagnostic ran clean. Could I be that unlucky and have two faulty modules in a row?

Maybe the coil? anyone?

 

[Uncle Benz]

There are 2 coils. Ignition system is duplicated. ie each bank runs independently. If a failure occurs on one side, the car will run on one bank. It will not stall though, so I don't think that is your problem. I again stress that I am no expert on these though. Have you looked at the wiring to the throttle valve on the middle of the vee?? often the insulation deteriorates badly under the outer binding.

 

[jibcl500]

http://pages.prodigy.net/jforgione/MB_DI.html

http://pages.prodigy.net/jforgione/MB_asr.html

have a look as these links. Once the engine has stalled does it restart straight away and run normally, do you have to leave it for 15 mins before it restarts.

jib

 

[jondoel]

yes I have to leave it for anything up to 50 mins before restarting then runs OK for the rest of the day.

 

[jibcl500]

Doesn't look like ignition module then, has the engine been pressure washed or steam cleaned recently,

jib

 

[jibcl500]

Actually on reflection I would say it is the ignition module, complex device, takes a lot of information from various sensors on the car, if you there are 5 connections to the module, it would only take one part of the module to fail to cause the problems you have.

is there anyway of swapping the module with someone just to try it.

jib

 

[jondoel]

Interesting links..

**UPDATE** 16/2

Ran the car in the drive for 20 mins then conked out. Waited 35 mins and it fired up fine and made a 60 mile journey no probs. Weird or what?

Jon

 

[50sflash]

Hi I would not rule out the air mass sensor or a fuel pump (I think there is two on this model) & fuel pump relay, When the car starts to misfire how long does it take to stall,? John

 

[50sflash]

Hi, just had another thought, I could be wrong but I think the 94 500sl 129 chassis had the same overload protection relay as the 94 e280 which can cause this problem, This relay is about £57. if you let me know the vin number I could tel you if it is fitted, John

 

[jondoel]

I discovered something else at the weekend - I started and ran it in the drive for 15 mins and as it started to miss and falter I kept the revs up at about 2000 for 10 mins which kept the engine alive and also warmed it up. Once a bit warmer, it smoothed out and the issue disappeared. It also restarted when I switched it off.

 

[SteveCassidy]

i'd go with the MAF

Personally, this sounds like my E55 when the MAF went. Might be the OVP relay, if there' sone in there - the W124's suffer from all kinds of gremlins because this half-fails, and it's a lot cheaper to get the uprated part swapped in than it is to speculatively change a MAF...!

 

[television]

All of the 124's have an OVP relay, normally the ABS lamp will come on when this is faulty, saying that the main problem with them is that they get bad soldered joints, maybe the voltage drops just a lttle under certain conditions.

The engine normally idles rough when faulty, though in the later cars the wiring is different.

With the OVP relay Pin 30 is the input 12v, and Pin 87's are the output and should have 12v also.

they can be fixed by blanket soldering the PCB.

malcolm

 

[alanthewes]

I had exactly the same problem. Is the car in daily use? If not suspect condensation in the distributor caps. Changing them does not help. Remove both, clean and spray in a bit of WD40 and give it a whirl. It cured mine for once and for all.