M104 holds back under load

[tintinmt]

Hi, I have a 300TE 24v (M104). It has a long standing issue whereby it seems to hold back (I hesitate to say misfire) under load e.g. pulling from a standing start or going uphill. In common with many of these W124 running issues many parts have been replaced but failed to give a long term solution. The car has new plugs, leads and distributor cap & rotor arm plus coils. I have had the car professionally 'repaired' on three occasions and each time the cure works for a week or two and then the fault returns. This includes replacing the distributor cap twice in the last 18 months. Recently, after many tests were carried out apparently, it was diagnosed as a broken wire on the camshaft position sensor (repaired) however the fault is now back.
The fault only occurs at full engine operating temperature. It seems to me that the offending item is maybe being disturbed during investigations but then subsequently fails again.
Otherwise all is good
Any ideas please?

 

[grober]

EZL ignition unit on the way out? They fail as they heat up. You could try renewing the heatsink paste between it and the wing. Servisol High Thermal Conductivity Heatsink Compound | Maplin This might help temporarily which might help pinpoint the fault if its the EZL starting to fail. It involves a couple of bolts some heatsink paste and half an hours work.

 

[tintinmt]

Would this be the EZL? (attached)

 

[grober]

Not taken at a very good angle but yes that's it. Make sure there is no corrosion underneath on the inner wing surface .

 

[spanner]

I've just had a car in with exactly the same symptoms and it was the EZL.

 

[tintinmt]

Hi Spanner, What did you do? Repair or replace?
Cheers, M.

 

[spanner]

Replaced.

 

[tintinmt]

Did you replace with new? What was the cost please?
Thanks, M.

 

[tintinmt]

I bought some heat sink compound and removed the EZL. See attached. It certainly did not look 'dry' but was a bit dirty. I cleaned off the old paste.There seemed to be a thin plastic film (like cling film) between the paste and the wing. Should I replace this somehow?
Cheers.

 

[grober]

Pretty sure that's there on the unit when new to preserve the heatsink paste. Normally heat sink paste is sandwiched between 2 metal surfaces to improve conduction. However the manual reads as follows. [ see below] I would be inclined to give the wing area a gentle clean up and replace the unit complete new heatsink paste and the old film if there's any left. Don't think the film has any electrical insulation function if that's what you are worried about.

here's a thread about it. It has the first pictures of the inside of one of these units I have seen.
http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1591615-anyone-opened-failed-ezl-before.html

 

[neilrr]

I've got a few 300-24 EZL units (W124, R129, W140) should anyone need.

PM me with your current part number.

 

[tintinmt]

I applied the new compound. The tube was quite small but I spread the material out with a spatula and it seemed to give adequate coverage. I then covered the underside with cling film to stop the compound attaching to the bodywork and put it back into position trying to be careful not to touch the compound against the various obstacles. It all went back together and the car started fine. It ran well on a road test and after reaching operating temperature seemed to idle better than before. Only time will tell....

 

[w124nut]

Glad that it appears to be the solution to the problem.

Please give us an update in a couple of weeks time on how it's going and if there have been any problems.

 

[WG M-B]

I find that the cal will usually cause cutting out issues

 

[tintinmt]

cal?

 

[grober]

Here's the "how to" translated from German
https://translate.google.co.uk/tran...%A4rmeleitpaste_und_Folie_erneuern&edit-text=

 

[tintinmt]

Unfortunately, the 'hold back' fault still persists. I am back to thinking about fault codes on the engine management. Does anyone have the codes specifically for chassis number 124091 engine 104980 please?

 

[spanner]

The engine codes on that model will tell you very little. You need to find another EZL that you can borrow (preferably from a known good runner) and install.

 

[tintinmt]

That would be nice! It's just that it is giving a blink code and I'm not sure what it's supposed to mean - even if it's not true.

 

[ray_hennig]

The car has new plugs, leads and distributor cap & rotor arm plus coils.

It's a good thing to replace the heatsink compound under the EZL but I don't think these symptoms sound like an EZL issue.

I see you have new HT components - what make did you get? These engines demand the best.

Have you measured the fuel duty cycle? Search "KE Jetronic duty cycle" on the web and invest in a forty quid multimeter with duty cycle measurement - try RS, Farnell or maybe even eBay for the meter.

Duty cycle should fluctuate around 50% when the system is warm and responding to input from the O2 sensor. If not, adjust it, as described in loads of places. Difficult adjustment and drifting often implies vacuum leaks that you should also solve.

Whether this is your problem or not, I don't know. But having the ability to make this measurement and to get it right will be of great use.

Bonne chance from Paris.

RayH