R129 SL500 misfire

[gez]

I seem to have developed a fault where if I accelerate hard, she pulls OK to about 4000 to 4500 revs then feels llike I have hit the rev limiter and, if I keep my foot hard on the accelerator, stops pulling and slows down to about 3000 to 3500 revs, after which she misfires and runs rough, I assume not firing on all cylinders, but does not stall.

Turning the engine off and immediately back on cures the misfire and accelerating gently to speed is OK, but hard acceleration will recreate the problem.

Any ideas, hopefully inexpensive ones!? She's due for a service in 500 miles so ideal chance to have anything required checked.

 

[colechelle]

cap your caps and rotors for signs of arking, real common fault on them!!!!!

 

[kth286]

gez

Car is going into limp-home mode, so a significant fault is occuring.

Ensure only go to techs that can read the fault codes on your particular generation of car.

What year is it ??????????

 

[jibcl500]

if its 1995 onwards I say the air flow meters had it.

jib

 

[gez]

Thanks for the inputs guys.

It's a '98 with 57k on it.

I assume caps and rotors are easy to replace. What about the air flow meter, is this a simple diy job? I've seen references to only buying the Bosch product.

 

[jibcl500]

You dont have caps and rotors on that engine, MAF 100% get it from a Bosch agent as its half the price compared with MB.

DONT BUY ONE OFF EBAY FOR £50!!!!!!!!!!!!!

 

[colechelle]

You dont have caps and rotors on that engine, MAF 100% get it from a Bosch agent as its half the price compared with MB.

DONT BUY ONE OFF EBAY FOR £50!!!!!!!!!!!!!

you sure????? i changed a set on a 1999 129 a week ago!!!!!!!

 

[jibcl500]

Same engine in a 98 Sl500 as my CL500 on 95 plate no dizzy caps or rotors on mine.

Gez post a pic of the engine.

jib

 

[gez]

The engine is an M113 (taken from the V5), see pics.

 

[jibcl500]

sorry my mistake again its the face lift SL, Air flow meter 100%.

jib

 

[Alex M Grieve]

Arking gets my vote too - especially if the loss of power is accompanied by rough gear changes.
You may not need to replace anything. Consider bringing the service forward and having it fixed at the same time. If this is the problem, dry out, clean, WD 40 and replace cover should fix it.
Can be a consequence of insufficent use and condensation somhow gets in and encourages arking.

 

[gez]

Thanks all, I will check out the caps and rotor before I spend on a MAF (best price I can get on a Bosch is £165.

A note and a question though: There were no rough gear changes, just a loss of power, almost like maybe loss of spark or fuel starvation. I have also noticed that in neutral the tick over has been a bit rough with some vibration, less so in drive and the car has not had much use for a while, though I always ensure the oil temp is up to normal before any hard acceleration.

Q: Is there one or two distributors and are they easily accessible? With 500 miles to the service thats still 1 to 2 months for my level of use, so I will probably check these myself rather than pay a dealer to check and no doubt change anyway.

 

[English Teacher]

You may want to read at least the last few posts in my posting 'engine stops after returning to idle from smooth start' within the ignition and electrics forum. I found that very careful cleaning of my MAF sensor with Isopropyl Alcohol (£7 from Maplin's) cured my misfire. Detailled cleaning instructions are contained in my posting. Good luck.

 

[Alex M Grieve]

Have you solved this yet? We are all keen to know.

 

[gez]

Only just getting round to buying a replacement MAF (£148 from Emissioncontrols.co.uk for a new Bosch) so planning to fit in next week or two. Had a quick survey of the engine, but this was in the garage late evening and light was bad. Front half of the engine cover pulls off easily, how is the rear half held on and is there much more to dismatle to get to the MAF?

Also, I've a large bracket under the front cover holding nothing. Had a look at the diagrams on the Russian site and can see this would hold an electric air pump. The notes imply this is not standard for all versions. I'm curious to check that this is correct that I do not have it on my R129 SL500 with 113.961 engine, and also to know what is it's function?

Thanks.

 

[4xxxx]

i just had exactly same problem on my c230k
it was the maf it was causing misfire on cylinders 1 and 4
a new maf installed and everything back to normal

 

[gez]

Just to close off the story, the car went to Oliver at Prestige in Horndean today who carried out the Service A that was due and also replaced the MAF with a new Bosch unit, matching the best price I could have purchased it for and with very little extra on top to fit and test. This was so much easier for me than replacing it myself and removed the risk and cost had it not been the MAF.

I can't believe the difference, the car pulls like a train, revs to the red line and just drives and sounds so much better than she did before!

Great job Oliver and thanks.