Misfire/Hesitatation/just not firing after rain

[zxrichie]

2001 ML320 V6

Hi guys, as above, after a period of rain when the car is parked, and i drive away, its very lumpy and seems like its misfiring, after a while the car shoots forward like i hit the NOS button!! After much reflection and a trip to my local garage who reads the codes, it appears that when i pull away cylinders 4,5,6 are not misfiring or not firing at all.

So what could be happening to affect the rh bank of 3 cylinders into misfiring or not firing until maybe it warms up. is there some component that is particular to cyl 123 and another for 456 that could be affected by rain....

Any help gratefully rec'd.

Rich

ps is there a online (or downloadable) parts catalogue, i remember some russian one some years back...

 

[grober]

Your engine is a M112 If you do a Google search on M112 + misfire you will get some ideas?

 

[markmifsud]

Bleed the fuel rail. Screw on cover at front left from the front. If that doesn't help, try swapping coils and leads between 6 and 3, see if the problem moves.

 

[BlackC55]

It could be a faulty maf too.

 

[zxrichie]

It could be a faulty maf too.

Hi, The MAF was my first thought, now here is a really funny thing. while its running lumpy and missing, if i pull over and get out, lock her with the clicker, wait 2-3 seconds, and then open her up (all doors, not just the drivers as i did at first) fire her up and away she goes, no problems...

Work that one out!!

it really is bugging me.

 

[grober]

ML320 Misfiring on 6,5,4 cylinders - Page 3 - Mercedes-Benz Forum

http://www.benzworld.org/forums/att...1459112-98-ml-320-misfires-cats.-location.pdf

 

[zxrichie]

Grober, thanks.from reading that post and a lot of others here and elsewhere, the misfire problem is always an issue. With mine, it ONLY happens at start up and if its been cold/damp/wet. once it warms up, all is good. In the summer, it never happens. Now i cant seem to join the dots on this one, which is why i,m asking around. i cant afford to throw parts at this problem (Air flow meter/MAF/call it what you like is £150) so any diagnostic test would be great.

Regards

Rich

 

[zxrichie]

Just a quick note, i think the electronic immobiliser is a red herring, because today it was happening, only running on 3 cylinders, i stopped , turned the engine off, started up and it was fine. I just dont get it, my options appear to be

Cat converter.
Coil pack
Spark plugs

So i think its time for a OBD2 look....

 

[zxrichie]

Can someone tell me if a faulty crank pos sensor could cause these problems?

anyone???

 

[grober]

I would think that selective failure of one cylinder bank would not be caused by a faulty crank position sensor. Normal pattern is engine cutting out when hot and restarting after cooling down and this progresses to complete engine failure to run.

 

[wu56Shoozz]

Okay try this.. and I'm serious. This used to happen with the VR6's. What was happening was the heat build up under the engine cover caused the plastic around the coil pack to go hard and eventually crack.. so when it was damp or rained it would run like a burst RS until heated up and by the time you had got it to a workshop to have it checked it would run as sweet as a peach.. the easy answer and temporary fix was to remove the coilpack (in this case just one) and bung it in the oven and heat until to hot to handle but not melt.. then remove and instantly soak in WD40 and leave then coat a fine coating of silicone grease all over (except inside the lead hole) and reinstall.. the wait for a rainy day and.. hey presto, no misfire!! So remove all the coil pack and try this and see how you get on..

 

[wu56Shoozz]

Spark plugs are always a good option.. a misfire is always on the HT lead side..bad or low plugs can always be a bugger.. again VR6's were notorious for this even although the plug itself had life itself.. the engine would tell you otherwise...

 

[zxrichie]

Hi guys, you know what really bugs me about forums, its when someone has a problem, lots of people try to help, as well as members with similar issues, and the thread starter obviously fixes it but never comes back with the fix!!

Rant over, and now the answer to MY problem, i really thought the MAF/Air flow sensor whatever people call it, was the issue, but at £160 for a Bosch part, its an expensive guess, so i pay £18 for one of those copy parts, now i know it might only last a few months, but it would save me a lot of money if it proves the principal, Which it did!! Now when i got in after that rain we had a few days ago, starts up , and accelerates away like it should, in fact its overall performance (especially accelerating) is mush sharper and responsive. So now i and all of you, know what my fix was.

Regards