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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 24142
Experience:  Over 15 years experience as a Mercedes dealer technician
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Just got this ml 163 the shat spent £4500 om chasing a miss

Customer Question

just got this ml 163 the shat spent £4500 om chasing a miss fire
JA: Tell me a bit more about what's going on so he can help you best.
Customer: its a 430 its hi on co readings on the 2nd fast idle run for the mot & i was told this is because that the chap has had it laid up for over 2 years . so i took it for a blast to warm up the cats ?? now i have this miss fire . if you bring the revs up to 4000 rpm engine is sweet but if you take it 4100rpm its like the rev limiter cuts in ,the old owner had new plugs, leads, injecters ,fual pump, fual filter, coil packs , etc could not fix it then he say he changed the cat on the left side & that fixed it ,but now its back so do i go for the drivers side cat next or is there something more i should be thinking of 1st . its only got 102000 on the clock .its on 1999 year
JA: Are you hoping to fix this yourself?
Customer: i was yes
JA: Is there anything else important you think the Mercedes Mechanic should know about your Mercedes?
Customer: thats all i can think of
JA: I'm sending you to a secure page on JustAnswer so you can place the $5 fully refundable deposit now. While you're filling out that form, I'll tell the Mercedes Mechanic about your situation and connect you two.
Submitted: 7 months ago.
Category: Mercedes
Customer: replied 7 months ago.
sorry that should of said,the last chap spent £4500 on chasing a miss fire
Expert:  Pete replied 7 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

One common issue on this model was the catalytic converters either cracking or clogging up.Mercedes had even released a recall for dealers to check the cats. for cracking issues with them needing replaced under warranty at no cost.I would have the cats. checked for any cracks to see if any are found.It is the welds that crack on them.If any are found I would speak with a dealer to see if they can still warranty this as sometimes they can get the recall re opened to have the affected catalytic converter replaced.

If no cracks are found then the exhaust back pressure needs tested to see if there is excessive back pressure.If there is excessive back pressure this indicates the affected catalytic converter tested needs replaced.I would have both tested.

One other issue with this engine is the mass air flow sensor.In allot of cases it will not set any codes when it acts up but it can send an incorrect air flow signal and cause rough running needing replaced.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 7 months ago.
thanks pete i think he done the mass air flow sensor as well . so i dont need to worry that its a sticking valve
Expert:  Pete replied 7 months ago.

Your welcome.

It is possible it is a sticking valve but I havent seen this issue on this model here myself unless the engine is really gummed up with engine oil build up.Usually this can be checked with a valve cover removed to see if this is a possibility here.

I would have the cats. checked and a back pressure test done as well.

Let me know if you need anything else and feel free to rate my help here.

Thanks Pete