CLK 430 misfire - radio interference

[Mikeroo]

Hi there

Bit of background: misfire at idle (lumpy) and sometimes so bad the car feels like it is going to stall, on light throttle and low speed acceleration from junctions and r/bouts car sometimes misfires so bad it seems like only 2 cylinders are actually firing. I can hear a cracking sound on radio which speeds up with engine rpm..... so I am thinking must be a HT lead or a coil pack failing.

Booked in for B service anyway and I tell the guy on the phone, he gets a coil pack in and a few leads to test. Outcome is no faults found when swapping all coil packs with a new one and swapping HT leads..... absolutely no faults stored on ECU either.

Plugs are 20k miles old and he tells me they should be good for 50k miles and they dont understand why such a bad misfire is not showing up on ECU. Next step is to try testing all injectors and swapping plugs.... any advance on this advice?

Thanks

Mike

 

[star]

Hi there

Bit of background: misfire at idle (lumpy) and sometimes so bad the car feels like it is going to stall, on light throttle and low speed acceleration from junctions and r/bouts car sometimes misfires so bad it seems like only 2 cylinders are actually firing. I can hear a cracking sound on radio which speeds up with engine rpm..... so I am thinking must be a HT lead or a coil pack failing.

Booked in for B service anyway and I tell the guy on the phone, he gets a coil pack in and a few leads to test. Outcome is no faults found when swapping all coil packs with a new one and swapping HT leads..... absolutely no faults stored on ECU either.

Plugs are 20k miles old and he tells me they should be good for 50k miles and they dont understand why such a bad misfire is not showing up on ECU. Next step is to try testing all injectors and swapping plugs.... any advance on this advice?

Thanks

Mike

Sounds like several of your plug leads are failing, you can check these quite easily or your air mass has gone down making it misfire on diff cyls.

 

[television]

Have to go along with Star, HT leads

 

[jberks]

I agree - I've had lots of problems with MB leads despite them being horendously expensive. Corrosion in the suppressor caps is a common one.
That or the MAS would be my guess.

 

[Mikeroo]

Thanks, that's exactly what I thought before booking it in, I am just confused after them saying it is not leads or coils...... how else can it interfere with radio like that, it has to be HT side doesnt it?

They also said they had checked with a new MAS so it want that either.... maybe I will check it into a independant for a second opinion.

Cheers

Mike

 

[jberks]

I'd have thought so. The only HT on the Merc is from the coil pack to the plug. Unless it's an engine earthing fault I can't see what else would give the symptoms you describe. That said, my dealer failed to spot my plug lead fault. They just kept plugging in the computer and finding nothing! Sometimes old fashioned diagnosis is the only way.

 

[television]

When the leads are effectivly open circuit, though the car will run, the timing will be out, as the spark gap in the break will delay the spark.

 

[star]

Check each coil/lead with a scope. might not show on star diag

 

[angus falconer]

Check all the leads and all the coil packs

I had a similar problem which was cured by two new leads and one coil pack.

 

[Mikeroo]

Is there a surefire way to test a coilpack with a multimeter? I mean on top of visual inspection for obvious problems. I dont think there is a proper way to test leads is there?

As the current leads are probably nearly 7 years old I have no issue with replacing them as it seems to be accepted wisdom they should ideally be replaced every 4-5 years anyway.

I'll be sure to post how I get on

Thanks for the advice

Mike

 

[angus falconer]

Is there a surefire way to test a coilpack with a multimeter? I mean on top of visual inspection for obvious problems. I dont think there is a proper way to test leads is there?

BSG Mercedes did this for me - not sure how they did it though.

 

[television]

Is there a surefire way to test a coilpack with a multimeter? I mean on top of visual inspection for obvious problems. I dont think there is a proper way to test leads is there?

As the current leads are probably nearly 7 years old I have no issue with replacing them as it seems to be accepted wisdom they should ideally be replaced every 4-5 years anyway.

I'll be sure to post how I get on

Thanks for the advice

Mike

It is not possible to test a coil pack on a multi meter as one short turn in 22,000 would not show up.

There are such things as transformer testers that can check it, the hardest job is to find someone who has one

 

[BlackC55]

It is not possible to test a coil pack on a multi meter as one short turn in 22,000 would not show up.

There are such things as transformer testers that can check it, the hardest job is to find someone who has one

Oscilliscope is the only way to go.

 

[television]

Oscilliscope is the only way to go.

Looking at the waveform tells you all, providing the operator knows what he is looking at, one does have all of the other packs to compare against the suspect one

 

[Mikeroo]

fixed

Sorry to dig up my old post but thought it best to continue on, car was originaly inspected by main dealer who told me further work was required as no fault code was being stored by ECU, when booked in for second B service since I took ownership I asked them to sort it, they have now confirmed it is the spark plug leads, they replaced numerous ones but still getiing ups and downs on test machine, assured me a full set will sort the problem so I am going with that. Looking forward to silky smooth idle and no horrible misfires.

 

[television]

Sorry to dig up my old post but thought it best to continue on, car was originaly inspected by main dealer who told me further work was required as no fault code was being stored by ECU, when booked in for second B service since I took ownership I asked them to sort it, they have now confirmed it is the spark plug leads, they replaced numerous ones but still getiing ups and downs on test machine, assured me a full set will sort the problem so I am going with that. Looking forward to silky smooth idle and no horrible misfires.

Thank you for posting back, that always makes everything worthwhile