S430 V8: Cyl 1 slight misfire
Thread Starter
Junior Member
Joined: Oct 2012
Posts: 57
Likes: 8
From: SRQ, FL
2001 S430 W220
S430 V8: Cyl 1 slight misfire
Hi Folks. I recently wanted to tackle a Cyl 1 misfire on my S430 MY 2001, with M113 V8 engine. I have 109K miles.
I've had an on and off CYL 1 misfire pending code that never manifested into a full on check engine light. The misfires are worse at cold start and I can feel it in the seat. Once the engine is warmed up there are very little misfires from cyl1 on the scanner misfire counter. Maybe 1 misfire every 30 seconds or minute. I don't think coils/plugs were ever replaced so I dived right in and just replaced all the coils and plugs with Bosch brand to get a head start on the issue. I did not replace the wires as I felt it wasn't necessary. It made the car feel far smoother and everything however the CYL 1 problem is still present. I have an advanced Xtool scanner that shows me the misfires and how smooth the cylinders are working which is a cool feature and based on that data, the problem is slight still but most noticeable at cold start. I haven't done anything to the fuel injectors but could this maybe be a bad injector? I looked at the fuel trims and they are all within spec, long term trims not more than +6 or +7. There are no other codes (neither ODB or MB specific) that are providing any clues.
I've had an on and off CYL 1 misfire pending code that never manifested into a full on check engine light. The misfires are worse at cold start and I can feel it in the seat. Once the engine is warmed up there are very little misfires from cyl1 on the scanner misfire counter. Maybe 1 misfire every 30 seconds or minute. I don't think coils/plugs were ever replaced so I dived right in and just replaced all the coils and plugs with Bosch brand to get a head start on the issue. I did not replace the wires as I felt it wasn't necessary. It made the car feel far smoother and everything however the CYL 1 problem is still present. I have an advanced Xtool scanner that shows me the misfires and how smooth the cylinders are working which is a cool feature and based on that data, the problem is slight still but most noticeable at cold start. I haven't done anything to the fuel injectors but could this maybe be a bad injector? I looked at the fuel trims and they are all within spec, long term trims not more than +6 or +7. There are no other codes (neither ODB or MB specific) that are providing any clues.
Super Member
Joined: Dec 2007
Posts: 980
Likes: 224
2005 S500 Designo
It sounds like you have a good handle on things. Anything I add would be speculation, but your speculation seems right on point.
My first guess was a valve cover gasket leak causing problems with the spark plug. My next guess would be low compression, but your next guess is better than mine: check the fuel injector.
Have you tried an italian tune up?
My first guess was a valve cover gasket leak causing problems with the spark plug. My next guess would be low compression, but your next guess is better than mine: check the fuel injector.
Have you tried an italian tune up?
Thread Starter
Junior Member
Joined: Oct 2012
Posts: 57
Likes: 8
From: SRQ, FL
2001 S430 W220
Thanks for your reply. I appreciate any input whether it would be guesses, etc. I have not noticed any leaks coming in there at that side of the engine. Perhaps I can stick in the borescope camera in cylinder 1 and check to see how it looks but I think I'll go for the injector first and see than maybe do compression test but how does one do that on twin spark system? lol. I guess either plug hole would be fine? I haven't taken the car out on the highway as of yet but I did go around town, Italian'ed it several times, floored it. The misfire is not noticeable at all while driving or anything.
Super Member
Joined: Dec 2007
Posts: 980
Likes: 224
2005 S500 Designo
Thanks for your reply. I appreciate any input whether it would be guesses, etc. I have not noticed any leaks coming in there at that side of the engine. Perhaps I can stick in the borescope camera in cylinder 1 and check to see how it looks but I think I'll go for the injector first and see than maybe do compression test but how does one do that on twin spark system? lol. I guess either plug hole would be fine? I haven't taken the car out on the highway as of yet but I did go around town, Italian'ed it several times, floored it. The misfire is not noticeable at all while driving or anything.
If you didn't see oil when swapping the spark plugs, oil is not an issue (you did replace the wires too, right?).
To test compression, unplug the wires and leave one spark plug installed while measuring from the other hole. Don't overthink it. A compression test is a PITA and a long shot, so looking at injectors is the easier move.
Is your secondary injection pump working?
Thread Starter
Junior Member
Joined: Oct 2012
Posts: 57
Likes: 8
From: SRQ, FL
2001 S430 W220
Speculation helps, but better would be someone having concrete knowledge on what might be causing the misfire.
If you didn't see oil when swapping the spark plugs, oil is not an issue (you did replace the wires too, right?).
To test compression, unplug the wires and leave one spark plug installed while measuring from the other hole. Don't overthink it. A compression test is a PITA and a long shot, so looking at injectors is the easier move.
Is your secondary injection pump working?
If you didn't see oil when swapping the spark plugs, oil is not an issue (you did replace the wires too, right?).
To test compression, unplug the wires and leave one spark plug installed while measuring from the other hole. Don't overthink it. A compression test is a PITA and a long shot, so looking at injectors is the easier move.
Is your secondary injection pump working?
Super Member
Joined: Dec 2007
Posts: 980
Likes: 224
2005 S500 Designo
Thread Starter
Junior Member
Joined: Oct 2012
Posts: 57
Likes: 8
From: SRQ, FL
2001 S430 W220
I couldn't believe this, but it was the coil wires causing the issue. I had used the same coil wires that were going into cyl 1 when doing my tune up. I swapped coil wires with known good cyl 2 and the issue went away on cyl 1 and according to the computer, now cyl 2 is slightly off spec but not as bad as cyl 1 was. I'll go ahead and order some new coil wires and I'll be on my way to a smooth running v8! Thanks gentleman.
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