Bad Misfire but no codes or MIL ?!
03-27-2019, 07:25 AM
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W220 S600 TT 2003
Bad Misfire but no codes or MIL ?!
Hello All,
My 2003 W220 S600 TT is misfiring...... grab a cup of tea and pull up a chair....
Start the car from cold and it idles ok (maybe down a cylinder), not perfect, but ok.
Driving along keeping the RPM under 4k and no problem, full power is available turbos spin up.
At present there are NO MIL or Check engine lights on the dash, the malfunction report states "No Malfunctions".
If you put your foot into it, you will get full power with what appears to be no misfire (above 4k) and then the cylinder shutdown
comes in and the car misfires at all RPM.
I've scanned it with an ODB scanner, nothing. I took it to an indy with a STAR and they said they can see *teeny* misfire
at idle, which is not enough to cause a fault code to be logged or the engine light to come on.
So at zero load there is a slight misfire, and when the load goes up, the misfire increases.
There is no smoke or weird noises during the misfire, it only really happens when you open her up.
If you turn the car off and then on, it will rev like a champ (all the way up to the 3k limiter when in park) and return
to the slightly lumpy misfire at idle. I am assuming this is the cancellation of cylinder shut off.
I immediately assumed coil pack or voltage regulator, but I would expect to see codes logged in STAR for that,
plus the MIL light coming on, as these W220's are very sensitive to detecting misfire from what I have read.
My indy is guessing it may be some form of vacuum leak, possibly inlet manifold gasket or some other piping.
If anyone has any ideas, I would appreciate it.
I would like to try and fix this myself (I'm selling the car) to keep costs low as possible, if anyone has any suggestions
of things to check, I would really appreciate it.
My 2003 W220 S600 TT is misfiring...... grab a cup of tea and pull up a chair....
Start the car from cold and it idles ok (maybe down a cylinder), not perfect, but ok.
Driving along keeping the RPM under 4k and no problem, full power is available turbos spin up.
At present there are NO MIL or Check engine lights on the dash, the malfunction report states "No Malfunctions".
If you put your foot into it, you will get full power with what appears to be no misfire (above 4k) and then the cylinder shutdown
comes in and the car misfires at all RPM.
I've scanned it with an ODB scanner, nothing. I took it to an indy with a STAR and they said they can see *teeny* misfire
at idle, which is not enough to cause a fault code to be logged or the engine light to come on.
So at zero load there is a slight misfire, and when the load goes up, the misfire increases.
There is no smoke or weird noises during the misfire, it only really happens when you open her up.
If you turn the car off and then on, it will rev like a champ (all the way up to the 3k limiter when in park) and return
to the slightly lumpy misfire at idle. I am assuming this is the cancellation of cylinder shut off.
I immediately assumed coil pack or voltage regulator, but I would expect to see codes logged in STAR for that,
plus the MIL light coming on, as these W220's are very sensitive to detecting misfire from what I have read.
My indy is guessing it may be some form of vacuum leak, possibly inlet manifold gasket or some other piping.
If anyone has any ideas, I would appreciate it.
I would like to try and fix this myself (I'm selling the car) to keep costs low as possible, if anyone has any suggestions
of things to check, I would really appreciate it.
