Missfire on ML320

[Robbieben]

I own a 2000 model Ml which has developed a misfire on left hand bank of cylinders. It only happens when you accelerate hard then ease off the throttle and then the 3 cylinders lose the electrical power to the coils. Swtch ignition off then restart and all is fine again

[ozzy]

What procedures have you used to diagnose fault, please explain in more detail.

[AusMBtech]

Once the ECU has detected a misfire it will shutdown the cylinders to prevent further damage so don't bother tracing why the coils have no power going to them, the injectors won't be running either.

Having 3 cylinders on the same bank shutdown at the same time though is a bit unusual for that engine because it's a twin spark plug engine. I would be leaning towards a fuel problem on that bank (mixture adaptions may be way off for the cylinder bank).

I'd check for fault codes with a scanner and check the fuel adaption figures for each bank and see if any figures vary greatly. It will be hard to diagnose without the right equipment.

[mbdoc]

Have the exhaust back-pressure checked on that side of the exhaust thru the front O2 sensor!

[Robbieben]

Originally Posted by AusMBtech

Once the ECU has detected a misfire it will shutdown the cylinders to prevent further damage so don't bother tracing why the coils have no power going to them, the injectors won't be running either.

Having 3 cylinders on the same bank shutdown at the same time though is a bit unusual for that engine because it's a twin spark plug engine. I would be leaning towards a fuel problem on that bank (mixture adaptions may be way off for the cylinder bank).

I'd check for fault codes with a scanner and check the fuel adaption figures for each bank and see if any figures vary greatly. It will be hard to diagnose without the right equipment.

You would advise that I go to dealer to have it checked out?

[ozzy]

Do you have the "check eng light" come on when fault occurs??. I hope so, this will assist in diagnosis. I would suggest having it scanned for fault codes and going from there, you don't want to leave it to long as it may damage the cat. let us know what fault code/s there are.

[alexus009]

Hello,

I also have an '99 ML320 has the same problem. I've replaced Cam, Crank, Spark Plugs, 3 news Coils on supposedly bad cylinders. All parts name brand are Bosch. I've also swapped spark plug wires around and still have the same problem. I've also cleaned Trans Connector, and other connectors. The codes i have are P0300, P0301, P0302, and P0303. Basically i am having problem on the pessanger's side bank. Things i have not done are clean out are throtle as it is not easy to reach. I have not clean or attempt to change/check MAF.

Any advice is greatly appreciated.

Alex

[Robbieben]

Originally Posted by ozzy

What procedures have you used to diagnose fault, please explain in more detail.

When missfire happens I have left engine running then have removed l/t wireplug connection to each coil in turn. Right hand bank of cylinders all have power to them, left hand bank all power has been shutoff. If ignition is shut off then engine re-started the engine runs fine again. During normal driving the problem does not occur, it only seems to happen after hard acceleration and the engine using high revs say over 4000rpm, during acceleration there is no problem it is only when you ease off the gas the engine then misfires and always on complete bank on left side as viewed from inside car, right side if you are stood at front of vehicle looking at engine. Missfire will not clkear until engine is shut off and re-started.

[mbdoc]

Sounds like excessive exhaust back pressure.

I would have that checked by a shop with a back pressure gauge.

[Bigdaddybenz]

Replace the CAT!........Probably not doing much for your exhaust vales, either!