I recently finished a protracted course of maintenance on our '99 ML 320 that included;
1. New left (driver's side) catalytic converters (two cans) and resonator due to melted cat #1.
2. Two new left side Oxygen sensors.
3. New spark plugs - the (relatively expensive) NGK plugs recommended somewhere in this forum.
4. Complete fluid change in automatic transmission, cooler, torque converter.
5. Fluid change in transfer case and both differentials.
It seemed to run strong after all these repairs, but I could detect a slight misfire. Recently on a very rainy day going over a mountain pass the CEL came on (urgh)! It was the P0300 random misfire, and P0301, 302, 304, and 305 misfire on those four cylinders. When I changed the plugs it was really difficult getting the wires off the old plugs and coil packs. I took them off the coil packs to test their resistance values. All the wires had similar resistance - to my memory they were 2k ohms each, plus or minus about 100 ohms. So I reinstalled them. I suspect and hope that they are the culprit to the misfire codes and am replacing them today with a new set of Bosch wires.
However, when using my scan tool I noticed a big difference in the LTFT (Long Term Fuel Trim) between Bank 1 and Bank 2. The difference was in the "Freeze Frame Data". The difference remained after clearing the CEL and error codes - the live data showed the same discrepancy. Bank 1 LTFT stayed constant at 1.5, while Bank 2 LTFT stayed constant at 3.1. I will attach some photos showing this data. I am curious to know what the units of these numbers are. I have no idea what would cause this difference. I suspect that it's significant but don't know where to start with this one. Can anyone tell me what causes it and how to solve it?
Thank You,
John Olson
1. New left (driver's side) catalytic converters (two cans) and resonator due to melted cat #1.
2. Two new left side Oxygen sensors.
3. New spark plugs - the (relatively expensive) NGK plugs recommended somewhere in this forum.
4. Complete fluid change in automatic transmission, cooler, torque converter.
5. Fluid change in transfer case and both differentials.
It seemed to run strong after all these repairs, but I could detect a slight misfire. Recently on a very rainy day going over a mountain pass the CEL came on (urgh)! It was the P0300 random misfire, and P0301, 302, 304, and 305 misfire on those four cylinders. When I changed the plugs it was really difficult getting the wires off the old plugs and coil packs. I took them off the coil packs to test their resistance values. All the wires had similar resistance - to my memory they were 2k ohms each, plus or minus about 100 ohms. So I reinstalled them. I suspect and hope that they are the culprit to the misfire codes and am replacing them today with a new set of Bosch wires.
However, when using my scan tool I noticed a big difference in the LTFT (Long Term Fuel Trim) between Bank 1 and Bank 2. The difference was in the "Freeze Frame Data". The difference remained after clearing the CEL and error codes - the live data showed the same discrepancy. Bank 1 LTFT stayed constant at 1.5, while Bank 2 LTFT stayed constant at 3.1. I will attach some photos showing this data. I am curious to know what the units of these numbers are. I have no idea what would cause this difference. I suspect that it's significant but don't know where to start with this one. Can anyone tell me what causes it and how to solve it?
Thank You,
John Olson