NCporsche

2001 ML 320 with 150,000+ miles. Check engine light came on, diagnostics said plugs and/or wires. Changed all 12 plugs (two per cylinder) and light went off. She starts running with premium fuel instead of mid grade that she has used for many years.

Check engine light returns burning steady, then quickly starts blinking and engine loses power. She gets off road, I come with my truck to swap out vehicles. ML starts back up, i keep speed down and get car home.

Riding slow and easy, car runs OK. Step on gas and symptoms return. Diagnostics show at 5000 RPM cylinders 2, 4, and 6 being shut off. Moved coil from 5 to 6 and again 6 shut off. I'm ruling out a coil problem.

A forum search indicates it might be the catalytic converter causing the rev limiter to kick in?

Any suggestions appreciated and I will update thread as I attempt to track down problem.

BTW, computer has not been updated by dealership in years. I've done maintenance, brakes, oil changes, alignment...

art_arev

Scan the car with a pro level scanner & post the codes

NCporsche

Two codes are showing. P0302 and P0306. Cylinder misfire detected (typically caused by a bad coil). As stated earlier swapped coil on 5 and 6, cleared codes, codes returned.

Problem occurred on fast acceleration hitting 4450 RPM and 23 MPH.

Maj. Dundee

Purchase an Exhaust Back Pressure gauge. With a cold engine, remove the front O2 sensor and install the gauge. Get the eng. up to operating temp.


First watch the gauge while at idle and the gauge should not go above 1 psi.

Then raise the idle to 2,500 RPM's and watch the gauge. Then raise it higher.

At no time should the gauge go above 1 psi. If it does, the CAT is clogged.

Then perform the same test on the other side.

NCporsche

Have performed the O2 checks suggested by the Major. Even checked O2 sensors behind CAT and both fore and aft readings along with port and starboard were good.

It's not the catalytic converter(s).

Maj. Dundee

Then you have to have the codes read.

Be aware that whenever the CEL is blinking, there is a serious problem.

NCporsche

Took ML to a German auto repair shop. He started car, got same codes. Lifted hood with engine running and quickly determined plug wires on cylinders 2 and 3 were not completely seated. Cleared codes and car is running at 100%.