Engine Skipping Intermittently

donnieknoxville · 08-18-2003, 07:27 AM

1987 911 Carrera Cab.

For the past 6-months, my Carrera has been experiencing intermittant skipping of the engine. RPM's drop suddenly (as if no spak to engine) for very short and unpredictable amounts of time. Problem occures at high load levels (accelerating hard at high RPM), when backing off the gas just slightly from a constant driving speed, and other unexplained times.

Replaced DME and problem appeared to dissappear for about a month, then reappeared. At that point, we found two corroded spark plug leads and replaced them and also replaced the distributor cap. Again, appeared to help for a while.

Most recently, the problem began occuring again and eventually lead to an almost total engine failure. When stranded in a parking lot, I was able to restart the car but not increase RMP's beyone 2,000 and any kind of load on the engine would cause it to cut out.

After conducting several electrical tests on air flow sensor, DME, spark plugs, O2 sensor, speed sensor etc, we ordered a new ECU.

New ECU got the car running above 2000 RPM again but did not solve the intermittant RMP drop problem.

Last Friday, I again found myself in a parking lot, able to sometimes rev the engine as high as 5,000 RPM, sometimes to 3,500 and sometimes only to 2,000 RPM. This time, I was able to drive as long as I kept the RPM under 2,000.

All of these intermittant problems appear to occur once the engine is warm.

Your thoughts would be greatly appreciated.

Don

scottb · 08-18-2003, 01:46 PM

This may be out of left field, but have you checked the alternator and regulator?

Steve W · Steve W's Garage

Have you checked or replaced the DME relay yet? When it fails, it will cut off your fuel pump intermittently. You can repair it by opening it up and resoldering the cracking solder joints holding the heavy relays on the circuit board.

greglepore · 08-18-2003, 05:43 PM

Cyl head temp sensor updated? Mine would cut out under load or somethimes hard cornering, felt like fuel starvation, but replacing the temp sensor cured it.

donnieknoxville · 08-19-2003, 04:22 AM

Thanks guys for all the help. Yesterday morning I suggested to my shop that they repace the cylindar head temp. sensor even though it was testing OK.

It worked and now the car runs like a race car.

They were able to confirm it was the correct fix because they finally got a reading on the sensor when it failed.

Phew! What a relief to have finally found the fix...

Don