Dan Dragner

I am at my wits end.....Been messing with this for 14 months! My early '86 has a slight miss at idle (feels like ignition). The miss gets much worse as the RPM's go up. Dosen't want to pull past 3500 or so. If I snap open the throttle to 2500 or so, the engine will run smooth for a few seconds, then begin to miss and even shudder. At cruising speed, you can feel a heavy missfire. The car seems to be using less fuel than would be expected. Engine fires instantly, no pinging. But the strange thing is every once in a while, the engine smooths out, and pulls MUCH harder. It's like an extra 100 horsepower. This usally happens after I go over a speed bump, or make a hard turn. To date I have checked/replaced :

Fuel pressure at idle 29
Good fuel volume
Vacuum at idle 26" drifts 24-26ish
New fuel filter, plugs,caps,rotors,throttle housing seals,intake gaskets,throttle switch, O2 sensor,temp II sensor.

Had the EZK, LH and Air Mass Meter units swapped on another car, all OK.

Injectors were serviced by Marren.

Had new cats. installed, and mufflers removed...exhaust not restricted.

Plug wires ohm OK, but look like originals.

Coils ohm OK. Put them in my Audi. Ran OK.

I have been using the Porsche Technik service manual for the LH and EZK systems as a guide. The only tests I cannot make are ones calling for an ignition scope. Everything else is OK and in spec.

I'm tired of being passed by Nissan Sentras! AND my smog test is comming up fast. My Porsche dealer (as a last resort) said plugged cats. and mufflers were to blame. WRONG! I'll deal with them shortly......
Thanks for any ideas or input, Dan

928 Brothers

Go back and check your coils and wires again. Bad 928 coils will work great on other cars, believe it or not. A 32 valve 928 needs a crazy amount of spark.

onthedge928s4

hi,
I had an 86 32v did the same thing it was the ign wires , they will ohm out ok and still not work properly I can attest to that i stumpped a shop and then fixed it myself. runs and started ok but felt like a mis and vibration they told me motor mounts hog wash i know how these sharks are supposed to run. you can snag a set of wires for 150.00 nad swap the ends or buy a wire set from jim at 928 international for about 300.00 it`s most likely the medicine your beast will respond to.. a small token of appreciation for the grins it provides on a regular basis

bob the bmw tech

DougM

Fire the car up in a dark garage with the hood open. See if there are any fireflies coming from the wires.

Steve Cattaneo

Start by checking the timing, crank at TDC number 1 piston up on compression stroke, now check the cam timing marks. You don’t have to remove the covers. Remove the air intake hoses you can see the cam timing marks through the air holes that are in the cover. Make sure all marks are properly aligned. Now check to see that the distributor rotor just starts to point to the number 1 ignition wire.
Buy a spark plug tester that goes in series with the plugs and wires. 928’s can run on one bank of cylinders (four cylinders, do not remove the plug wires to check for spark, you will fry your controller). If all the cylinders are firing this tells us the igniters and coils are working. The best tool is an oscilloscope with a KV tester.


Keep Us Informed,
Good Luck

Steve C

Nicole

I believe, that at DEVEK day's 928 maintenance session they said that when you do DougM's test you should spray a light mist of glass cleaner over the area of the wires. That would make the problem areas more visible. I have never tried this - my car has new wires already. However, my car did not exhibit the behavior you describe before the wires were replaced.

From my discussions with 928 mechanics, while troubleshooting the idle problems on my car, I would think that in your case one or two defective coils might be a very likely cause of the problem.

They explained that defective coils in the 928 cause more and more "drops" with increasing rpms. Maybe the car you tested them in dosen't require as big of a coil and therfore did not show the problem?