At 10:19 AM 10/30/2004, Andy Price wrote:
1982 16V US Auto RUNNING ON 7 CYLINDERS - Had been running this way quite some time, and worked well after replacing plugs and wires
initially for one week, failing thereafter, with occasionally useful effects tightening plug wires in the engine or at the distributor.
More recently, however, there has been nothing I could do to correct the previous misfiring problem, and now I am back on 7 cylinders and
dumping raw fuel into the catalytic. I missed the Frenzy 8 because of this due to Bill Gordon's 928 mechanic, Garry Sherman, informing me
that he had heard of a 928 catching fire and actually exploding operating under this same circumstance of running on 7.
Have already replaced spark plug wires, distributor lead, OEM spec plugs gapped to factory spec at .028", and the distributor cap (NAPA
for 1982 928) but not Rotor). An inductive timing light revealed no apparent mis or non-fires on any cylinders; my audio inspection of the injectors did not reveal any injectors not pulsing consistently and rhythmically. I have no idea what's up with this car, and the very short lived
8-cylinder operation is just cruel frustration it having been of such little duration for such comparably large cost. More money, more parts, nothing.
Throwing parts at a 928 problem can get very expensive very quickly...
A hard miss - that is, a very regular and noticeable misfire that is apparently on one cylinder - has a very limited number of possible causes on a 928.
Back to basics - fuel, fire, air, and compression are the necessities of life for a gasoline engine.
The most likely possibility for a fuel problem is a faulty injector, or a faulty connection to one injector. The quickest check is to use a mechanic's stethoscope (has a long metal rod to touch the injectors) to check for a regular clicking from each injector. Any injector that is not clicking at the same rate as the other seven is probably the problem.
It is possible that an injector can click and still not inject fuel, but listening for the clicking would be the first step.
It is possible that an injector can inject too much fuel, but not as likely as injecting too little.
It is possible, but not too likely, that a bad vacuum leak that only affected one cylinder could cause a hard miss. The quickest check here is to disconnect the rubber tubes and use the earpieces of the stethoscope and the attached tubes as a locator to listen for the hiss of a vacuum leak.
Any ignition-caused hard miss almost certainly must be between the rotor and the spark plug ground. This includes the distributor cap, the plug wires, and the plugs. Since all of these have been replaced with no apparent long-term improvement, it is possible but unlikely that the problem is ignition.
Possible but not likely, unless someone has left a shop rag in the intake or something similar.
Possible. The best check by far is a simple compression test. This would give a pretty certain answer one way or the other.
When you pull the plugs for the compression test, a visual examination of the plugs should give some indication of which cylinder has the problem.
My first guesses:
Bad connection on one injector.
I've heard someone replacing the Bosch Ignition amplifiers (end-stage) by new Hella brand units. This caused erratic behavior. Putting Bosch in solved the problem.
On my GTS, it cost me a couple grand to figure out my problem. The car
wasn't running well under hard acceleration and it would go into the 4
cylinder "limp mode" when I pushed it. The red indicator light would come
on in the ignition monitoring circuit in the passenger foot
After removing and cleaning the exhaust temp sensors, checking their resistance, changing coils, replacing the MAF, replacing the Temp II sensor, it turns out the problem was a faulty spark plug wire causing an intermittent miss under acceleration. This would cause the car to go into the limp mode and then barely make it home.
In addition to everything else, check your plug wires for corrosion or possible problems that might cause a plug to not fire correctly.