Ok, I have not mentioned this, but I have a problem that won't go away. We had a misfire on one cylinder. We went in and determined that we had a bad injector. Replaced the faulty injector only to find out the injector wasn't even getting pulses to fire. So we replace bad ECM. After doing that, we verify that the injector is working now. However, the misfire is still there and the van is gutless.

Start pursuing ignition problems and find a bad coil. Replace that, and problem still persists. (though it is running better at this point.) Find high resistance on the ground terminal at the distributor. Replace plug and that resolves the high resistance, but misfire still persists. I took it on a good test drive today, and the CEL came on three times, but no codes were stored in memory. I am about at my wits end here, seems everything that could go wrong has gone wrong.

Any ideas here? There are no vacuum leaks, the fuel pressure is normal, all the sensors seem to be working, the spark is now strong. Cylinder balance test indicates a misfire or weak cylinder on the same cylinder that originally had the injector problem. Has anyone else ever dealt with such a persistent misfire that doesn't seem to be caused by any of the usual problems?

For the record, this just happened one day, and became intermittent for a while before the cylinder just went completely dead.

 

"Find high resistance on the ground terminal at the distributor"???
must be a 3L, dist. and cylinder balance test?

often what causes an ECM FI output failure is damage to the FI wiring harness. they are not designed for a 0 ohm short to chassis but need the FI solenoid resistance to limit current flow. too much current flow and the good black electrons leak out of the ECU FI output FET

change cap and rotor , may have invisible to eye crack

swap plug wires between bad cylinder and another, does miss follow?

run compression and cylinder leakdown test double check the missing hole.
may be damaged valve from lean fuel condition to that cylinder, would only be sucking over fuel fumes from the other runners. exhaust valve got too hot and warped or cracked piston.
or valve floated and bent stem

 

Will try to do a compression test. The bad cylinder is #1, which at least is the easiest to get to on the passenger side. I will do a compression test and see what the story is.

For some reason the van is hard to start, and when it is running now, it seems to be excessively rich. I will try to see if this is actually the case, or if it is just one cylinder that is the problem.

And yes, sorry I forgot to mention, this is my parents '92 3.0L. My 4.0L is running great.

 

Again, try this first. In the end, most problems turn out to be embarrassingly simple.

 

Just a guess, but how is your ECT? When mine went bad, had trouble starting, and ran rich. I had to replace the ECT electrical connector as well. Again, just a guess.

M

 

I'm betting on the compression problem. Test cylinder pressure as is ,then pour in 2 tablespoons of engine oil & try again, if it's as good as the next cylinder, you have compression ring problem, if not much change you have valve leak, the odd inlet valve walks into the head or ex/ valve burns.

Does the CEL blink?

You dont have a faulty spark plug do you? some plugs dont fire under high load conditions. It might look good on an open air test, but thats not always the best test. A spark should jump a certain distance. If you do the compression test, shove in a new plug anyways.

 

I second checking the compression, sense you have pretty much replaced everything else, it sounds like a bad exhaust valve or rings. Sense it is an easy cylinder to get to, do that before throwing any more money at parts on it.

 

Tried that already, no effect. Spark is good on all cylinders now, and swapping wires doesn't help at all.

ECT could be part of the problem, but should not cause a misfire on cylinder #1.

The spark plugs are brand new, as are the wires cap and rotor. All Motorcraft. The old ones were behaving the same way, and installing the new did not improve anything.

I will be doing the compression check shortly and will let you know what comes of it.

Oh, before anyone else mentions it, not the cat is not the problem, it has already been replaced. Because of the misfire, the cat had overhated and fractured, so we replaced it. The old one had not yet plugged.

 

Well, even though the plugs were brand new, turns out the #1 plug was not seated properly. The threads were fouled out with carbon. We are going to see what we can do about it. Hopefully we can clean them.

 

That would lose you some compression, the taper seat is what creates the seel, not the threads. You probably need an M12 or M14 tap. Take a plug along to a machine shop & see if you can borrow one. The crumbled carbon will come out in the exhaust, you could try a vacuum hose or fill the flutes of the tap with vaseline or thick grease to catch most of it. A dab of anti-sieze just on the thread, might help them go in sweetly.

Aeroman

 

worst part is poor spark across the plug with high resistance to ground thru the loose plug threads

bet it was worse under load? on acceleration and on hills

careful with thread chaser, they can often cut cross threaded

 

K, well got it cleaned out. The performance is much better. It still has some hesitation off the line, I think I will just go in and replace all the plugs. The computer hasn't had a chance to relearn yet either.

 

Ok, so I've gone in and replaced all the spark plugs, and the performance is much better, however, there is still a problem. If I take the van for a short drive, it seems to run very well. I let it heat up to operating temperature, and it just continues to run well. But if I shut it off when it is warm, it will not restart until it cools back down, and it smells like it is flooding out during startup. Any ideas on what could cause this? It starts right up when cold, and just seems to run very well, its just at startup that this problem seems to occur.

PS, I just replaced the ECT sensor too, so that is no longer a contributor.

 

Sounds like you do have a flooding issue, see if your fuel rail holds pressure (35-40 PSI I think) at idle (fuel pressure reg might have problem) or possible leaky injector(s). Make sure you dont have any leaks in the intakes or at ex manifold to upstream o2 sensor. Any black smoke out the exhaust ?
Yours is OBD1 right ?

 

You may want to consider checking for a missing or leaking cap at the vacuum tree. One of the symptoms I was having was a "pop" during higher idle and what felt like a miss.

I know it seems and sounds stupid, ...... but you never know