Well, I rewired my EFI system this past weekend in order to get rid of my idle misfire. Bought a new Painless harness and put it in. But unfortunately, it did not cure the problem- it runs the same as before.

At this point, I'm assured that I have no electrical problems. Since every component on the EFI system has been replaced and/or tested as good, I've ensured good spark, all injectors are functioning normally, and every cylinder has compression. I'm starting to think a little more way-out-there.

Given: I have fuel, spark, and compression functioning properly- yet the #2 cylinder is misfiring and I'm getting a really foul odor eminating from the front of the vehicle.

Since I'm dealing with a batch fire system, could it be that at idle speeds, there is enough time before the #2 intake valve opens, for something to be sucking the fuel out of the #2 intake runner, thereby starving that cylinder? Perhaps another cylinder is doing it? I posted two other posts about my emissions system- perhaps a faulty setup since I'm running a 1990 engine in a 1971 vehicle (I'm only running a charcoal cannister and PCV).

I consider the fact that all spark plugs look normal- that is, the plugs indicate that the cylinder is firing normally at higher engine speeds. If I had a misfire at higher engine speeds, I would expect a blackened plug, but rather it is a very light tan (like all the others) which is just right. Somehow, the #2 cylinder appears to be getting robbed of it's fuel delivery at idle.

Any thoughts?

 

Have you thought about putting your O2 sensor on # 2's primary? You obviously wouldn' t want it to stay there, but it could give you an idea of if your barking up the wrong tree or not. Just some food for thought.

 

I could be way off here, but I would re-adjust ALL your valves. If the #2 valves are out of adjustment, it could cause a slight misfire at idle on that cylinder.

If re-adjusting the valves doesnt help, you could have a weak or bad valve spring(s) on the #2 set of valves.

But, I would replace the cap / rotor / and that plug and plug wire first.

 

Try putting the #2 cylinder plug wire on another cylinder and see if your misfire follows the wire. I had that happen once, one bad wire out of the box.

I agree to check you valve settings if that doesn't help...

 

I've done all of the above, numerous times. The misfire has never left the #2 cylinder no matter what was done.

It's like I said, I'm getting fuel, spark, and compression at above idle-speeds since I have no misfire there. I can also verify that the injector and plug are firing and that I have compression at idle speeds. But I cannot say that the fuel is actually getting into the #2 cylinder at idle speed.

However, a cold #2 exhaust header tube indicates that there is little or no fuel getting into that cylinder, which then says to me that somehow the fuel is gettin sucked out of that port before the #2 intake valve opens.

The heads and valvetrain are fine. I had Air Flow Research inspect them when I took them off. I've also readjusted the valves on multiple occasions. Leak down and compression tests indicate that the short block is also fine. Lastly, a new cam and lifters mean that the camshaft is not the problem.

 

That is a very odd sounding problem. Tough one...

What about fuel injectors? You mentioned they are functioning properly, how do you know if you don't mind my asking?

What kind of smell? You said it comes from the front, near the cylinder in question?

 

I'm gonna say that #2 Injector is bad. It may measure ok with a meter, and be plugged internally. It might "feel" like the miss goes away above idle, but it actually doesn't. With the engine idling, pull the connector off the #2 injector and see if the idle speed changes. You might have to disconnect the IAC motor first, as the computer will try to adjust the idle speed.

Dave

 

I've felt misfires at speed before. It's definitely noticeable.

The way I confirmed the injectors was to swap injectors around from one cylinder to another. I swapped #2 with #4 and then I again swapped #2 with #1. There was no change. The misfire remained at #2.

I've also swapped injector plugs and even swapped the entire bank of plugs from one side to another. Still no change.

I have went around the engine while idling, disconnecting one plug at a time. At each injector, the engine idle quality deteriorated further and the idle speed dropped. When I got to the #2 cylinder, there was no change. I repeated this process with the spark plug wires- same result.

The smell is hard to describe. It's not quite like raw fuel, and definitely smellier than average exhaust. I've heard that a lean burn can create an odor as much as a rich one. So I'm not quite sure what I'm detecting.

 

did ya pull codes from the ECM. I had a similar problem only mine was on cylinder 3 it turns out that the ECM was Bad.

Just Thinking Out Loud

 

I've gone through a couple of ECMs already thinking I had some sort of a short circuit in the harness. I ohmed out the wires numerous times, and believe it or not, I actually bought a completely new harness and put it in this past weekend just to be sure. Went to the wrecking yard, picked up yet another computer and put it in. But still the same problem is there. Pretty sure now that the ECM is not the problem.

I've been struggling with this since about November 2002. So I have had plenty of time to do just about everything imaginable.

 

I'm by no means a "mechanic" , but I noticed you burned your own EPROM, you might wanna triple check it. maybe put in a differant chip.

Just a thought.

 

I can't even count how many times I've tried to "tune" the problem out. I even have the CATS Real Time Tuner.

 

Dont rule out the possibility of a bad distributor!

Still could be a bad plug wire.

Also, MAYBE a collapsed lifter on #2 intake.

Possibly a blockage in the intake on the #2 runner?

 

I think your problem is mechanical in nature rather than electrical and EFI related.

I'd suspect a lifter that is bleeding down at low RPM.

 

Hmm, very weird problem. I would say that it may be one of two things, (shot in the dark)......possibly bad pickup coil/module, which is breaking up/missing at low RPM, and just so happens to cause the misfire in the same place consistently. Or, possibly something related to the lifters on #2, either the oil passage to the lifter is blocked, or the lifter bore itself is scored alot, leading to lifter bleed-down at low rpm, low(er) oil pressure. This assumes that you've done a true leakdown test on the engine, not just a compression test. I dunno, thats a very wierd problem, good luck with what you find. Sweet car by the way, I've got a 73 split bumper that will be complete eventually(fingers crossed)

 

A vacuum leak will cause a cyl to misfire at idle, then run OK off idle.

 

Yeah, that's another possibility. Especially if you're still using a lot of the stock plastic vaccum lines. They haven't held up so well on my car over the years, so I've ended up replacing about 90% of them due to failures.

 

do a compression test and/or leakdown ,
you must eliminate some possabilities to find the miss.
this will tell you what shape your valve seat seal and ring seal
are in.