Misfire Conundrum...

[rxb]

1999 Toyota corolla (1.8L, 1ZZFE eng)

original symptoms/problem :

1.very rough running and vibration at idle - seems to run better above 50mph though I only drove it enough to get home because of a...
2.Blinking check engine light
3.some oil seeping out of valve cover gasket on exhaust side (no oil in spark plug wells)

testing :

misfire confirmation

on my way home after the problem started, I did stop by autozone to pull the codes - only P0301. I confirmed that it is indeed only cylinder 1 with 2 separate tests - both temporarily pulling the spark plug boots one at a time and then pulling the fuel injector electricity one cylinder at a time, as well. Cylinder 1 had no change, all other cylinders dropped idle to the point of almost stalling for both tests.

result : only cylinder 1 misfiring and seems to be misfiring every time.

spark

the spark plugs had a little carbon build up and two of the spark plugs had a small amount of oil on the threads and electrodes. I replaced all four (they were probably due) and this does not fix the misfire.

I check all four cylinders with an inline spark tester; all four are getting spark. I also tested the plug from cylinder 1 out of the cylinder to see that it can produce a pretty good intense arc. At least half an inch through air.

result : spark is good all around

compression

compression test shows 175psi,165psi,170psi,170psi for 1 through 4, respectively.

result : all four cylinders are holding compression

vacuum leaks

First, I used propane to test for vacuum leaks all around the engine. No difference in idle. And then starter fluid to spray around the intake manifold concentrating on where the manifold meets the head for cylinder 1. Again, no difference in idle.

result : no vacuum leak (?). I would guess that a major vacuum leak would lead to random misfire and not the specific cylinder 1 misfire all the time that I am seeing. if I understand things correctly, the only way a vacuum leak could lead to a single cylinder misfire would be if it was in that cylinder's portion of the intake manifold gasket, right?


fuel

I tried to do the "screwdriver touching the fuel injector" test to listen for ticking/clicking, but the engine vibration and wobble at idle makes this inaudible. with the key in start, I see a voltage of 12.38 from each of the fuel injectors electric cables. And then .44ohms back to battery through the negative side. Electrical connections are all solid. The resistance across the four injectors themselves was consistent (13ohms)

I pull all injectors and clean them manually. I see 4 solid streams from each injector. Just to be certain I swap the injector from cylinder 1 to cylinder 4. No change. Still cylinder 1 misfiring 100% of the time.

other

Even though the valve cover gasket is seeping oil out of the side and not into the spark plug wells (that I can see), I go ahead and replace it. It covers my bases and was something I needed to do anyhow. no change.


So, long story short, I think I have spark, fuel, and compression for all four cylinders. Argh...

I feel like there are parts of the system that are in parallel - spark plugs, wires, injectors, etc. That is, one separate thing for each cylinder. And then some things are in series. Gas tank - fuel filter - fuel pump...or air filter - throttle body - intake manifold.

My assumption is, any problem in series affects all cylinders equally. Any problem in a parallel component would affect only that particular cylinder.

But I very distinctly have only 1 cylinder misfiring and it's all the time.

I must be missing something!

If my fuel pump were on the fritz, would it pump enough fuel to the first three injectors, but not enough to the fourth?? Cylinder 1's injector IS the farthest down the fuel rail. I guess it's not impossible(?)

Or maybe the intake manifold tube for cylinder 1 has an obstruction? I guess this would prevent enough air from entering the cylinder but not yield a vacuum leak. No clue how that would even happen. I can't find detailed diagrams of the intake manifold interior to see at what point it switches from series to parallel.

Any thoughts or suggestions would be greatly appreciated!!

-rxb

[Copytech99]

Move the #1 coil pack to another cylinder # and see if code, or symptoms change.

[rxb]

Originally Posted by Copytech99

Move the #1 coil pack to another cylinder # and see if code, or symptoms change.

this corolla is a 1999 and doesn't have interchangeable coil packs on top of each cylinder. think that started at 2000.

the wires go direct from the plugs to the side of the engine which has, what appear to be coil packs (two of the packs with two plug wires wires connected each).

I guess I can swap these as I believe the computer is responsible for all the timing and such?

[Copytech99]

Very sorry then, owned a 2000 and did not realize.

[rxb]

problem solved.

turned out to be a plug wire boot that worked fine out of the cylinder, but then must have been arcing to ground inside of the head (spark plug well). plug wire swap (at both cylinder AND coil) confirmed this as new the cylinder now misfires with the bad wire.

[Copytech99]

Glad you got it solved !!

I remember one time a set of plug wires suddenly dying without warning (believe it was on one of my Corollas, or my Prizm)

Thanks for update.