ULTM8Z

A lot of you guys are probably aware of what's happening with my idle misfire already, but here's some other information:

On cylinders #1 and #3 thru #8, when I pull off an injector plug, the Integrator value shoots up past 160. When I pull off a spark plug wire, the value drops past 90. Makes sense.

However, when I do this to the #2 cylinder, there is no response. I've tried moving injectors around as well as injector plugs, but no change. Same with wires and plugs. Leak down tests showed good on all eight cylinders.

How can this be when the ECM has no individual cylinder contol? It almost appears that the ECM is preventing cylinder #2 from operating.

Morley

Like you stated, the ECM has no control over individual cylinders, so that rules out the ECM.
You have a dead injector or an open in the connector/wires for it or a dead plug/wire.
Ohm out the injector (12-16 ohms is about normal) Check for voltage on that connector, each pin to ground should give 12 volts. Skip the noid light test because the other injectors are firing. If that all checks out good, look at your plug, swap it with one you know is working, did the problem move with the plug swap? Yes, replace the plug. No, ohm out the wire for the dead cylinder and replace if it is "high". To tell if it is high, ohm out another wire that is about the same length and compare. If the wire checks good then you may have a broken terminal in your distributor cap.

ULTM8Z

That's just it, I've swapped injectors with other cylinders, as well as injector plugs, spark plugs, and spark plug wires. Nothing I do seems to have any effect. I've also tried a whole different set of injectors, new plugs, another set of wires, and another cap. No difference. I've had the engine torn down to the short block, new cam lifters installed, the cam has been changed, the cylinder heads inspected, etc. I keep hoping someone has run into this kind of thing before but so far I appear to be unique.

91GTABird

Sorry off the subject but what is the Integrator value?

ULTM8Z

The integrator value is an indication of how the computer is correcting itself for fuel distribution and it operates on the short term. But here it is in plain English:

We know that the computer gets its air/fuel mixture burn results from the O2 sensor. If the O2 sensor reports too rich of a mixture on the previous cycle, the computer will pull out a little fuel to correct on the next one. This little correction will read out as a change in the integrator value. Ideally, if the computer calculated the perfect mixture, the integrator would hold at the nominal value of 128 at all times (the values can go from 0 to 256). However, since the mixture is rarely ever perfect, if the ECM corrects for a rich mixture (leans out the mixture), the integrator will drop a few points (sometimes a lot depending on how far off the original calculation was). If the ECM corrects for a lean mixture (richens it up) the integrator will raise a few points.

Fevre

Did you check to make sure you where getting juice through the #2 wire? Might be the cap/rotor connection is bad and your ecm/eng is already compensating for it. Might try a fresh cap and rotor or just check the voltage reading at the cap while the eng is running.

nasty355

i dont know if you have enough room for it or you may have tried it.try switching the injector plug from the #4 with #2 and see if the problem moves.if it does id have to say is in the harness.with verything tha you have checked is gota be something dumb and off the wall.if you canged ot injectors with known goodones then that should be ok.everyhtign mechanical checked out before.its either in that spark or in wiring for injectors.let us know what you find with everything and see what happens.good luck.eric

88TAJeff

Try checking to see if your reluctor in the dist. is cracked. Mine was missing on #3 only, and I chased it for a year until I found the crack. I did the same, changed plugs, injectors, wires, cap, rotor, etc. HTH,
Jeff

ULTM8Z

It's a new distributor. I changed it thinking something undetectable must be wrong with my old one. No such luck.

I've also switched injector plugs as well as entire injector banks (all four plugs from one side to the other)! No luck.

IS THERE ANY FREAKIN' WAY that the ECM could be causing the #2 cylinder to drop off at idle???????!? I can't begin to see how...

If my hair doesn't fall out naturally, I'll end up with none anyway after this problem does me in.

nasty355

i wouldnt think that the ecm could possibly have a problem with number one since you switched plugs and banks and no change.
so far what i know you checked.

new dist.
swapped injectors
switch harness to various injector plugs
pulled heads and took to afr to get checked
changed cam and lifters
im sure theres lotsa other stuff that i cant remember

did you check the plug wires or replace them???figuring you did.

oh yeah if you think it could be in the dist or you just want to mke sure.you could always rotate the housing and rotate the wires on it 1 over.if its in the dist that should show a movement to a different cylinder.

i know you been over this a thousand times and all.but i really dont think the ecm could cause the probs you got with just one cylinder especially on batchfire.if you have changed everything related to #2 then its something off the wall.you changed plugs,wires,injectors,injector plugs and banks.not much left.mybe its a longshot but the distributer idea could hlp or may not.wondering though is it possible for the ecm to alter just spark on #2????let us know what you find.eric

ULTM8Z

One other nagging symptom I've been having lately is an intake backfire. It's bad when it's cold, but still occurs fairly frequently when hot. When I'm below 2300 rpm, the car often stumbles badly and if I give it to much throttle, the intake backfire occurs.

I don't know if this helps in the diagnosis, but it's some more information anyway.

I've also put a spark tester on all of the wires and each one fires the tester off easily. What I've also done is to put the inductive pickup from my timing light on each of the wires to see if there is current flowing through them at idle. Each wire operates the timing light just fine too.

KYL98

What year computer is it? Is it the 730 ecm? You could have a burnt resistor in the computer somewhere that is only affecting that one cylinder. I know that sounds off the wall but it happened to me a long time ago. I had three injectors go out on the way to work....and had to have it towed to a Chevy dealer nearby. They replaced all of the injectors, but two on the driver's side were hooked up backwards. It ran fine for about 3 or 4 mths, but eventually I ended up with a dead miss in the number 5 cyl. I changed EVERYthing like you did...even the EST module....only to find out that the injector wasnt firing ....wasnt getting anything from the computer.....My car is a 91 if that matters. I had to have my ECM replaced after that. For whatever reason it wouldnt fire the #5 injector. I thought it didnt matter under "batch" fire, but I was proved wrong. Good luck.....HTH...

bnoon

Have you tried swapping out ECU's?

Also, I know you've had the engine torn down to shortblock and all and done a visual inspection, but have you done a cylinder pressure test and a leak down test to make sure it's not bad now? A bad gasket, bad valve seat, or a stuck lifter would throw off that cylinder's tune big time.

91GTABird

BNoon. What did your Contour run at the track?

DannyT

Not sure if you fixed this problem or not but realize that the #2 cylinder is the furthest from the O2 sensor. It is very common for rich/lean conditions to occur from the even/left side of the bank because the exhaust from that side doesn't pass the O2 sensor therefore it has no idea there is a problem. Does that make sense or am I missing something?

nasty355

did you find anything out here or fix the problem???

CamaroStud1988

maybe a broken valve spring .

ULTM8Z

Yeah, that was the impetus for me to put an O2 sensor on the passenger side of the engine. At the ECM, I can switch back and forth between the two. Ultimately I have the ECM running on the driver side during normal operation, but the second one helps for diagnostic purposes.

I located a shop in Van Nuys who says they're willing to put my car on an ignition analyzer... most people won't even touch it since it's so heavily modified. Hopefully they'll be able to tell me what the deal is.

CamaroStud1988

oops,i meant dead lifter. not valve spring.

86CamaroZee

I have done just about everything and cant figure it out. Its happening to me on cylinder 3, i have moved injectors, changed injector wires, mored spark plugs, chaged spark plugs, replaced all injectors with a different set, replaced my fuel pressure regulator, changed the distributor, moved the timing around, i tried 0 deg, 5 deg, and 12 deg, changed the esc, replaced all plug wires, did a compression test changed the ecm and the chip. It has a 1227165..... and still i can pull the spark plug wire off all cylinders and i makes a difference except for cyl 3. If anyone has a good suggestion as to what it might be please let me know im going nuts trying to figure it out

Morley

Check valve lash on that cylinder.

CamaroStud1988

im still going with lifter. they sould be hydraulic lifters.

ULTM8Z

An update of where I'm at on this.

I took it into a shop and they determined the engine is simply running extremely lean at idle- causing the #2 cylinder to drop off. In fact, at throttle tip-in, multiple cylinders are dropping off. It's probably a factor of the design of the intake manifold as to which cylinder drops. But here's what they did: they put temperature probes on all of the headers and confirmed that the #2 cylinder is indeed misfiring at idle. Then they manually squirted a some fuel into the throttle body and the idle smoothed out as well as the temperature evened out on #2 relative to the other cylinders.

They also put the engine on a scope and determined that the ignition is fine- spark engery is good to all cylinders. Therefore, something else is causing a severe lean condition at idle speed. On their scanner, the O2 sensor shows that it is pegged at .2 volts.

But here's the rub: when I put my own scanner on the engine, the O2 sensor shows fluctuations between .2 and .7 (not bad). The Block Learn is at 125 (also not bad). Is my scanner wrong? Something is apparently causing a overly lean condition that is not registering on my scanner. I'm going to have to play around with the calibration a little to see if I can change anything (I've tried before but to no avail, so we'll see).

At least now I have a better idea of what's happening now.

Fevre

Are you running a heated O2 sensor? If not I would not trust the readings at idle with headers unless you have it located on one of the primary tubes, even in the collector at idle it can cool off enough to give false readings.

ULTM8Z

Yes, it is heated. It remains in closed loop at all operating conditions (when the engine is warmed up and not at WOT). So I'm pretty certain there is not a problem there.

Fevre

Sounds like you got it all checked out, I feel for ya since it must be very frustrating.

ULTM8Z

Oh man. You don't know the half of it!

JakeJr

I've seen an intake manifold leak cause this type of "one cylinder" problem on a BB Chevy engine.

The #6 intake port was sucking from the lifter valley and made that cylinder - only - run very lean.

Because of the location, the "squirt the water around all sealing surfaces" didn't work.

I finally tracked it down when the leak became strong enough to begin sucking in a tiny amount of oil, fouling the plug.

Just my experience.

Jake

86CamaroZee

Ok My problem is exactly the same except its on cylinder 3, my valve lash is correct, the intake and exhaust valves are opening and closing fully and the timing and spark are right on, but at idle cylinder 3 is dead, i put a drop of motor oil on each header tube and started the engine the oil burned off all tubes except the one on cylinder 3. At first my o2 sensor was giving a fluctuating reading and my blms were at 128, now there at about 145 at idle which says theres a lean condition. what i dont understand is how the car can have a lean condition only on cylinder 3, on a batch fire system, that has perfect spark, timing, and comression.

Morley

There has to be something mechanically wrong with that cylinder or the fuel rail where that injector hooks up. Have you ever looked into the rail with the #3 injector removed to make sure the hole for the injector is drilled through and not obstructed in any way?

ULTM8Z

The only commonality between cylinders 3 and 2 is that they each fire at the ends of one crankshaft revolution. That is, if you look at the firing order on a small block Chevy - 18436572 - I believe the injectors fire on #1 and and #6 (batch fire). This means that a long time has passed (relatively) from the time the #2 (or #3 in your case) injector has fired to the time that the #2 intake valve has opened. With the air flow dynamics inside the intake manifold, perhaps other cylinders have scavenged some of the fuel from #2 (or #3) and by the time #2 intake valve opens, there is little fuel remaining for that cylinder. This may be an advantage of sequential fuel injection in this case. Though if true, this only holds for idle speeds. At higher speeds, the valves are opening and closing so fast that once the injector fires, by the time the fuel reaches the back of the intake valve, the valve is opened.

I don't know.... just a theory I was thinking about last night while trying to fall asleep....