once in a while engine miss

[artieb]

Hi, I have a 1990 Legacy L 5sp. I have a miss that is driving me nuts... It comes and goes smoothly, meaning gradually starts to miss then as smoothly as it starts, it goes away. Usually happens when you accelerate slowly or hit a small grade. I noticed it when I repaired the AC, but it can happen anytime, cold warm or at operating temp. usually warm. It may go 50 miles and nothing, then start it up within a few miles does it. I have shaked and tugged, and pulled connectors and the wiring. It smoothes out around 3200 or so rpm on a downshift. I have removed the thermostat with no change. I have replaced the knock sensor and used premium fuel no change. I can turn the engine off and coast and restart the engine no change. I have put new grounds on top of factory with the coil pack, ACV, no change. I put in new NGK plugs gapped @ .043 in. I have replaced the following coil pack, igniter module, plug wires, O2 sensor, All 4 injectors, fuel filter, MASS, gas cap, PVC valve, knock sensor, fuel pressure regulator ECM temp control sender, THE ECM. the same results. I have looked and felt, sprayed to look for a vacuum leak, no change. This has been going on for 3 months, and many tanks of fuel. When it's having this fit, it really uses the gasoline. I did notice when it was doing this, the fuel Gage would slowly go towards empty, and than drift back up, I out an extra ground on the electric fuel pump wire at the sender unit. I may have forgotten what else I did to this, and I'll be grateful to the winner of "Guess the Gremlin sweepstakes" Throw out what ya got! Thanks, Artie I have 2 codes stored in my ECM that I cannot erase, 22 knock sensor & 24 ACV valve. I have pinnout the knock sensor wire and that rang out. There is no CEL light on.

[Legacy777]

Artie,

Can you describe what repair you did to the AC? Was the miss there prior to you working on the AC?

You mention you can not clear the codes, have you used a multimeter and check the knock sensor wire for continuity? Have you tried using just the green diagnostic connectors to perform a more "active" diagnostic?

[artieb]

Thanks Legacy777, I just charged the ac , I didn't notice the miss before, now it can miss warm, AC on or off. And yes, I did a continuity on the KS circut fron ECM to Knock Sensor. I replaced the old sensor with a new one. I even watched the spike at the ECM, with a multimeter, by tapping on a socket and extension. I'm afraid I don't know what you mean with "just the green connector"? My Haynes told me how to read coded wrong, and I belive it was here that I learned how to connect the dianostic connectors to read coded. I did today hook up a fuel gage, and so far it has been 29-31 lbs without the miss, though. I was told to close my plugs down to .040. I thank you and I have been dealing with this for 3 hot months that may be why it hasn't done it before, Thanks, Again, Legacy777

[Legacy777]

Check out my site. I've got info on how to pull the codes from memory (black connectors) and how to perform an active diagnostic (green connectors)

www.surrealmirage.com/subaru/engine.html

[artieb]

I drove the Subie with a fuel pressure gage and took awhile, it startrd acting up, and my fuel pressure was 38 or a little higher. I'm goona look closer into the regulator, I would like someone to tell me everthing I need to know about this regulator. I guessing that above 36lbs it's suppose to open and bleed off fuel until the pressure fall into spec, then goes on from there?

[Legacy777]

If you're between 30 & 40 psi, your fuel pressures are fine. Check out my thread where I tested fuel pressures.

http://bbs.legacycentral.org/viewtopic.php?f=5&t=24723

[artieb]

Well let me ask this. I found the vacuum signal hose on the regulator to be marginal on the seal, and while it was, I noticed the fuel pressure acting differently than with the hose sealed? The hose had to heat up when warm with the AC going, different fuel supply demands, and leaking vacuum, which would make the regulator get a lower signal and raise the fuel pressure. It may take another 50 or more miles to see if this is it. Keepin' the forum updated. I had a hard time describing this miss, as it was different than any other I have been around in my 40 years of wrenching.

[Legacy777]

Well if the vacuum reference to the regulator is marginal, you may be seeing fuel spike and dips......not sure it's going to be causing your miss though.

Keep us posted.

[artieb]

I still have the miss, Or I should call it a MISS-Fire. I pulled a plug wire of the good running Subaru and grounded a spark plug, the miss I ahve been describing is actuall a misfire. I am only partialy missing on the problem Subaru. The fuel pressure is smooth between 30 and 40, and reflects the change in vacuum. I hope somebody is still hanging in there with me. I have a very hard time thinking that the new spark plugs would miss in the very same manner as the ones I changed?

[Legacy777]

What brand plug & wires are you running? What's the gap on the spark plugs?

When you replaced the ignitor & coil pack, did you replace them with new or used parts?

Have you checked the ignition wiring from the coil pack back to ignitor and then the ECU for continuity?

[artieb]

I wish Legacy777 was my brother-in-law, I could use some Subie knowledge! I am running NGK and were gapped at .043 and was told regap at .040. I replaced the ignitor and coil pack with working componants from my other 90 5sp Subie, and the problem stayed in the white wagon (DEMON SUBARU), and the junker ran perfectly. I did NOT ring out the ignitor or coil pack circuts, as I figured I would lose 2 cylinders with either the ignitor or coil pack, not a partial cylinder. I was looking for different brand of plugs and a Neon coil pack. Neon's coils have larger windings and would have more spark. Help!!! I know what happened, As soon as I decided to sell the white wagon, it started acting up, been messing around with this thing ALL summer, Thanks for whatever direction you can give, Artie

[Legacy777]

I'm kind of stumped. Can you describe the miss a little more. Does it happen at idle? If so what happens when you unplug each spark plug wire at a time? Same with the injector plugs. Look for any difference in how the engine responds based upon the other cylinders. It would be helpfull to try and narrow it down to a particular cylinder vs the whole engine.

[artieb]

Legacy777, I think were kinda stumped. When the demon goes into the fits, by the time I get pulled over, get out and open the hood, the miss is gone. I would imagine with a waste spark ignition system that If I pull 1 plug wire, I lose 2 cylinders. When the "miss" happens it's more like a weak spark? I'm really not an idiot, I have messed with autos for 40 years. I can only replace the plugs with some other ones. I don't think it's anything mechanical, valves, cam, lifter, etc... Someone had mentioned something like the old split-fire plugs, something that had 3 electrodes, or something like that. I thought about changing a heat range? It feels ignition based, not fuel? Did that make sense about the wiring between the ignitor, coil, and ecm, that I would lose 2 cylinders, if I had a bad circut ? I have some other things pressing and won't be into it for a few days.... Time to think, Thanks to all that has contributed, Artie

[Legacy777]

If you pull the plug wire, you will only lose that cylinder, not both.

Once you get upstream of the coil, then yes, the two cylinders are tied together. However like I mentioned, when pulling each plug wire, listen for the change the engine makes. If when removing the front two plug wires you notice less of a change compared to when removing the rear plug wires, that could be an indicator that coil, wire, etc could be problematic.

[artieb]

I'm getting back into this! What is the part # for the neon's coil pack? Or what years (of course 4 cylinder)would I ask?

[Legacy777]

You got me on the neon coil pack, I would not know.