1984 SVO random misfire. Help me plz

[geforce89]

Hi, Sorry if this is to long below. I'm having a few issues with my SVO. I have a 84 mustang SVO, It has the 2.3l turbo motor. It has a misfire at idle. It also misfires when you rev it to 3500rpm or 4000rpm. it goes lean and back to rich on the Air/fuel gauge when it misfires. Its a random misfire. I tested the injector waveform with a scope and when it misfires it appears to drop on the waveform and return to normal randomly.

I can hear it misfiring/small popping in the exhaust at idle. the rpm moves up and down sometimes too. Any ideas?

I have good spark plugs and good wires. new cap and rotor and newer ford distributor.

My mechanic buddy thinks its either I have weak injector driver transistors in the ECM or it could be my injectors being to big since I have 35lbs brown top injectors instead of the 30lbs green top injectors that came in the 84-85 mustang SVO's. Could that be why I have a misfire? The inectors being the wrong pound injectors for that ECM? Causing the ECM injector driver transistors to slightly overload?

The injectors in this car are triggered by a ground circuit to open and close the injectors and they are batch fired.

My buddy thinks the injectors are spraying to much fuel which is causing it to go rich then the ecm trys to compensate for the rich condition and makes it go lean.

My ECM is the ZBA code.

The puse width on the scope says it is running at about 1.4 milliseconds to 1.7 milliseconds injector pulse on time. Not sure if that's where it should be or not.

Is the 84 computer compatible with the 35lbs injectors without modification?

The SVO's in 1984-1985 came with 30lbs injectors which where green top low impedance injectors.

The injectors that currently are in the car are 35lbs brown top injectors and they have 2.9ohms of resistance each when I test them individually with an ohm meter. Which are low impedance injectors.

I took the injectors out and used my custom made fuel rail and injector pulser to test the flow of the injectors each and they all seemed to flow good.

When I drive the car it doesn't have that much take off from the stoplight/bottom end but has a bunch of power on the top end when the turbo is kicking in. I'm wondering if this misfire would cause this?

Sounds like timing to me but the timing seems to be fine when I check it both cam timing and distributor timing which distributor timing is set at 10* Before TDC with spout disconnected.

Any help would be a big help. Been messing with this car for a while now and cant seem to pin point the issue.

Thanks
Jeff

[KCoker]

I have run the 35lb injectors with the stock computer for years with no problems. Have you checked your fuel pressure? I have had missing problems with the wires more than anything.

[geforce89]

Thanks for the reply. Yeah my fuel pressure at idle is 37-38ish psi. The pressure regulator is working. My spark plug wires are the blue Ford Racing wires. I think they are 9mm wires.

[Spoolin']

Have you tried cleaning the VAM? Cleared up my random miss!

I'm running BT in my 84 GT Turbo, which should have GT, and it doesn't seem like its missing, if that helps. I do want to go for a later comp and VAM, but budget is a bit thin, now.

[chads84svo]

Have you tried cleaning the VAM? Cleared up my random miss!

I'm running BT in my 84 GT Turbo, which should have GT, and it doesn't seem like its missing, if that helps. I do want to go for a later comp and VAM, but budget is a bit thin, now.

I have a 84 svo and I had the same problems. I went to a la3 and #35 injectors. Problem is all gone. I have my old ecu if you want it and my #30 injectors. If you want them, let me know. Chad

[Spoolin']

Did you change VAM as well? LA3 is on my list, as well as a large VAM because i was told you cant do one without the other, and im pushing my luck
(and wasting fuel) with just the 35's right now.

[chads84svo]

Did you change VAM as well? LA3 is on my list, as well as a large VAM because i was told you cant do one without the other, and im pushing my luck
(and wasting fuel) with just the 35's right now.

All svos came with the iarge vam. You alreadyhave it. Justget a la3 and your good I got one of those too

[Spoolin']

84 GT turbo, here

[chads84svo]

84 GT turbo, here

My bad, thought this was the guy with the 84 svo. I struggle with this forum, that's why I don't post much.I need to get better csuse there are nobody up my way with a svo, or even a turbo gt. I would love to chat with some mustsng guys! My car is pretty bad ass, and I see on this forum that you guys love your cars like I love mine.my wife hates it, I'm sure I'm not alone! Lol

[chads84svo]

Your best bet is too get s la3 ecu to run the #35 injectors correctly.and then your missfire should be gone.my 84 svo hsd the exact same problem.I switched to s la3 ecu out of a 88 turbo coupe an #35 injectors.the classic 84 svo miss was gone! Cheap and easy fix and a nice upgrade.the repining of the ecu was so easy, 45 mins it wad done. Good luck. Chad

[geforce89]

I have a 84 svo and I had the same problems. I went to a la3 and #35 injectors. Problem is all gone. I have my old ecu if you want it and my #30 injectors. If you want them, let me know. Chad

How much do you want for the ecu and 30lbs injectors?

I can get a re-manufactured Cardone brand ecu computer from orielly autoparts for $85 under my shop account. I can also get brand new green top 30lbs injectors for close to $17 each.

Thanks!
Jeff

[geforce89]

Have you tried cleaning the VAM? Cleared up my random miss!

I'm running BT in my 84 GT Turbo, which should have GT, and it doesn't seem like its missing, if that helps. I do want to go for a later comp and VAM, but budget is a bit thin, now.

Yeah I cleaned the VAF meter. It didn't seem to help.

[chads84svo]

i could let the ecu go for 75$ and the injectors for 60$ the injectors have been tested and new o rings installed. they are good to go. i went with the #35 injectors so i dont need them. if you want them let me know.they are just collecting dust.