Misfire
 

Ok so Im working on a 91 crx si with a sohc zc, as it was driving down the road its stared missing badly, so first off i put new plugs wires cap and rotor, same problem triead swaping out ecu for known good one, smae problem, the only thing i can come up with is the ignitor maibe, all grounds are good, its really odd sometimes it will clean up and run like a dream until you let off and then its back to misfire all the way through the power band, any help would be much apreciated. Oh yea no CEL

Re: Misfire
 

I had a similar problem once like that, it was a bad oxygen sensor, unplugged it and the car ran fine so i knew it was it, got a new one and didn't happen again. It could also be the ignitor, but you would think that would be a constant thing.

Re: Misfire
 

Ignitors either function correctly or don't work at all, in my experience. I'm thinking more like a coil going south, or the like.

I've never fooled around with O2 sensors in OBD0, but for OBD1 they just cause a light stumble at cruise because the ECU "sees" a lean mix from the 0v coming in on the O2 sensor wire and tries to add fuel to compensate.

Re: Misfire
 

Thanks for the info, the only reason I was thinking ignitor is because it has a boucy tach at an idle but ill check the O2 sensor because it is a definate stumble and it will clear up sometimes, drive today and took to higher rpms and it runs like a champ at 6500+.
Thanks guys Ill keep you posted on the outcome if I figure it out I gotta spare coil so i guess i could swap that out real quick

Re: Misfire
 

Sounds like a thermostat housing or engine-chassis-battery ground problem.

Tach output is a seperate circuit inside the ignitor... they can go bad and start twitching the tach needle all over the place while the car runs down the road fine. However, the main duty and main circuit inside the ignitor is a high speed switch meant to charge and fire the ignition coil, and when it goes out you either start up and run fine, or do not start up at all, sometimes intermittantly until the ignitor goes totally dead. I'm pretty sure there has probably been a freak occurrence at some point in history where an ignitor was half-assed firing the coil during engine operation, but it's super rare and I have never seen or heard of it.

Coils will intermittantly break up or die, then start running fine for a minute, etc. This can go on for a bit (Atlee had one that would break up every so often that he drove around on for 6 months), but typically they die quickly when it starts happening. Minutes to a handful of days. The coil misfiring - possibly a crack in it's housing and causing spark to jump to ground inside the dist housing - might be playing havok with tach feed. However, I really would loosen, clean, retighten thermostat ground and check your main engine grounds to chassis/battery before I fooled with anything else.

Re: Misfire
 

So I double checked the grounds like you said and they are all clean and tight now still same problem, swaped out whole dizzy for known good one same problem, swaped oxygen sensor same problem, this things got me lost

Re: Misfire
 

It's a ground.

Bad connection at the ECU, maybe corrosion between thermostat housing and block, etc. Jumper wire from the thermostat housing wire to the dist housing to the battery ground will tell all.

Re: Misfire
 

some on put on like 5 ground wires from various locations on the engine to the battery and I cleaned and retightened all of them, should I still try jumping in another ground, ecu plugs seem to socket in nice and tight, thanks for the help man.

Re: Misfire
 

plug wires? ohm them out and make sure they are to spec, how are your spark plugs looking? gapped? gimme some info, sounds like a spark problem maybe, i was having spark spike at like 5000 rpms, and looked here and there, and it turned out to be one bad spark plug wire :6

Re: Misfire
 

I wish it was that easy.