Last year we did some transmission work and had some trouble with it only to figure out it was the pump... Then the opti died... Lack of funds held us off to this year. A friend had an extra opti lying around... Can't beat free.

Was able to test the trans and it works great. New clutches and updates, new torque converter. Started to get misfires at low rpms after the engine warms up. Started switching out and replacing everything. Did shoebox's opti test... Everything checked out. Kept hitting our heads. Switched out Maf, map, oxygen sensors, ICM, coil... Then the free opti died and wouldn't start, no code..

Went and bought a new/refurbished opti from American powerhouse.... Installed that with new wires and plugs. Still feels like a misfire only when warm and at low rpms.

Changed the fuel filter, hooked up the fuel pressure tester, acts like it should... Swapped out injectors...

Thought maybe the brand new torque converter (revmax) was the issue. Swapped it out with a known working Edge converter... Checked the U-joints and they look great.

Don't know what else to do besides maybe we received a bad opti?

Need some brains from shoebox and Ingineer

 

Best way to get help is to add a "Signature" with basic info about your car - year, model, engine, trans and any major engine mods. It's very difficult to provide accurate help without this info. Year of the vehicle determines how you scan it and what data (e.g. - misfire count by cylinder) can be retrieved.

 

Sorry... Having a retard moment and 1. Forgot to put that important info down and 2. Can't figure out a signature right now...

Anyway.... 94 z28, 503 cam, rockers, beehive springs, vented opti, all done a couple years ago.... When the pump went in the trans we upgraded the trans and installed a edge converter 2400 stall... I think that is about it, prolly forgot something.

 

OK..... OBD-1, no misfire detection. What is condition of the plugs and wires? Have you checked the injectors? Can you identify a colder cylinder by using an infra-red temp gun on the exhaust primaries? Have you checked the short Opti harness for damage, including the connectors on both ends?

When you installed a "vented" Opti, do you just mean a vented cap? Or did you actually change out all the parts required to install a vented Opti in a 94 - 95 timing cover, 95-97 timing set, 95-97 camshaft, new short Opti harness, air supply and vent line?

 

plugs and wires are new. I pulled all plugs a week after installing to see what they look like. They all looked good. I dont have a infra-red temp gun. I bought a new opti harness last year, and with the new opti it came with a new harness. We had the multimeter out and tested all connections and went through shoebox's guide on that.

Yes, we changed all the parts to switch to a vented opti... we did it when we installed the cam. We did that like 5 or 6 years ago, and haven't had a problem. I had to use it as a daily driver 3 years ago for 4 months or so until it started to snow, and at that time it was running great.

Just really baffling...

I think I might try and switch a different pcm into it, that we have laying around as an extra. There isn't too much more left that we can swap out.

 

I hate to even say it but disconnect the torque converter and see how it runs without it. I have a revmax in the garage right now... in the trans that is on the bench... I had a shake at around 1800 rpm that would not go away no matter what. unbolted the converter and smooth a silk. I am just waiting for my trans to get here, I have a new stall converter waiting for it.

edit: Just to be thorough, I did everything you did too. New plugs, wires, New opti, then a new M.S.D. opti, with new cap and rotor, moved the injectors around, scanned it new coil, borrowed an ecm, checked fuel pressure.

 

check your plug wires at night for arcing, last time i changed mine it looked like a casino advertizing under the hood.

 

^^^^^

and use dialectic grease on plug & opti boots. also you could have arcing between plug boot and plug wire heat shields (the stock ones) if you are using those...which make it next to impossible to see the arc if that is the case. you should also jack up the car on stands and while engine running look from underneath to see plug boot ends. if you cant see every part of the plug wire boot end...you are going to miss something

 

The wires are brand new, checked them and the brand new spark plugs twice already to make sure everything is connected and secure. It was doing the same thing with the old wires (which were beat up) and plugs.

We also thought it was the torque converter... Had an extra known working one in the garage, changed it out this past weekend. Still the same symptoms.

It seems that maybe it is a sensor because its after the car goes into open loop. We changed the coolant tempature sensor as well thinking maybe?... Still happening.

 

even with "new" wires/plugs....you can have a arc going on. Check the plug boot ends in the dark

have you checked the ICM and does it have the heat sink paste behind it?

 

Ended up being the new/refurbished opti spark... Put another one in and its all good now. What a pain in the a$$.