nickel261261

Normally I'm just a lurker here and find everything I've needed to fix just about anything here, but this one has me at my wits end to the point where I decided to finally make an account.

I start the car cold, engine runs smooth as silk, never been better the whole time I've owned it. After a minute or two, there's no injector pulse only on cylinder 6, everyone else is happy. At idle, it never comes back, but it does occasionally come back briefly at specific loads and RPMs.

Tried flashing a stock tune, tried a whole different computer, swapped 4 injectors in its place that all consistently fire on a bench power supply, ran a completely new wire from the PCM to the injector, nothing changes.

The work I've recently done has been swapping all 8 injectors for OEM ones (there were some cheap ebay ones when I got it), and swapped the fuel pressure regulator since it was leaking a bit, ran better than it ever had afterward, replaced the oil pan gasket and engine mount bushings (with the engine in the car). This started happening not too long after the oil pan gasket job, though I'm not entirely sure how that could have effected just one injector.

Anytime I try to research this I always end up with either a bad opti or bad VATS, but spark isn't an issue and the car starts and runs no issue so it isn't either of those.

Any help would be greatly appreciated. Let me know if there's anything else you'd like to know.

Injuneer

Have you scanned for codes? There is a code (DTC 18) for “injector circuits”, although it does not identify the specific injector. But if it sets, that would confirm the problem is in the circuit, not the Opti or VATS. Not sure how VATS would be involved in any case.

Maybe I missed it, but did you verify a constant 12 volts on the pink wire at the injector connector, both under cold and hot operation? When the code sets, one of the “action taken” is to deactivate the injector driver. Loss of 12 volts to a single injector could involve an intermittent connection in the splice that connects the 4 injectors, a fault in the pink wire to the connector, or a faulty pin on the injector harness connector.

nickel261261

Thanks for the swift reply. I did forget to mention that I had also checked that there was 12V across the two terminals on the injector connector regardless of when the measurement was taken. EEhack hasn't reported any DTC errors with either computer at any time during the process either.

I also continuity checked the pink wires across the harness from injector connector 2 to connector 6, as well as the yellow/black wire from injector connector 6 to the PCM's red connector. They both checked out.

To clarify a bit more, the issue doesn't appear when the car sits overnight and is completely cold, but comes back well before reaching operating temp or the PCM enters closed loop operation. This last time I tried it only took all of 30 seconds for it to come back, but ran smooth as silk just before.

chevykid

Checking continuity, only checks that there's a connection between 2 points, but how good that connection is, you need to "ohm" the connection to see if your getting close to 0 (zero) ohms.
continuity check on a meter will show continuity with 100's of ohms resistance.

Injuneer

My concern is that the joint in the splice, or the harness connector are opening up when they heat up. Maybe far fetched, but it’s even harder to think of a way the Opti or VATS system would selectively cause a single, specific injector not to fire. When I get a chance I'll review DTC 18 in the factory service manual.

nickel261261

Just checked this morning, we got 0.4 ohms from injector 6's connector across the yellow/black wire to the PCM, 0.3 ohms from the injector 6 connector to the injector 1 connector across the pink wire, and I got 0.5 ohms from the A2 ground on the PCM red connector to the negative battery terminal. And for fun I ohmed injector 6 and 1 since I already had the connectors off, one was 12.5 the other 12.4.

Injuneer

Was the engine hot or cold when you did the above tests?

nickel261261

Honestly I wish I had a problem with Opti or VATS at this point, at least those are a solved problem. And I just replaced the Opti with a Petris one less than 6 months ago since mine was actually having issues.

Just for fun, and as a suggestion from a buddy of mine, since I'm just blindly throwing darts at a wall at this point, I ran a ground wire directly from A2 on the red PCM connector to the negative terminal on the battery. Maybe it's a bad ground, I said. Well, if it is a bad ground, it's not that one.

And I'm honestly quite sure that it isn't heat related. Even the headers are still touchable by the time it starts missing, doesn't take very long.

nickel261261

I checked all those cold, the engine was still cool to the touch by the time I shut it off since it was missing for a couple minutes at that point. If you think it'll help I can get it up to temp and check again.

chevykid

too bad you don't have a stock 95 computer with the stock programing that hasn't been changed, to try.

One other though is, you have been checking the quality of the connection of the wire, what if there is an intermittent short to ground on the number 6 injector?

you might need a scope to see what the signal really looks like.

another thing is the opti does produce a signal to tell each cylinder when to fire, maybe the slot for #6 has some grease, oil or dirt causing it to miss read and confusing the computer in a way that the computer just skips #6.

Injuneer

He indicates in the first post he has flashed a stock program and tried another PCM. That seemed to rule out the injector drivers. He's also swapped and replaced the injector.

The thought on a blocked #6 slot in the shutter wheel is interesting, but I couldn’t figure out why that would be sensitive to heat. But, what if the shutter wheel is warped, or warps as it heats up? #6 slot is only 2° wide, one of the four the smallest.

shoebox

I may have missed it, but what is the method being used to verify no injector pulse? I haven't seen mention of a noid light.

nickel261261

I had disconnected the harness from the injector on the car and ran it with a different, known good, injector in my hand and felt for clicking is all, since I didn't have a noid light handy. They worked fine when plugged into a different slot on the harness, but not #6.

nickel261261

I drove the car to my buddy's place to put it up on a lift and see if there was any obvious wiring issues underneath that I couldn't see. About 5 miles in it seemed like the issue was starting to clear up, and by the time I got there it was running better than it ever has. Whatever it was, it never cleared up during any of the 50+ miles of driving and hours of idling I had done in diagnosing this issue and testing everything, but has now decided that it's done throwing a fit, at least for now. Hasn't come back in the 160+ miles of driving I've put it through in the couple of days since.

Not sure how I feel about this being the outcome, since now I don't get any peace of mind since I don't know what went wrong or how it resolved itself. But I guess for now I'll enjoy driving it in the nice weather.

If it comes back, I'll be sure to add anything else I can find out here. Thank you all so much for your help in trying figuring out what was going on.

Injuneer

Are you located in an area like Texas where there has been extremely hot weather for the past couple weeks?