My custom 89 started cutting out recently. It's most prevalent around 2k rpms under light load. It "lags" when the throttle is pressed, then recovers. If carbed, I'd suspect the accelerator pump. But, it's not.

If fuel related, I'd expect it to bog throughout. It responds to being "kicked". It can totally cut-out if I press lightly right around 2100 rpms on the hwy. Really, in any gear around that RPM.

I have a Moates piggy-back chip that I've wondered about longevity. I pulled it so many times during tuning, I wondered if it would crap out someday. ECM is one thought -- as it seems so RPM specific.

With 4-yr-old non-platinum plugs, I checked them and replaced them first. I also bought a TPS last week. Went to look for my USB/ALDL cable but can't find it! RATS! Of course, I'd have to mail order for another or hope it turns up one of these days.

Considering a trip to the shop to let them diagnose. It's a bit more of a PITA these days to do it myself. One stop would be to an AutoZone to borrow a FP tester. (FPump is one of the few things I didn't replace with the rebuild.)

I also considered fuel contamination with news of QT having diesel in some of their fuel. I haven't driven it much (2 times) since it started. Would be a PITA to run thru the nearly full tank of gas.

Vacuum leak? Would that be so RPM specific?

 

my first though would have been a burnted tps but thats off the board now

 

Or not adjusted correctly?

 

Replaced the TPS tonight -- after borrowing an aldl cable. Wish I'd checked the error codes first because the top TPS screw was "fused" in the TB. It sheared off and I had to drill/tap it for 10/32 (american). It was after 9PM and stores were closed.

Anyway...no change. I data logged and didn't see much wrong...except occasionally going a hair lean. Then I checked the error flags and found code 34 LOW MAF. I'll remove the accordian tomorrow to verify no leaks. Probably run it with the MAF unplugged and see if it improves. There was another test in the FSM to determine if the ECM is faulty.

So...it seems likely that the original MAF might finally be failing. I suppose the burn-off could be bad instead?

Probably have a dash light out too because the "Check Engine" light wasn't on -- even though a code was set.

I'm getting closer!

 

If you can find a MAF from an '86-'88 3rd gen Camaro it will work; I swapped one from my '86 IROC-Z into the prior '88 Vette and ran many years just fine.

 

Now, I think I've ruled out the MAF. It runs WAAAAY worse w/o the MAF. Plus the 34 code didn't reappear after being cleared. (It probably was triggered during startup after sitting over a week. It did sputter/stumble for awhile until fuel was flowing well.)

I suppose that's one symptom...though it's not bad if started within a day/two. Also, I reprogrammed the prom so it wouldn't wait several cycles to fire.

I also know there was a point where my 383 would cause stumbling if the tank was lower than 1/2 -- even in a straight line. Hadn't see that for quite awhile though. OTOH, I don't spank it for LONG stretches anymore. It would be a ticket-getter...if I did.

Can a failing fuel pump cause stumbling at lower rpm loads -- but "recover" to fulfill WOT loads? Didn't seem LIKELY so I'd dismissed that idea...as well as FPR. Nothing else is hitting my diagnosis though...so it's starting to seem fuel related. I did see lean condition for a couple of seconds in my scan. It never ran lean before....even for a second.

Would our ODB1 ECMS throw a code for lean misfire?

 

The fuel pump can do this. I had to replace mine a coupe of years back. The beginning symptoms were cutting out at lower to mid rpms while cruising down the street. It typically happened between 1800 and 2500 rpm. Given a little gas when it happened it would hesitate then correct. At first, I thought the dreaded opti. The MIL would even flash on occasion, so I thought misfire (ignition).

A couple of weeks later, at a stop light, with 3/4 tank, it acted like it was out of gas. Checked FP and sure enough, nothing. New pump, no issues.