HELP.. Getting ready to light a match to it

[jmaddox]

About 2-3 months ago I posted a question, still have not found the problem I think. Need some advise. I undated the information on what I have done.

I have found one thing that seems to have stopped the problem, but I think it's just masking it. Below you'll see that I have just replaced the ECM (Computer) but I put in a 88 v6 EPROM and the problem went away. It's a different model, and possible not made for the car, I think it's masking the problem and it soon will return. I do not think a Eprom chip can go bad in this way, they ususally either work or not right? ??

Orginal problem: Fiero cuts out under load above 60mph
Calling out the experts!!!

I have stumped 2 GM Pontiac Dealers

I have a 86 v6 Fiero, with about 198k... when I drive on the express-way about 60mph the engine will cut out and jump/buck every now and again... It's worse with the a/c on... The more load, like a hill or more weight in the car the worse it gets.

New Engine about 50k ago.
All new GM Injectors about 30K ago
All new parts are GM Only, no AFTERMARKET anything.

Just put these on or tested these:
New GM Ignition module
New GM pickup coil
new GM Coil
new spark plugs and wires
New GM TPS
New GM IAC
New Cat.,muffler,sprint exhaust manifolds, tailpipes, and tips.
New GM ECM
New GM computer coil to distributor wires
New GM Vapor canister
New GM fuel pump and filter (tested at 42.5 PSI Good
New GM AC Delco battery
New relocated GM RPM gauge device, moved away from coil.
Looked in dark for jumping spark from plug wire or coil.
Tested with old MAT, MAP, Engine Temp, to rule out.

Any ideas would be GREATLLY APPRECIATED.., before I light a match and collect on insurance... (just joking)

I'm dying here, the only thing left I think is injectors, but there not old and dealer said they all tested good.

[gsxrbobby]

Here something just off the top of my head, look and see if the wiring harness is ok when it goes through the firewall. No wires are open or rubbed, pinched etc...

[Rinwo]

Automatic or Manual?

[brooster]

If it ain't broke, don't fix it.

I can understand your concerns; you've spent a chunk of change. Was the PROM updated by GM? Perhaps you've stumbled on the fix.

Is the ECM going into closed loop? If not, you may have an O2 problem.

What is the alternator doing? Good voltage and amperage? Any AC voltage above .6? Belt clean and tight?

How's the ground circuits? Voltage drop test less than .2 volt DC.

If it works good, leave it alone.

[Jehu]

Burn baby burn!

[Blue02R6]

Other than what brooster said, I'd look at the air filter and intake tract for obstructions. Also check the plugs going into the coil, if they are damaged or lose they could have that effect.

[jmaddox]

It is a automatic...

The ECM is not in closed loop.

No air restrictions, good idea though...

No plug wire problems, replaced with new Talyor sprial pro wires... one of the best on the market.. I highly recommend.

No voltage difference at all when the car cuts out...

It's still not doing it with the 88 V6 Prom... still think it's just masking the problem.

[jmaddox]

Bad News, problem came back with the 88 prom chip..

Also, now have replaced the battery with a new AC/Delco 750cca
New O2 sensor and EGR value, egr soilnoid, and EGR tube.


PLEASE HELP.... I'm going to go by some matches tomorrow if I can't figure this thing Out!!!!!!!!!!

[Rinwo]

You say it cuts out, jump/buck can you describe it a lil more... once it does, does it stay low on power or does it just do it for a quick second?

when it does it, does it feel like the car is a manual and feel like its downshifting(without actually changing gears) or engine braking.

Cars lose some of its HP when a/c is on, so I'm not suprised that your problem is worse when its on.

Does it only happen in one gear? at a certain speed(around 60 or at an exact speed every time?)

Tis a very perplexing problem I'll give you that..... I'll ask some other friends and see if they have any ideas.

[Indy-1]

It does sound like the MAP sensor. That exact same thing happened to our '85 and we tried just about the same things you have. Was the old MAP you tried one that happened to be just sitting around? Did you try using a MAP sensor that was known to be good, like maybe one borrowed out of a good running Fiero? I went thru two brand new MAP sensors until I finally tried one out of one of my other running Fieros and the problem finally went away. Just a thought.

[FierceGT]

Have you checked the catalytic converter? If it's almost plugged, it can cause the car to lose power under load but can still idle and drive at slow cruising speeds fine.

[86gt4sale]

If I were you i would check the prom letter code and make sure it matches the ecm code cuz there are a few different apps..