upchuck86

I've been trouble shooting a poor performing automobile for a couple of years (1986 Camaro 2.8l V6). The car became sluggish and also lost a head gasket. Replaced engine with new GM crate engine and began trouble shooting the performance issues.
Replaced 'every' component including distributor, plugs, wires, MAF, EGR, IAC, TPS, Oxygen sensor, etc.
- Took it to garage; they only replaced some of the same components and gave up.
- Worked on it for months, and let another garage give it a try, they needed to recoup their investment so charged me another $600 and gave up.
- This time I took it home and replaced the ECM (after controversy about the correct ECM). Originally installed ECM for VIN = 1G1FP87SXGL138917 was part number 1227302, but Chevy dealer told me it should have been a 1226870. After getting the dealer to call GM engineers it was determined that the 1226870 was for later year electronic injection and my engine is Multi Port Fuel Injection. So I replaced my original ECM with a new 1227302 ECM, solved nothing. Car still tries to backfire with timing set correctly. The timing appears to retard when it should be advancing so I decided it was time to try a new PROM.
- New PROM ordered for a Broadcast Code = HNJ. With new prom installed (no other changes) it increased the idle rpm from 500 to 1200 and caused the Service Engine light to cycle on/off rapidly, and OBD error "Engine Will Not Respond". Adjusted the timing and TPS enough to drive the car (BTW - the Timing REF bypass connector did not switch modes, but will with the old PROM). The transmission would not shift correctly (which I did not know could be affected by the PROM, just ECM for TCC).
- Asked dealer to verify new PROM (Part # 16087038) with markings on the IC = 1608, AMBF, 7038. He verified that the part was the correct one, so I re-ordered part # 16087038 to see if it may have been bad. New PROM has same effect... rapid blinking of Service Engine light, automatic transmission shifting affected, etc., but good performance and response when not in gear.
- The Service engine light goes out when the old PROM is reinstalled, the shifting goes back to normal, but.... the distributor timing must be reset to eliminate backfire. Of course, the same sluggish performance reappears that I've been trying to resolve. The car has very slow acceleration from a stop, shifts into second and third smoothly, goes into lockup fine. It almost sounds like a carbureted automobile that has a severe air restriction, but of course it has great throttle response out of gear (distributor can be adjusted from backfire position to ping position without the service engine light coming on).

Any advice, suggestions, etc. Do you know how I can research the new PROM markings to get a schematic to compare to the old PROM to verify that this replacement part actually is identical (internal electronics) to the old PROM.

Thanks,

RBob

iTrader: (1)

Both the 1227302 and the 1226870 ECM were used in the '86 MY. The '7302 ECM is a newer model. The BCC HNJ is correct for the '7302 ECM.

The rapidly flashing SES light is because the new PROM is either the incorrect one for that ECM, or, it has not been properly programmed, or, it is inserted into the ECM backwards.

As for lack of performance, it is probably mechanical. Clogged exhaust, running too hot, retarded timing, lousy cam/heads in crate motor.

RBob.

steve8586iroc

I agree with RBob. Check the exhaust for a bad cat or a potato up the tail pipe.

Steve

upchuck86

Thanks for reply. New exhaust system. Various timing setting for experimentation were tried (timing light shows retard when advance should occur PROM?) GM engineers tell me the 680 ECM was for later model with EFI but manuals never updated. HNJ superceede by AMBF and AJUC BCC. Both new ones I ordered were AMBF (set one to chip house to verify program to HNJ). Trying to get an AJUC but too hard for dealer (says I gotta take the one I get for the part number ordered). Trans/eng performance good in 2, 3, and TCC lockup OK downshift good at freeway speeds. Thanks again.

JP84Z430HP

The AMBF appears to be the latest, according to Caldata. I wouldn't worry about the AJUC.