F-body-fan

For testing purposes, is there any reason I can not test a 1987 5.7 Prom chip in my 1989 5.7 car?

I looked at the wiring pinout & all I see missing is the 89 has VATS & the 87 prom is programed for the 9th injector cold start.
So other than a long crank for cold start, this should work the same correct?

Or are there other 87-89 nuances that might effect how it would run?

Thanks!

Tuned Performance

iTrader: (92)

The only difference might be fan switch setting , so if the fan kicks on koeo the switch setting is different for ac pressure switch.
87 used csi so cold starts might be harder.

F-body-fan

Thanks!

F-body-fan

Whelp, looks like I have a bad prom chip.

A problem I have been having with the 87 since last year where its been starting hard & sets a maf low voltage code 34 right after start up. I chased through everything & could not find the problem. I even tried another ECU, but with this same original prom not thinking that the actual prom could be the issue so, I kept looking hard at all the wiring & kept coming up without an answer.

I wish I could test the 89 prom in the 87 to confirm my new findings, but that wire that belongs in connector location B6 said no.

When I put the prom in my 89 & it ran exactly like my 87 has been & set code 34 exactly the same as well.

Tuned Performance

iTrader: (92)

What’s the 89 bcc aujl aujm something like that ?
I’ll have a few aujl in a week or so.

F-body-fan

The 89 is APYU (3516) But thats one thats working great in the 89

The problem child is the 87 ABWN (8656) this is the one throwing the 34 code & running erratic.

Have you seen proms go bad like this? I have read of other members having bad ECU's & know they get changed out often enough.
I just never suspected a bad Prom. I'm still a little in disbelief.

Tuned Performance

iTrader: (92)

Usually if bad you get a code 41 or 51 for lost data but flip. I can update the chip on the abwn with a later tune . The abwn seems like a good tune I haven’t seen many proms fail.

F-body-fan

Wish I had something I could plug into the 87 to confirm its the prom, But when I put the ABWN in the 89, it does the same thing. a little erratic & throws a 34
Put the APYU back in & it runs perfect again. So I am 50% convinced thats my problem.

The strangest thing out of all of this is the only problem I have had with this car was cold start ups. the 9th injector worked fine, it would just struggle for the first 5 seconds & then good for the day. Been like that for as long as I can remeber. Decades!

Anyway, last year I followed Vaders post on setting the min air procedure which I had never done on any of my TPI cars. After I did that, the cold starts were way better, but the CEL came on right after words. I was so sure it had something to do with that. So I tried lowering the TPS closer to .47, put the throttle plates closer to were they were, but nothing corrected it. But just maybe, the disconnecting of the esc & or iac sent the prom over the edge? I cant explain why it happened otherwise. Not a big believer in coincidences with stuff like that. But just might have been this time.

F-body-fan

Would it make sense to write to a prom that is already being flaky? Sure not apposed to giving that a try.
The car is 100% stock, no mods whatsoever. still has a working 9th injector as well.

Tuned Performance

iTrader: (92)

I’d replace the prom with an eeprom to eliminate it. Then flash an eeprom. I unsolder the prom solder in a dip socket then press in a newer flash prom. Just a thought. It’s odd no other errors throw the chip has a checksum it should match the bits in the tune.

tequilaboy

B6 is the FMAF input.

Are you suggesting that your 87 has a frequency maf and that the ABWN bin that you have is setup for a frequency maf? It does not appear to be based upon the version that is available on gearhead efi.

Tuned Performance

iTrader: (92)

B6 for vats

tequilaboy

Sorry, forgot about VATS.