Jeff91RS

iTrader: (1)

I just swapped a 350 and T5 into my 91rs 305 auto. I used the stock L05 tune except I modified it for the stick shift. Car ran, not well but it ran. I took it into the exhaust shop and it runs horrible.

After concluding the freshly rebuilt 350 was mechanicaly sound I started messing with the tune. I noticed it runs the same with any type of tune and that if I remove the PROM chip while its running it runs the same. It also runs the same with no chip. But the CEL does flicker rapidly with no PROM insalled.

It seems like my 8746 recognizes the PROM but does not read it.

Am I correct in thinking its time for a new ecu? My guess is he welded and didn't disconnect the battery.

Jeff91RS

iTrader: (1)

Anybody? I think I am posting this in the right forum. I hate to throw parts at a car.

efi-diy

If you decide to change the ECM - you might want to consider installing a megasquirt with the '746 adapter this way you can tune it quickly without having to keep burning eproms. http://www.diyautotune.com/catalog/m...0d9c8cc892d412

RFmaster

1) SES light - what does do during ignition key off - to run position. SES should be solid on, blink off, solid on until engine fires up and runs.

2) Pull codes - short pins A&B of the ALDL connector - observe SES light with ignition on, it should blink 3x code 12 followed by trouble codes if any.

Verify and post back

//RF

Jeff91RS

iTrader: (1)

1) I believe the SES light remains on constantly, no blink but I could be mistaken.

2) I'll post back by tomorrow noonish as it is almost 2 am.

Jeff91RS

iTrader: (1)

While that is very tempting, I am a bit strapped for cash. Plus even though I am very confident working with electronics I do not know if I would be up to buying an unassembled ecu.

Jeff91RS

iTrader: (1)

2) stays on constantly

efi-diy

Well you can purchase an assembled & tested MS for a few more $$.

RBob

iTrader: (1)

Another test for the '8746 ECM (and the '7747 along with a few others) is to pull the PROM out. Then do a key-on, engine-off. The SES light should flash rapidly. If it doesn't then I'd say the ECM took a hit.

The '8746 was used in the 89 - '92 TBI f-bodys along with Caprices of about the same vintage. Although I think it is the '89 through '90 or '91 time frame for Caprices. Lots of them around so $25 or so from the nearest yard.

RBob.

Jeff91RS

iTrader: (1)

No still blinks. Its like the ECU knows if the PROM is there but doesn't read it. It blinks rapidly if I take the PROM out and erase and reinstall it. So it knows if there is a valid program on the chip.

I have almost convinced myself its the ecu but I also wonder if my PROM chip is the problem.

RBob

iTrader: (1)

Without the PROM in place the SES should flash (blink) rapidly. This means that the ECM can't get a good checksum from the PROM. A blank EPROM should do the same. The reason is that these ECM's have the checksumming code within on-board ROM, not in the PROM.

So by getting the fast flashing/blinking SES the ECM's main CPU is running. If it didn't do the fast flash then for sure the ECM is dead.

Even with the fast flash there still may be other issues with the ECM. Double check that the PROM is installed with the notch toward the inside of the ECM. Burn a fresh PROM and try it. Or, get a stock GM '8746 PROM (have any laying around?) and try it. Even if it is just a key-on, engine-off check for the SES blink.

If none of that checks out, I'd try another ECM.

RBob.

Jeff91RS

iTrader: (1)

The SES blinks with no chip, but just comes on solid when there is a chip in. I also cannot get my datalogger to work anymore. I am just gonna pick up an 8746 from Denny at ThirdGenRanch tomorrow.

Jeff