I'm now able to get a check engine like thanks to the help on this forum. I'm getting a Code 51. The shop manual is quite clear: Faulty Mem-Cal, check the pins are OK. If OK replace mem-cal, if code returns replace the ecm."

I searched the forum for Code 51 and mem-cal information and I learned quite a bit but I still have a lot of questions. I see a lot of people here pulling out the eproms, reading, comparing, modifying etc. That sounds like fun for the future but right now I just want to get this car drivable. Can I buy a more or less OEM mem-cal and just plug it in to see if that fixes the issues of terrible running, bad idle, stalling at low rpm? (I've already done the obvious stuff of checking timing, plugs, wires and electrical connections.) The Code 51 seems to be the big hint.

I've seen a number of places referenced in this forum but a lot of the posts are old and some of the links don't work anymore. Is there a recommended place to get one of these? It would be nice to understand more in the future, but as I said, I'd like to get the car running well enough to drive it to the smog check.

 

In your older thread you mention the 1227165 and that's correct for the car. Code 51 I believe can also mean 'incorrect' so I'd remove the PROM and identify it if possible. Remove the PROM from the ECM and see if there's information visible through the windows of the likely 'blue' PROM cover. Information would be on a silver label XXXXYYY(Y) (XXXX - 4 digit #, YYY(Y) - 3 or 4 letter code.

Is there a SPID label on the console door? With the various option codes on the SPID it could be confirmed that it's applicable to the car at all.

It would be safe to assume that most any PROM for an '86 would work.

You did confirm the PROM is seated correctly?

I generally use this as a BCC code ID tool. There used to be a FREE GM tool but not free any longer. If it's an original PROM and maybe the ID is missing from the BCC list I've an older GMSPO catalog that might. You'll need an .xls reader. The BCC list also has the PROM ID code that a scanner would see if it were functional. I don't know that if 'no data' is referencing only 'run data' or not, I've never had a CODE 51 on any car I've scanned. It might be an interesting test for the scanner you're using.

BCC lookup.xls

 

Thanks. I looked at the eprom and the label says BUC 9555. And yes, the ECM is 1227165.

I might be a bit confused here. The mem-cal is the light brown plastic connector with the blue cover that is seated into the ECM. The PROM or eprom is the actual chip that is inserted into the mem-cal. Please correct me if I'm wrong on this.

I double checked that the mem-cal was properly seated in the ECM and that didn't help. So I pulled the mem-cal again and removed the blue cover to look at the chips themselves. The eprom seems to be very firmly in place. In fact, it almost looks like it's soldered in place. I'm not sure if I'm seeing tiny solder joints or if I'm just seeing the reflection of the chip pins in the shiny sockets. In any case, it seems to be pretty firmly in place. It didn't budge when I tried to slide a tiny screwdriver under it. I didn't try very hard; I didn't want to break it.

The SPID label was in the glove box behind the driver's seat. There is nothing special. This was built as a totally generic car. Power seats, window defogger, AC, L98 engine, automatic, 2.59 rear, etc. Anything in particular I should be looking for? Thanks for the spreadsheet.

 

It is possible to damage ECM board improperly installing PROM. You gently press PROM in then flip locking tabs in. If PROM is pressed in where tabs lock themselves, that when the board cane be damaged. PROMs don't fail very often and are hard to find. ECM would be a better first guess. ECM should be unplugged when removing or installing PROM.

 

Here's an update on the Code 51.

I got a new mem-cal from Scott Hansen, http://scotthansen.net/. It came in two days. I installed it and the code was gone and the cooling fan was no longer running when the ignition was on. The car started right up and ran great. I don't want to say it "purred" but the hesitation, stalling and almost backfiring were all gone. I drove it around the block a couple of times.

I pulled it back in the driveway to watch for the temp when the fan came on and the car died. It didn't sputter and die, it just turned off. Didn't want to restart. The scanner wouldn't work. Jumping the diagnostic pins showed a solid check engine, not even a code 12.

Removed the negative battery cable, the car would now flash a code and the code 51 was back. The scanner would now work and showed a code 51. The car started fine, ran for several minutes and did the same thing. Solid check engine light, scanner doesn't work, engine won't stay running etc. Disconnecting the battery seems to clear the problem.

I followed Chart A-2 in the shop manual for the solid check engine light and it says to "check for open in ALCL diagnostic terms "B" and CKT 451 to ECM" How do I do that? Not quite sure what that means.

 

I'm sure Scott did you well.

CKT 451 is pin A9 on the ECM and passes through C237 cavity E to the B cavity of the ALCL/ALDL WHT/BLK wire. Unplug C237 and check for continuity to pin B of the ALCL/ALDL, if you've continuity there then remove the (24 pin) connector and check continuity WHT/BLK ECM connector to C237. If you've got continuity there also you're back to the 51 and likely an ECM. Did you retry the original PROM?

Scott is a good guy and I'd likely ask Scott for suggestions.

For ECM PIN OUT see 6E3-A-7. See 8A-201-10 (B) for C237 connector.

 

Here's another update.

The '86 ran for shorter and shorter periods with the new mem-cal until now it won't even start. With the old mem-cal re-installed, it starts and runs (poorly, as before).

I have ordered a cable from moates.com to hopefully do some datalogging. I also bought a "new" ECM 1227165 on eBay. I'll try both of these when they arrive.

In the meantime, I was hoping to build my own cable but I haven't found a good schematic yet.

Finally, I wonder why the car would run well with the new mem-cal for 15 or 20 minutes and then cut out. Then run for shorter and shorter periods and get harder and harder to start. To the point that it won't even start now with the new mem-cal. Can my ECM somehow "damage" a mem-cal? It must have been OK when I first got it. The car ran pretty well at first.

 

I wanted to post the resolution to this issue and close out this thread.

The Code 51 was a result of a bad ECM. There was a blown varistor, so once the ECM heated up, it threw the code and put the car into limp home mode causing it run very badly. I replaced the ECM and then worked with Scott Hansen to program the mem-call for my car and now it's running fine. I was able to easily pass the California Smog requirements and get the car registered for the first time in the 24 years that's it's been sitting and forgotten in an old garage.

It's got a little leak in the brake master cylinder reservoir and it's got issues related to the heads up display the GM engineers installed but other than those things, it's a 1986 Corvette with only 32,000 actual miles.

Thank you everyone who helped me figure this out.

 

Is the BUC 9555 an original eprom ?
I've the same eprom, but ECM has been opened one time, I think. Don't know if this one is original.
Have you put this one back in the new ECM ?