Nightwolf769

Hi all, I'm new here and to the Camaro world.
I have a very perplexing issue with my 90 RS 3.1L. The car has sat for some time before I bought it.
The car will start and run for a while, no set length of time, then just shut off. Then it seems as if the ecm goes into diagnostic mode by itself without jumping the pins on the connector under the dash (fan cycles over and over, multiple relays click, check engine light flashes, etc) and while this is going on, the car won't restart. Recently it did it, and while the key was still on I yanked the ecm fuse, waited 20 sec, shut the key off, waited 30 sec, reinstalled the fuse, then it started right up.
Would this be indicative of a bad ecm? Has anyone ran into this before? I'm literally ready to pull my hair out!

Thanks

RBob

iTrader: (1)

Yes, it does sound like the ECM went bad. The original service number is 1227730, with a couple of newer numbers for the same ECM.

If you need to use yours as a core be sure to remove and keep the MEMCAL from it. That needs to be moved over to the new ECM.

If you want to further diagnose the issue, rap on the ECM while it is freaking out. See if that changes how it is acting.

RBob.

Nightwolf769

Thanks Rbob, I started to suspect the ecm when I noticed it freaking out before, but I wiggled some wires last time and it quit, thought I found it, but nope.

Tuned Performance

iTrader: (92)

https://www.thirdgen.org/forums/engi...s-memcals.html

J.C. Denton

iTrader: (1)

Had the exact same problem about 10 years ago with my former 3.1 Firebird. Was a bad ECM. But I found a used ECM with the AZTY Memcal so I never figured out if Memcal or ECM went bad. Was just happy that my car ran like new after weeks of try & error diagnosis.
Last year I had a bad Memcal at a friends 3.1. Injectors stayed in "watering can mode", so after 30 seconds with (bad) running engine the plugs and oilpan got flooded in gasoline.
So, both parts can go bad, but you seem to have just a bad ECM. Make sure to get a 7730 ECM and swap out the Memcal.

Nightwolf769

When you say 7730 ecm, which number are you referring to? I found this one

That says it will fit my car, all I need to do is put my memcal in it.

J.C. Denton

iTrader: (1)

I mean the Service No. The above ECM will not fit. You need the Service No. 01227730 if you really do have a 3.1 V6.

Nightwolf769

Gotcha, cool! Woulda been pissed if I bought it and it didn't work. That should be the same service number that's on the one in the car correct? Haven't gotten a chance to pull it yet...
Thank you, I really appreciate the help and info guys!

J.C. Denton

iTrader: (1)

Yes, it has to be the same number. Go pull it to be 100% safe what you need. You just need a 7mm socket and about 3 minutes of spare time to pull the ECM.

Nightwolf769

Ok, and just to be safe, the service number is the only one that needs to match?

J.C. Denton

iTrader: (1)

Yep, it can also come off a V8, you either have to switch out your own Memcal to the new ECM to get it running.

Nightwolf769

Good to know b/c a local junk yard has a few 3rd gens, but I think they were all 8's, didn't know the ecm's were the same. After I verify my number, I can go ecm hunting.
Thanks J. C.

Tuned Performance

iTrader: (92)

The 1228874 is the derm, srs ecm.

J.C. Denton

iTrader: (1)

Thanks Tuned Performance, I knew something was wrong about the posted picture... no Memcal Code on the tag...

Tuned Performance

iTrader: (92)

Btw the ecm is located under the passengers side dash. It’s bracket is held in with two 7mm screws.

RBob

iTrader: (1)

Only the '90 - '92 TPI and '90 - '92 MPFI use the same ECMs. No other f-body uses the '7730. Although there are a bunch of other GM vehicles that also use the '7730 ECM. Any of these can be used with the '90 MPFI MEMCAL.

Note that your ECM should be on a slide mount. Drop the hush panel (if there is one), then push the bottom of the ECM toward the front of the car until the velcro lets go. Then pull it straight down and out.

RBob.