Ok here's the deal. I have a 91 firebird 305 TBI. Up until a couple days ago it ran fine, albeit with the est unplugged. With it plugged in it wouldn't stay running in gear. Now it won't run at all. It will crank but I see no spray from the injectors nor does it seem to have spark. I have replaced the cap, rotor, wires, plugs, distributor, IAC, all vacuum lines, and the battery. Here's a list of what I have checked:

Coolant Temp Sensor - @ 91°F 1792ohms
Compression on all Cyls is within spec
TB is getting fuel w/adequate pressure
Coil is getting power
Throttle Position Sensor - .6v@idle & 4.45v@WOT
MAP Sensor - 5.03v@Pin C, 5v between Pins A&C, 4.8v@Pin B (KOEO)
IAC - 54.8ohms between Terminals A&B, 55.7v between Terminals C&D
Pickup Coil - 857ohms (Should be between 500 & 1500)
Ignition Module is Good

Needless to say I am at my wits end. As near as I can tell from all this is that the ECM is bad. What are everyone's thoughts on this? Any help would be greatly appreciated?

 

Sound like the almost the same problem im having with my 90 rs. all my readings are good too. but my injectors are firing. i'm gonna spring for the ecm i think next payday. i guess when you have eliminated all parts except the ecm then it has to be the ecm. the only thing you haven't done that is did was test the wiring harness. the plug that goes from the ignition control module to the ecm plugs. mine has 4 wires.I just did a continuity check with a ohm meter. lots of people have told me the wiring harness on these cars have problems but mine checked ok. just throwing something against your wall and seeing if it sticks.. post anything you find may help me figure mine out if you get your rolling. thanks

 

I know the harness you're speaking of but how do I test it? Thanks for the suggestion.

 

Someone probably tell you better than me but this is what i did.
if you have a haynes or chiltons it has the wiring diagrams in it if not im sure you can search them out on here. the plug color code wires that correspond to the same colors on the one of the connectors to the ecm. i just used the continuity tester on my ohm meter to test from the ecm connect to the corresponding wire on my ignition control module plug
if your leads on your meter are not long enuff you may want to run a short peice of wire with a small pin of some kind on it (so u can move it to different connections on the ecm plug) and just run it out your door so your meter leads will reach it.
it s kinda a pain in the rear but it gave me some peice of mind about my harness being bad.
someone may tel you completely different on this one this is just what i did and i am by no means a professional i just work with what i have. and sometimes thats not very much!!!! good luck

 

Ok I'll try that. Thanks for the suggestion and if anyone else has input on this please let me know. I have the wiring diagram but to be honest I'm this close (holding thumb and forefinger 1/2 inch apart) to getting a carb.

 

Have either of you looked into a possible VATS issue? It's possible for the VATS to allow the starter to turn, but not allow the injectors to fire.

 

I had thought of that. Is there a way to bypass it? I've read somewhere on here that you can do that. Possibly re-programming the prom to eliminate it. If that is the case how would you go about doing that? Or possibly an ECM from a car without VATS? Thanks for the help!

 

my Vats is bypassed so its not that. Macmatt search the forum here its really easy to do if you got a soldering iron and a couple bucks for a resistor from radio shack. ive seen the instructions on here b4 for bypassing Vats. It will save you a lot of heartache later on if your resistor in your key goes bad.

 

Oh I've already done the resistor pack bypass and it works great. I just thought that the VATS could still cause problems. Like camaronewbie said. I think he means the actual vats module that talks with the ECM. I could be wrong though.

 

If it is the VATS once I get the car running again I'm gonna visit GM's headquarters and drop kick whoever invented this right in the nuts. Worst system ever, and like most things GM has done lately it was probably a good idea that was poorly executed.

V.A.T.S. - Veritable A$& ******** Shove
Because when it goes bad you're basically f*$%ed!

Sorry for the comment but as much as I like these cars it is now no mystery why GM almost went under.

 

I know you had mentioned you checked the Ignition module and the pickup coil, but those are the two biggest factors in having spark and injectors firing correctly... and it sounds like one of the two isn't doing its job. I've had distributors straight from the store have bad modules installed in them, how'd you check yours to make sure the one you have is working properly?

 

I had it put on a machine that runs some kind of load test or something. They have them at autozone. It's really cool because they can test most makes and models there.

 

Ok now that I've ranted/vented a bit I have a question about the VATS.

Since this is entirely possible I wonder if testing the VATS is possible. Theoretically couldn't you test for the 5v refference signal at terminal B6 on the ecm? I would think that would narrow it down, and if you are getting that signal the only thing left it could be is the ECM itself. What do you guys think?

P.S. - I have read this and it has been a great insight
https://www.thirdgen.org/vats_passkey_system

 

Ok here's what I did. I took the ECM out and tested for the 5v ref signal from the VATS and low and behold the reading was 2.55v so I am presuming the VATS module is bad. Seeing as I have no idea where it is or how to get to it to test the harness in between the two I'll probably just get the bypass module.