Well here goes. . . . . Long story long, short as I can anyway.
Picked up an '86 Trans Am, been sitting for sometime (6yrs), halfway into reman engine install, brothers gave up, car sat, then I found it. 305, TPI, auto, blah, blah, but looking to keep the TPI and all else as stock as I can. Installed mild cam XE256 comp, got the top half of engine back together, all bracketry and such in order and fired her up. Bit rough, but running. Due to plentiful snow, and general lack of outside vehicular motivation in winter, she sat. Well, it's nice now, and she won't fire off, well not correctly anyhow.

Car starts for a few moments on cold start injector only (not well), verified this by unpugging other injectors, then cold start. It had a couple of questionable injectors (by resitance testing), so I replaced them, and tried again. No luck.

Seems the problem lies with respect to main injector pulses, or lack thereof actually. I cracked open harnesses, all appears well, good continuity to injector plugs, 12v to hot side as should be. Made up some "test' harnesses to go to injectors just to make sure, easy enough to by pass all in case of questionable wiring, voltage drop on load and such, but no luck.

Fires off, so do not suspect reman distributor I installed to complete install, and also reman computer done for same reason (boneheads left old one on floor to get soaked)

Just baffled confused and want to keep the TPI, but its got me stumpped.

Any help would be greatly appreciated.

 

Have you checked the fuel pressure?

 

Yessir round about 38-40 Psi (old guage but fairly accurate)

 

Have you used a noid light ? You can still have spark and a bad icm or a issue with the purple and white wire from the icm to the ecm. You might check the grounds behind the rh cylinder head.

 

Did borrow set of noids, as far as the grounds, took them off, cleaned, and reinstalled, I know that is a common one. Assume they are good (now,) Got the code 12 from PCM, and would think if comp ground, should not fire off cold start injector. I also did run secondary ground to case of PCM.

Maybe after dinner, I'll get back out there and trace that wire.

Thank you
-jon

Purple/White wire, I'll have to check that one,

 

Don't ground the ecm case, the ecm, injector driver ground, o2 ground are all behind the passenger side cylinder head. The distributor reference goes to pin B5 of your ecm. The csi is totally separate from your ecm and is controlled off the timer switch.

 

Ok, did not realize csi was on separate control circuit. I'll unground the case, recheck behind head wires, and probe the B5 position for reference signal.

Just got to find the DVM, hadn't used it for a while.

Thanks again

 

Im not sure the sequence of events that lead you to replace the distributor but Im not a fan of aftermarket icms and only use delphi or acdelco.

 

Agreed, but easy grab from work, as far as what led to it (dist replacement). . .knucleheads leaving half submerged in a bucket of water for a few or so years turning it into a mostly big mass of poo whilst they "did" the motor swap.

 

So, no pulse to injectors while cranking using noid lights for testing? The ecm must receive a spark reference to pulse injectors. Was it running with the current distributor? What has changed since it last ran?

 

It was running, but that was before the deep freeze. I put a battery in it some fresh fuel,turned the key, and it fired, sort of, then dies. I hadn't done anything since the frost set in.

That is when I began trying to diagnose.

The car has spark, fires off from fuel from cold start injector then dies. That is what kind of has me baffled here. I'll have to check the reference wire to PCM I suppose, and try to take it from there. Just looking for some suggestions, maybe off the wall that someone may have encountered, or a more common problem.

 

Checked for ref at b5, indicates signal when cranking from distributor, and the short time as I can tell it runs.

 

Can you post a video so we can see and hear what's going on? It may help us to diagnose for you.

 

hello.i just joined yesterday and was reading your problems.i have got a 91 formula that would start but die after a couple seconds.i had replaced everything.distributor.ecm.fuel regulator.plugs.fuel pump.sending unit.and all kids of sensors.so on an so on.then found my problem.if you take a volt meter and put it on ohms.test the injectors itself.they should read 14 to 16 ohms but not below 10.if I disconnected my #3 injector it would start and when I connected it back up it would die. That injector had shorted out.when this happens the ecm will shut the car down.everytime I unplugged it it would start.u may may a shorted out injector or injectors

 

I'm trying to remember if there are left and right bank fuses for the injectors located in the fuse box or maybe just a single fuse for the injectors...

 

Good information, I'll make a note of that!

 

In the fuel pump circuit is an oil pressure safety switch, make sure the oil pressure sensor is hooked up/working

 

Can't at this time, but pretty straight forward, fires off, roughly chugging, for about three seconds, mainly on driver side only (verified by exh manifold tem rise), no response to accel pedal. No inj pulse to other injectors.

 

Thought this was the problem as had a couple of sketchy injectors, and switch with new set I had from previous undone project. None shorted.

 

Does not appear to have one. I'll have to check more closely. Although, that would run fuel pump, or keep it running, I may be wrong, that is not tied to injector pulse as far as I know, I can keep pump running using fuel pump diagnostic lead, no bit of difference, no injector pulse.

Thank you

 

Just want to say thank you in advance for all your help, keep the suggetions coming, I may be looking over something very simple, and making it more complicated.

Forgot to mention, fuses are good for injection, both 1 and 2.

 

I had a ECM go bad while driving my 87 305 TBI Chevy p/u and I just barely made it to the dealership. It chugged, smoked, popped and stumbled horribly. I would recommend another replacement. I know your car does not have a vats module. Vats came out in 89. Are you sure the ECM is specifically for your year model and the internal ECM mainboard and chip is correct one. Sometimes there can be a mismatch.

 

I have read your message over and over many times.and as you know there's all kinds of things that it could be.one person gas mentioned.are .you sure that is the correct ecm?that is a good possibility.so this is what I'm wondering.you had said there is no short in the injectors.so I'm taking it you are reading good ohms.around 14 to 16 ohms.so you are getting 12volts with key on.but no pulse when trying to start .dont know if you had tried this or not.pull one injector at a time and try to start it untill you have done them all.and see if you get any different reaction.if not I'm thinking it just might be in your ignition switch .it may be shorting out.ive had that happen to me before.but in a different kind of Pontiac.just trying to help.(unplugging one injector at a time is how I found my problem ).

 

. . . .
The injectors check out. I'll have to get back on it tomorrow, i'll check ign switch, and got ECM from work today. Far as can tell it is the right ECM, but will do some leg work tomorrow. Thank you folks for the suggestions, I'll keep you posted.

-jon

 

If the ecm doesn't do the trick post up the letters off the memcal in the ecm. Someone could have swapped in a later year memcal that contains vats.

 

I had a similar problem recently too. I ohm'd out the injectors, checked fuel pressure, changed plugs, checked spark, even swapped out the cold start injector. Then I got a noid light and chased the pulse from the ICM to the ECM. Unplug one injector, then unplug the 4 wire connector from the distributor. Taking a test light from the positive on the battery briefly tap the reference wire going to the ECM (I think it's purple). This will simulate a pulse from the distributor to the ECM. This should fire one of the injector banks and turn on the fuel pump relay for a couple seconds. That should be the same pulse you were chasing before but this will verify the injectors and the ECM. If you don't get that pulse it is possibly an ICM or pickup coil. However in my case I had an aftermarket harness that had an ignition power problem. I tapped into accessory ignition power, which cuts out in the crank position of the ignition switch. After I found that out I applied ignition power that doesn't cut out while cranking and it fired right up.