Just picked up a 94 formula, LT1 automatic, with a no start condition. I was told the car was running well, SES light came on and the car died. No idea if any of that is true. I was told the following parts were replaced, shotgun method with no troubleshooting.

-opti
-MAP sensor
-coil
-ICM
-injectors

Right off the bat after getting the car home it was obvious the fuel pump was not running. Did not prime with the key on. Checked the fuel pump relay, I have 12v on the orange wire from IGN but it looks like no ground on the green wire from the PCM. Jumpered the relay to fire the pump and it works fine with 40psi fuel pressure, still no start.
Started thinking bad PCM since there was no ground to pull the fuel pump relay, I have no tach movement when cranking, and I have no SES light at all. I removed the cluster and verified the bulb is there, it does not light at all at any time, key on or cranking. Tried scanning the computer with the key on and could not commincate to it.
Tried two other PCMs, one from a 94 caprice with the LT1 auto and another from a 94 Z28 LT1 M6, no difference with either one, no tach signal and no SES. No security light either.
So now I am thinking no power to the PCM. 15 amp PCM fuse in the fuse block on the dash is good, is this the only supply of power to the PCM? I have the DVM ready, anyone have the schematic of the power flow to the PCM or a few places I can check for it? Thanks!

 

Check all fuses with the DVM. Some will have power with the key OFF, others will have switched power when the key is ON.

You can get an idea from here: http://shbox.com/1/ignswschematic.jpg

 

Thanks, I will be digging into it tomorrow, troubleshooting is fun I take it 1994 and 1995 have the same wiring distribution?

 

There are minor differences in the fuses and wiring, but conceptually they are the same.

 

Very similar, but not identical. I did not have a 1994 diagram to give you.

 

No problem, I will start bugging at the pink and orange wires at the PCM and work backwards. Thanks for the help, you and Fred kick **** and your site is a great resource!

 

First problem fixed, had no PCM power on any orange wires..traced back and found that the power is supplied through the RADIO/ACC fuse..which was removed, probably by the previous owner when he removed the stereo. Good one, blow the radio fuse and kill the car .
Next problem, still no start, sprayed starting fluid in the throttle body and it ran a couple seconds until the fluid was burned off..so ignition works but no fuel. I will start searching threads, I would think the opti is good since the ignition side works but no injectors firing. What to check next?

Also I was now able to scan the computer, no histrory or current trouble codes. I realize the PCM was powered down for awhile, are the codes lost in that case? If the opti had a problem would I get the opti high or low resolution code from just cranking?

 

Not sure on the PCM question, but maybe check any fuses that run the fuel system, if there is any. I figure if he killed the car by pulling a fuse, maybe he got fuse pulling happy.

 

Just checked a few things, have 12v to the injectors and all injectors ohm out ok at 14.5 ohms (they are new). Off to the store to get a noid light set to see if I can narrow it down further.
VATS is removed with an inline resistor, SECURITY light comes on at key on and goes out during cranking, so I assume the VATS is working ok. Last conversion car I did I tested this by removing the resistor and the SECURITY light never went out during cranking (was a 93 but should be the same).


EDIT Noid light shows no signal to the injectors..so it runs with starter fluid, has 12v to the injectors, but the PCM will not fire them. Ideas?

 

ok, strange but the injector signal is intermittant. Sometimes when cranking the light flashes, other times not. I tried starter fluid and it actually started and ran for 5 minutes or so, then I shut it down and tried to restart, nothing. Has not started since. Ignition always works, but the injectors are intermittant.
Is the same opti signal used for both the ignition and injectors? I verified VATS is working, car will not crank with the resistor pulled.

 

No opti signal = no injector pulse. Got any trouble codes now?

 

no codes, only a history code for when I had the MAF unplugged when trying to start it. No current or history opti codes.
I wont rule out the opti since it is not an AC delco unit, I know it was purchased on Ebay from a seller I have not seen bashed yet on the forums, but I know the ignition side is always working. Is the low resolution pulse used for the ignition and the high for the injectors? Will the opti test procedure on your site rule out the opti? I have to see if that signal is there when the injectors are not working. Your test procedure is to verify the opti is sending signals for the coil to fire, but I know that always works (starter fluid always burns).

 

The PCM uses the high and low res pulses to set the ignition timing. It uses the low res pulse for injector timing. If you have DTC 16 for the low res pulse, the PCM shuts down the fuel system.

 

No DTC 16, not current or history.

 

Find the reason the ses light is inop. Pwr,grd,etc. No ses light = dead computer.