Doaburnout96

Without writing a huge story, I was given this project. Previous owner swapped in an auto fir his wife and never finished the conversion. The guy that gave it to me never got past the alarm system to get it to crank let alone run (it was said to have been seen to run before purchase) i have the vats resistored off and the theft relay removed with a jumper across to allow the engine to crank. I have the fuel pump out because it’s bad (tested in car with 12v to the connector under the hood) and verified the pump was bad once it was out. Now before i buy a new fuel pump I’ve been trying to verify proper fuel system function. I have the fuel pump relay out and can’t get the 12v for 2 sec on the prime wire from the pcm (dark green and white). I checked the wire for continuity from the fuel pump relay connector to the pcm and it was good. No power coming out of pcm when I probed there also. I also checked all 4 grounds that i could find in the pcm wiring, all have continuity.
Is there anything I am missing that could cause this lack of prime voltage? I think the pcm is bad. Also, i have plugged in a scan tool and it said it couldn’t connect. I verified voltage at obd connector with meter even though the tool wouldn’t work without. Any help is much appreciated. I don’t want replace the pcm if it’s ok. Thanks

Injuneer

Have you verified the body control module is sending the 50 Hz fuel enable signal to the PCM?

Doaburnout96

No, i haven’t. I’m unsure how to check for that. I thought maybe i had circumvented the bcm by bypassing that relay. I also have some eBay device that says it does this for aftermarket alarm installs but was holding off using it because the instructions are generic and I hoped to fix everything correctly after i verify the engine and tranny are good. Any procedures you can supply would be very much appreciated.

Injuneer

96 and up, with the BCM, the key resistor connects to the BCM. If it matches, the BCM sends a ground to the theft deterrent relay, controls the SECURITY light as required, and sends the 50 Hz signal to the PCM. They just moved the 93-95 theft deterrent module into the 96/97 BCM.

Courtesy of Shoebox:

http://shbox.com/1/bcm_1996.jpg

If your multi-meter has a frequency function, you would measure the signal on the dark blue wire from pin D6 on connector C3 of the BCM to the PCM pin A25. You can buy a device that supplies the 50 Hz fuel enable signal.

Baker Electronix - GM VATS Bypass

Doaburnout96

I have become very familiar with shoeboxes website lol. Please correct me if I’m wrong but the way i understand is that the bcm signal only controls the fuel to the injectors and not the fuel pump. Also would the bcm cause the pcm to be unable to be read by a scan tool?

Injuneer

The factory manual uses the words "will not allow fuel injection". To me that could be interpreted several ways.... not running the pump, not pulsing the injectors, or doing both would prevent "injection". Unclear to me.

If you did the resistor bypass correctly, the BCM would activate the theft deterrent relay and send the fuel signal. You indicate you had to bypass the relay. Was that because you just assumed it needed to be done, or because it didn't work after you did the resistor bypass?

I've never heard of anyone being unable to connect with the PCM because of a BCM problem.

Doaburnout96

i resistored off the vats and now the security light extinguishes but it wouldn’t crank. I bypassed the theft deterent relay to allow the engine to crank. Most people would just part the car out but since I got it for free I figured it would be a fun challenge and i could always part it out later and try to break even. Can you think of any way to verify the pcm is ok?

Injuneer

What are you trying to scan it with? Have you checked the wiring to the ALDL port? And from your first post, appears you verified 12V on pin 16 and ground on pin 5.

Did you check the PCM BAT fuse and the PCM IGN fuses?

Beyond that, find a friend who will loan you a PCM from their 96 or 97.

Doaburnout96

Yeah. I’ve checked fuses multiple times with meter. I think the thing to do is to install this module that puts out the 50mhz signal and see what happens.

Doaburnout96

I installed this device that sends 50mhz signal to pcm. It did make the bcm quit clicking lol and no more alarm. But still no voltage for fuel pump prime.

Doaburnout96

Can anyone think of another check for voltage that would let me know the pcm is working?