gulf_coast_228

I have a 1992 firebird I've recently swapped an LS1 into as well as converting from a 700r4 automatic to the T56 manual. Last Friday I was able to drive the car but the clutch didnt want to engage. I took a look at the pedals and noticed something wrong with them and had to replace. Sunday I finally get to the junkyard and pull the pedals from a 99 Camaro and get them installed. Looks better and it looks like it works.

I go to give it a test drive and the first thing I notice is the fuel pump doesnt prime. Turning the key just turns the engine over without starting. On a hunch I hook up my scan tool with the key in the Off position. It comes on but of course it has a link error. The key needs to be in the On position. So I turn the key and the scan tool goes dead. Turn the key off and it comes on again. On and it goes dead.

The only thing that changed between Friday and Sunday is I was under the dash and put those pedals in. I have no idea what I might have bumped that would have caused this. I dont remember unplugging anything or any wires coming loose so Im totally confused as to whats happening here.

Has anyone seen this before?
If it helps I have the Hawks LS1 conversion harness. PCM fuse isnt blown either. ECU fuse under the dash is good as well (is that even still used?)
Im lost.

Pocket

iTrader: (24)

Call Hawks first

Next, pull out your meter and trace the fuel pump circuit (4 wires)
The scan tool going dead with the IGN cycle is disturbing. Perhaps you forgot to plug the IGN switch back up with the pedal conversion?

gulf_coast_228

Would I still be able to engage the starter by turning the key if there was an open somewhere in the ignition circuit that prevented feeding power to the ECU? I only unplugged the two sensors on the brake pedal but its possible I might have nudged something out of place.

Not sure if this is relevant but I found out this car used to have some kind of alarm system that had been disabled some time in the past. There's a lot of extra wiring under the dash and some black box that is just dangling above the pedals that doesnt look like it belongs. Is it possible this thing could interfere with power to the ECU? Ever heard of it happening?

If/when I get the call from Hawks I'll update the thread.

Jay_rich

iTrader: (4)

Did you happen to toss a tune on the PCM in between all of this work?

Usually if the PCM is not getting signal or the fuel pump is not priming that means you fried the PCM. Ive done it on my old LT1 before. Battery got a little low when dumping a tune in and fried it.

I would check that you are getting power to the PCM first though. If so check to see when you turn the key on if the fuel pump relay is getting signal.

Jay

gulf_coast_228

Hawks had to do some tuning on it, I think to disable VATS. I'd think the same but it was working and driving last Friday, I just could barely get it in gear since the clutch pedal was messed up. All I did Sunday was replace the pedal assembly. Didnt touch anything else so I dont think its a tune issue.

Checking for power to the pcm is on my checklist.

gulf_coast_228

Ok here is an update on this.

I did some testing tonight. Looking at the 1992 wiring diagram for the ignition switch from the key there's a large pink wire that goes from that into the connector at the firewall. This wire gets power when the key is in the ON position. When the key is in the ON position the PCM fuse is also receiving power.

Going by the attached document, on the blue PCM connector pin 1 should be my ground and pin 20 should always be hot since it's battery voltage. When tested, this was true. It is receiving voltage with the key in the OFF position.

Pin 19 (the pink wire) is the Ignition 1 Voltage. It did not have any voltage until I turned the key to the ON position at which point it then showed voltage.

Even assuming I bumped something under the dash, accidentally disconnected something, whatever, it still appears that the PCM is receiving the power it needs. I have no idea why my scan tool dies when I turn the key into the ON position however.

My buddy says check the fuel pump relay. I haven't done that yet because I've been under the assumption the PCM wasn't sending the signal to it since my scan tool goes dead when I turn the key, but this is something I will check tomorrow.

If that's not it, should I be looking to buy a new PCM?

gulf_coast_228

Fuel pump relay seems sound. As suspected it is not receiving signal from the PCM. When I jumpered the relay the fuel pump engaged and I built pressure so at least its not that.

2 oddities that I cant tell if its supposed to happen or not- with the key in the On position my test light turns on when I touch it to the casing of the PCM (grounded to the chassis).
- With the key in the ON position my multimeter is showing about 120v (it's on the 12v setting) on the #20 pin mentioned above. Key off it shows about 12v.

I have no idea if thats normal or not. There's no pinched wires, nothing broken off or scraped, nothing disconnected under the dash. I'm at a complete loss here.

Pocket

iTrader: (24)

120v is impossible on a 12v system. Move your meter setting one click higher than what you expect to read, so for a 12v system, most have a 20 or 24v setting

The PCM casing should NEVER have a charge. Unplug the PCM and check that pins R1,R40, B1, B40 are all grounded

gulf_coast_228

Pocket, those pins appear to be grounded.

gulf_coast_228

CORRECTION: They only appear grounded with the key in the OFF position. As soon as the key is turned to ON my meter no longer reads a ground. That looks like why the scan tool dies!

Now that I figured that, what would cause this?

Pocket

iTrader: (24)

Baffling for sure. Ground through a relay perhaps?

Whatever it is, Id remove it from the car and ohm it out. Not sure if the pedals repair had anything to do with your issue. I do know 100% that you should never loose ground on the PCM under any circumstance. That can be a broken/forgotten engine ground and all the power running through something like a relay until it is switched on, then the ground is lost. Whatever it is, you need to trace the whole thing. Easiest method is removal

gulf_coast_228

I wanted to update this issue. We found the problem. On the LS1 wiring harness there's a ground that bolts behind the driver's side header. Last time I looked it was good but that was when we put the engine in. It had come loose and so the wire was not making a good ground connection. With that tightened up the car started today!

I knew it had to be something simple but it was a matter of tracing the problem down, especially the unique symptoms. Thanks for the advice and help everyone!

WTR388

Thanks for coming back and posting the solution... I hate when people solve the issue and don't report what it was, in case someone else has a similar issue.

I'm roughly 4 weeks from hopefully firing mine up!