Need some help from the electrical guru's!!

[mmync]

I have been trying to diagnose the intermittent "Cranks but no start" problem on my 1996 Buick Regal 3800, for 3 years now with no luck. Being that I am not a mechanic, I had no knowledge on how to diagnose a problem or where you would even start. But I've been reading my ass off and learning as I go. I have a feeling I'm getting really close, and hope my latest find will be able to finally figure this out. I just need someone to interpret it for me. When the car doesn't fire, you can hear & feel fuel pump relay ticking really loud and fast. And what I found was, there are 4 contacts that the relay plugs into. When the car wont start and I check the contacts with a volt meter, the 2 contacts that are towrads the rear of the car are both giving out positive voltage. The contact on the drivers side shows around 12.3 volts(+) and the other contact which is closer to the passanger side of the car and has the Dk grn/white wire coming off of it is putting out about 11.8(+) volts. So they are both putting out (+). And then if I hook my volt meter up with 1 wire going to each of those contacts it will read about .5 volts, which I assumed was supposed to not read anything since they where both (+). When the car finally started, I rechecked the same 2 contacts, and now the contact on the passangers side (Drk grn/wht) is putting out a (-) signal. So, I would assume that what I need to figure out is what would be causing the Drk grn/wht (fuel pump control wire) to put out (+) instead of (-). I hope I am on the right track, and hope it will be an obvious sign to one of you guys.

Thanks

[maxwedge]

Start by checking for 12v on the pump wire at the tank during the prime event, if good the pump should prime to 40 psi or so and start. If not start going back to the relay. The pcm controls all these circuits. You really need to check for fuel pressure and spark when this happens for the besic diagnostic first step.

[mmync]

Originally Posted by maxwedge

Start by checking for 12v on the pump wire at the tank during the prime event, if good the pump should prime to 40 psi or so and start. If not start going back to the relay. The pcm controls all these circuits. You really need to check for fuel pressure and spark when this happens for the besic diagnostic first step.

Thanks Max, I have not checked the voltage at the fuel pump when the problem has occured, but here is some other info that may or may not have any value.

1. Fuel pump, plugs, wires, fuel filter, air filter, pcv, IAC valve, fuel pump relay all replaced in the last month.

2. It is definetly getting spark.

3. It is definetly getting fuel. I can't remember the exact psi, but I do remember that it was well within range. I even called the mechaninc at the dealership and told him what the psi reading was, and he said that it was definetly getting enough fuel.

4. I even rigged up an always on relay just so I could use to help diagnose the problem, and when it wouldn't start I popped the other relay in and I heard the fuel pump constantly running, but it still didn't start.

5. Left it at the dealer 3 times for a week each time, but they couldn't figure it out because it is so intermittent and would always start for them.

Like I said I am not a mechanic, so sorry if some of the things I say do not make any sense or if I don't know how to describe a certain part, but for some reason I keep thinking the problem is from something like the pcm, vats key, ignition, or some kind of sensor or switch from the brake or gear shifting system, if that is even possible. (I did try putting the car in neutral when it didnt start, but that didn't work)

[Mickey#1]

I'd try a different PCM. The junkyards around here will take them back if it doesn't help. Use the prom chip from the original PCM in the 'new' pcm.

[mmync]

Well, its 4:00 am, dark, cold, I don't have a garage, and I couldn't even guess of where I am supposed to check the voltage at the the fuel pump. I got under the car, but its still to dark out for me to find anything. But I did pull up the back seat, and there are wired running from behind the back seat to the passanger side of the car, and then up to the fron of the car. I found a grey wire back there, but no drk grn/white. Not sure if that grey wired is the right wire to check, but I checked it anyway and it was putting out 10.13 volts. FOr all I know, that grey wire may have been the wire that powers the lights around the license plate.

[maxwedge]

If you can start it with carb cleaner or starting fluid sprayed into the intake than it is a fuel issue, look under the l/s front sill plate there is a harness under there that has a ground buss junction that can cause problems for the grounding of the fuel pump. When this occurs you would also usually loose the power windows.

[Mickey#1]

Ground bus won't make the fuel pump relay click rapidly. Get the PCM, what are you waiting for?

[mmync]

Originally Posted by Mickey#1

Ground bus won't make the fuel pump relay click rapidly. Get the PCM, what are you waiting for?

It wouldn't surprise me if that was it all. After about 20 minutes it will fire right up. But it has to be 20 minutes of sitting without trying to start it. I could try starting it every 2 minutes for 10 hours and I wouldn't get lucky even one time because it has to sit. Is swithcing out the PCM a pretty easy job? What's the most I should pay for one at a junk yard approx?

[mmync]

I forgot something. One other thing that I noticed, is that the Haynes manual that I have says that the wires going to the relay are blk/wht, org, dk grn/wht, and gry. Those are not the color wires that are on my car. Mine has grn/wht,org,gry and like a peachish or pink colored wire.

[Will Help]

Sounds like the Crankshaft Position Sensor to me. Next time it fails to start, take a hose and spray some water on the CPS. It is down at the crankshaft pulley. If it starts then that is your problem. As long as the key is on, it keeps heating up. After it cools for awhile it usually starts.

[Mickey#1]

Will Help - The crankshaft position sensor won't make the fuel relay click.

MMYNC - I don't know what color the wires are on your Regal. I paid $50 for a computer for an 89 Bonneville. Call around, I think they give you a better price when they know you're comparing prices. It's an easy job to do.

[mmync]

Actually, for the past 2-3 years that I have taken my car to Autozone to have the codes read, the error code for the ckps showed up. But the last time I took it there it was gone. I took my car to a shop last month to get the ckps changed, and they told me that it was fine and that my problem was the fuel pump so they replaced that. That did help with my car stalling, but I had a feeling that it wouldn't do anything for this problem. And the couple times I dropped my car off at the dealer, they told me that there was no error code for the ckps. But I am not sure if it only shows when the problem is occuring, then goes away????? The abs light is also on, but I am not sure if that could even be related in anyway. Autozone has also told me that some evap & Egr codes where coming up. Once again, not sure if those could be related in anyway. Just tyrin gto give you guys as much info as possible.

[Rottweiler28]

I would also think about the ICM I think its called, the plate under the coil packs) as my friend had a similar problem then after swapping this out his worked fine.