99 f350 no start. No wts light or cel. Pls help!

[jsbelectro]

New here to posting, but have been here alot for previous help. So one day I went out to start my truck and it started okay, it ran for about 5 minutes and then shut off. I restarted my truck and it ran for about 10 minutes, and then shut off. Ever since then I cannot get it started. The fuel pump quit working on the truck, and after lots of diagnosis I have come to the conclusion that the PCM was not sending the ground control to the fuel pump relay. Further investigation includes multiple ground circuits not to the glow plug relay, the fuel pump relay comma and possibly the IDM. I am ready to take it to the dealer comma but I cannot right now. I am a longtime mechanic and I am really trying to figure this out. I have also purchased a new PCM , and that seems not to be the problem. I have downloaded all the wire schematics for the pcm connector, the 42 pin connector, obd connector etc. I have tested all the grounds, the one constant 12+ and the 3 grounds. All tested good. I am kinda stumped though on a couple things. With the key off when I go to check some of the computer controlled ground circuits at the pcm plug like glow plug, fuel pump relay, and wait to start light, I get about 11volts+. But when I manually ground those circuits, they will work as they should. Is it because when I'm using my dvom on a grounding circuit, is it completing a ground or completing a circuit, or am I reading some residual back voltage from the coils in the relay associated with that ground. The second stumper is when I manually ground one of the ground control circuits is that there is no arcing or sparking indicating a ground line has a short to +. I have taken the under the hood fuse/relay box out and inspected it, and it seems good. That is without completely tearing it apart.

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[jsbelectro]

Well I checked every fuse box and all was goid. Went back to basics and checked all my grounds and hots to the computer, checked the relays, fuses, ignition wires, took all the big plugs apart, pulled wire looms looking for corrosion or a short to ground/power, and went to my refrence line that was supposed to be 5 volts, and I barely had 1 volt. Started unplugging sensors on that 5 volt refrence line, and got to the EBPV sensor, and everything came to life. Truck starts and runs. Just need to replace that sensor now. What's bizarre is that having that sensor short to ground actually caused everything to point to a bad pcm. I want to thank everyone for all your help and I will stick around to help any of you when you need it.

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[JLDickmon]

Well I checked every fuse box and all was goid. Went back to basics and checked all my grounds and hots to the computer, checked the relays, fuses, ignition wires, took all the big plugs apart, pulled wire looms looking for corrosion or a short to ground/power, and went to my refrence line that was supposed to be 5 volts, and I barely had 1 volt. Started unplugging sensors on that 5 volt refrence line, and got to the EBPV sensor, and everything came to life. Truck starts and runs. Just need to replace that sensor now. What's bizarre is that having that sensor short to ground actually caused everything to point to a bad pcm. I want to thank everyone for all your help and I will stick around to help any of you when you need it.

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When a bunch of sensors or devices share a common ground, it's really not all that uncommon.

I can name a couple of things off the top of my head. GM has a 141 page TSB out on their CAN network in the trucks, and I can recall the old 3.1 Chevy's that would short an injector and shut the whole system off.

 

[79jasper]

It seems the ebp sensor doing that is fairly common.
Not the first time I've seen that.

Btw, it's not the ebpv sensor. It kinda has no connection to the ebpv it self.

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[jsbelectro]

Yea I kinda figured, that sensor is in line with 4 or 5 other sensors on the 5v reff line that all end up back at the pcm on the sig return. I'm sure the ebpv is controlled by the pcm. The ebps just tells the pcm the exhaust pressure and adjusts fuel accordingly as well with other sensors. I know not even some of those chevys, but newer vehicles can have 10 or more pcm 's on the CAN line and can become fairly difficult to diagnose unless you have a very good scanner.

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