Gumby22

The purge valve is on the intake manifold but the vent valve is by the tank (and it’s also powered by the eng1 circuit) - its only function is to completely seal the EVAP system during leak testing either by the PCM or when a shop commands it closed for smoke testing.

The MAP (Manifold Absolute Pressure) sensor only receives a 5 volt reference from the PCM - it’s not on the eng1 circuit. The MAF (Mass Air Flow) sensor being unplugged wouldn’t completely keep the engine from starting but it would cause hard starting/extended cranking and for at least a minute or two the engine would be running very rough.

O2 sensor data is used for closed loop. Without it the PCM can’t make the necessary fuel trim adjustments.

DwayneInBC

Thanks gumby, I wasn't really sure what it was under there, but I did see a few mouse droppings, so I'm going to really have to inspect those wires good.. Bad to say, but I'm hoping I find the problem in there

William Kisselstein

If it runs and runs fine, then just quits as opposed to running rough or poorly and throwing a check engine light at you, then I doubt it would be the O2 sensors or the MAF sensor. Maybe if all four O2 sensors produced no data but that seems unlikely. The computer just assumes based on voltage what's going on. The symptoms to me indicate a short is occurring that blows the fuse. That it ran, then started doing this after they changed the fuel pump, tells me to suspect the work they did - if the fuse blew the first time it quit, they would have had to change it before it would run again, and it would not have run on the start fluid they sprayed into it. Therefore the garage should fix it and at no cost to you.

When I took mine apart the only wires anywhere near the fuel tank were the four wires going to the fuel pump. There were vents and the charcoal canister but I don't recall anything wired to that stuff. Just plastic lines and a couple hoses.

1996-2002 have a steel fuel tank with a plastic shield under it which also serves as a mount for the charcoal canister and the fuel filter. The only way to get the shield off is to drop the tank, it's one big piece.

If you can't get the shop to actually fix it, then you're going to have to get a scan tool on there and see what it shows you. If something is shorted or disconnected you should be able to find it in the live data. Even with the blown fuse, with the ignition on, you should be able to see no data reading from the circuits on that fuse.

For instance with mine the coolant temp sensor on the intake quit and caused it to not start when hot, it had to sit at least an hour before it would start again. In the live data I found the sensor reading something like -68' F when it was 85' outside. That reading had the computer adjusting the fuel and timing such that it could not run when the engine was at operating temperature.

DwayneInBC

After long searches, and jiggling of wires to see if I can cause the short to appear, I decided to go get an obd2 scanner (millennium 30). Got it plugged in and gave me a p0452 code (Evaporative Emission Control System Pressure Sensor Low Input) current and pending. Yes I checked the gas cap lol. Does anyone know if this is on the eng-1 circuit? And could this actually be the issue I'm looking for?. If so, then I feel this fault lays with the shop that put in the fuel pump but I don't want to be going to them pointing my finger if I'm out in left field here.. I'm open to anyone's thoughts on this.. Thanks again everyone

Gumby22

For GM specifically this code refers to the fuel tank pressure sensor, which would be mounted on top of the fuel pump module assembly.

I’d forgotten that this era of GM trucks and vans can be a real PITA to match the correct replacement pump. There were several options depending on the emissions requirements, so matching the correct aftermarket pump can be tricky.

Make sure not to delete that code so your shop can pull it. Between that and the fuse blowing with wiggle testing the harness, it’s a good possibility they are at fault.

DwayneInBC

Thanks gumby, you've help a lot.. I did clear the code, but the minute I started the van, the code came right back. At this point, I don't know if they miswired something, or pinched a wire, or if the sensor could pull enough power to blow the fuse. But I think your right, it's time to take a walk down to the shop (not sure the van will make it) and have a heart to heart with them.. I'll let everyone know what comes of it.. Thanks again

William Kisselstein

Did they change the pump or the entire unit? Most of the time you change the entire unit.

"low input" would imply not enough voltage in the signal, which to me would imply potentially a broken or poorly connected wire. Which aims right back at the changed pump, since as I mentioned the pigtail is supposed to be changed with it.

DwayneInBC

Again this morning the fuse blew again. So I decided to take a closer look at the fuse box itself. Seems that connecti g sickest for pin #30 for the fuel pump relay was pushed down out it's socket. Thought about just replacing the whole fuse center, but it's wired in, no connectors (thank GM). I ended up in bolting it so I could get a finger in there to try and pry it up. At the expense of my finger I managed to get it up, but won't lock into place, so I held it there, and plugged the relay back in. Seems to have stayed in place with my fi Ger as a wedge. Put it all back together, and again she's running. The Obd2 code has also cleared it self when it started. Not sure how all that was related, but I'll take it. I don't know if this is goi g to fix that fuse blowing issue, but I'm hoping it does, time will tell.. If not, back to scratching my head..

I want to say thank you to everyone who put in their time to respond, and a special thanks to you gumby. I appreciate all your input
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