99 Express Fuel Pump CRAZY problem
 

I have a 5.7 liter one ton 3500 van. My van has problems in rainy or damp weather. At first I thought it was the fuel pump (still might be) Vehicle chugged along and eventually died. I was in view of an AutoZone. The guy at the counter came over with the code reader and my said I had a MAF sensor issue. Purchased that, no effect. Van would start 20% of the time and stall when I gave it gas or put it into gear. It would idle, but very lean. smelled lean. The AZone guy told me to check the fuel pressure. Key on 61-62, start then goes to 53, road speed 58-59. I am assuming the pump is good. Tell me if I am wrong. If it rains I have trouble. Should I crawl under with a hose and get everything wet and hope I can reenact my issue? I don't want to be miles from home and get stranded and be at the mercy of what mechanic is available. I have already changed wires, cap and rotor, PCV valve. I misted the entire top of the engine with the doghouse off and got everything really wet without issue. The MAF sensor is of course new. Thanks in advance, Eric

To me "a MAF sensor issue" means next to nothing without the actual P-code and the freeze frame data that goes with it. You just wasted a single chance at taking a snap shot of the engine parameters at the point of failure. It sounds like you've done all you can and thus it's probably time to take it in for service.

I disagree. There are still plenty of things I am capable of "self diagnosing" with the help of forums such as this one. I have NEVER taken a vehicle for service without first trying to save myself a bunch of money. So far I have next to nothing invested in repairs compared to one trip in for service. I can throw parts at it all day long, I don't charge myself incredibly high labor fees either. I have five kids and I would much rather have food on my table than the owner of the stealerships' table.

Most likely a fuel issue but even that can be a number of things. I'd start with the basics like changing the fuel filter first to see if it improves, if so then that could've been the issue. Check your grounds and battery connections and check fuel pump and fuel injection harness for chafed and damaged wiring. Check your ignition system (distributor cap, rotor, wiring, coil, etc.) It can also be some debris in the tank clogging up the pump, I've had this issue before, debris had caused the pump to intermittently not build enough pressure causing rough idle, stumble, low power, and of course stalling. I had to drop the tank in order to remove the pump and when I looked inside, it was full of crap, cleaned it out and retested, working perfectly. Also, might want to check for fuel injectors for sticking, the CSFI fuel injector poppets have been known to stick either closed (which would also cause your problem) or open. GM has a kit to change the fuel injection spider assembly (with all injectors) back to MPI, reference GM p/n 89060440 (if this is your problem and you end up having to change this, remember to get an upper intake manifold gasket set as the upper intake manifold plenum needs to come off to access the fuel injection spider assembly.

Hope this helps,
Luke

Even though you have had the fuel pump tested, it could still be causing the problem due to a bad connector in the wiring.

Check all the wiring connections going to the fuel pump. Look closely for a discolored terminal inside one of the connectors with melted plastic around the edge of that terminal. On my '97 Express van I found the connector near the front of the gas tank had a bad terminal in it. I bypassed the one terminal in the connector with a jumper wire and solved my fuel pump problems.