Engine Performance problem
1996 Chevy Express V8 Two Wheel Drive Automatic 120K miles
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I purchased the Van a year ago and right of the bat the Fuel pump went out. Had a new GM fuel pump installed. Went on a 2000 mile trip up to Colorado and back with a full load. No issue on the way up, but on the way back during the drive the engine hesitated while we where going down the Freeway @ 65 mph, but never stalled. When we finally made it back into Phoenix we hit some stop and go traffic and once again we were in the fast lane doing 50 mph when the engine shutoff. It started right back up and I made it home, but the engine was acting as if it wasn't getting fuel. The engine check light never came on, I am assuming that no codes would be present. I noticed when I backed it into the grauge it smelt like their was a gas leak or the engine was running rich. I checked the tail pipe and it smelt like a very strong fuel oder. I also checked for leaks and a clogged air filter, and I found no leaks and the air filter was fine. I thought maybe the O2 sensors were acting up, not sure how to check and also some friends mentioned the charcol canister check valve and maybe a fuel injector stuck open. Any ideas on what to check?

First, have it scanned for any trouble codes. It would also be a good idea to check the fuel pressure with the engime off and with the engine running. If possible, drive the vehicle with a fuel pressure gauge connected. This will help you see what is going on when it acts up.

I verified that no trouble codes were present on computer. I measured the fuel pressure with the ignition on I get 60 psi. With the engine running I get 52 psi. I drove it around with the pressure gauge hooked on and I see fluctuation between 52 and 60 psi, seem to move around the most when I accelrated. I am assuming this is normal. My repair manual doesn't show the correct opperating pressure for the fuel injection systems. The van also didn't hesitate or stall. I did all this at night when the out side temperature is under 100 degrees. The van seems to start having problems when the outside temperature gets over 100 degrees, I plan on checking tomorrow as well. Are their any sensors that would start to give false signals due to extreme outside temp?

Fuel psi spec. 60-66psi.

Does this mean that the fuel pressure should be between 60-66 psi when the engine is running or when the ignition is on without the engine running? It seems to hold pressure after I shut the ignition off, so I don't think their is a leak. Would you recommend changing the fuel pump or are their other causes?