I've been looking everywhere and can't seem to figure out what's going on here. Randomly my truck will drop below 500rpm and die on start up. The fuel pump was replaced 2 years ago with an OEM one and shows 58psi during start and run. I'm wondering if the IAC or maf are bad. I've heard a bad maf can actually send random check engine codes such as o2 sensor(which mine shows). Because its an intermittent problem usually once every other week for only a few seconds(truck runs normal after a few start ups) maybe the PCM isn't catching it. Any ideas? I do not want to drop another tank because someone wants to yell fuel pump because its 2psi under spec....

 

Correct fuel pressure, volume, and leakdown rate on these engines is critical. If they are not within specs, you WILL have driveability issues, guaranteed. It may or may not set a DTC in memory if it is out of spec.

At the service port, regulated fuel pressure is tested with the engine OFF and the fuel pump activated. It must be 60-66psi. It must remain above 55psi for at least 10 minutes after the pump shuts off, (leakdown). Even if it passes these two tests, it doesn't necessarily mean the entire fuel delivery system is OK.

When you test fuel pressure at the service port, the reading indicates the LOWER of regulated pressure or maximum fuel pump output pressure. For example: If your regulator is set at 62psi, and the fuel pump maximum output pressure is only 58psi, that's what you'll see at the service port, (58psi). For this reason, we need to know what the maximum output pressure and leakdown at the pump is. With 58psi at your service port, we know that a problem exists, but without having all four readings, we can't figure out what the problem is. We don't even know for certain what your regulated pressure is, until we know what max output of the pump is.

Testing maximum fuel pump output pressure and leakdown is done at the fuel filter outlet. All fuel pressure and flow must end at the tester. It requires an adapter between the fuel filter outlet and the pressure tester. The pump is activated, and the pressure reading is recorded. Deactivate the pump, wait 10 minutes, and record the pressure reading.

Fuel pressure and leakdown are not monitored by the PCM, so it can not set a DTC if there is a problem with it. Fuel delivery is a basic engine necessity, and it has to be correct for the PCM to control the engine correctly. Bad fuel delivery system=bad performance. Same as a computer: bad information in, bad information out.