Fuel pump runs too long at start up?

I ran a fuel pressure and flow rate test on my fuel pump a while back. It passed the pressure test and seemed to have plenty of flow, but it has always taken about 7-8 seconds to shut off after I turn the ignition switch on (but not started yet).

I am wondering if a partially plugged fuel filter could be in any way causing the fuel pump to run so long before shutting down????

It does it repeatably. In other words if I turn the power on, off, on, off every 10 seconds with out starting the jeep it always runs for 7 to 8 seconds before it shuts off.

What ever the cause of the long run time on the fuel pump, could this be the cause of the low power at WOT? If so what are all the fix options?

Sounds more like the anti-drainback thing, how long does it hold pressure after you turn it off, if pressure drops right away the anti-drainback is shot, some here replace it with a BMW valve that goes up in the front. You don't mention your year so I'm just guessing.

Not sure, don't remember if I tested that. It does always take about 4 to 5 seconds of cranking to start, like clockwork. I always wait for the pump to shut off before cranking. If the pressure dropped, wouldn't the pump restart itself if I waited long enough, or is it a one time on/off then wait for the ignition signal to restart the fuel pump thing?

I beleive how long the pump runs when the ignition key is first turned on is completely under the control of an internal timer within the ECM, and is set at arround 3 seconds. When the engine is actually cranking, the ECM again turns on the pump. 7 to 8 secs on-time may be a sign of a problem with the ECM; however, that in and of itself would not be something that needs fixing. IMO. The Renix 4.0's always take longer to crank than the newer models.

It is a 1987 OEM 4.0 Renix, Wagoneer (not the Grand), 4x4 Ltd.

Thinking about it it seems like I must have tested the fuel pump and drain back valve with the power on and ignition (engine) off first. I know I tested it with the engine running because I remember testing the fuel pressure both with the vacuum line removed and attached to the pressure regulator.

So 7-8 seconds on for fuel pump with the Renix 87 "ECU timer" may be OK?

If I retest it and find out it is the drainback valve leaking, where can I find out more about the BMW valve and how to install it?

I'm saying fuel pump on-time when the ignition key is turned on, but the starter is not engaged should be 3-4 secs, not 7-8 secs. The on-time is set by an internal timer in the ECM, and is not variable. The 7-8 secs on indicates a problem with the timer, but probably not a problem that requires fixing. The check valve in the fuel pump should hold 19 psi of fuel line pressure for at least 30 minutes after the engine is shut down. (start engine and record pressure; turn off engine and wait 30 minutes, then note pressure again; it should not be below 19 psi). If it fails the "leak down" test, the problem is either with the check valve in the fuel pump or the pressure regulator, or, of course, a leak elsewhere in the pressure side of the fuel system.

Well I timed it again today and actually got 3-4 seconds. Go figure. So I guess its on to looking elsewhere for the gremlins.

I will keep checking it now that I know what it should be for mine (87 Renix). I think I got alarmed when I read somewhere in another thread that it should only be one second, but they did not say what year they were talking about.