1995 Ford Explorer Fuel Pump Control

This is a timed event on your car.... the time is closer to 1.5 to 2 seconds. At key on, the PCM is a busy little boy.... he peaks at the BARO, the ECT, the IAT and a few other little things as well as turning the fuel pump on briefly to charge the fuel rail (the spray pattern of the injectors relies, to a great degree, on the pressure drop the fuel experiences across the injector orofice). I firmly believe, but haven't proved it beyond a doubt, that some strategies will also pulse ALL the injectors briefly to purge any air or vapours. This strategy may also be temperature dependent.

Once the PCM "sees" rpm signal (PCM strategy *may* dictate a minimum value) it will once again turn on the fuel pump relay.

HTH

Thanks Jim, I suspected that was the case since I didn't see a pressure input in the Chilton wiring diagrams and one of the three dealers also said it was a timed even as well. Now to the problem, on ocassion the engine won't start and I've noticed during those times the fuel pump runs continuous in key on position. After cycling the switch several times and I hear the pump stop then I can start the engine. Otherwise I can let the pump run 2-4 minutes and try repeated cranking without the engine starting. It appears the PCM is not completing its start sequence. Is there other test I can perform or should I consider the PCM history. I will add during the on/off switching the voltage is stable to the PCM and other indicator lights on the dash appear normal while in this continuous pump on mode. thanks again

Jim Warman wrote:

I suspect a problem in the ignition... A certain type of failure in a TFI might cause that. If your particular engine has one.

"D>

I don't see how the TFI could cause the PCM to keep the fuel pump on longer than the 2 second prime period in the switch key-on only position if its fixed timed period, however I'll research that.

breakdown in the electronics cause a spurious signal out the PIP.

OR one of the contacts in the ign switch, itself... but that should be more evident... relays clattering, etc.

I'll have to defer to BYMs prognosis... To my detriment, I have seen this concern discussed before but, since I so very rarely get to work on something this "old", I don't ever pay that much attention to the resolution.

That the fuel pump stays running yet the car refuses to start, this thought has a great deal of merit. Look at it this way... if we remove the relay and short the load terminals so that the pump runs continuously, this should have no affect on starting or running. If, however, the PCM is seeing a spurious rpm signal, it will command the fuel pump "on" and, at the same time, be incapable of supplying spark at the correct time (if at all)..

Intresting theory, but there is no need to purge the injectors.

As soon as there is a crank signal the PCM turns on the pump.

And you will not see one on a 95. The PCM does not look at fuel pressure. It is a timed event via the PCM.

Install a fuel pressure gauge with a line long enough to tape to you windshield. The next time the problem occurs look at the pressure. If you are at least 35 to 40 psi before you crank the engine the you do not have a fuel delivery problem. You need to be looking at the ignition side of the system.

get serious!

Don.. note I dont know if your engine has a tfi or not.

If it does, next time it does that, pull the TFI connector and see if the pump stops

And there ya go... Havent there been one or two cases where the CPS was flaky?

We are already looking at the ignition side of the system.

The fuel pump... which you CAN HEAR.. is the symptomatic tell-tale.

Ok, I'll bite. How does a TFI module that has only a connection to the PCM for ignition via a square wave voltage and one return square wave for timing purposes keep a relay that is turned on and off by a PCM keep said relay on? That square wave is called the PIP signal. No pip, no crank signal to relay ground command from the PCM. It's that simple. Do not make it more than it is.

And as soon as no crank signal, PCM turns the pump off. Your point? The TFI will not cause the pump to continue to run period. A stuck relay will though...........

You have a problem with no fuel pump run when engine crank, I might go along with your little theory. But I'll bet you get some kind of ignition related code. Like 211 PIP circuit failer maybe a 212 or a 214. My statement stands. PCM sees PIP, PCM turns on relay. PIP goes open relay turned off.

Oh BTW, there is no TFI module on the vehicle. A 95 Explorer should be a 4.0 engine with a EI High Data Rate ignition system. Sp what connector is he going to pull off?

WHAT-EVER!