1995 Ford Explorer Fuel Pump Control

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Hello All -
I got a question the local Ford dealers can't answer, three different dealers = three different answers. 1995 Explorer Question. If you don't crank the engine the but leave the
switch on, the fuel pump will stop after 2-3 seconds (normal condition). What terminates pump? Is it a timed event controlled by the PCM or is the PCM responding to a pressure transducer or some other event? This is not a relay question, I realize the relay starts and stops the pump, but under what condition does the PCM send the off command to the relay?
thanks don
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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

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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:

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

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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.
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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.
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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)..

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The TFI will not cause the problem. But it can cause the PCM to not see a crank signal wich would then cause the PCM to not turn on the pump. YOu are not verifing the fuel system by reling on your ears use a guage to check if the fuel pump is running or not.

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get serious!
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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.

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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
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wrote:

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?

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What about the post you replied to didnt you understand?
Either freakin help solve the problem.. or go away.
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wrote:

Now if you actually meant to say a TFI can cause a no start condition not a fuel pump constantly running I apologize.
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wrote:

Not speaking for BM but I have seen that before. The problem wasn't the TFI module but the ignition PU. This was back when the SBDS first came out and I was looking at the inputs at the 60 pin connector. The fuel pump was running and the injectors and coil were firing which flooded the engine. IIRC the PIP signal was indicating several thousand RPMs even though it wasn't turning over at all. Anyway a new pickup solved the problem.
Of coarse a 95 Explorer doesn't have a TFI and if it was getting an errant signal from the CPS I would thing injectors should be clicking also. Bob
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No you didn't see that.That is the same thing as saying that the alternator is going to produce voltage while the engine is not running. It aint happening.
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NOTE: This does not obviously apply to the problem at hand...
You're getting on my nerves. The pickup is a hall-effect device, the thing is electronic. People who DEAL with causal failure would not find the premise impossible... happens all the time, though rarely; And that is NOT a contradiction. Think 'millions'
You dont know WHO 'Bob' is, You dont know that he isnt a pro in the shop...yet you call him out with a statement that any experienced electronic tech would find amusing.
You dont know who I am. You dont know my background, yet you dismiss me out of hand.
That is risky territory
Yet your diagnostic step -measuring voltage at FPR- ignores the event chain you yourself described. Not to mention suggesting the OP check his fuel pressure.
This is a problem solving group, not a teaching group. It's all good that you are able to point out mis-perceptions... fine!
But we dont dont need lectures on how it works.. or step by step analysis of circuitry.
By the way, the last time we had someone on here who dealt with the group the way you do, it took years but he was finally harassed off the group by constant complaints to his various ISP's
in fact this is getting to smell a lot like...
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wrote:

I don't care if I am getting on your nerves. That hall device will not do what he described period. The permanent magnet does not alternate if polarity and can not shunt it self, why do you think there is a vane wheel between the semiconducting material and magnet? So no it does not happen all the time. Hall devices do not fail in that manner.

No I don't know who Bob is, and yes I called him out. I believe his statement is a fabrication. Any experienced tech would.

I don't care your background. I've given you every opportunity to clarify, explain your statement. Why should I take your word as gospel. I don't know you from jack shit. My training and experiance tells me what I called you out on is crap. If it's not, again, explaine your self.

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<snip, hit the wrong key, so I'll continue>

I did not ignore any event chain.

The information I gave the OP tells him how he will find out for sure with out any doubts as to what is the reason the pump stays running. PCM or relay. A simple check that will take less than 5 minuets. Far better that disconnecting connectors on parts you know nothing about. Do you check air pressure in tires by letting it out or do you use a gauge? The answer and reason should be obvious.

Go right ahead, complain all you want, I've done nothing wrong. I will come as go as I want. Now with out your patented self important crap like "you don't know who I am" Explain how that hall device will keep the relay on. You feel it will, why, I want to know.

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Well you're the one who called ME out and said it's not possible. You prove it... Keep in mind probable and possible are not the same. I never said it was probable, only that I had seen it once in the last 20 years. I've repaired a LOT of cars in that time. If it was a common failure I'd have seen it a lot more than once. Bob
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