1995 Ford Explorer Fuel Pump Control

Reply to
Fred Miller
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DON, if you followed the advice and hooked up the fuel gauge and verified that a fuel pump does indeed put pressure on the fuel rail, maybe we can proceed.

Since, occasionally, the PCM is obviously not turning the relay off

And since the FP staying on coincides with the engine NOT starting, we might assume the problem has to do with a fault in either the PCM itself, or in the ignition-sense inputs.

We can rule out the FP Relay sticking and, also, the drive circuits for that relay because the engine doesnt start.

I ASSSUME no codes were stored and that makes it even odder.

So the next time it wont start and FP stays on, open the hood and listen closely for any odd sounds and try to locate them.

While under hood in that case do a gentle 'tug-test' on the wiring harnesses around the engine to see if the FP stops

Also look up the harness to the CPS and find the connector.. I suppose there COULD be some odd occurence with the CPS being wacked that might not be stored as a code.

Another questi>

Reply to
Backyard Mechanic

What about the post you replied to didnt you understand?

Either freakin help solve the problem.. or go away.

Reply to
Backyard Mechanic

..

Okay...I'll be looking forward to your ideas on how to help him.

BTW, how long have you been on here?

Reply to
Backyard Mechanic

Not obviously, that IS an ASSUMPTION on your part. Need to put a volt meter on the primary side of the relay to confirm that. Other wise the only assumption is that the transistor in the PCM is bad, so that means the Processor must be replaced. It's more likely the relay sticks.

No you can not rule out a sticking relay. A stuck closed relay or a transistor in the PCM keeping the relay energized will not stop the engine from running. If other circuit in the PCM are bad then yes there is a possibility the PCM is at fault, and the running fuel pump is only a symptom. But instead of using fingers and ears use voltmeters and gauges.

Stuck closed relay would not give a code.

The next time you think the pump is continually running when it should not, check the voltage drop on the ground side of the relay. If you see 12 volts, the PCM is not making a ground the relay is bad. If you see .05v or less, that is a live grounded circuit, replace the PCM.

That would be down by the harmonic dampener. An A/C voltmeter is needed here to test. Back probe pins 5 and 6 of the EDIS module. Crank the engine you should see a A/C voltage. If you have one and know how to use it, install a scope in the same palce as the voltmeter pins 5 and 6. With that your will be able to see the missing tooth used for timing. A bad crank sensor will not give a code.

Reply to
Fred Miller

I understood your post, and am aware that you do not understand what is on his engine, other wise why would you suggest pulling the tfi connector if it has one? Also I've asked, so Krusty, please enlighten a not so old older person how the TFI module will keep the fuel pump on. If you dont belive the TFI can keep the pump on, then say so.

This is your post below.

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>

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

Reply to
Fred Miller

A fuel pump relay sticking is not uncommon but on most Fords the pump will run until the battery is dead. If the pump shuts off with the key it can't be a sticky relay. Bob

Reply to
Bob

Ok, its a timed event controlled by the PCM. But the PCM, on ocassion, does not turn the pump off even before cranking. I know ahead time if the engine will start by listening to the pump. If the pump goes off as normal the engine will start when cranked. The question still is, what would keep the pump on beyond the 2 second period? It appears either the PCM is bad or some input is keeping the PCM from completing the timed sequence. It is a 4.0 with EI however before cranking, before I have a RPM or PIP signal the pump should turn off. Since it doesn't have a pressure input its not fuel related, the computer can't make it to the next step in its logic start sequence. What static input test are performed, would a high or low input on the O2, MAF, TP, etc. cause the logic lockup. I assumed a lot of folks had seen the problem and the answer would be apparent.

If we solve why the pump continues to recieve an on signal before cranking then we solve the problem.

Reply to
Don

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

Reply to
Bob

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.

Reply to
Fred Miller

You don't know if the pump relay is sticking or the PCM is keeping it on. You are only assuming that. The only way you will know this is by using a volt meter. Put a voltmeter on the negative side of the primary circuit of the relay. If the PCM is keeping the relay grounded you will see a voltage drop ( a voltage reading of .05v or less ) if you see 12v the ground is open meaning the PCM is NOT keeping the relay grounded. Don't believe me? Do a google search on DC series circuits. You will find that it is true in all DC circuits that when the circuit is open source voltage will be present on all parts of the circuit up to the open. That will be before and after the load ( the negative wire or ground is after the load ). The PCM is the only device that turns on and off the relay, and it is unlikely the ground has got a short. The PCM only tests the continituity of the circuits it can see, the tests can not prevent the engine from running. Dont take running steps before you walk. You may have more than one problem.

Reply to
Fred Miller

pedantic and F343532g irrelevant!

It is not the relay or the relay driver.

The coincidence of the engine not starting while the FP remains on... and the engine running fine in other cases call for the examination of INPUT circuits OR the possibility of internal logic failure in the PCM.

Reply to
Backyard Mechanic

Dont interrupt the teacher!!!!

Reply to
Backyard Mechanic

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...

Reply to
Backyard Mechanic

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.

Reply to
Fred Miller

that you are able to point out mis-perceptions... fine!

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.

Reply to
Fred Miller

My Krusty, that's the same crap ol red seal hurricane pulls..................

Reply to
Fred Miller

Funny you should refer to him.

Reply to
Backyard Mechanic

Okay... Contrary to your statements, neither the CPS or Hall pickup in the distributor are 'dumb or passive circuits'

They are solid state, multi-element, as is CERTAINLY the TFI. And they ALL likely have signal shaping circuitry within.

Which work by means of positive feedback, IOW 'hysteresis'. The effect is that the output of the shaping circuit remains at a state until the input signal reaches a level high enough to overcome the feedback of the output, at which time the output switches and reinforces the input, then it remains at THAT state until the input drops low enough to overcome the feedback, again.

Now, the same circuit as takes in a ramped or sine signal and outputs a square wave can with little modification be made into an oscillator.

The modification is usually done by adding capacitance or a separate negative feedback element. and they obviously require no external signal to oscillate

Now, suppose that the housing/coating for one of those MODULES had cracked and moisture might have invaded... if it happened to contaminate at just the right area of the circuit, that might have altered the characteristics just enought that until, the substrate warmed, negative feedback -say from an adjacent circuit trace- would occur and the circuit would oscillate. Of course that is only hypothetical, but you can take this to any circuit designer, describe the scenario and i believe he'll vouch for the theory.

AGAIN: a very rare problem, right?

And i want to point out to you AGAIN that the OP implied that the FP Relay turned OFF when the key was turned off... else there would have been mention of the battery running down and difficulty in actually getting the FP to shut off.

So AT THE LEAST, the PCM Power relay controls the state of the FP relay.

Which means that, given the engine ALSO wont start at the coincident point, that something earlier in the chain must be holding the driver transistor on and at the same time, altering the known events that drive the logic so that the engine wont start.

Whether that is happening inside the PCM, itself, is unclear.. it could be... but it sure aint happening at the FP relay. And BTW.. when a driver transistor shorts, it's DONE FOR! and most circuits have no fail-safe that prevent the short from looking like a short when the main supply is off, remove power, it's still shorted. That's how you can find it with an ohmmeter.

Now.. let's look at the other assumptions. No Codes. What does that tell you? It tells me that the PCM doesnt know there's anything wrong. Which means the fault COULD still be in the PCM but narrows it down quite a bit.

Now... I'm done. if you dont understand my thinking, then go back to your Fords Tech Manuals and branching troubleshooting charts.

Reply to
Backyard Mechanic

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

Reply to
Bob

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