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Does PATS disable the voltage to the fuel pump?

tritone88

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Hi this is my first post on this forum. 2000 V6 4.0 sohc.

I have combed through about 50 posts on a no-start issue I'm having.

Symptoms:

The car began to have inetrmittent problems starting. Sometimes it would fire up. Other times I couldn't start it for hours.

Checked all the stuff suggeted by members here:

Only 6volts to the fuel pump inertia switch when ignition switched on. Should get an inital spike of 12v for 2-3 seconds but it doesn't. Never gets the full 12 to operate the pump even during cranking.

Tested fuel pump relay and it behaves like it should. Even swapped other relays in and out with no effect.

Removed fuel pump relay and sent 12 volts through relay contact directly to the inertia switch and the fuel pump ran so all wiring from relay to pump is good.

So then I read about the PATS system and how it can disable the car. When I turn the key to on but not start, the anti-theft light continues to flash and never stops. Check engine light remains illuminated so PCM is probably functional. When I try to start, anti-theft continues to blink.

So my question is: Does a malfunctioning PATS system somehow disable or lower the voltage between the fuel pump relay and the inertia switch?

Some say the car will never even crank over if the PATS is malfunctioning. Any help would be appreciated.

Thanks
 
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BobWiersema

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If that light is flashing you definitely have a PATS problem. When mine started acting up I was able to start it by slamming the tilt wheel up and down. That worked for a long time till I got around to replacing the receiver in the steering column.

Bob
 
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2000StreetRod

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PATS disables fuel injectors

On my 2000 SOHC V6 Sport a bad cause results in PATS causing the PCM to disable the fuel injectors but allows the ignition and the fuel pump to function. I experienced this on the third day after purchasing my Sport. Key Duped
 
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tritone88

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Well thanks to everyone who has replied so far. 2000StreetRod, I've read about 20 of your posts on fuel and such. I followed the diagnostic about checking the fuel circuit and I even cleaned the ground behind the drivers kick panel. Unfortunately to no avail.

Also I verified the wiring by hotwiring 12 volts to the relay socket #87 (Voltage out to the inertia switch) and the fuel pump ran like a champ. This would indicate that there are no wiring issues from the relay to the pump.

Interesting that you say the fuel injection gets disabled but not the fuel pump circuit. You and I have the same vehicle so I wonder if Turdle's reply that a malfunctioning PATS disables the fuel pump pertains to another flavor of vehicle. In passing the dealer mentioned that PATS can disable different models in different ways.

Very confusing. Anyway, if it is true that the PATS does not disable the fuel pump circuit, then I'm at a bit of a loss. Tonight or tomorrow, I'm going to disconnect the fuel pump relay and "extend it" with 4 wires so that it is still connected to the socket and functional. This way I can hook up the volt meter to various pins to observe what is happening when the key is turned on and then when the engine is cranking.

If all is well, I should see the relay activated (i.e. 12 volt spike at 85 and 86) for 2-3 seconds KOEO. When cranking I should see continuous 12 volts at 85 and 86. With 12 volts energizing the relay I should then be able to measure 12 volts going from pin 30 to 87 out if everything is working correctly.

From my reading, I understand that relay pin 87 out goes directly to the inertia switch. Since I never get 12 volts at the inertia switch, either the PCM is not sending enough voltage to activate the coil in the FP relay or somehow the 12 volts is being drained between 87 and the inertia switch.

Does this all sound reasonable?

My thought about malfunctioning PATS was that somehow PATS was overriding the 12 volts sent from the PCM to the FP relay that activates the relay coil.

I'll report back tomorrow or the next day on what I find in case anyone is interested.

If you or anyone else has any other thoughts, please let me know.
 
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Carguy3J

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Yes, it disables the fuel pump. You are on the right track.

On my 2000 SOHC V6 Sport a bad cause results in PATS causing the PCM to disable the fuel injectors but allows the ignition and the fuel pump to function. I experienced this on the third day after purchasing my Sport. Key Duped

Ok, now I'm confused. I thought PATS disabled the IGNITION, on 2nd gen Explorers? As in, the fuel pump should function normally, it should crank fine, but it will never start because there is no spark?
 
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BobWiersema

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On my 2000 SOHC V6 Sport a bad cause results in PATS causing the PCM to disable the fuel injectors but allows the ignition and the fuel pump to function. I experienced this on the third day after purchasing my Sport. Key Duped

On my 98 it shuts down the injectors. I have tested this. Also you will get an error in the ECU. Like I said, if that light is flashing you have a PATS problem and you need to address that first.


Bob
 
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2000StreetRod

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separate issues?

On my 98 it shuts down the injectors. I have tested this. Also you will get an error in the ECU. Like I said, if that light is flashing you have a PATS problem and you need to address that first.
Bob

I agree with Bob. You may have a voltage drop issue also but your most important issue is to resolve the PATS disabling. The Owner's Guide states that when the ignition is Off the THEFT indicator should flash briefly every two seconds. When the ignition is switched to On or Start the THEFT indicator will light for three seconds and then go out. If the THEFT indicator stays on for an extended period of time or flashes rapidly then . . .

If you have good fuel pressure at the Schrader valve then PATS is your primary problem. Try another ignition key. Remove everything from your key ring.
 
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tritone88

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PATS and Fuel issue solved!!!

Thanks everyone. Just to be perfectly clear about the problem: No fuel being delivered anywhere and the fuel pump was not priming when the key was switched on and was not pumping when the engine was cranking over. So no fuel pressure to schraeder valve and no fuel to injectors.

My first test was to see if there was 12 volts to the inertia switch under the passenger kick panel. No 12 volts, only 6 volts even when cranking. There must be 12 volts there otherwise the fuel pump won't run with less.

Checked relays and continuity from relay to inertia switch and all was well. That's when I noticed the PATS anti theft light continued to flash with key on and even when cranking.

I then posted to the board because I had read that the flashing should stop with the key on and wondered if somehow PATS could be affecting the voltage in the fuel pump circuit.

Anywho, various people responded that I must find the trouble with the PATS problem first. So I called the guy who owns the car and he told me there was another key under the bumper. I pulled it out, put it in the ignition, turned to on and voila!!! the theft light went out. At that point I hooked up the voltmeter to the inertia switch again and cycled the key off and then on. Amazing! A 12 volt spike appeared for 2-3 seconds. I cranked the engine and a continuous 12 volts flowed through the inertia switch and powered up the fuel pump just like it should.

The key the guy gave me, must be a copy or it must have gotten deprogrammed. It says "ILCO" on it and it looks like it has a battery in it. Pretty sure that isn't one of the stock keys that came with the car. Whatever, I'm gonna review the threads to see if I can reprogram it for the guy using the good key. I thought I saw a writeup about this somewhere.

So I am reporting empathically and without any confusion that PATS does indeed disable the fuel pump circuit. I know other members have other opinions and/or experiences with this and it may be that their models are disabled in other ways, but this here Explorer has the fuel pump circuit disabled. A locked PATS somehow sends a signal to the PCM to lower the voltage in the fuel pump circuit to 6V so the pump cannot run.

On an aside, it is interesting to note that the car did start once or twice over a period of a week with the key that had somehow become unprogrammed. Maybe because it is an aftermarket key with a battery and maybe the battery was going low and finally died. I can not explain this. I swapped the good key with the bad key several times and like clock work, the bad key left the anti-theft light flashing and the good key turned it off immediately.

Thanks to everyone who replied to my questions. I couldn't have figured this out without this board and its members.
 
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tritone88

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P.S. Addendum to my problem solved message above.

Turdle, looks like you were dead on right about PATS disabling the fuel pump. How did you know this?
 
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Turdle

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P.S. Addendum to my problem solved message above.

Turdle, looks like you were dead on right about PATS disabling the fuel pump. How did you know this?

I think it happened 2 times here-once while James was remote tuning the Turdle Mounty I swapped PCM's before he disabled the pats.

Then , techieman33 tried swapping his PCM from one mounty to another and same thing happened.

School of hard knocks is how this guy learns
 
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2000StreetRod

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thanks for the update

Thank you for posting your solution and including details! When I used my key that has no microchip (but works the door locks) I had fuel pressure at the Schrader valve even though I had cranked the engine numerous times and it had been a full day from the time the engine last ran. I didn't measure the pressure with a gauge so it may have been low. I guess it could have been left over from the previous day.

According to my wiring diagrams the fuel pump relay energizing coil receives power when the PCM power relay is energized. The PCM enables the fuel pump relay by grounding the other side of the energizing coil. The voltage that you measured at the input to the inertia fuel shutoff with the fuel pump relay inactive is the input voltage for the PCM pin that monitors the status of the fuel pump relay. Being an input to the PCM, it has no current drive capability.

The PCM firmware could be programmed to either enable or disable the fuel pump with a bad key. I just tried my non-chip key and my chip key. My fuel pump is quiet and I could not hear it run with either key. On a warmer day in the future I may check the non-chip key with my fuel pressure gauge.

It takes two functional PATS keys to program another key. Otherwise, you have to go to a PATS capable locksmith or the dealer to program another key. A special box is connected to the OBD port and the PCM "learns" the identity of the new key. The process takes about 20 minutes. Once you have two functional keys it takes about 10 seconds per key for each additional one. It's a good practice to have three functional keys. Then if one is lost, only the cost of cutting a replacement third key is incurred since the owner can program it himself.

I'm glad you have your problem solved!
 
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budwich

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Its good that this has been resolved. However, it does sound rather "strange"... Please explain exactly where you put your "red" and "black" leads to measure your voltage during your tests. Once that is known, I think there will be a further explanation for the "results". I agree that the "bad key" was the cause BUT the readings provided are rather "suspicious" at least based on the way the circuit appears... of course anything is possible with only "black box knowledge".
 
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tritone88

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I did lots of tests but I am assuming you mean the test at the inertia switch.

Okay first I disconnected the inertia switch and jumped the pins to bypass the inertia switch. As you know, the black green comes in from the fuel pump relay side and the pink/black goes out directly to the fuel pump.

I then connected red test lead to the jumper and black to ground on the chassis.

The way the circuit works is that as soon as the key is switched on, but not cranked, 12 volts should spike at the inertia switch for 2-3 seconds which then powers the fuel pump enough to prime the line. Voltage then drops off. When the engine is cranked, there should be a continuous 12 volts at the inertia switch which runs the pump while the engine is trying to start.

When the PATS was flashing with the bad key in the ignition, in both conditions, KOEO and engine cranking, I never measured the full 12 volts. Only 6 volts came down to the inertia switch and therefore only 6 volts got to the pump which is not enough to run it.

Once I put in the functional ignition key and the PATS system went off, I got 12 volts with KOEO and then when cranking, I got the full 12 volts which in turn powered the fuel pump just as it should.

Is that clear enough?
 
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budwich

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Very good.... thanks for the explanation. It is indeed interesting. I know that post 1998 (I think) that the returnless fuel system uses a form of "pump control" (along with a "damper") to control fuel pressure.... but how it is achieved isn't obvious... at least to me. Based on most of the circuits that I have seen, the "switched 12v" drive for the pump comes basically from the battery thru a "few contacts" to towards the pump as you have indicated. There doesn't appear to be a point where voltage "variability" can be achieved hence my "suspicion" and I was suspecting a "floating ground" although your tests appear to negate that. It is unusual that they would try "pull down" the voltage as opposed to switching out the ground. Anyways, thanks for the further details.
 
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tritone88

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Hey no problem. I appreciate your interest in the issue. I may be missing something and if so I am certainly open to other suggestions. Without a shop service manual and an accurate wiring diagram and a description of exactly how the PCM operates when the PATS is in disable mode, it's all grunt work and hopefully some logical suppositions.
 
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BobWiersema

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The 2000 fuel pump schematics, if anyone want them.

fuelpump-vi.jpg


fuelpump2-vi.jpg


Thank you for posting your solution and including details! When I used my key that has no microchip (but works the door locks) I had fuel pressure at the Schrader valve even though I had cranked the engine numerous times and it had been a full day from the time the engine last ran. I didn't measure the pressure with a gauge so it may have been low. I guess it could have been left over from the previous day.

Also Dale,
If you use a invalid key it will set a P1260 code in the PCM. On my 98 this would cause the Theft light to flash quickly while driving. Once I connected my laptop and cleared the code the problem went away. It would only do that once in a while and I thought it was related to the new key I programed so I stopped using it. Problem continued until I plugged in and found the code. Strange things these PATS devices.


Bob
 
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tritone88

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I have a pretty advanced OBD II code reader. There was only one code set. Lean fuel mixture in bank #1 or something like that. No P1260. Are the PCM codes accessible through the OBD II port or is a separate scanner required on some proprietary port?
 
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tritone88

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Just an aside. I worked on a 96 Cadillac once and by pressing a combination of buttons (temp and something else), the dash would display all of the various codes stored in the computer for every system in the car. They would all be listed by system and then it would prompt you to erase them if you chose to do so. How cool is that?
 
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budwich

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That's kind of the "standard ex" fuel circuit that I was referring to. From my "experience" in readings circuit diagrams, the "strange" measurement of "less than 12v" is certainly hard to explain as I know of no way that the PCM can pull the voltage down... however. basically, what I do see is that the relay (fuel relay) is NOT operated and hence any voltage (less than 12) at the inertia switch is just "float voltage".... and of course, with an invalid key, the relay should not be operated.... but my "mistake" was "misreading" the OP subsequent post about "finding operating voltage" on the fuel relay. Of course, that is always true CAUSE the PCM isn't switching in a voltage to operate the relay, it switches in a GROUND. So of course, the relay is NOT operated (cause of the bad key) and that was indeed the problem and nothing really to do with the "less than 12v being "seen". Basically, the PCM was not ioperating the fuel relay because there was a "theft condition". So it wasn't really that strange... :)
 
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