Does PATS disable the voltage to the fuel pump?

[tritone88]

Oh yes I see what you are saying now. I agree that the PCM was probably not turning on the FP relay and thus operating voltage was not sent to the inertia switch. I was not aware of the concept of what you call "floating" voltage which was what I measured at the inertia switch when the relay was not activated. I don't understand where this 6 volts comes from if the circuit is not enabled. This is why I assumed incorrectly, that the PCM was somehow interrupting the 12 volts from the relay and allowing only 6 to pass to the switch.

If I understand what you are saying, there is a residual or "floating" voltage always present in the circuit (6 volts in this case) that is not at its 12 volt capacity because the relay was not activated by a ground from the PCM.

Is that what you are sayng?

 

[budwich]

Kind of... yes.... basically, any kind of "open circuit" is a "funny circuit" to measure voltages on. In this case, its "open circuit" because the relay isn't operated so any DC voltage readings along that circuit path thereafter could read any number of voltage levels depending on what is in the circuit.... "steady state open circuit voltages" tend to float to some level.

 

[2000StreetRod]

Solid state input voltage

Bob, thanks for posting the associated wiring diagrams. As I posted earlier, Pin 40 of the PCM is an input. It allows the PCM to monitor the status of the fuel control relay for diagnostic purposes. The PCM is a solid state device. I don't know what logic is utilized but I suspect most of the logic is TTL since 5 volts is one of the reference voltages. The PCM probably utilizes solid state switches for 12 volt control of relays and solenoids. Anyway, even most inexpensive voltmeters these days have a very high impedance which means they draw very little current to perform a measurement. There is always some voltage to ground present on the input of a solid state device. The particular input of interest is probably a voltage comparator that compares the fuel pump relay output to a low current bias of 6 volts. That is the voltage that was measured at the inertia switch.

 

[budwich]

As streetrod was pointing out, all you did with your voltage measurement when the fuel relay is NOT operated is measure the "internal works" of the PCM circuit that is monitoring the fuel relay operation.... not much value unless you were troubleshooting something inside your PCM.

 

[tritone88]

Right, not much value in and of itself, but it did tell me that the expected 12 volts wasn't there at the inertia switch. That was essential.

BTW, someone (Bob?) supposedly posted a 2000 schematic diagram but I can't see it in this thread nor do I see a link to it. I see the post that indicates it was posted, but I don't see it. How do I get to it?

 

[BobWiersema]

Right, not much value in and of itself, but it did tell me that the expected 12 volts wasn't there at the inertia switch. That was essential.

BTW, someone (Bob?) supposedly posted a 2000 schematic diagram but I can't see it in this thread nor do I see a link to it. I see the post that indicates it was posted, but I don't see it. How do I get to it?

No idea why you cant see that but these are the links.

Image 1

Image 2

Bob

 

[budwich]

Right, not much value in and of itself, but it did tell me that the expected 12 volts wasn't there at the inertia switch. That was essential....

Actually, it led to a "conclusion" that some how the PCM "varies" the amount of voltage that it provides to the fuel pump in a "roundabout way" as opposed to you determining that the fuel pump relay was not operated which would have led to more direct question of "why" which would have probably led to the "bad key" focus as opposed to the "less than 12v focus"... anyways, water under the bridge in the "troubleshooting strategies"... the resolution is the important part cause I hate vehicles and systems that don't work. Glad there wasn't a lot of "part swapping for nothing" which I also hate...

 

[tritone88]

Budwich, I totally get your point now. I can see how that may have been misleading. I tried to just present the facts and nothing but the facts which included a 6 volt measurement. Sorry if I was implying something else. As you said problem solved in the end and I didn't throw parts at it like many people do in desperation. Thanks mostly to this board!

Bob, thanks for reposting those links. For some reason I can see them now but they weren't available to me in your initial post. Weird...

 

[BobWiersema]

I hope this PATS thing is not an epidemic. For some reason my Theft light was flashing rapidly while driving today, then it stopped. I do carry a spare key, if the problem returns Ill try it.

I don't know what logic is utilized but I suspect most of the logic is TTL since 5 volts is one of the reference voltages. The PCM probably utilizes solid state switches for 12 volt control of relays and solenoids.

Dale,
How about a quick computer lesson. Since I do PLC device programming, my head is stuffed full of useless information regarding these device. You are correct, TTL logic is the foundation that all these devices are based on. I believe the early devices were pure TTL circuits, (no programming required). However they have progressed into highly sophisticated purpose built PLCs (Programmable logic controllers). The logic is no longer performed by the TTL circuit, but by the firmware. Every function of an automotive ECU could be performed by standard PLC devices, however it would take too much hardware and you would end up with banks of these things. So its all streamlined down to one or two purpose built controllers. The devices I program are for HVAC and they are also streamlined for the application. But deep down inside they are all just fancy TTL circuits developed in 1961 by James Buie (I think).

End of today's lesson, now back to that flashing theft light.

Bob

 

[Runnin'OnEmpty]

I ran into this thread during a search, and have
a question:

Since PATS turns off the fuel pump relay ground,
could a ground circuit be hardwired to an inside
switch and run the engine? (Assuming a PATS
problem)

 

[budwich]

unlikely.... but to correct the statement a bit. The PATS doesn't actually turn the fuel pump relay down, it "sends stuff" to the PCM which turns the relay down. The difference is that the PCM also then has "opportunity" to do a few more "things" if it wants or not. Others with more PCM insight might add some detail but I don't think stealing a ford is in your future with this technique...

 

[Runnin'OnEmpty]

unlikely.... but to correct the statement a bit. The PATS doesn't actually turn the fuel pump relay down, it "sends stuff" to the PCM which turns the relay down. The difference is that the PCM also then has "opportunity" to do a few more "things" if it wants or not. Others with more PCM insight might add some detail but I don't think stealing a ford is in your future with this technique...

I had thought that maybe the fuel pump relay ground pin
could be hardwired to a constant ground, and this would
defeat PATS....? It would negate the PCM from turning off
the fuel pump after 2 seconds if not started I guess...
By the way, what's the purpose of turning off the FP
anyway, maybe for safety reasons...?

 

[budwich]

Not sure why you think the fuel pump relay is that important. IF you really want gas, you just run a jumper from your battery (or other 12v source) directly to the fuel pump lead.... you don't have to involve anything including the pcm, the relay or the PATS for that matter... BUT if you think this is a "PATS workaround"... as I said "stealing a ford with this technique isn't going to happen"... I think there is a bit more than gas supply involved...

 

[Runnin'OnEmpty]

Thanks for the info Budwich, and no, I'm
not a car thief.

I'm just trying to get an idea of how the PATS
system works in the event it ever goes south
on me. Personally I don't like a system like this
that apparently gives so much trouble. I'm sure
thieves figured out how to bypass chipped ignitions
long ago, since virtually every auto mfg uses
them now.

The previous posts seemed to indicate that PATS
shuts down the power/ground to the fuel pump relay,
but like you say there must be more to it than that.
If that was the case, a thief could simply jumper
the fuel pump....

 

[budwich]

IF your PATS goes "south", so do you so to speak ... :-( or find a car thief that knows how to get around it... I don't think that there are many on this forum... Its usually an expensive trip to your dealer... :-( Having said, a number of posts usually find that the PATS itself isn't the culprit but other associated equipment (ie. pickup, wiring, key among other things).

 

[2000StreetRod]

PATS disables FI

On my 2000 Sport when a non PATS key is utilized the PCM disables the fuel injectors so it doesn't matter if you have fuel pressure.

 

[Runnin'OnEmpty]

On my 2000 Sport when a non PATS key is utilized the PCM disables the fuel injectors so it doesn't matter if you have fuel pressure.

After re-reading the postings, it seems that PATS disables
both the fuel pump and injectors. Oh well......

On a side note, I bought 2 extra keys at an ACE Hardware
and the keymiester programed them at the counter. The
keys have the same coding as the original key, but they
contain a battery inside. One day these batteries will die
and the vehicle will not start, all because of PATS.
Something else to worry about.....

 

[Runnin'OnEmpty]

PATS and Fuel issue solved!!!

........
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.

......
The ILCO key is a clone that's sold by ACE hardware, among others. It indeed has a battery inside that can be replaced. The battery generally lasts from 3-5 years. A discharged key will retain it's programming, so after a battery replacement, it should work again.

 

[koda2000]

If you only have one original key (your second key is apparently a clone) you can not reprogram/program any keys yourself. Get a real key off eBay or Amazon (around $10) and have a locksmith or the dealership program it. With 2 different OE type keys you can program more keys (IIRC up tp 5) yourself. The procedure for doing this is in the owner's manual.

IDK if the ILCO key has a battery in it. If it does it may work once you replace the battery. Worth a try I guess.

 

[Mark Anderson]

Wow, i just read thiswhile thread....terms and lingo over my head....

My issue.....i have a 1999 ranger 4x4 automatic that had a factory 3.0, but it died..i stated reading on several different forums how a 4.0 sohc was a plug n play conversion...so i found one..dropped it in...and the engine to body connector (refered as 115) doesn't match my plug...turns out ford made an early model harness and changed it in august of 01..my motor is dated 12-19-2000...i went to local dealer...got copy of my 99 plug but they couldn't pull up anything for the early plug...the newer plug shows just about a total match to the 99..but so fsr i can't find a harness at any of the4 pick n pulls like it...
Also i grabbed the keys and column reader, pcm and harness from donor motor explorer...turns out pats receiver in right kick panel has too many wires to swap it into the ranger..also the plug under the abs module is different...the 4.0 has 2 extra wires...
So basically at this point i can crank it over...but won't start without giving it a manual squirt of fuel thru the throttle body...i know it's a pats issue from all the reading I've done here...
So I'm hopeful someone here can help me get my ranger going..long post, i know....but I've been fighting this for weeks now with no luck..
Again, thanks mark