Hello All,
Ima new member I gotta 2002 F150 w/ super crew cab (i think thats what they call it) with a 5.4L triton engine. Its got 4X4 for low and high speed. It still looks good (grey) on the exterior but if you get underneath it ... boy those rocker panels are simply just dreams of metal where now tis only rusty flakes and grit. I think one day I'll make a sharp turn around a corner and the cab will continue straight on down the road as the engine wheels and frame make the turn and speed off without me. I just did the heater core with it outside in 7degree temp... oh what fun. It ran great and hot for a 5 hr drive afterwards and ran good most the next day but as my girlfriends son was out and about with it later that day, it just up and died. Luckily he was already where he needed to be at his friends house, but now again Im faced with having to crawl about in this awful weather to get the old gal going again.

No pressure at the fuel rail, checked all the fuses and relay. The relay failed the testing and I replaced it. But again no pressure at fuel rail, I get a millii second of voltage (+12v) at the blk/pnk fuel inertia switch when I key on. And there has been an intermittent Mil for the past month or so. The first time it appeared it was for cyl #1 too lean (don't remember the precise code number). At that time I figured it might be just a semi plugged injector so I used some gas additive of a STP injector cleaner and sure enough the Mil went away. It reappeared a couple weeks later and I did a repeat with the same results. All the while it was running great except for the heat, which as I said I just did two days ago.

So now my plan is to get down and back under the tank and test for any voltage to the fuel pump connector when it is keyed on. If Im right, I should be testing the pnk/blk and grnd for voltage at the fuel pump connector...Right? And then Im gonna use an ODBII scanner to pull the codes, and go on from there. At this time I only have one question, that being whether or not this 2002 5.4L has one of those Fuel Pump Driver Modules between the inertia switch, pump and pcm. Or if it is just straight thru to the pump from the inertia switch. Oh I guess I have another question as well... that being it is a very very short time I register a voltage at the inertia switch. I mean milli seconds not seconds of voltage. I've gone through several wiring diagrams on F150's and the only thing I could see possibly having an affect on that circuit would be if there is a Fuel Pump Driver Module inline with that circuit. But so far I haven't seen anything like that on my F150, if it has one where would it be located? And if it doesn't have a FPDM interfering, why is the voltage for the pump so short, it should be on for at least a couple seconds shouldn't it? Well time to get suited up and climb under her, I'll be watching later on for any input from you-all ...Any and all input is welcome.

 

There is no fuel pump module on pre 2004 F150s... 70% of the time, the problem is the fuel pump.. You turn the key "ON" , not start, and the pump runs for 3 seconds, builds up pressure in the fuel rail, then shuts off until the truck is started.. You can measure voltage during that time. I would think the voltage at the fuse and inertia switch would also show this.

 

If the voltage at the inertia switch went to +12v for 2-3 seconds I might have been inclined to think of fuel pump. But as it only went to +12v for a milli second, not. I would have programmed in a safeguard into the circuit so that if there was a high resistance (which could let the smoke out of a chip in the pcm) at key on, the circuit would trip off.
I tested the voltage back at the fuel pump connector and at key on it reached a whopping +.098 v for the same milli second period I got the voltage at the inertia switch. So I disconnected the line at the pump connector and tested the impedance of the pnk/blk line to ground... between 20k and 80k ohms. I disconnected the yel/drk grn and pnk/blk line of the inertia switch and did an impedance check of the yel/drk grn line to ground and had infinity at all impedance settings (which is what it should be in key off). I did an impedance check at the inertia connector of the pnk/blk to ground with the fuel pump connector disconnected and again the 20k to 80k ohms. I guess I have a shorted line somewhere between there and the fuel pump connector. Is my thinking right, or am I seriously missing it somewhere?

Oh also the Mil code was P0174 Bank 2 too lean

 

Your meter is NOT reading impedance, it's reading RESISTANCE.

If your meter is slow to respond, that's all you'll see. This is a job for a test light in your case so that you can distinguish which path must be taken.

That is exactly the opposite of how magic smoke works. Basic Ohm's Law equation.

Those readings appear to be normal. Your understanding of what you're trying to do is very incomplete and that lack of understanding is leaking you to incorrect conclusions.

 

maybe plug a light bulb into the fuel pump electric plug and ground it... then turn on the key and watch the bulb ???

 

That's exactly what I told him to do....

 

If you got +12v at the PK/BK wire at the inertia switch and got +0.098v at the PK/BK wire back at the pump, sounds like that's where your voltage is disappearing. Its not even making it to the pump.


So that high resistance of the PK/BK wire to ground shows that the PK/BK wire is not shorted to ground.


But how about testing the resistance of the PK/BK wire from the inertia switch back to the fuel connector harness. You'd like to see less than ~5 ohms resistance, but if that's where your voltage is being dropped, I would expect to see a high resistance due to a bad spot in that circuit.


Good luck.......

 

Impedance is a comprehensive expression of any and all forms of opposition to electron flow, including both resistance and reactance.

So getting back to the ol gal. Yeah I had already tried every thing that everyone had commented on trying. Had written I had tested the pnk/blk line totally disconnected from every thing else at the fuel pump connector and the inertia switch connector when, where I found the 20k-80k impedance to ground. However, later determined, by totally isolating just the pnk/blk line from fuel pump connector to inertia connector, the line its self had developed the impedance of 20k to 80k. But, as I had written if by testing the line (totally disconnected to anything else) to ground and finding it to have 20k to 80k impedance, yes it would mean it had a high resistance short to ground if it on the other hand had infinite resistance, then that would indicate there was no short, and if it had a low impedance reading like 100ohms, that would mean it had a very substantial short to ground. The lower the impedance the higher the current flow, and conversely the lower the voltage drop, the higher the resistance the lower the current flow and the higher the voltage drop over/thru the component being tested.

I found the anomaly was in the segment of the pnk/blk line/bus/wire starting from the male connector just under the engine coolant tank in the engine compartment, and the connector at the inertia switch. The line itself has some how developed an impedance of 20k to 80k ohms. According to all schematics I've been able to get my hands on there should be nothing else on that pnk/blk line/bus/wire in that segment. So I tapped into the line just behind the male connector there (at the connector under the engine coolant tank), and spliced it on to the pnk/blk connector just before the inertia switch and it runs fine.

So I fixed it, but I don't like how I fixed it. If I had more detailed info as to the exact path of the cable that contains that line, I'd be better able to determine at exactly what point that line becomes defective. I wish I had a Ford Shop Manual for F150's. I had one once for my '88 5.0 Mustang and boy that sure was helpful finding out an engine control module was part of the windscreen wiper motor. How or why they stuck it in there anybody's guess, but I would have been lost without it(shop manual).

It always pays to get the Shop manuals from the dealerships at time of purchase of your vehicle. This truck is one my girl friend's vehicles and as much as I love her, what it costs for me to get it for her (shop manual), compared to what I make in income .... well she really wouldn't appreciate the sacrifice I'd have to make. Besides, then she'd expect me to get them for all her vehicles. I mean she's the rich one, she should be getting them for me to fix her cars. From what I save her and her daughter's and son's cars and on and on I save her thousands a year. But she still charges me rent... imagine that. I guess that's why she's the rich one ha ha.

So If'n you-all got a picture of the path of that cable, starting at the male connector (think it had 8 wires in that cable bundle) just under the engine coolant tank, to where it comes out at the inertia switch behind the passenger side kick panel. I'd sure be grateful, I hate to do bypasses like that. It's so jury rigged, I'd rather remove the segment repair it properly and replace it. Thanks to everyone puttin your input in. But as to the comment of not understanding how the system works whatever.... I've gotta lotta experience designing circuitry like amplifiers, H-pads, full wave bridge rectifiers, building and programming of adders, if then, nor, nand circuits etc etc, if I use terminology differently than what your accustom to well not surprising. I was taking a computer engineering class a few years back to finish up a degree I had started on a dozen years before and found that there was no more such a thing as arctan any more I think its now just atan. There were other definitions I found that had become antiquated as well but.... oh well in this day and age things just get renamed just to make us old timers feel guilty for livin it seems. Anyway again thanks for everybody's input, hope to hear someone has the scoop I'm seeking.