Still no Fuel After Searching

[HawaiiFiveOh]

First off I would like to say hello and Happy Holidays to everyone here. I have been a "lurker" for some time just to use the search feature, but now I need some help!

A little background on my situation first would help I think: 92 ex. that won't start. Fuel pump fuse checked ok, fuel pump relay ok, dropped the tank and pulled the pump; put 12 volts to it and the pump works. So... throw it back together and I still get nothing. I pull the plug off of the fuel pump relay and check it.. I have a constant 12 volts with the key off and nothing anywhere else, Good right. Key on I still have my 12 volts constant plus I have another terminal with 12 volts and one with about 6 volts. The catch is i never lose these two voltages even after the normal 3 or 4 seconds. Those secondary voltages stay at the plug as long as the key is on.

I stopped by ford today to talk to a service guy, he says its got to be the pcm.

So I figured I should ask the people who actually know these trucks before I start looking for a pcm. Thanks go out to any help you guys can give me.

 

[Creager]

Ok enlighten me, is the motor even turning over? Are you getting spark?

Can you hear the fuel pump prime when you first turn the key on?

 

[HawaiiFiveOh]

Yes the motor turns over and I have spark. When I turn the key on the fuel pump does NOT prime. Like I said, when i turn the key on I have the constant 12 volts on the fuel pump relay plug plus I have two more terminals with voltage on them 12v on one 6 on the other. However this voltage does not go away after the "priming" time period is over.

 

[DeRocha]

Are you getting any power at the inertia switch?. Check the voltage on both wires. They should read 12v while the tac>0 otherwise if you only turn the key to run (not start) it will come on for a few secs.

 

[MrShorty]

Interesting. Here's what I would expect to see (all voltages assumed to be measured relative to a known good ground):

1) (yellow??) wire from fuel pump fuse: 12 V at all times
2) (red???) wire from EEC relay: 12 V when key is on.
3) (ltblue??) wire going to computer: 12 V when fuel pump is not commanded, 0V when fuel pump is commanded (if that makes sense).
4) (greeen??) wire going to inertia switch and then to fuel pump: 12 V when relay is closed, 0 V when relay is open.

Since you don't positively identify which wire is seeing which condition, I can only make educated guesses. And you only list voltages for three wires, so I'm going to assume the 4th is 0V. Therefore, I assume that the lead with 12 V at all times is the main fuel pump power lead, the lead with 0 V all the time is the lead to the fuel pump, the lead with 12 V key on is the lead from the EEC relay, and the lead with 6 V key on is the lead to the computer. I also have to assume that you are looking at the fuel pump relay and not the AC WOT cutout relay.

With those assumptions made, a bad PCM is a possibility, though not the only possibility. Things I would look at:

1) Does the fuel pump run when you ground the fuel pump test lead in the self-test connector (same wire as the relay to computer lead)? Do you measure the same 6V at the self-test connector as you do at the relay?
2) Are the computers three grounds all good?
3) Is the relay to computer wire in good shape and making good connections at all connectors?
4) I don't know that there would be anything diagnostic in it, but I would pull codes from the computer before deciding for certain that the computer is bad.

 

[HawaiiFiveOh]

Are you getting any power at the inertia switch?. Check the voltage on both wires. They should read 12v while the tac>0 otherwise if you only turn the key to run (not start) it will come on for a few secs.
QUOTE]


I would assume that yes I am getting power at the inertia switch because i get voltage at the plug back at the fuel tank. If I get any other voltages I can't be sure, will have to check when I get home.

Mr. Shorty--> thanks for the input, I will look into it even deeper this evening and get back with some more info.

 

[CDW6212R]

That fuel pump priming when the key is first turned on is very important. You should hear the pump for a short period of time, say 1-2 seconds. My 98 is occasionally not triggering, or very briefly(not enough). I'm looking hardest at my PCM. Good luck,

 

[DeRocha]

The inertia test is easy to do and confirms the operation of the entire electrical circuit that comes before it. (ignition,pcm and relay)..The pink wire/black stripe on the switch goes directly to the fuel pump. As I wrote earlier you will only get 12v @ the inertia switch if the engine is rotating/cranking or for a few secs after turning the key to run.

When my fuel pump went it had blown the fuse under the hood. I swapped out the pump and the new one worked fine... I connected the old pump directly to the battery and it fired up and ran just fine. (don't run a fuel pump without liquid as you'll destroy it in short order). Anyway when an electric motor gets old it will develop cracks in the insulation coating on the electrical windings. These cracks allow power to be leached from the motor and cause an every increasing amp draw just to keep the motor operating. Once the amp draw exceeds the fuse the circuit is broken and time for a new pump...

 

[HawaiiFiveOh]

little more information

Okay, here's some more stuff I have been able to find out.

The fuel pump relay with the Key On has the following voltages:

black w/ yellow --12 volts ( this is constant, key on or off)

red -- 12 volts

green -- ~6 volts

lt. blue -- 12 volts


I checked both wires at the inertia switch, I have voltage coming and going through that.

I also checked the plug that hooks into the fuel pump itself back near the gas tank. There are four wires in that harness, I would assume two for the fuel pump and two for the fuel level sending unit. Voltages are as follows:

pink w/black --~6.5 volts

yellow /black --~8 volts

black -- 0

orange -- 0

As for the questions you asked Mr. Shorty,

1. fuel pump does not run when i ground the test lead at the test port. And I do have voltage there.

2. The grounds should be good, I honestly don't know where to look for the three of them.

3. The wire appears to be good, I can ohm it out and seems to be fine and the connectors.

4. Didn't try for codes, like you said, not sure I would find any.

Well...thats what Ive got so far, any ideas?

 

[MrShorty]

I'm not too surprised that my suggestions didn't help out, they were based on faulty assumptions. Now that we have more complete information, lets go from here.
Do you have a wiring diagram? Are you reasonably familiar with DC electricity?

Looking at what you're seeing, and what I would expect (from my post above), 3 of the four leads look normal for a Key on Engine Off state (KOEO). ~6V on that green wire (goes to the pink/blk wire at the pump) doesn't look right; I would expect that to be 0V at both ends of the wire (can I assume you are also measuring this same ~6-6.5 V at both leads of the inertia switch?). A few tests/measurements I would suggest:

1) What do these voltages look like with the fuel pump test lead grounded (fuel pump theoretically "on")?
2) fuel pump ground intact? On my '92, the fuel pump ground comes back through the wiring harness and is bolted to the driver's side fender under the hood.
3) If you unplug the fuel pump relay, it should only show continuity between the red/blue leads. All other leads should show open circuits (near infinite resistance). With the fuel pump relay unplugged, what do these voltages look like?

 

[DeRocha]

6v on both inertia wires indicates the switch is working and electricity is able to flow through it. The switch will register 6v if the engine is not cranking and 12v if it is cranking or for a few secs during initial KO (key on).

Put your meter back on the switch and prop it in position so you don't have to hold the wires and still be able to see the meter..Turn the key on and if working correctly you should see the volts go up to 12v and then drop back to 6v after 2-3 secs..

 

[HawaiiFiveOh]

Alright fellas, I will see what I can come back with.

As far as wiring diagrams, all I have is whats in the back of a haynes manual, certainly not the best help. And dealing with a dc circuit shouldn't be too much for me to handle, I mess with electricity at work pretty much daily.

Thanks again for the ongoing help.

 

[nova801428]

First, I have a 86 Ranger and my problem is the same as yours. What is a pcm, is it like a eec when I get power from the relay mine is always on, which I don't know if that is normal. I wish someone could know these exact problems to help, but after two months or so of research I still haven't fond the cause. This way might not save you money but time: Take it to a shop and get it diagnosed for $75 or so, then fix it yourself. If you find the problem please post it. Thanks

 

[Craig]

Lucky find, this thread. I'm having similar problems with my 94 V6. Every now and then, after being shut off for a SHORT time (5-20 min) it won't start. I get no prime from the fuel pump, so it barely runs for a few seconds then no more. If I let it sit for 15 minutes or so, it all works like normal again. It never has failed to start after sitting all night or for long periods.

I have a fairly new pump and have checked most (key here, most) of the wiring and it appears fine. Why the refusal to prime or pump after a short shutdown, and then all ok after a short while resting? It never stops running after a successful start (which is 95 percent of the time). This is irritating when I stop for gas or the grocery store.

I'm still digging and will pass on any finds. In the meantime (not meaning to highjack, because it's related) - - any ideas?

 

[HawaiiFiveOh]

Craig- that sounds familiar lol. Just this time the truck refuses to start up again. I haven't been able to do much trouble shooting lately for I had some wisdom teeth pulled, needless to say I have been under the weather. Fear not, as soon as possible I will be back with my findings. Good luck with it.

 

[budwich]

My guess is that its your fuel pump. Yes I know you tested it (bench tested). However, that doesn't mean that the pump works. It means that if it is "just sitting there", it runs. Motors have to start in some form and under load.... either thru a starting capacitor (large motors) or some other form of "help". I have had a problem previously with an old GM S10. The thing wouldn't start intermittently. Changing out the fuel filter didn't help. I dropped the tank and pulled the pump. Small little motor and assembly but expensive ($150 plus at that time). Bench tested that motor and it worked fine every time it was powered. Dropped it back in the tank, bolted up.... nope, the motor wouldn't get going. It could have been that it "lost a pole" or was "slightly shorted" in the windings somewhere resulting in insufficient "working umph" to get it going and doing it job. Sorry for the long story but that's my take on this as H50 seems do have done alot of good stuff trying to get thru this. Money's on the pump.

 

[Craig]

Did it again, and now I can't get any pump action. I switched relays around (EEC and FP same), cleaned all connectors, etc. Pump ran a couple times (prime) but not enough to get a start. I am going to try to bypass ALL the crap and apply some power to the pump at the interia switch. If it runs steady, I'll install a cheater switch in the glove box to use as a limp mode to get home. The switch will only work with the ignition on, of course. I don't think it really matters to bypass the prime and just let it start and run, other than it bypasses some safety features (other than inertia). I twisted my knee on the ice, so I can't do this for a few days - - so if anyone sees a problem with this idea (or can tell me which wires to apply 12 V or Grnd to, I'd appreciate it). Thanks

 

[DeRocha]

I see no problem with wiring a switch to provide power to the pump as a munual overide as you have indicated.. Normally when you start the engine you move the key from off to run to start @ which point the pump will get power the entire time unless the engine stops cranking..

 

[Craig]

@ which point the pump will get power the entire time unless the engine stops cranking..

Cool. I didn't think it would be a problem, and it will hopefully avoid going through all the stuff that I think is causing the problem, since it's not getting juice at run or start lately. We'll see, huh? I just have to figure which wire gets 12 volts and I'm off. Can't be too hard with only two to choose - I hope. I'll letchaknow...............

 

[HawaiiFiveOh]

Finally got back around to looking at this truck again and still don't have the thing running. I know its not the fuel pump and just to be sure i replaced it anyways, it had a year warranty. I pulled a computer from the junkyard and tried that...no go.

6v on both inertia wires indicates the switch is working and electricity is able to flow through it. The switch will register 6v if the engine is not cranking and 12v if it is cranking or for a few secs during initial KO (key on).

Put your meter back on the switch and prop it in position so you don't have to hold the wires and still be able to see the meter..Turn the key on and if working correctly you should see the volts go up to 12v and then drop back to 6v after 2-3 secs..

This is almost what happens except now as I am sitting here I can't remember what is odd about what my truck does. I can't remember if it keeps 12 volts on it or what. I will get back on this.

I did notice today that when the key is turned on the fuel pump relay does pick, but it drops out after a second at the most, not the 3 seconds it should be up to prime. If I try to crank the truck, the relay picks and drops out just like having the key in the on position. Nothing changes from the key being on to cranking.

As far as I can tell, the grounds are good. They all seem to ohm out good to any ground. I even followed the ground from the fuel pump itself to the front of the truck.

I am working on getting a wiring schematic from ford or local shop for this thing and hoping this will help me.