Hey, I an trying to figure out what's going on with my truck. Could someone let me know the symptoms of a faulty PIP or TFI? I can get my truck to start when it's cold or when I spray ether into the throttle body. The fuel system is good, but it's shutting off my fuel supply after a few seconds of running. I can feather the gas to keep it running for another minute or so, then it's dead.

I have been reading that perhaps the PIP isn't detection the engine motion right and shutting off my gas? Or perhaps the TFI is faulty or overheating? A new (refurb) dissy is about $120 for me, plus the pain in the **** of retiming, so I'd rather not throw money at the problem to eliminate one thing or another.

So, anyone know if these symptoms sound right, or a good way to check the PIP or TFI for trouble?

BTW, I am throwing a 95 or 96 continuous code, but the fuel system is good.
also, my ride is an 88 F250 5.8L EFI 4WD dual tank.

thanks

 

Put a test light on the wires at the Inertia switch and a fuel pressure gauge (most auto parts store will rent one to you and you get your money back when you take it back) on the fuel rail.
Start the engine, you should 35-42 PSI pressure on the gauge and the test light should be on.
If the fuel pressure drops below 30 PSI with light still on you have a bad pump.
If the light goes off and the engine dies and the fuel pressure is still at 30 PSI or above then you have a bad TFI module, PIP sensor, Fuel pump relay, EEC (PCM) Power relay, Computer or wiring.
Let us know what you find at this point and we will try to help you narrow it down and fix it.

My guess now is that you have a bad fuel pump or the wiring is bad from the Fuel Pump Relay to the pump.

 

subford, am I just checking for voltage across the intertia switch to see if it's still getting juice? That is, can I just use a voltmeter rather than a test light? Can I just stick a pin through the insulation on the inertia switch and run my voltmeter between those leads?

My autoparts store won't loan me the pressure gauge, so I might just have to bite the bullet on that one.

If the pressure is good, will it stay pressurized long enough for me to leave the cab and look at it in the engine compartment (no helpers today)? Or, do I need to have the pressure gauge and the voltage test located next to each other?

 

also, where does the 'hot' for the high press fuel pump come from? Is it from the FP relay or the EEC relay?

 

You are checking from the wires on the inertia switch to ground (body of truck). Yes you are checking for "juice" (power).

FP Relay by way of the inertia switch.

You can use voltmeter rather than a test light but the voltmeter will not load the circuit and will give you a false reading that you have power when you do not sometimes. Then you will look in the wrong place for the problem sometimes for days.

You need to see what is happening at the same time to know what is going on.


/

 

Don't foget about the throttle posistioning sensor........

 

what deos the TPS have to do with it? Could that cause this problem?

 

a TPS can cause erratic throttle control, a searching idle, and most relevant no idle. Once the engine completes it's open-loop warm up, it relies on the TPS for throttle position. the haynes manual will give you the test procedure.

 

The TPS will not generate the codes he has or turn off the fuel pumps.
I would not trust the haynes manuals 100%, OK I guess if you do not have anything else.
Get Ford manuals for your truck.

 

The parts store had a delay on th epressure gauge. I am going to go get it in about an hour. I'll check an dpost back in a little bit.

I thought the TPD shouldn't be an issue, or even if it was, I thought I might throw a TPS code somewhere.

Subford, where do I get one of the FORD manuals?

 

ebay or Helm Inc.

 

Ok, I can't get the pressure tester until tomorrow. But, I just did the light check in the inertia leads. The light comes on and stays on after the engine dies. Then I can hear the relays all click and the light goes out. So, although I don't KNOW that my fuel pressure is hurting me, can I sort of rule out the TFI and/or PIP yet?

I am starting to wonder if my intank pump is bad. But, I will wait to try and fix that one until I get the fuel pressure tester to see if I am getting enough pressure or not.

Subford, I just changed my high pressure pump, so I know it's not that. If my low pressure pump dies, would I get these symptoms? If I use up the fuel I have in my reservoir, would the truck dies like this?

I am starting to get suspicious of something clogging the intank filter and dropping back out after a little time passes. But, without the prssure test on the fuel line, I am only guessing.

I should get this done by tomorrow afternoon or the day after. I'll repost then and we can see.

 

Yes I would think you could rule them out, that is normal operation for the Computer to turn off the FP relay after the engine dies (no PIP train).
It is possible that low pressure (boost pump) in the tank does not have enough pressure to lock the selector valve to its tank and when it quits the valve is closing off the selected tank. How about when you switch to the other tank, does the same thing happen?

try taking the fuel hose off at the selector valve and putting it in a bucket and then ground pin #6 of the test connector, turn on the key and see what flow you get from the in-tank pump.

 

subford,

I did the low pressure test into the bucket and it seemed to work fine. It was flowing pretty quick. But, that was on the rear side of the reservoir. i don't know if it was enough pressure to activate the valves in the reservoir or not.

My front intank pump was bad when I got the truck (so I was told), so I havne't ever tried it out. I don't know what's in the tank, so I don't want to try it until I get the tank cleaned.

I am going to go ahead and buy the pressure tester tomorrow and try that. If it's not the fuel delivery, then I want to be as sure as I can. So, I will rule the fuel system in or out and let you know.

I will post soon.

 

ok, I checked the pressure this morning. When I first tried it, the pressure was at 40ish. I started the truck and it ran for about 2 minutes, all with the prssure at 40. Then it died (just because it does that sometimes -- it's old). I restarted it and it ran for about 30 seconds and the pressure dropped down to 20psi and the truck died. I jumpered on the fuel pumps and the prssure would not build up past 20psi.

So, I am going to go get a few fuel line stubs and bypass the reservoir. If the truck runs without the reservoir, I will get a new one of those. If the truck dies without the reservoir, then I will attack the tank adn pump.

I am suspicious now that there might be some crap in the tank that it blocking the intank pump. Either that or the pump is just dieing and turns itself off after a few minutes of heating up.

If anyone has anything to add, please do. I will post later to say how the bypass of the reservoir went. I will probably be asking for advice on dorpping out the rear tank or taking off the bed shortly.

Thanks