1995 F150 5.8 Fuel System Electrical Help
11-12-2014, 04:38 PM
#1
Junior Member
Thread Starter
1995 F150 5.8 Fuel System Electrical Help
Greetings,
Great forum here, thank you to the moderator(s) for providing this. I am new to the forum, and need some help with my 1995 F150 5.8L 4WD. I do have an extensive automotive background, but am stumped. My F150 has an intermittent no-start condition. It is not related to environmental temperature or amount of driving. The condition comes and goes, and I can not duplicate it on demand.
When the truck does not start, or starts and stalls within a minute of running, I have determined that there is no power going to the Inertia Switch, via the DK GRN/YEL wire (input wire). I have found that the fuel pump relay has power to it and have tried a few different new relays. I have also replaced the ignition switch (not lock and cylinder), on a hunch, but have not been able to fix the problem. I see in the wiring diagram that the DK GRN/YEL wire also goes into the PCM, but I can not tell what it does from there. Has anybody here experienced this as well, or can give me a suggestion as to why I am losing power at the Inertia Switch? I do have 118,000 miles on it, and no other problems. In case anybody wants to know, I have recently replaced cap/rotor/wires/coil/plugs/fuel filter and all hoses and s-belt, all due to preventative maintenance, as I let my teenage daughter drive this truck and do not want her to have a failure on the road.
The problem existed prior to the maintenance I mentioned, so there is no correlation to the service I have already performed. I should also mention that there are no codes.
Any suggestions or assistance would be much appreciated. I thank you all in advance!
Mike
Great forum here, thank you to the moderator(s) for providing this. I am new to the forum, and need some help with my 1995 F150 5.8L 4WD. I do have an extensive automotive background, but am stumped. My F150 has an intermittent no-start condition. It is not related to environmental temperature or amount of driving. The condition comes and goes, and I can not duplicate it on demand.
When the truck does not start, or starts and stalls within a minute of running, I have determined that there is no power going to the Inertia Switch, via the DK GRN/YEL wire (input wire). I have found that the fuel pump relay has power to it and have tried a few different new relays. I have also replaced the ignition switch (not lock and cylinder), on a hunch, but have not been able to fix the problem. I see in the wiring diagram that the DK GRN/YEL wire also goes into the PCM, but I can not tell what it does from there. Has anybody here experienced this as well, or can give me a suggestion as to why I am losing power at the Inertia Switch? I do have 118,000 miles on it, and no other problems. In case anybody wants to know, I have recently replaced cap/rotor/wires/coil/plugs/fuel filter and all hoses and s-belt, all due to preventative maintenance, as I let my teenage daughter drive this truck and do not want her to have a failure on the road.
The problem existed prior to the maintenance I mentioned, so there is no correlation to the service I have already performed. I should also mention that there are no codes.
Any suggestions or assistance would be much appreciated. I thank you all in advance!
Mike
Last edited by Photomike; 11-12-2014 at 04:41 PM.
11-12-2014, 05:11 PM
#2
As I understand it, the relay has 2 circuits : 1 - turn on the key and the pump will run for 2 seconds to prime the system. 2 - when the motor is running (turning ?) and only if so the PCM will allow the pump to run constant.
So you should see power for 2 secs after cycling the key but if the motor isn't running (I'm not sure if it has to be running or just turning, but I think running) after that, you won't see power.
Your problem could possibly be related to a faulty ground.
I have also seen where the wire that the relay plugs into gets corroded and causes problems.
To inspect that you have to unclip the relay box and get a look at the wires underneath. That's just a possibility but I've seen that one and it was a bear to track down.
Could also be a PCM problem of course, but before going there I would usually advise someone to start by checking all grounds and with any possible fuel related problem, check the fuel pressure.
Pumps can act up before they go and these trucks will not run without sufficient fuel pressure. The operating range for your truck is 30 to 45 psi - but if you're not getting 40+ key on engine off, that's a bad sign (and a possible reason for your issue).
If you had your own tester, you could also check pressure when it acts up.
Just in case it's not fuel related at all, have what you need in the truck so the next time it won't run you can check for spark. The PIP (pickup in the distributor) is famous for failing intermittently for a while before it gives up the ghost completely.
Those are a couple possibles for you to look at anyway.
So you should see power for 2 secs after cycling the key but if the motor isn't running (I'm not sure if it has to be running or just turning, but I think running) after that, you won't see power.
Your problem could possibly be related to a faulty ground.
I have also seen where the wire that the relay plugs into gets corroded and causes problems.
To inspect that you have to unclip the relay box and get a look at the wires underneath. That's just a possibility but I've seen that one and it was a bear to track down.
Could also be a PCM problem of course, but before going there I would usually advise someone to start by checking all grounds and with any possible fuel related problem, check the fuel pressure.
Pumps can act up before they go and these trucks will not run without sufficient fuel pressure. The operating range for your truck is 30 to 45 psi - but if you're not getting 40+ key on engine off, that's a bad sign (and a possible reason for your issue).
If you had your own tester, you could also check pressure when it acts up.
Just in case it's not fuel related at all, have what you need in the truck so the next time it won't run you can check for spark. The PIP (pickup in the distributor) is famous for failing intermittently for a while before it gives up the ghost completely.
Those are a couple possibles for you to look at anyway.
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Photomike (11-12-2014)
11-12-2014, 05:29 PM
#3
Junior Member
Thread Starter
Thanks Chris, I sincerely appreciate it. I thought about removing the relay box, but was leery due to mileage and age and was hoping for an easy fix (wishful thinking I know!). I am worried about damaging some wires in the loom. But, I like your thinking that it could be the relay connection. I will try that first exercising extreme care! The first thing I did was to check fuel pressure when I started my diagnosis. I have eliminated low fuel pressure as a cause. I went as far as to check for fuel delivery before, and after, the fuel pressure regulator and there was nothing. I also checked for pressure at input side of the filter when it didn't start. There was nothing. That is the point where I could not hear the fuel pumps cycle on for 2 seconds and started with the electrical tracing. I have 2 tanks and 2 pumps, switching from one to the other makes no difference when it doesn't start. When it does start, I can switch between the two with no interruption in fuel. I did verify, last time it started, that the circuit to the Inertia Switch is energized for 2 seconds during Key On Engine Off. Your thought of a possible PCM problem occurred to me as well. I do have spark at all times, whether it starts or not. I will check that relay box and post my findings. Thank you again sir!
Mike
Mike
