Ford Repair Questions? Ask a Mechanic for Answers ASAP
Okay so when it does not start do you have all three ? Fuel pressure, spark and injector pulse? To check injector pulse you really need to use a 12 volt test light, place the test end on the power side and the ground end on the other wire and crank the engine over. If you have pulse the light should flash.
I can post a flow chart but first I need to know what signal is dropping out.
Not a problem, post back when you ready and we can work from there.
To check your injector, place your standard 12 volt test light test end on the power side of the injectors and place the ground end of the light on the other wire and then crank the engine over, if you have pulse the light should flash, check it this way for me and post back.
Best way to check the spark is to remove a couple of the spark plug wires from the spark plug and hold the spark plug end about a 1/4 inch from a good ground and crank the engine over, you should see a nice blue spark jumping to the ground.
Okay, if you have good spark, injector pulse and proper fuel pressure then the next thing you need to check is the compression, pull your spark plugs and run a compression test and let me know the results.
Okay well if you are sure you have good compression good spark as well as proper fuel pressure and injector pulse then the engine should start and run, are you sure the distributor is installed properly?
If you have a good spark then the PIP is fine.
Well if you have all the signal as well as compression then the engine should start, are you sure the distributor is timed right?
There are no safely features that will kill spark.
Well it try to start if you spray staring fluid into the throttle body?
If it start with starting fluid then I would pop the injector rail up and see if the injectors are squirting when you crank it.
It should be starting and running just fine if you have good spark, injector pulse, good compression as well proper fuel pressure like you are saying it has. Are you 100% sure you have all of these?
I would check all of the as far as compression goes and at least four of the injector for pulse, something has to be being overlooked here.
No problem, Im here everyday, let me know and we can work from there.
This sure does sound like a failing fuel pump and if its doing it on both tanks its not uncommon for both to fail simply due to the age of both, I would verify you are getting cranking battery voltage at both pumps and is so then suspect both have failed.
Take your volt meter and while cranking the engine check to see if you are getting battery voltage at the power side as well as a good ground, if you have power and ground and no pump action then the pump has failed.
The fuel pump is controlled by the computer (PCM) grounding the fuel pump relay . If the relay is grounding correctly by the PCM then check and see if you have power in and out of the inertia switch while cranking the engine.
If you have power in and out of the inertia switch while cranking then you should have a running fuel pump while cranking as well .
Well if you are maintaining 32 PSI then the problem is not the fuel pump. Are you loosing voltage to the pump when it will not start?
Have you checked the voltage at the inertia switch while cranking to see if you loosing it there as well?
Well that's what I would do to at least rule the inertia switch out. If you are loosing power to it then your back to the either the PCM is not grounding the relay or you have an open from the relay to the inertia switch.
The fuel pump relay is controlled by the ground switching signal from the PCM, the power wires are the red and the yellow wires. If you have power on them and the relay does not energize then try grounding the tan/green wire from the PCM at the relay and see if the pumps runs. if it dose then the new PCM is defective.
Are you checking this with the key in the run position?
The red wire is key on power from the ignition switch, the yellow is constant power. Will it run if you supply power to the red wire, if so then check the circuit from the switch
Actually I just reviewed the wiring diagram and the red wire is power out, the yellow is constant power and the ignition feed will be either red/green or white light blue, you should have to hot wires at the relay with the key on, do you?
Okay then what are the color of the wires you have at the relay?
The yellow wire should be hot at all times.
So which one is hot besides the yellow wire, do you have a good ground on the black wire at the relay?
Okay if you have power on both and a good ground the the red wire which power the PCM as well as the injector should be hot with the key on, is it?
The PCM should not need to be reset on a 1988, turn the key on and see if you have power at the power side of the injectors, if the relay is okay you should have key on power there.
The red wire is the power feed out of the EEC relay, it powers the PCM as well as the injector and all the actuators.
If you have key on power on the key on power wire as well as the constant power wire and a good ground then yes if you are loosing power to the red power out wire.
At the ignition switch. You just told me both wire have key on power , was that correct?
Okay but you still need to make sure you have the key on power source as well as the constant source which you have proved you do if the truck is still running..
The red wire is power out of the relay, you should have two wires hot with the key on, the yellow wire and the white /blue and or the red/green wire from the ignition switch. Do you have that? The red wire is only hot now because you are jumping power to it.
How did we get to the fuel pump relay, I have been talking about the EEC relay which is the main relay that power both.
Okay something is getting lost in translation here. The red wire to the FP relay comes from the EEC relay.
Okay then the problem is with this wire, why don't you just overlay a new wire from it to the FP relay and be done with it. Much better then tearing the harness apart trying to find the open.
The red wire feed all the EEC system actuator as well as the injector and the PCM from the EEC relay. If you are only loosing it at the FP relay then overlay a new wire and you should be fine.
Yes it does, it power the PCM as well as the injector and all of the actuators on the engine. Just make sure you have a key on source to the FP relay and you should be fine.
No problem, took a while but I thing we finely got there. Please take a moment to rate my service so I can get credit for my time, the question remains open for follow up even after doing so, all you need to do is return to this question if need be.Thank you again.
You need to run the wire right from the EEC relay where you know it has the right amount of power. You can not leave the constant power wire is because you need the pump to shut off with the key.
The voltage out of the EEC relay is battery voltage just like any other relay.
Im not sure what you are saying, if you hook the new wire to a key on power source it should work just fine.
Okay are you sure the PCM is grounding the relay on the tan/green wire?
I have lost track of which relay you are even working on, the FP relay should have a tan/green wire from the PCM that grounds it to activate the FP relay while cranking and with the engine running.
When you jumped the relay to direct power it is going to run the pump, but in order for the relay to energize with out direct power (jumped) , its going to need the ground from the PCM.
Okay the ground is supplied by the PCM, are you 100% sure you do not have a bad PCM. It sure sounds like you do.
If you not getting the ground from it to the FP relay its a pretty safe bet its bad. The only way to test it is to replace it with a known good one. It sure sounds to me like the PCM is the real problem if the truck run with the relay grounded.
If it runs with the pump grounded than that means the PCM is not grounding it. You can not leave it connected to the yellow wire because the pumps will not shut off, you need a key on source.Im done for today. Ill be back on tomorrow but I am not sure how much more I can help you, we keep going over the same stuff and I am afraid I have done all I can from here.
The tan/green is ground switch to activate the relay with the key on by the PCM. If the PCM is grounding and hold it while the engine is running then the PCM is fine.