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Ron
Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 33469
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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1988 Ford F150 with 302 cranks but won't start It

Customer Question

1988 Ford F150 with 302 cranks but won't start
It ocassionally starts but dies
Submitted: 1 year ago.
Category: Ford
Expert:  Ron replied 1 year ago.
Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
In order for the engine to start and run you need good spark to the spark plugs , proper fuel pressure (32 to 45 PSI) and injector pulse. If you can check each one of these things and post back with which one you are lacking I will try and help you get this resolved.
Customer: replied 1 year ago.
We checked the spark plugs the old fashioned way by pulling one and watching it spark against ground. Fuel pressure at the rail is 42 PSI & injector pulse with a multi-tester from the pulse module
Customer: replied 1 year ago.
If you can post some type of flow chart I can follow to eliminate the problem systematically I would appreciate it
Expert:  Ron replied 1 year ago.

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.

Expert:  Ron replied 1 year ago.

I can post a flow chart but first I need to know what signal is dropping out.

Customer: replied 1 year ago.
Ron,Work got in the way for now. I haven't been able to go out to the vehicle and retest. Please be patient as I may be able to get back to the truck after work tonight
Expert:  Ron replied 1 year ago.

Not a problem, post back when you ready and we can work from there.

Customer: replied 1 year ago.
Ron,I'm finally back to you with an answer. I believe we are missing the pulse to the injectors. When I test with a test light and first turn on the key both conductors have power at the plug grounded to the battery. When the key is turned to start we get nothing - that might be the test light is electronic. What do we do next?
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
We have a pulse - double checked fuel pressure and its at 40PSI on the rail. What would be the best way to double check the spark
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
we have a very strong spark
Customer: replied 1 year ago.
Just to note we changed out the complete ignition advance assembly which came with a new rotor and cap because we thought the PIP was bad initially
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
compression is 140 - 150PSI
Expert:  Ron replied 1 year ago.

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?

Customer: replied 1 year ago.
We changed the distributor because it would sometimes run and sound perfect then it would stall and not run again for days. Since we've changed it we had the same situation. We may need to change the timing slightly but the engine should still start
Customer: replied 1 year ago.
The thought was that the PIP wasn't working correctly because the distributor shaft had worn out the bearing to the point that it was sometimes not making contact
Expert:  Ron replied 1 year ago.

If you have a good spark then the PIP is fine.

Customer: replied 1 year ago.
Agreed - I wouldn't be here with you if it was easy
Expert:  Ron replied 1 year ago.

Well if you have all the signal as well as compression then the engine should start, are you sure the distributor is timed right?

Customer: replied 1 year ago.
Maybe not - so to confirm what would you do?
Customer: replied 1 year ago.
Remember it ran with this setup so the timing can't be that far off. My thought is that something is electrically or safety wise intermitently locking out the spark.
Expert:  Ron replied 1 year ago.

There are no safely features that will kill spark.

Customer: replied 1 year ago.
maybe the gas isn't good enough to ignite but again it did run at one point well enough to go fill both tanks about 3 months ago
Expert:  Ron replied 1 year ago.

Well it try to start if you spray staring fluid into the throttle body?

Customer: replied 1 year ago.
we're charging the battery back up from trying it. At one point we used starting fluid to start it but once the new distributor assembly was in it was starting without the fluid although still hard to start
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
they could be plugged or simply not working - my only thought would be why does it run so smoothly when it runs?
Expert:  Ron replied 1 year ago.

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?

Customer: replied 1 year ago.
Our spark & compression test were done on cylinder number 5
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
That will take some time _ I won't be back to you before the end of the day
Expert:  Ron replied 1 year ago.

No problem, Im here everyday, let me know and we can work from there.

Customer: replied 1 year ago.
We got it started with the use of starting fluid but it will stall if we step on the gas pedal. That leads me to believe that its a fuel pump. Trying to confirm which fuel pump is my next question. At this point with a dual tank system no matter which one I run on I get the same effect. It will run at 30 PSI and as soon as I step on gas pedal it goes down to about 20 PSI at which point it starts to stall unless we let up on the gas pedal again. Is there a better way to confirm that its the high pressure pump or is ther more than one fuel filter on this truck?
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
what's the official test procedure for the fuel pumps?
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
I’m finally getting back to you on the 1988 Ford F150 won’t start – After measuring voltage at the fuel pump and not hearing it run we decided to replace it – while replacing it we tested it out of the tank and it ran intermittently. Finally we thought we had the problem but after chasing down the parts and getting the new pump in and running (we can clearly hear it now) the vehicle still won’t start. We are definitely loosing fuel pressure when this happens - the relay doesn't click so it's happening electrically before that. To make sure we got our hands on a new electronic control module but we still have the same problem. To reiterate when it runs which is for about 5 minutes it is smooth - what control would force it to stop? Could the inertia switch be going bad or is that a manual reset? What about the oxygen sensor - does that have enough effect to stop voltage completely?
Expert:  Ron replied 1 year ago.

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.

Expert:  Ron replied 1 year ago.

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 .

Customer: replied 1 year ago.
the PCM is what we changed to no avail
Customer: replied 1 year ago.
the new fuel pump actually gives us about 32PSI when idling and goes up to 36 when the engine is revved.
Customer: replied 1 year ago.
If not a control the only thing left would be wiring but usually that's one way or the other and in my estimation never times out around the same five minutes each time unless it's overheating in some way.
Expert:  Ron replied 1 year ago.

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?

Customer: replied 1 year ago.
Expert:  Ron replied 1 year ago.

Have you checked the voltage at the inertia switch while cranking to see if you loosing it there as well?

Customer: replied 1 year ago.
not yet
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
I'll check it and get back to you
Expert:  Ron replied 1 year ago.

Okay

Customer: replied 1 year ago.
We jumped out the inertia switch and had fuel pressure. Still had to use starting fluid to get the engine started and it eventually lost all pressure and died again. Still no gas pressure and no power to the fuel pump relay.
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
I have power on the yellow but not the red
Customer: replied 1 year ago.
when using a digital DC volt meter I get trace numbers on the red wire. What does this wire connect to - how does it get power?
Expert:  Ron replied 1 year ago.

Are you checking this with the key in the run position?

Customer: replied 1 year ago.
that's correct
Expert:  Ron replied 1 year ago.

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

Customer: replied 1 year ago.
It runs and pressurizes upon jumping the yellow to the red. Unfortunately that red wire goes into a wire loom and dissappears immediately. There is a red wire up the steering column which I suspect is to the ignition switch. You're recommending puling the ignition switch out to check the contacts?
Expert:  Ron replied 1 year ago.

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?

Customer: replied 1 year ago.
no I checked all the wires and only the yellow was hot
Customer: replied 1 year ago.
the yellow wire is actually constantly hot with or without the key on
Expert:  Ron replied 1 year ago.

Okay then what are the color of the wires you have at the relay?

Expert:  Ron replied 1 year ago.

The yellow wire should be hot at all times.

Customer: replied 1 year ago.
okay then that's working properly - what do we do next?
Expert:  Ron replied 1 year ago.

So which one is hot besides the yellow wire, do you have a good ground on the black wire at the relay?

Customer: replied 1 year ago.
the relay has the red - yellow - another yellow that could be a faded tan and is not as heavy as the constant power yellow- brown
Customer: replied 1 year ago.
I have no other hot wire although I should - I think we are on the right track with the red wire - which other wire switches with the red wire?
Expert:  Ron replied 1 year ago.

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?

Customer: replied 1 year ago.
when I jump the yellow to the red I have fuel pump/pressure. I haven't tried to start the engine yet and actually disconnected the negative on the battery to see if the PCM needs to reset so it will power the red wire. Do you want me just to try and start the engine with the red to yellow jumper connected?
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
I left the jumper in and started the engine. It's idling now and I'm waiting for it to quit. If it runs for more than 5 minutes than that (red wire) is the problem - I just need to figure out where it goes and then I can run a new wire connected to the same switch.
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
Does that mean that the EEC relay is possibly bad - as in bad contact because we can hear that click
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
I think we can rule out the ground as it is still running - the key on power wire must be working as all the dash lights come on. Where's the best spot to check the key on power wire?
Expert:  Ron replied 1 year ago.

At the ignition switch. You just told me both wire have key on power , was that correct?

Customer: replied 1 year ago.
I still have the red wire jumpered to the yellow and the truck is still running. It's up to temp and hasn't shut down. That's why I believe the issue is with the circuit and possibly the EEC relay. As a matter of fact the EEC relay feels warm which indicates to me that the contacts are somewhat if not completely burnt. I have nothing left short of the wires to replace so I'm looking at a new relay as we speak.
Expert:  Ron replied 1 year ago.

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..

Customer: replied 1 year ago.
I only have power to the red wire because of the jumper. My question is could this be the power on from the key switch or is it as you say the power from the EEC relay?
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
I only have the yellow wire hot at the fuel pump relay and like you say I'm jumping out to the red wire which is allowing the truck to continue to run. I don't have a white/blue wire and the red wire is solid in color.
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
I've been working on the fuel pump relay the whole time until you said that the red wire comes from the EEC relay I hadn't really looked at it. I'll be back with the info on which wires are hot from that relay shortly
Expert:  Ron replied 1 year ago.

Okay something is getting lost in translation here. The red wire to the FP relay comes from the EEC relay.

Customer: replied 1 year ago.
Ok just checked the EEC relay and yes I have 2 hot wires black with a yellow strip & yellow with a black. the 2 other colors are blue and solid black. The blue wire clearly turns into a red wire with some type of resistance style connector
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
Can you see on your wiring diagram if that red wire goes to any other connector/relay or is it just directly from the FP to the EEC?
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
ok I found the connector from blue to red on EEC relay says fusible link - that may be the problem - I just want to make sure that I use the correct wire as once the blue turns to red it goes directly into the wire loom again and I can't trace it. That being said instead of cutting the wire and replacing it I think I'll just keep that wire and join another to the FP relay because it sounds like it sends power to several other important items. Do you think this is the best way to do it?
Customer: replied 1 year ago.
By join I mean run in parallel with the existing wire
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
Ok I can handle that sorry for the confusion I just want to make sure
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
I ran the wire in parallel as we discussed but there's some type of short that won't send enough power to the fuel relay. How do I find that? If I cut the wire coming from the EEC I'm pretty sure I'll loose all the other items that are needed to run the truck. Can I just leave the jumper in from the constant yellow to the red at the FP relay?
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
Is there a high voltage and low voltage output from the EEC?
Customer: replied 1 year ago.
If so I'll just try it on the other switched output leg
Expert:  Ron replied 1 year ago.

The voltage out of the EEC relay is battery voltage just like any other relay.

Customer: replied 1 year ago.
Something on the output circuit I'm on is drawing too much amperage
Customer: replied 1 year ago.
the problem could be some other accessory that was installed into this circuit that shouldn't be there. We got this truck from a guy who didn't know what he was doing but attempted to do it anyway.
Expert:  Ron replied 1 year ago.

Im not sure what you are saying, if you hook the new wire to a key on power source it should work just fine.

Customer: replied 1 year ago.
I agree but after I hooked it up and went to run the truck it wouldn't power the pumps so I tried the test light and although it lights it's very dim and doesn't beep like it does when the circuit is at full power
Expert:  Ron replied 1 year ago.

Okay are you sure the PCM is grounding the relay on the tan/green wire?

Customer: replied 1 year ago.
I'll go check the Tan/green wire although if you look at the colors I listed above I don't have those exact colors
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
oh ok I'll go check i thought that was a given since it ran so long
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
Ok when it's jumped it runs no problem as soon as I remove the jumper it stops even with the parallel wiring in place. I can't check the ground when running because of the above statement. When I just turn the key on without the jumper the fuel pumps do not energize and the ground is good and clear to the tan/green stripped wire
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
In worst case I'll run a wire from the fuse block on a circuit that only works when the key is on direct to that red wire on the FP relay. The big problem with that is sooner or later the real problem is going to rear its ugly head. Is there any other way to check the PCM?
Customer: replied 1 year ago.
Just to confirm I tested the ground with the key on and not while cranking does that make a difference?
Customer: replied 1 year ago.
By the way I'd love to send the PCM back
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
just to confirm the only jumper I'm using to make it run perfectly is from the yellow hot wire. Let me go take the tan wire and ground it to the radiator to see if it will power the pumps
Expert:  Ron replied 1 year ago.

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.

Customer: replied 1 year ago.
no problem when you get back I took the time to run the test light from the constant on yellow to the tan/green which should be a switched ground from the PCM. Whether the key is on or off I still show a good solid ground as it powers the test light beeper which means the circuit is complete. Let me know if that means the PCM is bad. I plan on doing the same test with the old PCM to see if we get the same result. Let me know if this is what you intended me to do to test the PCM.
Expert:  Ron replied 1 year ago.

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.