OT-1988 Ford F-350 Main Fuel Pump Wont Run

1206SWMO · Nov 16, 2015

In June my 1988 Ford F-350 with a 460 started acting up...On damp mornings it had no or weak spark but later in the day it would start and run fine..I put a new coil on it and its never ran since then as then the main fuel pump wouldnt come on..It will run on ether so it has spark..

There was nothing wrong with the old fuel pump but I put a new one on it...Its also had a new fuel pump relay and a new ECU relay but so far nothing has worked..The fuel pump safety switch has been checked...

I know thats theres several more things that it could be but I'm thinking its the computer....I'm not real good on electrical stuff...What do you think it is?? I'm sure that some of you have had similar problems....The old girl still has lots of miles left in it so I need to get it fixed without taking it to someone that will charge plenty to fix it..The 1988-90 Ford F-350's sure have tons of wiring and aren't easy to diagnose..

John M · Nov 16, 2015

Dual tanks?

1206SWMO · Nov 16, 2015

Yes,dual tanks and the pumps aren't that old....When you turn the key on,the main pump in the frame rail won't cycle for 1-2 seconds like it used to...It was easy to hear it from the drivers seat...No juice is getting to it..

MARK ROBKE · Nov 16, 2015

Are you sure it' not getting 'juice'-voltage? Just because it is not running,it still could be not be receiving voltage.Check the connection and measure the voltage : one time I had one that ran poorly.The problem was a corroded connector;I believe it had a fault code also.Mark

Haley · Nov 16, 2015

If it has dual tanks it could be a bad selector switch.I worked on tons of those trucks when I was at the dealership in the early ninetys but my memory is very foggy now.I will say that I NEVER had to replace a Ford computer around your year model.That does not mean that yours could not be bad but the likelyhood is slim to none.Keep in mind that the pump will only run for approx 2 seconds once the key is turned on with the engine off.Does the fuel pump relay click when the key is turned on? If so you can unplug the relay and jumper the two big wires together to send voltage continuous to the pump with the key on engine off to check the wiring. From the best I rember the computer has to see a tach signal to ground the pump relay so it will run after the 2 seconds.I have seen many bad ignition modules and distributor pickups on these trucks but if yours is firing I would think that part is o.k. Have you checked the little ground wires off of the negative battery terminal to the body? If the fuel pump relay clicks when you turn the key on you can be fairly certian that the wiring is o.k. If it clicks I would jumper it and check at the tank for voltage in the pump wire.Also keep in mind that some of these trucks came with three pumps,one in each tank and a high pressure pump mounted on the frame.Hope this helps.

cjackman · Nov 16, 2015

Those trucks are pretty notorious for the computers to fail. I actually had to replace mine this summer on my f350 with 65000 miles. The capacitors start to leak and they will act up. If you were close I'd let you try mine to be sure. They're easy to swap.

Sprint 6 · Nov 16, 2015

Sounds like you need to take it to a professional. That vintage of Ford product is not easy to fly blind on. You say you don't want to take to someone who will charge plenty, but you want to keep hanging parts until it runs. Which is going to cost more in the long run?

Hobo,NC · Nov 16, 2015

The fuel pump safety switch has been checked.

Pull the connector off of it and take a good look at the connector...
Do the same at the main EFI relay and the fuel pump relay...

If all fails take it to someone that is old enough to have cut there teeth on them... They are not that hard to diagnosis other than fighting aged out wiring and issues that mother nature has had a effect on... It still cost the same maybe more as a new one to work on... I get more are ship it...

jimg.allentown · Nov 16, 2015

This would not be hard to diagnose if you had the Ford Volume H service manual. However, failing that, we revert back to the hard way....
First, as already stated, the computer turns on the fuel pump for about 2 seconds when you turn on the ignition. You need to check for a signal at the fuel pump relay. Connections should be one terminal is ignition hot, one to the fuel pump, one to ground, and the signal wire from the computer.
I do have a 1988 Volume H at my garage, but since I am at home now, it doesn't help much. What I CAN do is to get my manual tomorrow, and post back some color codes, pinouts, and component pinpoint tests.

jimg.allentown · Nov 16, 2015

OK, found my manual. When you turn the key on, you should bet a 12-volt reading from pin 22 on the computer connector. This is a tan wire with a light green stripe. You should get this voltage for about 2 seconds, then it should turn off. You should also have 12 volts with the key on at pin 37 and pin 57 of the computer. These are RED wires. You should also have 12 volts at pin 1 of the computer. This is a black wire with an orange stripe.
When I say 12 volts, I really meant to say battery voltage - whatever that may be depending on your battery's state of charge.
Especially check your grounds. Pins 20, 40, and 60 should ALL be grounded to both the engine and the chassis (body).
The wires will be a black, and two black with a light green stripe.

IF you do not have the voltages above, it leaves only the computer to be the problem. Ford computers have been EXCEPTIONALLY reliable. They can fail, but it is rare. In my experience, I have replaced only two of them for failures. One was on a Mercury Sable that caused a transmission problem and the other was on a Windstar that would not control the idle.

Also, there is an outfit in Florida that repairs automotive computers. Last I knew, he was quite reasonable on his price. I had to get one for another car, and it cost me under $200 with shipping. If it turns out that you need a computer, I can look up his information for you. BUT, do the diagnosis FIRST to determine that you really need a computer.

My email is open.

notjustair · Nov 16, 2015

I have two vehicles around here that have the fuel pump wired to a switched accessory. I am the only one to run them so I know not to turn on the key without immediately starting it. They have been that way years and work just fine. If they use a full 12 volts just run a wire back to it from the fuse box.

jimg.allentown · Nov 16, 2015

You can do that, but it is dangerous. First, the safeties built into the system are designed to prevent the fuel pump from running in the event of a collision or a fuel line rupture.

You should know that the high pressure pumps in those systems can empty a 20-gallon fuel tank in about a minute. Bypassing those safeties can result in turning a fender bender into a raging inferno - or in the case of a 27 year old vehicle, a ruptured fuel line into a deadly spray of highly flammable gasoline. While you are free to take any such risks that you can justify, I would think it unwise to recommend them to others. Just my opinion.

After all, I just detailed a diagnostic for the guy. Would it not be better to fix it right than to take high risk chances? Take a look at the liability that people on this forum spell out over a plugged tire. This is ORDERS OF MAGNITUDE more dangerous than plugging a tire.

jimg.allentown · Nov 16, 2015

One other thing that I forgot to mention in my last post: there is an inertia switch in the circuit as well. If I remember correctly, it is behind the passenger side kick panel. Be sure to check that out as well.

blue water massey · Nov 16, 2015

on the distibutor of hat vintage of ford everything is a white or grey box affair about 2x4x1/2"
has an oval plug with a bunch of wires running out of it
I think its called an ingition pickup?
90 times out of a 100 its the problem
dampness was it's weakness
I always carried one in the glove box in every ford I owned that had one as well as the proper tool t change it out as most sockets are too thick walled to remove the two little recessed screws
but check the impact/accident fuel pump shut off switch to be sure it didn't trip your owners manual will tell you where to find it

M-MAN · Nov 17, 2015

You will do well to remember that power has to go through that ignition switch before it go's to the pump relay or computer. Not saying that's your problem but it is a weak link. They go bad often enough that your Ford dealer will have one on the shelf for about $25.

WAYNE-N-TX · Nov 17, 2015

Sure glad you asked this question. I have a '89 F350 with the same problem, have been looking for a wire that a rat chewed on. It's in the shed, been there several years.

Hobo,NC · Nov 17, 2015

(quoted from post at 18:27:40 11/17/15) Sure glad you asked this question. I have a '89 F350 with the same problem, have been looking for a wire that a rat chewed on. It's in the shed, been there several years.

Google it.

https://www.google.com/search?q=198...hxe67l8kCFcsrJgodGl4NkA#imgrc=qxgaCXGuJjbniM:

https://www.google.com/search?q=198...oAGoVChMI7Pyfq7yXyQIVRSgmCh03QQ4N&dpr=1.1

Worth its weight in gold for diagnostic work on those old fords.

http://www.ebay.com/itm/THEXTON-EECIV-SYSTEM-BREAKOUT-BOX-FORD-/301800731644

http://www.ebay.com/bhp/ford-breakout-box

jimg.allentown · Nov 17, 2015

Ignition switch was already proved out- if you read the whole thread, you will see that he said it did have spark, and that it would start and run on ether.
So, I ask, why send him to check a component that has already proven good?????

jimg.allentown · Nov 17, 2015

That little grey box is called a TFI module. Its purpose is to amplify the signal coming from the PIP sensor in the distributor (profile ignition pickup) to send to the E-core coil. Already proven good, as the engine will start and run on ether.

The problem here is that the fuel pump is not coming on when the key is turned on. That proves that the ignition switch, ignition module, and the entire ignition system is functioning properly.

The issue here now is to troubleshoot the fuel system.

What is supposed to happen is this:

When the ignition switch is turned on, the computer gets turned on. First thing is that it sends a signal out to turn on the fuel pump for a few seconds. This is to make sure that there is fuel pressure at the injectors for quick starting. When the starter is activated by turning the key to the start position, the starter engages and begins turning the engine. This produces a signal from the distributor that the computer reads. This signal is used by the computer to verify that the engine is turning, and turns on the fuel pump circuit. At this point, if everything is working correctly, the engine starts and runs.

In this case, the fuel pump is not running. Since the ignition system is already proven to be working, the problem is in the fuel delivery system.

Could be a broken wire. Could be a corroded connector. Could be a failed relay. Could be a bad or tripped inertia switch. And finally could be a bad computer.

What it is NOT is an ignition switch or ignition module. In this case, it has already proven good, so why point the guy in the wrong direction??

Jason S. · Nov 17, 2015

(quoted from post at 01:00:17 11/17/15) In June my 1988 Ford F-350 with a 460 started acting up...On damp mornings it had no or weak spark but later in the day it would start and run fine..I put a new coil on it and its never ran since then as then the main fuel pump wouldnt come on..It will run on ether so it has spark..

There was nothing wrong with the old fuel pump but I put a new one on it...Its also had a new fuel pump relay and a new ECU relay but so far nothing has worked..The fuel pump safety switch has been checked...

I know thats theres several more things that it could be but I'm thinking its the computer....I'm not real good on electrical stuff...What do you think it is?? I'm sure that some of you have had similar problems....The old girl still has lots of miles left in it so I need to get it fixed without taking it to someone that will charge plenty to fix it..The 1988-90 Ford F-350's sure have tons of wiring and aren't easy to diagnose..

A couple of things to check. There were some trucks built in that are that fuel pump will not turn on unless there is oil pressure. It read off of the sending unit and a bad oil pressure sending unit would not let the fuel pump run. I can't remember off of the top of my head which engine combination it was that had that. I will have to look. Secondly check your grounds, my 1986 F250 had fuel pump issues and it was the same set up as yours and it was a ground problem. They ground thru the sending unit to the gas tank, and from the gas tank to the gas tank straps to the frame. The ground wire runs to the plug on the sending unit and just grounds to the sending unit body. If there is any rust on any of those they will not ground properly.

Erik Ks farmer · Nov 17, 2015

I had a 91 F250 with identical symptoms, there is a pewter rod in the steering column engaged by the ignition switch that activates the fuel pump relay. Check that this rod is not broken.

1206SWMO · Nov 17, 2015

Thanks Jim...I found a place on the internet with pictures that shows what you are talking about....I have a friend thats pretty good on electrical stuff but he hates working on these year Fords with a passion..He used to own a repair shop..

1206SWMO · Nov 17, 2015

Right now I have less than $150 in new parts....A computer will be around $150 but I will check out some more things before I get one....Theres not very many good repair places left in my area and most hate these year Fords as they are a wiring nightmare..Most are $50-80 per hour and it doesn't take long to run up a huge labor bill on a truck thats worth $1250 at the most..

My wife says that I should just forget the 1988 F-350 as I got 5 years out of it for $2500 and find a good 1995-97 Ford F-350 with a Power-stroke..Theres a real nice 1997 F-350 PS in my area for sale with decent miles but its a little over priced..

1206SWMO · Nov 17, 2015

Thanks Erik..

1206SWMO · Nov 17, 2015

Thanks..

1206SWMO · Nov 17, 2015

It had a new one 10,000 miles ago..

M-MAN · Nov 17, 2015

Having spark is only one contact and one or two wires off the switch. It proves nothing. It's been a while but I'm thinking there are four sets of contacts with that many necessary hots coming out and going in different directions. This ain't 1950 when there was one hot in and one hot out and one contact inside. Every hot coming from the switch has to be there or she ain't gonna run. If I'm not mistaken one of them runs straight to the fuel pump relay which runs to the pump that isn't working so it makes perfect sense to me.

1206SWMO · Nov 17, 2015

It has 3 pumps...The in tank ones were replaced just before I bought it...The relay clicks when you turn the key on..

jimg.allentown · Nov 18, 2015

I have in my hand the Ford factory service manual in the correct year and the correct vehicle for this situation. This includes wiring diagrams, color codes, and pinpoint tests to determine the exact cause of the problem. That coupled up with over 20 years of experience is why I posted what I posted.
Since you apparently know more than the people that built the truck, I will defer to your superior knowledge and judgment.

OT-1988 Ford F-350 Main Fuel Pump Wont Run

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