Same truck I had problems with earlier in the year~'88, 5.0, 5spd, 4X4.

At the first of the year, truck would die randomly. Would turn over fine but had no power to the fuel pump. Then magically it would start working again. I finally discovered a loose ground for the fuel system, thanks to a member here, and the problem went away. Then a couple weeks later it quit again, but a new high pressure fuel pump fixed that.

Now a new problem has come up. At first it wouldn't crank, and the pump wasn't coming on like it did before. After trying it a few times, the pump would run and the truck would crank. Now the truck won't start at all, and the HP pump is running all the time with the key on. My son just went and checked it, says that fuel is in the rail and under good pressure.

Any ideas where to start? I've replaced both relays, even swapped them around with no change. Replaced the module on front of the distributor too, all of this within the last three months. All I can find on the internet is either a bad wire from the fuel relay to the computer, or a bad computer itself. I'm going to dig back in come daylight and chase the wiring down, but I'm lost again.

I checked all of the connections at both relays, had power everywhere it was supposed to when it was supposed to. Have not checked spark yet, we ran out of daylight. I'm not sure about how much pressure is getting to the rail, son is kinda green.

Point me in the right direction, please!

 

Pump running all the time while key is turned to run engine not running is a sign the computer is bad.

Pull it out then remove its cover, inspect it for leaking capacitors.

First post this thread is a good example what you'd be looking for in the computer,

https://www.ford-trucks.com/forums/1...fried-pic.html

Might not be quite that obvious though so look at them all real close, use a magnifying glass if necessary. Caps might also be bulging, top of cap no longer flat, pushed up internally with domed appearance.

Not to fear if catch it early on it can be repaired, the better option over buying a new one too.

 

Well, I pulled the computer out this morning and cracked it open. There were a couple of what looked like bad spots in it to me. They didn't look like the pics in the link, but I'm no electrical guru either. Fortunately for me my Dad is a guru and he lives just down the road, my son and I are going to have him look at it shortly.

I went to our local "what passes for an auto parts store" to see about a reman unit. The needed all sorts of information on the truck then stated that they would have to send it off, not just a simple exchange. Given the reputation of Cardone units, I took my ECU and left.

 

The pump that continues to run is a curve ball, I have had so many pickups in the distributor go bad that I had to buy the tool to remove the gear. And that for sure would give you a no start no fuel, its like a crank sensor in the distributor. When you unplugged the ecm did the pump still run? keep us posted and you'll be on your way.

 

It's obvious that, when they look bad they are bad, but electrolytic capacitors will often "leak" electrically long before they show any visible sign of bulging or actual leakage. They have to be tested for ESR or leakage at rated voltage to be sure. A simple capacitance check won't do this. If they are 25 years old though, might as well just replace them when the board is out anyway.

 

When I unplugged the ECM, the pump did not run. Plugged it back up and it wouldn't stop again.

The module on the front of the distributor was replaced three months ago. It could be faulty again I know.

 

I dont mean the ignition module, yes they go bad alot, I mean the pickup inside the distributor. the module plugs into that. there's a stator and a reluctor ring thats how the coil knows when to fire. And the ecu uses the same stator to know that the engine is cranking and to close the fuel pump relay. The eec power relay is the only relay that gets power when the key is on. the fuel pump relay has constant power for the fuel pump feed term. 30 when the key is on the eec supplies voltage to the coil side of the fuel pump relay and the ECU completes the ground to turn on the pump. Check the tan and light green tracer for constant ground, that would keep your pump relay closed anytime the key is on. keep us posted

 

possible fuel pump contacts welded togeather grn/tan & pnk/blk I think. this would also cause pump to run all the time. I may be wrong on wire color its been a bit. Unplug relay when its goofing up to see if it shuts off

 

If the pump runs all the time with the computer plugged in, and not all with the computer removed - the computer has more than likely failed.

Basically it's wired in such a way internally that the fuel pump runs until the processor starts up. If the processor never starts up, the fuel pump never stops. There's supposed to be a fail-safe limp mechanism to fire the injectors at a fixed pulse to limp you home in the event of a processor failure, but it never seems to work.

 

yea, ive got the same problem.truck has sat 4 years.so far ive replaced both fuel pumps,fuel filter,fuel pressure regulator,relay,coil(coil was broke where wire plugs into,but was still working.changed anyway.)distributor cap(also looked bad,but still firing..)i now have the ecm out,will check in the morning to see if pump still running.before replacing ecm....mine is a1987 302 but same problem are they the same

 

opened up the ecm,the board looks perfect.no signs of anything wrong,will now go see if pump still runs with it out

 

I asked Dad to look at the board yesterday, he didn't see anything that jumped out at him. There were some brown spots at the base of a couple of capacitors, he said this may be where a little of the waterproofing sealant pooled heavier than in other spots. Neither of us saw and capacitors that appeared to be swelled, or that were obviously leaking. All in all, everything looked alright.

Guess we're going to back up and regroup.

 

Can you post pics of the board? It might be helpful for other members. I dont want to doubt you or your father either.

As another member mentioned, check the wiring at the fuel pump and the dash selector switch if dual tanks.

Also, can you pull codes? Can you run the Key On, Engine off test or the Key On, Engine Running test?

If fails on both, then PCM has failed. Either processor failure or other.

 

All three caps are under $5 @ Radioshack.
As was mentioned these things have a lifespan.
If the board is already out why wouldn't you replace them???
PCM is over 25 years old.
Be sure to maintain polarity.

 

Once sleeping beauty awakes, I'll ask him where the box is and try to put a couple pics up. The wiring to the pumps is good, I chased it all down the other day.

Was not able to pull codes before I pulled the ECU. In a previous thread I was trying to figure out another issue and found that the wiring for the EEC and fuel pump relays had been hacked up by a PO. In the process of chasing down wires with this issue, I found where the wiring had somehow been cut. One of the wires in question went to the test port making it impossible to pull codes.

I did repair the wiring that was damaged, with the exception of wires that were no longer needed. By no longer needed I mean that they had been replaced with new wiring of the proper type. After repairing, I tested again with the ECM in and out with the same results.