I have a 1988 F250 7.5. I had the ignition switch actuator break the other day, got it fixed. Now a week later I drove it to the store and it won't start.

It does have spark. I thought the fuel pump was not running, very noisy street and could not listen under the truck and cycle key at same time. I replaced the rail fuel pump. Now thinking the fuel pump is/was good.

I have solid power from the fuel pump relay to the fuel pump, in other words power is on all the time. It will not shut off after a few seconds (like normal) Key off, relay not energized, key on constant power.

The check engine light does not come on, when the key is turned on. I have not been able to check the injectors. The truck is still in the parking lot. Just getting some ideas when I go get it. I am leaning towards the ECM.

 

Given the symptoms I agree, bad 'puter.

 

Any good places to look for one?? Zone has got reman cardones starting at $100 depending on number.

 

I hate Cardone, but they are just about the only game in town these days.

You could remove yours and inspect for signs of leaking capacitor(s). Your may have only one. Also look for signs of burned components or moisture damage.

If it is just the capacitor(s) they can be replaced.

 

Brian Ski 44: If you spend any time on this forum, you will realize that there are some people here who really know their stuff -- rla2005, subford, Conanski all come to mind -- and, I am not one of them.

But maybe you can learn from one of my mistakes...

Lesson: "Mechanics look to the component. Electricians look at the wiring."

I replaced the ECM in my wife's Dodge Dakota 4 times before I realized that I only needed to clean the three 32-pin(?) receptacles to make a good connection to the computer pins for the 5v sensor input and control output signals to make everything work right. No new computer needed.

So, before you buy a pcm, maybe try really cleaning the receptacles well with CRC ELECTRONIC CONTACT CLEANER using MICRO Q-TIPS (not files) and then spray the holes DEOXIT GOLD G5 ?

This is discussed here:

https://www.ford-trucks.com/forums/1...o-files-4.html

If you find that you truly need a computer, I can highly recommend AutoComputerExchange.com They put up with me ordering and returning a total of 4 perfectly fine computers and issuing a refund of the $279 purchase price with a slight restocking fee (great company) -- when I figured out it was never the computer in the first place.

So, before you buy a remanned pcm or have yours repaired, clean and enhance your contacts especially if someone has inserted the DREADED DIELECTRIC GREASE INTO THESE LOW VOLTAGE COMPUTER-TYPE CONNECTORS!!! Look down the page in the above link for the picture of what dielectric grease did to a connection in my Miller 350P.

 

Appreciate the input Tim, but the OP's symptoms are indicative of an internal computer issue. Never hurts to check the connector when they remove the computer to inspect...

Only one other time I ran across the dreaded fuel pump run all the time that turned out to be external to the computer. Missing ground on the upper radiator support. This was found after the truck had been totally disassembled/reassembled as part of a rebuild.

 

rla2005: 10-4. Since you raised the issue, I don't remember if the computer is grounded through the computer plug or through the two bolts that hold it to the firewall. Stupid question, I don't know the answer to, but I would like to know if you happen to know?

P.S. I was once told by one of the examiners during an oral exam when I asked a question: "Tim there are no stupid questions. Only stupid people asking questions." It was a slightly embarrassing moment in front of my peers and all.

But I passed the exam.

 

The main computer ground is through Pins 40 and 60 to ground G101, passenger side inner fender near the battery. There is another ground on Pin 20 that is tied to the cab of the truck, G104.

I believe I read somewhere the computer case is also grounded. Makes sense since it is held in with a metal bracket.

As stated before G101 is the main computer ground. Without it, the truck will not run.

 

Thanks rla2005! This is how I learn. I appreciate your knowledge and experience and that you are so willing to share it!

Now back to Brian Ski 44!

 

I don't think mine is grounded through the case. The case is held in place by a single bolt through a plastic connector and a plastic bracket.

BTW the fuel pump kept running 5 minutes or more while I was trying to do a scan. No info at all from the computer, all while hearing fuel run through the rail. Nice to have the truck back at home. Even though it was not running. Still no check engine light either.

BTW Not sure if this is related or not. When I would stop somewhere for about 1 minute the truck would not want to start. It would take some cranking to get it to fire. IE if I would run into the post office, toss a package on the counter, run back to the truck it would not fire right away. If I had to wait in line 2 minutes or so it would fire right up. This time I ran into the store, no line grabbed something quick and ran out, it never started again. It has been doing this for several months, but rare to be in and out of a place that quick. Maybe something needed cooling down?? It always ran great once it started.

 

Tim thanks for the idea, I have used dielectric grease before, it is usually clear. Some of the stuff I have seen from the dealer is a tan sticky goo. Like in your link. I never did like the stuff, I remember seeing it used on tail lights in the 70s GM cars. Even on a heavy contact 1157 bulb it would still not make a good contact.

I already pulled the computer and the pins looked pretty clean. I will give the connector and computer a good once over. Thanks

 

Well I ordered a new computer from the zone. $100 exchanged. I popped it in and turned the key to on. Check engine light came on, fuel pumps fired up and shut off after about 3 seconds, I hit the key and the beast roared to life. Thanks all for the help.

 

Glad to see you got it resolved. Let's hope those Cardone folks actually refurbished the PCM or just slapped a new label on it.

 

Hey it had a shiny box on it!!! Only others I found was blue streak. But not in stock and I could not even order it.

All I can say is it runs now....