1987 Ford F-150 Missing and stalling when warm

Tiny
BOB ANTHONY
  • MEMBER
  • 1987 FORD F-150
  • 6 CYL
  • 4WD
  • MANUAL
  • 134,000 MILES
Hi, Thanks for being here, My truck has some wierd problems. It sometimes misses, I mean like someone turned the key off, the tach goes dead, sometimes it seems to catch and take off again, other times it stalls and dies completely. Ater a few minutes it usually starts again only to have it die again further down the road. Another strange thing it does sometimes is when you step on the dimmer switch for the headlight there is a momentary miss. OBDII shows no codes. I have replaced the ignition module, the ecm, both fuel pumps and the relay, new cap, new wires. All that is left is the distributor pickup and the ecm relay. This is an intermitant problem but appears to get worse when the truck is warmed up. Any ideas? Bob Anthony

updated 1/15/10
I am planning to get the truck inside this week as there is a lot of snow on the ground around here. I will go over the grounds with a fine tooth comb. Do you know of any diagrams that have the ground locations on them. I have a Haynes manual and it has wiring diagrams but there is no mention of where they are. I noticed today when the engine died after opening the hood that the wiring harness that has the plug that connects the ignition module has been soldered together as if the plug was replaced or something. I will check that out too. Another thing I noticed today was that after cranking the motor with the transmission in neutral trying to restart it after it died that it did not start until I put the tranny in first gear! Any ideas about that. It seems that it only stalls agter the moter has warmed up and I have driven it ten or fifteen miles. I have wiggled the ignition switch when the engine misses and it has no effect. I am wondering about the ECM control relay, and also the fuel pump relay. Is there a separate relay for the high pressure pump? I appreciate any light you may be able to shed on this intermittent problem. I have spent a lot of doe replacing things that did, nt need to be replaced. There are no trouble codes showing up. Thanks for your time Mike.
Sincerely, Bob
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Sunday, January 10th, 2010 AT 4:19 AM

5 Replies

Tiny
MERLIN2021
  • EXPERT
Check power and grounds for ecm, check coolant temp sensor, and make sure the tach wire isnt grounding out someplace. May also be a fualty ignition switch!
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Sunday, January 10th, 2010 AT 4:46 AM
Tiny
BOB ANTHONY
  • MEMBER
Hi Mike,
Checked all the grounds I could find under the hood and under the truck. I pulled the fuel pump relay and the ecu relay. The fuel pump relay had aluminum contacts on it and there was a white oxidation on the prongs that I cleaned off manually and then sprayed the contact points and the plugs with contact cleaner. I checked the connection to the high pressure pump and it seems to be loose. It is held on by a plastic clip and I can move it around easily. I test drove the truck home_twenty miles and it did not miss a beat. The next day I drove it back to town, the same twenty miles it coughed twice but did not stall. Coming home it ran flawlessly again. I think I did something that helped as it usually dies a couple of times in either direction, so it is defenitly better than it was before. Thanks for the help. Bob
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Saturday, January 16th, 2010 AT 11:47 PM
Tiny
MERLIN2021
  • EXPERT
OK so it's a wiring problem, and that connection to the ignition mod sounded suspicios to me. That starting in gear means the clutch interlock switch above the cluth pedal needs to be replaced, this may also cause problems. Check email, Am sending a few PDF's to assist you.
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Sunday, January 17th, 2010 AT 6:44 AM
Tiny
BOB ANTHONY
  • MEMBER
Thanks Merlin,
It only starts in gear when the clutch is depressed. Could this have something to do with the meutral safety switch? Thanks for the wiring diagrams they are much easier to read than the ones I have in the Haynes manual. Although I can't be sure I keep thinking about the dirty connections on the fuel pump relay that I cleaned. Could low voltage due to the bad connection have damaged the contact points inside the relay? The relays are not the type I used to be able to take apart and examine so I suppose the only way to find out is to replace it. There are three pumps on this truck, two in the tanks and one [high pressure] on the frame under the driver's door. Do they all work off of one relay?
Thanks Merlin for all of your help, Bob
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Monday, January 18th, 2010 AT 1:07 PM
Tiny
MERLIN2021
  • EXPERT
Fule pumps are on the same relay, If it doesnt start in gear without the clutch, it's OK.
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Monday, January 18th, 2010 AT 2:22 PM

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