MarkThomas Posted January 19, 2021 Share Posted January 19, 2021 My '86 F250HD 5.0L EFI runs great. Just finished a pile of replacements and fixes to get it running right. This morning, drive in to work, it stops running all at once. I turned the key off, then back on, she fires right up no issue. At lunch it did it again - same remedy. WTH? She has a brand new Distributor with all new fire. I've tested the fuel pressure and it's within the specifications in Chiltens. Most of the sensors/regulators have been replaced - MAP, IAC, EGR, etc. I will say this, I couldn't get it running right and took her to a mechanic and he found the rear of the intake plenum gasket was gone and replaced the gasket, he also installed the distributor (and ICM) for me and checked the timing (and advance), but had to fix several connections in the distributor connector cable. Like I said, it runs great. Smooth. Cruising along and just all of a sudden the engine isn't running. All the lights, battery, elsewise electronics appear to be running. Cycle the ignition switch off and back on and bam - she's running great again. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted January 19, 2021 Share Posted January 19, 2021 Mark, If you have to fix distributor wiring you should look into a remote TFI kit with a heatsink from MCaulley racing or FatFoxx. What does it say on the radiator shroud sticker, and what is the GVWR of your truck? Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 20, 2021 Share Posted January 20, 2021 Mark, If you have to fix distributor wiring you should look into a remote TFI kit with a heatsink from MCaulley racing or FatFoxx. What does it say on the radiator shroud sticker, and what is the GVWR of your truck? I doubt it is a wiring problem. Turning the key off and back on shouldn't fix wiring, but it seems to cause the engine to run again. Given that, I think you have an electronics problem. Maybe the TFI? The pickup in the distributor? Link to comment Share on other sites More sharing options...
ScubaSteve Posted January 20, 2021 Share Posted January 20, 2021 I had a similar problem on my 86 F150 5.0 efi truck when I purchased it. The previous owner fought with the problem and could never figure it out. His mechanic also replaced the distributor and did a tune up. What I found was bad wiring connections in the engine harness for the tachometer signal. The way I understand it to work is the computer primes the fuel pumps when the key is turned on then when the computer get a tachometer signal from the distributor it turns the pumps back on and keeps it on until the engine is shut down and it looses the tachometer signal. I don't think the computer will energize the fuel pump relay again after the signal is lost until the key is cycled again. My truck would randomly die and then start right back up like nothing was wrong. It was a real pain to track down until i got frustrated and pulled the complete engine harness and started checking every wire. The thing that makes it hard to find is that once it stalls you cant tell what happened. Did the pumps shut off because the engine died and lost the tachometer signal or did you loose the tachometer signal and the the pumps shut off. Hope this helps, Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 20, 2021 Share Posted January 20, 2021 I had a similar problem on my 86 F150 5.0 efi truck when I purchased it. The previous owner fought with the problem and could never figure it out. His mechanic also replaced the distributor and did a tune up. What I found was bad wiring connections in the engine harness for the tachometer signal. The way I understand it to work is the computer primes the fuel pumps when the key is turned on then when the computer get a tachometer signal from the distributor it turns the pumps back on and keeps it on until the engine is shut down and it looses the tachometer signal. I don't think the computer will energize the fuel pump relay again after the signal is lost until the key is cycled again. My truck would randomly die and then start right back up like nothing was wrong. It was a real pain to track down until i got frustrated and pulled the complete engine harness and started checking every wire. The thing that makes it hard to find is that once it stalls you cant tell what happened. Did the pumps shut off because the engine died and lost the tachometer signal or did you loose the tachometer signal and the the pumps shut off. Hope this helps, You know, that would do it. If you lose the tach signal the computer will shut the engine down. Good idea! Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted January 20, 2021 Share Posted January 20, 2021 I had a similar problem on my 86 F150 5.0 efi truck when I purchased it. The previous owner fought with the problem and could never figure it out. His mechanic also replaced the distributor and did a tune up. What I found was bad wiring connections in the engine harness for the tachometer signal. The way I understand it to work is the computer primes the fuel pumps when the key is turned on then when the computer get a tachometer signal from the distributor it turns the pumps back on and keeps it on until the engine is shut down and it looses the tachometer signal. I don't think the computer will energize the fuel pump relay again after the signal is lost until the key is cycled again. My truck would randomly die and then start right back up like nothing was wrong. It was a real pain to track down until i got frustrated and pulled the complete engine harness and started checking every wire. The thing that makes it hard to find is that once it stalls you cant tell what happened. Did the pumps shut off because the engine died and lost the tachometer signal or did you loose the tachometer signal and the the pumps shut off. Hope this helps, It's not the tach, it's the leading edge edge of the PIP signal from the distributor, that resets each timer. Link to comment Share on other sites More sharing options...
MarkThomas Posted January 20, 2021 Author Share Posted January 20, 2021 Mark, If you have to fix distributor wiring you should look into a remote TFI kit with a heatsink from MCaulley racing or FatFoxx. What does it say on the radiator shroud sticker, and what is the GVWR of your truck? What you're calling the TFI (Thick Film Ignition), I called the Ignition Control Module - they're the same thing. We installed a new one - Motorcraft - with the new distributor. Do you really think it could be a bad TFI/ICM when both the distributor and TFI/ICM are new? Link to comment Share on other sites More sharing options...
MarkThomas Posted January 20, 2021 Author Share Posted January 20, 2021 I had a similar problem on my 86 F150 5.0 efi truck when I purchased it. The previous owner fought with the problem and could never figure it out. His mechanic also replaced the distributor and did a tune up. What I found was bad wiring connections in the engine harness for the tachometer signal. The way I understand it to work is the computer primes the fuel pumps when the key is turned on then when the computer get a tachometer signal from the distributor it turns the pumps back on and keeps it on until the engine is shut down and it looses the tachometer signal. I don't think the computer will energize the fuel pump relay again after the signal is lost until the key is cycled again. My truck would randomly die and then start right back up like nothing was wrong. It was a real pain to track down until i got frustrated and pulled the complete engine harness and started checking every wire. The thing that makes it hard to find is that once it stalls you cant tell what happened. Did the pumps shut off because the engine died and lost the tachometer signal or did you loose the tachometer signal and the the pumps shut off. Hope this helps, My truck doesn't have a tachometer - does that mean the EEC-IV doesn't use a tach signal? Link to comment Share on other sites More sharing options...
MarkThomas Posted January 20, 2021 Author Share Posted January 20, 2021 It's not the tach, it's the leading edge edge of the PIP signal from the distributor, that resets each timer. Isn't the PIP sensor (which is like the old crankshaft position sensor) located in the distributor? Shouldn't that too be new since I bought a new distributor? Link to comment Share on other sites More sharing options...
MarkThomas Posted January 20, 2021 Author Share Posted January 20, 2021 You know, that would do it. If you lose the tach signal the computer will shut the engine down. Good idea! Since I don't have a tachometer, how do I know if I lost tach sensor signal? When it happens again, what do I do to see if the pumps are still on? I have a fuel pressure tester, should I keep that in the truck and when it shuts off just coast over on the shoulder and screw the pressure tester on? Link to comment Share on other sites More sharing options...
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