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'86 F150 5.0L fuel injected spark issues


scotts90ranger

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So my brother has a '86 F150 with a 5.0L, 4x2 auto trans fuel injected. It has an occasional stalling and or no start issue that comes and goes randomly. Knowing what I do I imagine it's a TFI issue, he's of course not a fan of firing the parts cannon... I've honestly not had personal experience with Ford's with distributors (I've only had DIS 2.3L's and 4.0L's, and a diesel...) but know that both the pickup in the distributor and the module on the side can be troublesome, and new parts are a crapshoot... last time he had issues I scrounged for a 2.3L distributor I had floating around and he put the module and pickup from it in there but it lasted a couple years before having similar issues...

So, thoughts? I imagine the fuel injection uses the pickup in the distributor for the rpm input, I've heard of using some HEI parts to make things work but don't remember where I saw that, it's just a farm truck that's ugly... it's not a daily driver or anything but I'd be willing to do some machining and or soldering or whatever to get something going...
 


rusty ol ranger

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So my brother has a '86 F150 with a 5.0L, 4x2 auto trans fuel injected. It has an occasional stalling and or no start issue that comes and goes randomly. Knowing what I do I imagine it's a TFI issue, he's of course not a fan of firing the parts cannon... I've honestly not had personal experience with Ford's with distributors (I've only had DIS 2.3L's and 4.0L's, and a diesel...) but know that both the pickup in the distributor and the module on the side can be troublesome, and new parts are a crapshoot... last time he had issues I scrounged for a 2.3L distributor I had floating around and he put the module and pickup from it in there but it lasted a couple years before having similar issues...

So, thoughts? I imagine the fuel injection uses the pickup in the distributor for the rpm input, I've heard of using some HEI parts to make things work but don't remember where I saw that, it's just a farm truck that's ugly... it's not a daily driver or anything but I'd be willing to do some machining and or soldering or whatever to get something going...
If the fuel pump is running tell him to replace the module with a motorcraft one, 9/10 thats it. There are ways to test the module but being its a random issue a test might not catch it.

Make sure the replacement module is the proper color (there are grey and black ones, 86 is more then likely grey but verify).

Distributors are not that expensive either if the module dont take care of it.

It could possibly be an ignition coil but that should give a pretty normal cold run/hot fail.

Have you pulled codes?
 

scotts90ranger

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I haven't done any troubleshooting on it myself yet, I'll try to pull codes, that would make sense...

It's a dual tank unit, shouldn't it have 3 fuel pumps? low pressure in each tank and a high pressure in the framerail or are they not like Rangers? It apparently isn't picky on which tank it's on but checking for fuel pressure is on the list to check although he says it doesn't have spark

Thanks
 

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It will have 3 fuel pumps like you said. I have essentially the same truck. I would also suspect the TFI module. Somewhere in the 90's they started using remote TFI modules that were more reliable, would take a small amount of wiring to retrofit that. Probably need to hit up a junkyard. I'm not aware of a way to do an HEI conversion or anything like that and keep the fuel injection intact although there may be something out there....... kinda seems like MSD or Accel made aftermarket TFI modules. I think these systems work fine, when they're working, easier to fix it than cobble up something else... have seen a bunch of trucks get carburetor conversions, not a huge fan of that.
 

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Yes, HEI is a way better spark system than TFI but can't be used with Ford computer's fuel injection system

Spray fuel into the engine, 50/50 test, to confirm its a no spark issue

The Hall Effect sensor inside the distributor was not a common failure, can fail, just not as common as TFI module
And TFI module failure was 90% heat related, so would cause issues AFTER engine bay warmed up, not cold starts
1986 should use the Grey color TFI modules, not the black ones

And at 35 years old the wiring could be the issue not the electronics
So confirm No Spark issue first with 50/50 test
Then get out the Volt meter and test wiring

Go here: https://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

get the TFI work sheet and print it off, seen here: https://www.therangerstation.com/tech_library/images/tfi_worksheet.jpg
 

scotts90ranger

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Ok, been a while but my brother got the ol F150 back out and it would be useful to run... of course it started right up for him and worked mostly using it around the farm on short trips but we were talking this morning and looked at it and think we found the issue, fuel pressure goes away completely. It will stall while running and not start back up unless you cycle the key a handful of times. It was on the front tank the only times it happened but it's not super consistent... When it stalled you could feel the fuel pump relay next to the brake booster click and could hear the high pressure pump so I don't think it's that one. Getting a new fuel pump relay would probably not be a bad start, it's original with an E3 marking on it...

So, the fuel tank switch circuit, how does that work? Looking at the tank selector valve there's no wires so I'm assuming whichever low pressure in tank pump is running pushes a plunger one way or the other to switch between? How does the circuit to the fuel pumps through the switch work? Low pressure pumps are usually only 1-2A so is it just through the dash switch?

I could re engineer the system but it's probably easier to get the stock stuff working...

This silly thing likely only has 125k on it, it's got an 8.8 and someone put overload springs on it like an F350 would have, no rust other than where the paint fell off and the inside of the bed is beat up pretty good... needs a muffler but that's about it other than this stalling issue...
 

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Found this wiring diagram: http://www.garysgaragemahal.com/uploads/6/5/8/7/65879365/4652683_orig.jpg

Looks like the Tank selector switch does control power to Lift pump in the selected gas tank, also fuel level sender
So could be an issue with the switch

High pressure pump gets 12v all the time, so if you hear it working with key on then not a relay or inertia switch issue
So could be switch or lift pump itself

Pumps(electric motors) don't usually stop once running, their normal fail is they just won't start one day, but certainly possible since they should have a thermal limiter built in
 

rusty ol ranger

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Found this wiring diagram: http://www.garysgaragemahal.com/uploads/6/5/8/7/65879365/4652683_orig.jpg

Looks like the Tank selector switch does control power to Lift pump in the selected gas tank, also fuel level sender
So could be an issue with the switch

High pressure pump gets 12v all the time, so if you hear it working with key on then not a relay or inertia switch issue
So could be switch or lift pump itself

Pumps(electric motors) don't usually stop once running, their normal fail is they just won't start one day, but certainly possible since they should have a thermal limiter built in
You sure thats not for later trucks?

Pretty sure they ran a vacuum switcher up untill 87 or 88.
 

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Not sure I have ever come across a dual tank Vacuum Switch, in any year Ford or GM

Just Electric or Manual(next to Drivers seat)
 

scotts90ranger

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They used vacuum on some of them? Odd, this one definitely just has the two supply lines, one outlet and the 3 returns (IE 6 ports total...) and what looks like a small filter or something on the bottom (didn't dare touch it for the moment...)

Thanks Ron!

It was starting to sound like a switch contact, we'll look into that, maybe drop the tanks (maybe just the front one for now) and look at the top connector, who knows what mice have done, there's a nest inside the coolant reservoir since the little cap was missing... dang vermin...

I wouldn't suspect a motor to stop while running either, but a switch contact to lose connectivity while working is odd too, but dirty contacts or bad brushes can do odd things... at least after like 5 years it happened while I was there and it wasn't a rush or in traffic or something dumb, knowing is half the battle as GI-Joe taught me... :)
 

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It is a canister type filter, cap should unscrew
It also serves as a reservoir for the high pressure pump
 

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