1986 F-150 302 Engine - Turns over but won't start except with BOOST from Jump Box

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Asked by Oct 07, 2016 at 08:33 AM about the 1986 Ford F-150 XLT Standard Cab LB

Question type: Maintenance & Repair

My 1986 F-150 302 Engine, turns over but won't start except on the
BOOST setting from my Jump Box.  I have changed out the starter,
solenoid, coil, cap/rotor/cables/plugs.  Put a big new 900CCA battery in it. I
had the alternator bench tested at AA checked good and it don't drain
battery.  I have checked for spark and compression at the #1 plug.
Distributor spins the rotor and I haven't messed with any timing related
components.  Any help would be appreciated I can't go anywhere until I fix
my truck

10 Answers

25,755

If it starts with a boost from a jump pack, then there is nothing wrong with the starting circuit. I think either your battery is not up to the task (I have an 1100 CCA battery in my car). Even though it is a new battery, you may want to haul it in ans get it load tested. You may also want to make sure the starter is getting full voltage, so try a voltage drop test (see attached pic).

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I ran the checks you stated KenF. My battery cable voltages checked good from battery to solenoid, solenoid to starter and from battery to solenoid. I also did resistance checks while I was at it, they are all 0.4 ohms and full conductivity from negative battery to frame. I am headed into town in a few minutes and will get a load check on the new battery. The battery was my original thought, as I had a 590CCA battery in it that came with the truck. Had it load tested and actually checked out at slightly above rating. Replaced battery anyways being I knew it was to small for the truck.

10

Battery checked good at Advance Auto. Still in same boat.

19,800

Will it start with a jump from another battery when the other vehicle supplying the boost is not running?

10

OJ, the truck will jump off from another vehicle while running with a high RPM / foot on accelerator. It won't start from an idle vehicle.

10

New problems, went to move the truck today. I cranked it up on Boost realized I hadn't reconnected the air intake. Shut truck off. Tried starting without jump box, did not start however truck keeps trying to crank had to disconnect negative lead off battery to stop ignition. Keeps igninting every time I try to connect negative battery cable. Also discovered a broken yellow wire near coil haven't yet figure out where it goes yet. May have been a capped wire as previous owner did some electrical jury rigging. I am adding a few photos of the wire if any ideas.

1 of 1 people found this helpful.
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2nd photo

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3rd

19,800

Locate the starter relay, it's probably bad. It uses low voltage to switch a higher voltage. This is normally the cause of the vehicle trying to start itself.

1 of 1 people found this helpful.
10

Thanks everyone I figured out the issue. The start by itself was caused by an internal short in the solenoid. The not starting without boost was caused by high resistance across the coil on the fuel relay.

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