Hello all, just bought a '86 F150 xlt I'm going to clean up as a daily driver.

specs are;

5.0 efi,
auto,
68,000 miles,
been sitting at least 3 years.

Went to San Antonio and drove it home to Fort Worth (ran terrible, but made it), but now cant keep it running.

I've tested the fuel system, both in tank pumps have been replaced (1 was bad), high pressure is working properly.

When I start the truck, it runs fine for about 30 seconds, then sputters, backfires through the intake, and eventually dies. this repeats till key is cycled off for about 30 seconds, then it starts back at the beginning of the description.

I cant keep it idling long enough to check the timing, and not sure what to check next. Thought I'd check with the collective.

Thanks in advance!

 

Have you changed the fuel filter?

 

Should have put that in original post, sorry.

new in-line filter,
new tank screen filters,
and bought a filter for the switching valve, (which did not have a filter in it) but it doesn't fit, the pickup tube is too long. so the bowl was cleaned, and re-assembled without the filter.

 

Latest update,

bought a fuel pressure gauge, when key is turned on, pumps prime, but no readable pressure.

when cranking, or running, runs 35-40 psi, but drops as soon as pumps stop.

high pressure pump? or fuel regulator?

which of these holds the residual pressure from backflow?

Thanks,
James

 

Replaced the high pressure pump, and now have proper pressure, and pressure retention.

Still will start, then fade and die with fuel, and vacuum pressures remaining constant. If I keep working the throttle, I can keep it running, albeit poorly.

Tested the tps, and had faulty readings, so it was replaced. Still having the same issues.

Anyone have any other ideas?

 

Have you cleaned the tanks or at least drained the old gas? After sitting 3 years, the gas had to be bad.

 

Possibly clogged injectors? Did drive it on old gas? Overall condition, exhaust manifold leaks, intake manifold leaks? Bad coil or wires?

 

No way to drain tanks when I got there, rear tank was pretty much empty, front had 1/2 tank.
Immediately went and filled front tank with premium, and added whole bottle of Techron injector cleaner to the tank. Ran that tank through with performance improvement. Refilled the tank , and drove on home with no issues. Never used rear tank.

A week later, when I had time to get started, I now can't keep it running, and started this thread.

What's the best procedure to clean the injectors? Usually, I stick to carb powered vehicles that I plan to maintain myself, so this is a learning curve for me.

Thanks

 

Overall, good condition. Gone over everything and visually inspected, found one vacuum leak on the a/c door control line and fixed. Went over intake with starter fluid, no fluctuation. No visual/audible exhaust leaks.

 

Update, ran diagnostics and got map sensor code, lean code, and rich codes.
Tested map sensor, and replaced it due to having squirrely values.

Truck now runs better, but still shuts down after about 30 seconds.

The quest continues.