Got a 1987 f150 4.9L that has been giving me a fit for the last few months. It is hard to keep running when first starting and then will rough idle once warm. Also when I press the gas pedal it will try to stall and I have to pump it for a bit. It will backfire under the hood when I press the gas hard also. Anyone experience this before?

 

Is an '87 300 carbed or EFI? Can't remember offhand.

Adrianspeeder

 

efi

 

Sounds like a leak in the intake manifold, or a vacuum leak elsewhere.
Did this problem start all at once, or has it gradually gotten worse?

Do you have access to a vacuum gauge?
http://www.classictruckshop.com/club...ts/vac/uum.htm

Just thought about this a little more...
Low fuel pressure (bad fuel pump, clogged fuel filter) would also cause most of your symptoms, except the back-firing.
That's why I pointed towards a vacuum leak.

 

Has gradually gotten worse. Once I get started takes about 2 minutes of pumping and playing with accelerator and then it will idle and stay running. I have already changed fuel filter also. Don't have a vacuum gauge. Get error code 82 with koeo. Was able to actually run it down the road the other day and runs OK until a hill and then major power loss. Also hard to get going on takeoff if I don't rev up before letting clutch out.

 

You're going to have to check fuel pressure and vacuum to try and narrow down the problem.

According to my info, 82 is "Air management 1 circuit failure (AM1/TAB)".
^^^But, that should only be a KOER code.

 

Thanks for all the help so far. I borrowed a vacuum gauge and plugged into intake manifold and had a reading that stayed steady between 18-20. When accelerated above 2000 RPM it would go to about 23-24 and then return to 18-20. When I floor it it would drop rapidly to about 10 and then return when released.

 

That vacuum reading could be a little higher, but by all means it's not bad.

Time to look at fuel pressure, but I don't remember where exactly to check on that engine.

 

Got a fuel pressure test gauge, now just gotta figure out how to test it.