MG66mustang

Idle issues for my 1989 F150 5.0L XLT Lariat.

She has 239K and I've had it since 1996 at the time 69K. It was a flood truck I later learned.

To say the least, the EFI stuff just confuses me.

I have changed many parts due to codes and just an educated shot in the dark.

Since April I have changed the O2 sensor(code), Have replaced Idle Air Control Valve(stalled, rough idle), MAP(code).

Distributor(cardone), control module, Ignition switch, coil,(no spark)

Rotor, distributor cap (MSD), wires, plugs, as a tune-up.

It still idles rough, backfires into the intake, on acceleration, feels like it is starved for gas while driving, but has 40 psi at the fuel rail.

Getting ready to replace the Throttle Position Sensor(orig), as just off idle it seems to have some power but more pressure causes it to stumble and bog down, feels like it advances too far.

Just getting to be a frustrated Old School Mechanic.

I need some suggestions

MG66mustang

Well I guess this is not much of an issue for you guys. It is to me so I guess I will have to go elsewhere to find my answers.

Thanks for all the help.

Just call me Sean

iTrader: (1)

Have you checked the timing? Made sure it didn't jump time?

MG66mustang

Yes I checked it and the freeplay in the chain is still less than 10 degrees. replaced it at 94k was not too worn then. New gears and roller chain.

Yesterday reset the TPS to .97 V and it was only set to 0.99V, its' better but still backfires on med. acceleration. After $200+ in parts and time spent I am just running out of places to go.

Mike

Just call me Sean

iTrader: (1)

Your truck has three fuel pumps. One in each tank and one on the frame. Sounds like a tank pump may be getting weak.

MG66mustang

Yes it does,

I replaced the rear tank pump maybe 1998. Two of the gaskets for the breathers on top of the tank rotted away, good old ethanol gas, couldn't get them at NAPA only FORD then, so I used silicone to try and seal them, with no luck, (gasohol eats right through it) and stopped using that tank ( I had two).

I replaced the "mid-tank plastic" pump maybe 2005, found it full of wood chips, in the screen and tank, no idea where they came from. I also found wood chips in the fuel reservoir for switching tanks, and cleaned them out as well as a new screen, and replaced the frame (high pressure) pump a little later.

I can hear the frame pump run 2-3 sec. at key on, and I can hear something that sounds like a pump from the filler cap on the mid tank but can't be sure that it is the tank pump ( frame pump is pretty loud). I have run the tank dry a few times, "good fuel gauge", mostly use mileage. So the tank pump could be bad and the frame pump sucking up gas from the tank, but not enough volume under load.

A replacement pump is $60 and the complete assembly, gauge etc. is a little over $100, gas gauge works when it wants to kinda. It's hard to throw more money into the truck, and convince the wife I need to, I am on a very limited income, at this point (real part time work). But it is paid for and has been a good truck for many years, I can't replace it.

I have 34psi at the fuel rail (Harbor Freight is so cool) at idle and 40 psi on stationary acceleration in the driveway, but I can't seem to leave the gauge hooked up and drive it, too much fear, and the hose isn't long enough to be able to read it and drive.

I'm getting too old to be climbing under the thing all the time, but too cheap and stubborn to stop.

Just call me Sean

iTrader: (1)

Frame pump gets noisy when it's dying, or when it's starved for fuel.

MG66mustang

Thanks Sean,

I will have to check out the tank pump more. I just filled it, wed. so I need to drive some gas out of it, too heavy for me to work with.

Mike

decipha

backfiring through the intake is running lean, definitely a fuel supply issue

do not change the TPS, it doesn't affect fueling in any way

most likely your injectors are clogged from the wood chips you found in the tank, with that mileage its about due for a good cleaning anywho

yank the injectors out and use a pick to remove the filters from the top inlet of them, then flip them upside down, blow about 200psi of compressed air through the bottom of them and toss them back in with some new filters

Chris_1

iTrader: (1)

Have you checked the TPS rotational voltage ? It should climb and fall steadily as you move the throttle. Steadily is the operative word. If the voltage stumbles at all, that will affect your engine. Easier to test it first (and cheaper, if there's nothing wrong with it).
40 psi with no vacuum to the modulator should run the truck ok.
Injector cleaner in the tank sometimes helps. (but I wouldn't think wood chips would make it through the filter)
You can use an LED test light to make sure the injectors are getting a pulse.