Old body style.
It starts, idles, and runs fine but lacks power up hills.
I've checked the base timing, injectors, plugs, wires, fuel pressure, and all are good. I've looked all over for a vac leak.

If I disconnect the IAC (idle air control valve) the motor slows to around 750 rpm and the engine doesn't quit and it does not suck any air thru the black hose below the iac and The butterflies are fully closed, Doesn't this indicate a vacuum leak? Is the engine supposed to quit when the iac is disconnected? Is the IAC supposed to close when the engine is given throttle?

 

Mods please move to appropriate forum. Thanks.

 

Moved to 1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks forum

 

Looks to me like you have a vacuum leak. The engine should idle in the 500 RPM range or stall with the IAC disconnected.

Have you checked for codes (KOEO & stored codes)?

When did this problem start? Any parts replaced previously?

Age/miles on the plugs,wires,cap,rotor and filter?

 

Define "lacks power". If you are wanting it to go up the hill without you giving it any gas or kicking out of OD, that you will not get.

 

Sure you can... Depends on how fast you're going though. If you're turning anywhere above 2000 RPM a healthy 460 will climb most average hills like they aren't even there.... That's the upside to owning a torque monster....

 

No codes others than 111 1 111

I just got the truck.

170,000 miles all the normal
stuff is newer. Plugs, wire, cap, rotor.
Fuel regulator checks out ok.
After cleaning the IAC it seems to adjust idle quicker when putting it into gear. It drops quite a bit when you disconnect IAC but does not die.

 

Moderate hill, empty truck, struggling to stay above 55mph. It will downshift. Trannys not slipping. It's like it's timings retarded. When I tested the TPS unplugged with one lead on the center wire and the other lead on the left side I see full range or basically no glitches as I turn the TPS ****. like an ohm meter on a potentiometer. When I check the right side I see full range then it cuts out about 3/4 of they way thru the TPS rotation. Is that supposed to happen?

 

How new? Have you pulled the plugs to inspect them?


Please define "ok"


You previously stated with the IAC disconnected the idle RPM was 750. That's way too high. Inspect the throttle stop screw for signs of tampering. If that checks out then you have a vacuum leak somewhere.

 

I always test the TPS voltage output. Test it with the Key On Engine Off.

Some reference material of how the TPS operates: TPS

 

I'm going to check it plugged, key on, in as you suggested. Thank you!
Below is the most thorough and easy to understand video on TPS testing I've found. Being Half color blind is a pain.

 

Nice light brown, gap within specs. They must have replaced in the last year.

I'll check it again. Plates look closed to me, the screw was barely doing anything, plates were at full rest/closed position. I am suspect of a vac leak but I've looked everywhere concerning a vac leak.

Fuel regulator vac hose was disconnected while I had the gauge hooked up and it ran up the pressure to within specs.

 

Original and stock Exhaust?

Catalytic converters 18 year's old?

Perhaps you have a restricted exhaust? That would give a sluggish engine when trying to climb hills with added rpm and not achieving it.

As was asked earlier, what fuel psi did you record as being ok?

 

What was the PSI at idle w/vacuum hose on? Hose off? Under load?

 

I suspect multiple issues here. If the truck has been running lean the converter is probably toast. One step at a time.....