My truck is a 1986 F-150 2WD, 302 EFI, dual tanks, auto, with 166M miles.

Normally, I just turn the key to start it up but recently had to depress the accelerator slightly to get the engine to fire - truck then coughed and sputtered like a carb vehicle in which the choke was not working.

Have replaced the air filter, breather element, hi-pressure fuel pump mounted on the frame rail, distributor cap and rotor (tip was corroded), and spark plugs (plug wires are fairly new and inspected ok).

Removed and cleaned the EGR (replaced the gasket where it mounts to the TB), and removed and cleaned the IAC.

Also inspected the vacuum hoses but found no leaks.

Got a code reader today - no DTC's on the KOEO test but did get a 31 on the Continuous Memory test.

After installing the plugs today, I started the truck and it again mimicked a carb'd vehicle with a choke malfunction (coughing, sputtering, wanting to cut off).

Kept it running by patting the accelerator.

The longer it ran the less it sputtered and finally after about fifteen minutes it would idle without my patting the accelerator (though it still shook slightly).

Drove it around the neighborhood and it shifted very roughly but the engine seemed fairly smooth after the tranny shifted to high gear.

Wondering if maybe the fuel filter has become clogged (it has been changed maybe a year ago) or if the in-tank pump is contributing to this behavior.

Sure appreciate any help.

Thank you.

Tom

 

Change the fuel filter and check the fuel pressure.

 

Even though you cleaned the IAC, it may no longer be functioning properly. Did you also clean the T/B with coating-safe T/B cleaner (not carb cleaner)? What you're doing to start it indicates a problem with one of the two devices. Check the adjustment of the TPS; if it has moved, you're going to be chasing this thing for a very long time if you don't you get it re-adjusted

 

When cruising does the truck "buck" at all? Thats a good sign of the TPS being an issue. But first check the fuel pressure, its easy and will either eliminate one possibility or get you on the right track.

 

89 - Changed the fuel filter today; made no difference. Please explain more about checking the fuel pressure. Have not driven it out of the neighborhood yet so unsure about the "bucking" at cruising speed.
Strange - Changed the IAC today; made no difference. Also replaced the EGR but no joy. TB was cleaned by mechanic not too long ago and it appeared ok on inspection. Bought a TPS today but yet to install it. Unclear about "adjusting" the TPS - looks like the TB must be removed to replace the TPS so how would I "adjust" the TPS after it is changed and the TB reinstalled?
Thanks to you both.
Tom

 

The first thing I'd suggest is replacing the FP & EEC PWR relays. They're known to cause this type of problem, so it's a good upgrade even if it doesn't solve the immediate issue. For more info, read this thread.

You replaced the frame fuel pump, but what do you know about the in-tank pumps? Crawl under the truck & unplug the high-pressure pump. Then jumper the FP relay pin in the DLC (shown at the bottom of this diagram) to ground, turn the key on, and listen to the selected tank for that in-tank pump. Switch tanks & listen for the other one. You can also disconnect the line from the BACK of the hi-pr. pump & see if there's any flow (it's only ~5psi there), but use a catch-pan & have a fire extinguisher handy. Then reconnect the hi-pr. pump & remove the jumper.



Ignore the rest of the diagram - it doesn't apply to your truck. Only the bottom panel is correct for you.

If you get no flow from the disconnected fuel line on one or both tanks, it's possible that the dual-function reservoir (the black plastic bottle on the frame) is jammed. I've heard that they can be disassembled, cleaned, & repaired, but I've never done it. A user named Sixlitre on FSB has described the procedure, so you can probably search it up there if you decide you need to.

To adjust the TPS, loosen its screws & use a digital multimeter to measure its output, then twist & tighten it down to set it within this range. Then check for a smooth progression throughout the range of motion.

 

Steve - Very helpful response. Read the thread on replacing the FP & ECC PWR relays. Having trouble locating them. Haynes states the relays are located in a "power distribution box in the engine compartment on the left side fender apron" but I have not been able to find such a box. There is some wiring / connectors laying on the fender well below / in front of the master cylinder - are these the relays? Concerning the in-tank pumps, will try your test procedure (front tank has not worked for some time though I did replace the "dual function reservoir" a year or so ago in trying to get the front tank working). Really interested in the TPS issue as I have a new TPS ready to install. It appears the TPS is mounted to the bottom of the TB held in place by fasteners that go vertically into the TB with very little clearance below the fastener heads to be able to turn them after the TPS is installed on the TB and the TB mounted back to the manifold. Do you adjust the TPS after mounting it to the TB but before remounting the TB to the manifold? Finally, reading the TPS voltage diagram, it appears I need to adjust the TPS to a voltage of 1.2 volts with KOEO then tighten the TPS fasteners? Am I getting this right?
Thank you.
Tom

 

You're reading about the trucks that already have the new-style relays. Yours are like the first photo, so they should be in front of the MC. But they might be on the R wheelwell closer to the battery. They're not visible in this pic, but look around here.



They could also be under the dash, which is probably where your EEC is, above the gas pedal. If it's not there, it could be under your seat. Ford was pretty creative with EEC placement on pre-'87 EFIs, which is why I can't tell you exactly where they are. When you find relays that look like the pics in that thread, compare the wire colors to find out if you've got the right ones.

Release the pressure from the radiator first, then pull the throttle body to get to the TPS. You can install, adjust, & test the TPS before putting the TB back on. 1.2V would be at about 13°; at closed, you want 0.5-1.0V .

 

Steve - Good comments. Being cautious, I removed the TB but left the two coolant hoses hooked up. Got some TB cleaner and will clean out behind the butterflies in the TB and throat of manifold then replace TPS. Do I put the new TPS on, connect the pigtail, then back probe the sensor side of the hookup to check the voltage, adjusting the TPS to get to .5 to 1.0V? Sorry, this part of the procedure is a little unclear.
Thank you.
Tom

 

The meter doesn't supply any voltage to it, so yes, it has to be connected & key on. There are 3 wires. One is the VREF circuit, and it'll be either Or/Wh or Br/Wh. Test voltage across the OTHER 2.

 

Steve - Ready to install the new TPS but unsure which wire is which. The three wires from the truck's harness to its connector are orange, black, and green. Three wires from the present TPS to its connector are orange, black, and green. Three wires from new (yet to be installed) TPS to its connector are orange, black, and green. Best I can tell (guessing from the photos in Haynes), orange is what Haynes calls TP Signal, black is what Haynes calls Signal Return, and green is what Haynes calls Vref. The manual's instructions for setting TPS voltage call for "connecting the negative probe of a digital voltmeterto the terminal of the TP sensor with the black/white wire,and the positve probe to the terminal with the dark green/light green wire. So I would be back-probing Signal Return (black) and Vref (green) which is NOT what you instructed me to do. Should it just disregard these confusing instructions and back-probe orange (which I think is TP signal) and black (which is think is Signal Return) for setting the voltage? Thanks. Tom

 

OK, the new TPS is installed. There seemed to be little to no "adjustment" after engaging the TPS's flange with the TB's "paddle" for the butterflies. Checked voltage across black/green wires of the new TPS and it was .993 (manual called for 1.0 volts) so I locked it down. Cleaned TB behind butterflies and throat of manifold with TB cleaner while I had it apart. Reassembled everythihg and started it up. Still acts like a carb vehicle in which the choke is not working but does not require as much "patting" of the gas pedal to keep it running till it warms up. Took it for a drive - the engine revs too much before the tranny shifts but it is dirveable. Got it up to about 70 on the expressway - the engine speed seems to vary when I hold the accelerator constant, like the engine is "searching" for the right speed (failure to "set" the TPS correctly)? It seems each of the things we've done so far have helped the truck run a little better but I don't think we've yet found the cause of the coughing and sputtering. Still open to suggestions. Thank you. Tom

 

The EEC adapts to slight variations in all the sensors, and the TPS is one of the MOST adaptable, so anything from 0.5-1.0V is good enough.

Have you tested fuel pressure yet? Have you found those relays?

 

Steve - Have not checked the fuel pressure yet. Found a relay(?) on the firewall near the brake booster. Relay is labeled E3TB, 9345, A2A and was green in color. Made a photo for your use but am unsure how to post the photo here. Could it be the fuel pump relay?
Also, were the wires I used for testing the TPS voltage (green with positive probe and black with negative probe) the correct ones? Still am unsure about that.
Thanks,
Tom

 

Do its wire colors match those given in the other thread?
Did the reading change per the graph as you moved the throttle?