My '86 F150 5.0 3 speed auto dies at part throttle. It is around 55 mph which isn't good. If I let off or give more pedal it starts running again. Idle and WOT it runs great. I can't tell if fuel is shutting off or if it is ignition. I can't replicate it in the driveway. Some times it doesn't do it. CEL is not on. TPS wearing out??

 

Did you try pulling codes?

 

Autozone can pull your codes, fyi. Free, too. My truck apparently doesn't have a check engine light, so I couldn't do it without rigging up a light for under the hood, and since I was heading to town anyways, I let my friend at Autozone pull my codes. Mines an '86 5.0, too.

 

I have a code reader and nothing showed up the last time I checked it. I only drive it occasionally to haul wood or tools. I'll check it again now that spring has finally arrived here in Ohio.

 

From what my truck has done with a bad TPS, I would think your problem may not be the TPS? Unplug your TPS and see what happens. Mine was stuck idling at 1500RPM, so I unplugged it and set the idle screw and I'm idling at 900RPM now. But, I need to get another one... or can you clean these and usually fix them?

Wow, anyways, I almost hijacked the thread. Make sure your code reader works by unplugging the EGR for a bit, then pull the codes. I unplugged and plugged mine back in within 4 seconds while it was running, of course, and it showed up when I got the codes pulled. So, that should be an easy way to make sure your reader is working.

Otherwise, maybe check over the plug wires, or watch it run in the dark.

 

I just pulled codes again. 23, TPS voltage out of spec, was in the initial codes. 53, 63, and 31 were in the memory. 53 & 63 are TPS voltage to high and to low. 31 is an EGR EVP or PFE sensor voltage to low or EGR not closed.
While trying to remove the throttle body to get at the TPS the lower left bolt is frozen in the housing. That will be fun getting out. At least it is where I can see it. UGH!

 

Check your reference voltage on the EGR position sensor also...although I haven't seen one kill a truck yet, I've seen the EGR solenoid cause a 31 code and really poor running at part throttle. You could have a combination of problems.

 

Well, looks like it's pointing to the TPS. Did the EGR show up because you unplugged it like I mentioned to check your code reader?

Get that TPS out yet?

 

Heck yeah it is the TPS! It wears in the spots you run it most and then you get dead spots. You can't replicate it in a driveway because if you had that much throttle dialed on in neutral it would be reving in the red. You can check it with an old analog multimeter (swing needle type), dead spots will show and the needle dropping to -0- or fluctuations in the swing.

Kenny

 

I did not disconnect the EGR, The code was in the stored memory. I actually have an old style multi meter! I'll have to try that.

 

While trying to take the throttle body off to replace the TPS the lower left bolt is siezed and with very little effort the bolt head rounded off. UGH!!! I'm letting it soak with PB Blaster for a few days. The joys of an old truck.

 

That sucks, man. I just replaced my TPS and, man, I'm back to loving to drive my truck. It sucks driving anything when it has a problem. It'll be worth it.

 

I finally had time to work on it. Still could not remove the stripped bolt on the throttle body so I removed the upper intake. The TPS screw were a pain also. One came out using vise grips and the upper portion was rusted almost half way thru. The second broke. Luckily it came out with vise grips. My Father in law had a TPS from a '86 or '87 Mustang. Put it on and all is well. Runs great again. Never sieze went on the TPS screws and on the EGR nut. I'll clear the codes and run it some and pull the codes again. Thanks all.

 

Well, I guess after all the extra work, having it run perfect again made it worth it. I'm glad I changed mine when I did. It was sucking down the gas with the bad TPS.