so the history:
'95 F250 302 EFI 5-speed 2wd standard cab
recently tuned up with: 6litre tune up, Motorcraft plugs over gapped, timing to 16*, new fuel filter
air pump removed, cats hollowed with Thrush welded muffler, MSD iggy box added, new coolant temp sensor, new ignition control module, new TPS, cleaned throttle body

so it's been having this problem since September and all these parts/fixes have been done since and haven't fixed it: as i cruise at highway speed and HOLD the throttle steady around 70+mph, i get a sputter and jerk in the motor. if i speed up or back off it's fine. if i try to resume 70-75mph (haven't tried it going faster), the problem comes back. i figured once the PIP was replaced just 2 weeks ago that the problem would finally go away, but to no avail!

any help or pointer is greatly appreciated! my mechanic is a good friend of mine with all the gadgets, but he's stumped as well. oh, no engine light or codes present either.

thanks, y'all

 

Have you pulled the plugs and examined them? Your problem sounds like a lean miss and the plugs will show that.. all of them white is an overall fueling deficiency(old O2 sensor) or an air injection system leak(valve or crossover tube behind the motor), while if only 1 plug is white the corresponding injector is dirty. The other possibility is crossfiring plug wires or arcing to a metal part of the motor.

 

A dead spot in the TPS could cause an issue like this too. It might be worth a quick look at the TPS resistance or signal voltage through the sweep of the throttle.

 

TPS would be a good guess.

 

2X

or VSS

If you have cruise control get it to the point that it acts up and then set the cruise. If it still acts up then the TPS is not the likely issue.

 

thanks for the suggestions. it couldn't be the cruise control because the truck isn't equipped with it.
honestly, the TPS wouldn't surprise me at all. when i originally changed it back last October, they sold me a dud and i had to replace that one as well. worth a shot at this point. how would i test the resistance? (be kind, i'm not the mechanic)

 

I wasn not suggesting the CC as the issue. Those with a CC can set it and when you do it takes the TPS out of the picture. Then if it does it, its not the TPS. Its a quick check verse the voltage testing.

I have a TPS testing procedure some where but I have to run. Later on I can post it if no one else steps up by then.

 

i have to ask how the cruise would elimnate the tps since the cruise pulls a cable that moves the throttle body that operates the tps ?

 

ah! i get what you mean now.
had done the voltage testing prior to installing it right from the box since the previous one crapped out as it was brand new. worked then, but you're saying it should be done through the entirety of it and not just closed and wide open??? <---- if i understand correctly

 

Pretty much. You should also perform a bump test as well and connection wiggles while your at it.

The warm idle voltage should be .65 to 1.27 or so
The chart is basically linear in that WOT (76%-94%) is about 4.5
So 37%-47% TP should be in the range of 2.25


CIRCUIT / PIN / WIRE COLOR

SIG RTN / 46 / gray/red

VREF / 26 / brown/white

TP / 46 / gray/white

Basic TPS bad test
Key "OFF".
Throttle Position (TP) sensor disconnected.
Key "ON", engine "OFF".
Measure voltage between VREF circuit and SIG RTN circuit at the TP sensor vehicle harness connector.
Is voltage between 4.0 and 6.0 volts? If so replace TPS

Add on- Instead of trying to drop my PDF's in here.
http://easyautodiagnostics.com/ford_...tps_test_3.php