My 92 f150 has been running rough at around 30 to 40 mph and around 60 and 70. It has a 5.9 v8. I have recently replaced the plugs, plug wires, dis cap, and fuel filter without it helping this problem at all. Someone said this could be my transmission or throttle body. Any ideas?
How did the plugs look?
Pour a bottle of Chevron Techron in the tank.
Test the fuel pressure and compression.
A couple of the plugs looked bad and a couple of wires but thats it.
They did make the engine run a little better but it didnt fix the problem. And how do you test your pressure and compression
Define “looked bad”. Use the attached chart.
Fuel pressure is tested with a “fuel pressure test kit”, which is basically just a fitting with a pressure gage constructed of materisla impervious to fuel.
A compression test is performed with a “compression test kit” is basically the same thing excpet the gage is an air pressure gage and the fitting is designed to interface with the sparkplug holes.
In both cases instructions come with the gage.
Post back a sto how the “bad” plugs looked. The condition of the engine’s internals can often be determined just from this evidence alone.
they just looked exactly like dry and wet fouling
That would suggest that you’re burning oil in those cylinders. Allow me to suggest a compression test to see if those cylinders are wearing out. At 19 years old, I would not be surprized. Post back with the readings.
Well if they are then what?
“then what?”
Rebuild or replace the engine.
Or just accept the rough operation at those frequencies.
But first find out.