hey all,

i just came back from a trip through yosemite with my 1994 super cab f150 4x4 351 3speed with od. it has a camper shell. going on the flat highways it was just fine, but once i got to the mountains, i started to have some problems that i'm hoping you will be able to help me diagnose.
going up gentle inclines i had a hell of a time keeping it in od: the truck just didn't seem to be able to keep up speed so i would have to shift to 3rd, either by turning the od off, or by gassing it. on the steeper inclines i even had to shift to second (by putting the pedal to the floor) and even then the truck couldn't go that fast. it felt like my parking brakes were on (they weren't) or i was pulling a trailer ( i wasn't). it got so bad that today it overheated. at one point i was having a hard time overtaking trucks that were actually pulling trailers. needless to say, that was embarrassing.
another symptom was when it shifted from 2nd to 3rd, or from 3rd to od, and the rpms were at the lower range of the gear i shifted into, the truck would start shaking. the shaking would stop when i got it to downshift to the lower gear. i'm not sure this makes sense, so please let me know and i'll try to elaborate.
i'm getting pretty poor gas mileage, like 10-13mpg. i have knobby all terrain tires.
i had the transmission checked by a couple of transmission shops and they said it's okay.
i recently changed the spark plugs, wires, cap and rotor.
please help; i want to use this truck to take my family and me and a trailer to baja california and back.

thank in advance!

 

oh, and all 8 of the old spark plugs looked nice, besides having a .08 inch gap (just a little light tan coating) when i removed them.
the other thing i did on this truck is change the rear drive shaft u-joints.

 

Sounds like your saying that the motor lacks power. Hows the fuel filter, what gap you set on the plugs, what about the air filter, do you have/borrow a vacuum gauge?

 

Where do you live?

I'd start with checking the base timing, look for a vacuum leak (start with a vacuum gauge reading), fuel pressure, and correctly gapped spark plugs.

 

You also may want to check the fuel pressure and pull the codes from the computer ( codes can be set without the CEL coming on.) Last but not least do a compression or leak down test.
regards
rikard

 

thank you for your responses!

i gapped the new plugs to .044 inches. i live in the bay area, but noticed the problems when i was up in the sierra mountains.

sounds like the general consensus is to do a vacuum test? how is that done?

thanks!

 

double check you got all the plug wires routed correctly. I messed this up myself recently, truck would run fine on the flats, but put a load to it and it would stutter and had definitly low power. Turns out i had 2 wires switched.

 

You may be able to borrow one from a place like Auto zone, or buy one under 30. bucks. Warm the truck up, turn her off. On top of the intake there should be a capped vacuum port, hook the gauge there and restart the motor. Look over here:
Reading your vacuum gauge

Vacuum Engine Timing | MILEPOSTS Garage (Tech Tips) I do this, but a timing light may be better for you, just ignore the carb talk.

 

thank you blue rebel, i changed the wires one by one. so i didn't number them (the replacements were not labeled). but if i did in fact mix them up, how do i check for that? i know the cylinder numbers, but i'm not sure i remember them on the dist. cap.

i suppose a shop could look at it and tell me pretty easily.

 

i will do a vacuum test. thanks slip ford man.

 

Here you go:

 

wow! thank you so much. hopefully my wallet's sake (or not, for my ego's) that's the problem.