Hey guys, I am a noob to this board, but have been tinkering with engines for awhile. But this problem has me stumped.

302 in an 86 4x4 F-150. It has a really rough idle and no power. Someone had told me it was the cats So I cut them off and the problem was still there.

I pull the codes and was given this list: 31, 21, 51, 53, 63, 22

I have checked each sensor they correspond to and they all check out. EGR was hung up, but is fixed now.

Could I have fried my Computer??

Thanks

 

I doubt it's the computer. Clear all the codes drive it and see which ones come back right away (hard faults). Could be something like a vacuum leak.

-Jon

 

yea most of these codes seem like sensors that where unplugged with the key on evp sensor, ect sensor, tp sensor, and map sensor. i would clear codes and see if they come back. i think this is done by removing STO connector when codes start to flash CEL lamp.

the evp sensor that monitors the egr operation could be bad those things fail most often.

 

Based on the description of the idle, I'm putting my 2 cents on an egr valve that's stuck open.

 

If all those codes do come back i would be looking for a broken engine ground wire.

-Jon

 

Cleared the codes a couple of times.

The TPS and EGR related codes always come back. And others pop in and out.

EGR was stuck. Fixed it up and still runs rough. I will check out the engine ground.

Thanks

 

A bad tps, or one that's out of adjustment, can cause the symptoms you describe. As far as actually testing your TPS, this is best done with a DMM that has a bar graph, but any MM will work. Disconnect the TPS from the harness, and attach your meters pos. lead to the Green wire pin, and the neg. lead to the Black wire pin, at the TPS connector. Set your DMM to ohms (4k scale), and rotate the throttle slowly by hand. Observe the DMM. It should increase and decrease smoothly with the throttle opening and closing. If it jumps around at all, replace the TPS. If it passes, before you hook it back up, turn the key "on" and measure for voltage (20dcv scale) between the orange wire and the black wire at the harness connector. It should be 5.0vdc (+/- .4vdc). Turn key "off".

Bring engine to operating temp., and shut off. To adjust the TPS after it's in place, you will need to access the green wire while the TPS is connected to the harness. You can try to backprobe it with a DMM lead or pierce the wire with a very small safety pin. Attach the DMM pos lead to the pin (or backprobe), and the DMM neg lead to good engine ground. Turn the key "on". Set your DMM (to 20vdc scale). With the throttle closed, at idle, the DMM should read no higher than .95 vdc and no lower than .75vdc. If it does not fall within this range, loosen the two TPS mounting screws and rotate the TPS as best you can until you reach that range. Sometimes the plastic openings on the TPS need to be widened to allow more movement. If and when the TPS falls within that range, slowly rotate the throttle, while watching the DMM, to WOT. It should rise smoothly, and read over 4.5 vdc at WOT.

Take care,
~Chris