volcomstone550

as listed in the title my newly acquired 1992 f150 2wd auto 302 will not rev past about 2000rpm in idle or drive without completely falling on its face(literally flooring the car does nothing but make more noise but produces no power) and bucking horribly and the intake noise changes from a normal sucking sound to a gurgle vacuum noise, the truck starts and idles flawlessly with perfect 10degrees of timing with spout out and advances properly with it in. The Truck is completely un-drivable and only does about 20mph and will maybe slowly gain more speed but any touch of the peddle does nothing.

new parts replaced
new cat
02 sensor
TPS (properly adjusted)
plug wires
TFI ignition module
Reman PCM
new Fuel pressure regulator
plugs not that old
new fuel filter
new upper and lower intake manifold gaskets
cleaned and properly working IACV
new map
new coil

Ran KOEO codes and did KOER codes too. KOEO codes 31 85 33 34
KOER codes 31 25

this didn't really reveal anything that would help my situation,


so my best guess are as follows, MASSIVE air leak causing a lean condition so the truck wont rev, PCM not happy with something and cutting timing, spark, and or fuel.

I tried spraying fuel into the throttle body to see if it would pick up some revs while I was simulating the issue but did nothing leading me to believe its not a fueling issue, also with the fact that the truck has dual tanks dual fuel pumps and both pumps don't change the problem.

ANY IDEAS????

Marc D

Although you have made a huge attempt at repairing your motor, you have spent a lot of time and money and now created an impossible situation. The computer has now gone into a default mode and your original problem is probably not even throwing codes any more. The codes you listed are EGR flow and manifold pressures not fuel.
I highly recommend you take the truck to a shop that can put it on a "Big Boy" computer and find the source of your problem, which may be the computer itself. Good luck

RLXXI

Have you checked all the grounds?


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volcomstone550

well the computer is new. and there is only one setting on the computer. the old computer wouldn't even pull codes and kept the fuel pumps priming all the time. to the best of my knowledge there is no default or limp mode on these computers just one program and it always trys to run that. what is a big boy computer? I don't think there are any better obd1 diagnostic computers than a handheld that really is no better than the paperclip trick and read the cel on the dash

RLXXI

Have you performed a compression check on the engine?

volcomstone550

all the grounds are in place. I could try and add another ground strap from engine to chassis but I doubt that's the issue. the compression should be fine because the truck was running just fine, it was horribly rich and idling very badly before the maintenance but atleast it would drive like it should and had decent power. I have double checked everything I installed and im missing something, it has to be something I did to cause this issue

RLXXI

This is one of those gotta be there with proper testing equipment to determine the problem. You really should start at the bottom and go from there, get a compression tester and make sure all cylinders are at or above 100psi with no variation of more than 10% between cylinders. If that's good then stick a fuel pressure gauge on it and make sure it's around 30psi.

Other than that I would have to have hands on.

Good luck.


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volcomstone550

well the point I am trying to make is that the truck didn't go from working fine to no compression overnight. I thought maybe the knock sensor was putting the ecu in some kind of limp mode but unplugging it does nothing. The truck does cut off immediately when unplugging the map sensor....don't know if that's relevant or not. if I come back with decent compression and fuel pressure whats after that??

RLXXI

As I said it's hard to say without hands on but a timing chain could jump a tooth or 2 on shut down and cause problems that a compression test will reveal.

How many miles on the engine?


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volcomstone550

120k on engine and chassis. all original. I would think if timing jumped it would throw the light off. I will double check that the crank at 0 points to #1 spark plug tomorrow