I have an 89 2wd, 6cylinder 4.9 eng. The truck runs good and cranks good, but I don't know why my truck shuts off while driving, especially when in passing gear it seems to wanna shut off around 55 beyond. Idk what to do I've dropped the tank cleaned it and got new master fuel pump, new fuel relay and fuel filter. And it the problem still persists. Note right before it shuts off in passing gear there's a loss of gas and the truck jerks a little. And if I stop before it shuts off it'll remain running. I really dunno what to do atm.

 

Have the codes read, some auto parts do this for nothing. Get back to us.

 

Funny how it's 55MPH, that leads me to believe the cat could be partially clogged. How is your fuel mileage? Does the engine "breathe" well when putting the engine under a heavy load at lower speeds?

By removing the O2 sensor and try to replicate the symptom. If the symptoms go away with the O2 sensor removed from the exhaust "will let excessive backpressure escape," your cat is clogged. With the PCM stuck in open loop, it's going to run a little rough and rich so keep that in mind.

 

Could it be a bad alternator?

 

i am haveing the same issue i have an 89' v8 5.0L and when it first started it was about when i hit 55mph but now its whenever i try to accelerate and it sounds like it backfires but im not sure if it actually is, i have replaced the fuel injectors all 8 of them cleaned the spark plugs and replaced a fuel regulator. do you think that it is still the o2 sensor? when it is in neutral or park i can rev the engine just fine no issues but when its in gear i get this issue for reverse or any drives. it can get going just fine when i idle but once i apply the pressure to the gas pedal it wants to die out

 

Remove the O2 sensor from the exhaust and engine harness, if the problem goes away, replace the cat or whatever is restricting the exhaust.

 

You guys need to check your fuel pressure.

 

Seen this movie w/ my 87' E-150.

 

those specific symptoms are just screaming clogged exhaust, 51% probability I say

 

My truck does close to the same thing and I know for sure it's not the cats.
My fuel pump is getting weak.