1989 k-5 350 tbi idles fine and revs up fine in park or neutral, put in in gear and step on the throttle then it acks like half the plug wires got pulled off it does not backfire but acts like its starving for fuel. It started running like this overnight, ran fine when parked 1 night then ran like this when started the next morning for work. Can a in tank fuel pump run with enough fuel to idle and not supply enough to run properly under load.

Thank You
wrencher73

 

When was the last time you replaced the fuel filter?

 

Replaced filter the same day and it did not help

 

The fuel demands are not that high on the TBI motors, but they do require 8-10psi of pressure. So that would be one place to check.

 

Check your fuel pressure. I have a lot of people insist on changing the fuel filter, but have never seen it help in most gasoline engines that utilize in tank electric fuel pumps. It almost sounds like you do need a fuel pump. I would suggest performing a fuel pressure test to confirm, though. It is some what common for a bad fuel pump to work ok under no load (like revving the engine rpm), but stumble badly when put under a load (like when put in gear)

 

Thanks for the input I will try that next, The manual says 9-13 lbs fuel pressure is that about right.

Wrencher73

 

8-10psi is typically where they are set.

 

about your fuel pump volume delivery question the answer is YES!!!! I have a 91 full size blazer 5.7L TBI and it started acting up once every couple of weeks like it was trying to cut off just for a second or two and then finally the fuel pump went out about a mile from home, it would fire up and idle but as soon as i would just barely touch the fuel pedal it would stall, it is hard to just look at the injectors spraying fuel into the throttle body with the breather off, because it looks like it plenty of fuel going in BUT IT'S NOT, i didn't have my fuel gauge with me at the time but i did have a can of flammable gum cutter and when i would throttle it up by hand while spraying gum cutter into the throttle body it ran fine but without the gum cutter it would shut off, not saying this is your problem but maybe you can try what i did because it's a fast easy test to determine if it is the filter/fuel pump or both.

GOOD LUCK

 

I betcha it'll help if your Fuel Filter is gummed up, its worth taking off and making sure before you go off and buy more expensive parts.

I agree with Kyle, check the pressure...
I had my fuel pump go out and when it did I could listen to the pump try and compensate for the fact that it was gummed up. Apparently the plastic filter on the bottom of the In Tank Fuel Pump had desentigrated and clogged it up.

 

ended up being a bad fuel pump, only had 6 lbs of pressure. after dropping fuel tank and replacing fuel pump, pressure jumped to 12 lbs and truck runs great.

Steven K.