fuel problems

[aaron71white]

I have a 94 gmc sonoma with a 2.2l 4 cyl. i am having problems with my fuel system. when i first crank the truck it does fine. when i drive about a mile it starts running rough. it really seems like the truck is lean of fuel. the truck starts missing and kind of jumping, but it is only when i accelerate. i can turn the truck off and crank it up and it runs fine for about a mile. there is new filters, fuel pump, sending unit, fuel pressure regulater, spark plugs and wires. when i put the new fuel pump on it ran fine for about two day, then started running rough again. i have put the truck on a diagnostic tester and no codes are being read. any help with this problem will be greatly appreciated.

[blazes9395]

This sounds like when the on board computer is running in open loop, your not having any problem, but when it goes into closed loop, you start having trouble with it. It takes about a mile or so for it to go in closed loop. When the ECM goes into closed loop, it then uses information it is getting from the oxygen sensor to control fuel delivery. In open loop it doesn't use the O2 sensor for feedback. Take a look at the oxygen sensor and see what its doing. It could be a lazy sensor, not causing the SES light to be set, but still bad enough to cause driveability problems.

Either way, before you change it, get a scanner on it and see what the sensor is doing when it is in closed loop.

[aaron71white]

Thank you for some help. i just put a scanner on it and its not saying anything is wrong. today i found out that i hane an exashed leak toward the tail pipe, would that have anything to do with it? what throws me off is, when i put a new fuel pump on the truck, why did it run good for a day or two and then start acting up again.