Hesitation under load

[gogogsr]

Hey guys, my ex as 300,000 km on it and it's a 93 V6 4.0 L 4x4. Recently while i was driving low fuel it started buck, so i went and fill the tank and problem was solved, for now (i thought, bad fuel). 30 minutes later same thing happened, the check engine comes on and off and its only happening when i run under load. When the truck is cold it looks fine its only after a few minutes of driving around. What do you guys think it could be? i'll change the fuel filter this afternoon. Thanks alot guys

 

[MrShorty]

Because the CEL comes on, I'd probably start by pulling codes (see the stickies in the EEC-IV forum). I'd probably also put a fuel pressure gauge on it and see what the fuel system is doing when it acts up.

 

[gogogsr]

ok, so i did check the codes and i got code 522 and stored 172-176-185-186. I dont know code 522 but i checked the 4 others and they are all related with fuel. Would bad fuel be a cause?

 

[Iron Weasel]

DTC 522
Vehicle not in "PARK" or "NEUTRAL" during KOEO or Park/Neutral switch circuit open.

DTC 172
Lack of heated oxygen sensor switches indicates lean (bank # 1).

DTC 176
Lack of heated oxygen sensor switches, indicates lean (bank #2).

DTC 185
Mass air flow lower than expected.

DTC 186
Injector pulsewidth higher than expected or mass airflow sensor lower than expected.

To emphasize what MrShorty said, you should hook a fuel pressure gauge up to it. Also check for vacuum leaks and make sure you aren't getting any unmetered air into the engine. An easy way to do this is to take a can of carburetor cleaner and spray around the vacuum hoses, throttle body, and intake manifold - if the RPM's increase as you do this, you found a leak.