1996 Jeep Cherokee 6 cyl Four Wheel Drive Automatic 100200 miles
After sitting for any more than a couple hours my Jeep lags, and feels like its almost going to stall when I turn it on and hit the throttle for the first time. After this occurs, it picks up after the initial lag and will run fine. If I run it then turn it off and let it sit for a few minutes it will accelerate fine at first, but then a few hundred feet up the road the lag will occur. Again, after this brief lag it runs fine.
Basically it seems like there is air in the fuel line, and my only thought is the fuel pump is going bad.
I got curious and after sitting for a few hours I started the Jeep up, and while it was out of gear I applied some pressure to the throttle. RPMs rose, and when I pulled out there was no lag. Any chance this helps to narrow it down? Any other simple tests I can run with minimal tools?
To rule out the fuel pump you need to check the fuel pressure other things that can caused your problem as follows: Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)
Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include: Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires