Hi, my mustang 1994 V6 with manual transmission has weired problem. It comes and goes, sometimes when driving over a bumpy road it will happen.
Mostly it runs well. BUT sometimes stalling suddenly happens and my mustang has very few power. Even it cannot go up the hill. If I floor the gas the car wont go but if I ease on the gas the car starts to build revs. The engine check light comes on but then it goes away. It has a Predator chip in the ECU from the previous owner and my OBDII says the check engine light is from a too rich fuel mixture. I think the chip might be messing up the fuel mapping. Can I just remove the chip?? My car also has an aftermarket exhaust so could the O2 sensor be malfunctioning? All of this work was done by the previous owner and I bought the car from a dealer so I have no way of getting in contact with the previous owner.

I already changed the coil pack, spark plug wire, and crank angle sensor.
When I turn the ignition the fuel pump keeps making noise before I start the car and the radiator fan also turns on even when the car is cold.

 

Using the correct octane gas for the tune?

 

Thanks for your replying!
I do not know what the correct octane gas is, but I often put 93 octane gas. My mustang gets hesitation no matter what kind of gas(87, 89 or 93) I put.

 

Ah. (3 octane is the hardest to burn. The higher the number the harder to ignite. But since it does it with all then *shrug* sorry.

 

Sounds like too rich gas to spark when this hesitation happens. Black smoke comes out from muffler and i checked the plugs. The plugs were wet with gas.
l cleaned injectors by putting chemical in vacuum hose. But it did not make any difference