I have a 95 jeep cherokee with a 4.0 high out put eng fuel injection, the injectors are good, I have changed the pluges,wires,cap,and rotor. and replaced several vacume lines and still I have a problum. after I drive and the motor heats up it will not start normal I have to use flooding start by holding the gas pedal to the floor once it starts with pedal still on the floor I get a rough idel and black smoke out the exhaust. but when it’s cold it starts great. I also get some hesatation when I take off from a stop, and also when coming to a stop some times it will not kick down to an idel it will try to run and I have to shift to neutral and it will then kick down. I think it might be the fuel pressure regulator but Im not sure?
An easy check is to use a fuel pressure gauge on your truck. Does it have a fuel pressure test port? I know GMs and Fords do, and it is extremely convenient when looking for fuel pump and regulator problems. This will at least confirm fuel pressure problems or not.
pushing pedal to floor clears flood,so i agree you have too high F/P.AND CHECK FOR CODES.fuel trims should be through the roof,and crazy O2 readings
It could also be related to the cold start system. I don’t know if your car uses a coolant temp sensor or a separate enrichment valve, but either one could cause your problem.
Yep, it might be the fuel pressure regulator; but, how’s a person to know? One way is to measure the fuel pressure with a gauge, with, and without, the vacuum hose connected. How does one do that? Follow the instructions in the Haynes, or Chilton’s, repair manual. It’s not free; but, it’s much cheaper than one fuel pressure regulator.
You’ll, also, need to check the idle control motor, and the MAP (Manifold Absolute Pressure) sensor [a sort of vacuum sensor], and the engine coolant temperature sensor (cts). These require the use of an inexpensive tool (less than an idle control motor)— a “voltmeter” (electrical digital multimeter) to measure ohms and volts.
Also, use a carb/throttle body cleaner to clean the intake tract, idle passages, throttle plate and bore.
To check for a bad fuel pressure regulator, run the engine for a minute and turn it off. Now remove the vacuum line from the regulator. If gas leaks out of this connection, the regulator is defective and requires replacement.
If the regulator checks out fine, then check for a faulty coolant temp sensor for the computer, or a defective thermostat that’s stuck open.