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Starting Problem

98CherokeeClassic

NAXJA Forum User
Location
North Carolina
About a week ago m 98' 4.0 inline6 crunk up and idled really low and rough. I cut the jeep off and after a few minutes i turned the key again an it cranked up and ran just like normal. Then the next day i drove it to town and back without any problems, but then that night it i crunk it up and it idled low and rough again, then i cut it off and tried to restart it a couple times and it would fire, run for about 2 sec. then cut off. after 4 or 5 tries it wasn't even firing so i figured fuel problem. i replaced the fuel pump and both strainers and still nothing. i pulled the plugs and they all look fine and i'm getting spark. anyone have any idea what this could be?
 
Hallo. Maybe an old classic CPS (Crank Position Sensor) sensor is getting tired.:rtm:
But if that is not the case, you can also bye a fuel pressure gauge and test the fueldelivery.

p.s. All the relays and electric connectors (TPS,MAP and CPS) ok?

'92 XJ
 
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If your IAC is stuck shut (or just sticky), you can often get it to start using around 1/8 th pedal. Though it will likely stall again as soon as you release the pedal all the way. IAC sometimes gets sticky and starves the motor of air at idle.
Sometimes after it warms up the gunk causing the IAC to stick softens and regular function will return.
This can also be a sign of low battery function, a marginal battery may not have enough juice to start and at the same time adjust the AIC. In my experience the AIC needs all the juice it can get to function properly, especially when it's gummed up.
Once your plugs get fuel fouled, starting can become really iffy.
 
If you have spark, it shouldn't be CPS. IAC seems likely, can be tested with voltmeter. After cranking, if you pull a plug, is it a little (at least) wet with gas? Check for 12V at injectors. PCM completes ground when firing injectors, but should have constant 12V when key is on.
 
Alright, replaced the Crank Position Sensor and Fuel Pump and both strainers. Also bought a new fuel pump relay for the under-hood fuse panel. The fuel pump is not pumping fuel with the old or new relay in, but took a test light and found one hot female connector for the relay and used a jumper wire to send back power into another of the female ends (by-passing the relay), then the fuel pumps starts pumping fuel and the jeep will then start and run fine. so, what can be wrong now, are both the old and new relays bad? Throttle Position Sensor (TPS)?
 
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Ok, so the primary circuit is good, i.e., there is B+ and you can jump it and the pump runs.

So, your other part of the relay is the triggering circuit, requires presence of a ground and voltage. Check the ground, and if good check the voltage side.
 
Ok, so the primary circuit is good, i.e., there is B+ and you can jump it and the pump runs.

So, your other part of the relay is the triggering circuit, requires presence of a ground and voltage. Check the ground, and if good check the voltage side.

ok, so when looking at the fuse block from the passenger fender, the top and right both have power when the keys turned on, the bottom one is grounded according to my multimeter, but not getting a ground on the left prong, where could the ground be disconnected? also, every fuse in both inside and under hood fuse panels are ok.

thanks for all the help so far, gotta get this thing running by tomorrow though
 
The fuel pump relay has two circuits. Hopefully your wire colors are the same as my 2000. The circuit that you jumped to make the pump run before should be from fuse 22 (under the hood) to the relay to the pump. The circuit that activates the relay comes from fuse 11 (fuse box inside vehicle near passenger door) when the key is on, and is a darkbrown/white wire to the relay. The activating circuit ground then is a brown wire to the PCM. It will not ground (activate) until the PCM makes it do so. Check the wires and plugs in this circuit. If you ground that wire to the body or engine (temporarily), it should make the pump run.
 
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