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jeep cranks but wont fire?

fuelfox4949

NAXJA Forum User
Location
fridley
98 jeep xj, 4.0, auto,

just looking for a good starting point what to look for to get my jeep back up and running this is what happened...

was cruising down the road 55mph on cruise control, then it stuttered so i put my foot on the gas and it had nothing, put it to the floor and nothing happened. it was almost like it was out of gas. yes i have gas in it almost a full tank. so i pulled it to the side of the road and it stalled. tried cranking it over but it would not fire up. put it in neutral and was wiggling the shifter while trying to crank it but that didn't work.

so last night while waiting on the tow truck i was working on it. i turned the key and i could hear the fuel pump prime, i replaced the fuel pump relay/fuse, pressed the schrader valve and fuel came out. all the fuses in the pdc were working.

then i put a plug in every spark plug boot and cranked it and there was spark, i even replaced each spark plug, i tried a different rotor, the cap and plug wires are only 2 months old so there fine as i could tell nothing cracked and contacts look clean,

so i am looking for ideas what to check next, i'm thinking pulling my iac off and trying to clean it? maybe clean my throttle body out however it does not look dirty at all, maybe get a new ignition coil? Cps?
when i turn the key to prime the fuel pump then push on the schrader valve about a 1/2 once to 1 once of fuel comes out, is this normal or should that be highly pressured and more shoots out?

so any help and ideas i can get would be much appreciated thanks fellas!
 
Try shooting some carb cleaner down the throttle body and see if it fires. If you have spark, then pretty much the only thing left would be fuel. It sounds like the injectors aren't firing.

You can get a NOID light to check the drive to the injectors.
 
i checked the ohms of my fuel injectors there all 11.8. i just cleaned the throttle body and pulled the i.a.c out and cleaned that. still no start! i sprayed some carb/throttle body cleaner into it and it ran for a good 2-4 seconds.
does this mean maybe i have a weak ignition coil?
 
i disconnected the cps and tested it and showed no resistances so i think that is not at fault.
im still getting spark in the plugs and off the ignition coil when i ground it to the block.
im starting to run out of ideas i hope someone chimes in soon.
is replacing a fuel pump very difficult? do you have to remove the tank or can it be done still installed? any special tools?
 
Check fuel pressure. Just opening the schreder valve and having some fuel come out won't tell you enough. 97+ you have to drop the tank to change the pump.
 
The most likely suspect is the CPS. It can fail when hot, and test OK when cooled again.

Is the spark bright blue and snapping, or orange/yellow ? The coil can be tested. The fuel pump should be tested before replacing, simply install a tester at the fuel rail and jump the fuel pump relay.

The following have caused a no-start on my various 97-01 XJ's, multiple faulty CPS, blown fuse, dirty/corroded contacts on relays, damaged relay socket that had partial contact. The damaged PDC relay socket took forever to diagnose, one of the relay tabs was cracked. It would sometimes make light contact and sometimes just push away from the relay prong.
 
when i placed a bolt into the ignition coil wire and grounded it to the cylinder head it was yellow/ orange color that leaped a solid inch. im going to get a tester for the fuel pressure when i turn the key i can hear the pump kinda buzz not hum for a quick second.

when i hook a tester to the schrader valve even though the jeep wont start will it give me a accurate pressure reading?
 
connect the tester to the valve and crank the engine. priming the pump should raise it a few pounds, then while cranking the pressure should rise to operating level within a few revolutions and then mostly stay there

you may also have pressure but no injectors firing which is why old_man said to get a noid light, but pressure problems are most common

97+ you have to drop the tank to pull the sender assembly out the top
 
i replaced the cps and that had no effect.
i tried spraying starter fluid into the throttle body and that wouldn't get it to run.
i bought a fuel pressure gauge from harbor freight.
i hooked the gauge to the hose then to the schrader valve, turned the key, heard the fuel pump kinda buzz for a few seconds then it clicked under the hood tried to start it and still wouldn't fire and the gauge needle didn't even move.
so either i got a bad gauge or i am doing something wrong.

tomorrow i plan to go to autozone to rent an actual fuel pressure gauge from there and see if that helps. fuel is just trickling out of the schrader valve when i depress the check.
 
i had about half a tank and stopped and filled it up. then i took off down the road, 10 miles later is when it died so i know it had fuel in it. i never let my tank get below half full due to Minnesota winters.

yeah i cant get the fuel pressure gauge to even move so i think the harbor freight gauge does not work. or maybe the psi is that low? i will get a different gauge tomorrow when autozone opens.

checked all my fuses and relays again under the hood and under the passenger side.
 
i put the gauge on a tire and it worked. so I'm not getting any pressure from the schrader valve, which leads me to believe that the fuel pump is shot.

i traced the fuel lines to make sure none of them were leaking and thats why i have no pressure. but i could not locate any lost fuel.
 
yes i just ordered a Bosch whole assembly should be here this week. i should hopefully have it together by next weekend.

if it fixes the problem i will be sure to reply and let others know in hopes of helping them as well...
if this does not work i shall be back very angry!!! hahaha
 
so after i installed my fuel pump i am now getting pressure at the schrader valve, tomorrow i will try to get a pressure reading.
the jeep fires up.... but only if i hit the gas! i have to keep giving it gas tell it warms up then it sits and idles between 500 and 600.
sometimes it dies, sometimes it runs. so i am back to confused.
i cleaned the throttle body and i.a.c for the 3rd time. my i.a.c does not look bad but i will be trying to replace it out asap. also put in a spare tps but that did nothing for it.
i cleaned all the grounds in the engine bay, checked the fuel lines for leaks, and was looking over vacuum lines cracks but found none.
i put a spare cps in and it would not idle at all and thru a "cel" so i put my original back in and the "cel" went away and idled on its own when warmed up.
i may possible put my old 02 sensors in and see what it does. i put in new ngk in august last year.
the battery was disconnected for almost a week so i figured it would take a couple warmups for the pcm to learn. could this possibly be the reason to have to give it gas to fire it up?
once again any suggestions would be great to hear. thank you
 
....the battery was disconnected for almost a week so i figured it would take a couple warmups for the pcm to learn. could this possibly be the reason to have to give it gas to fire it up?

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging.

Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem.

The symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal.

The ECU will relearn the idle settings after a short period of driving and the engine will start and idle normally.
 
yeah Tim i had the negative battery disconnected for the week. i just took it up and down 610 highway to get some miles on and let it learn and run.

i figured it was in relearn mode i just never had a jeep [this one or my old blue XJ] that i had to give gas to get it to fire and run.
i stopped at the store it was idling in the high 600s came out and started it with out giving gas and it barely got going before it started idling again in the high 600s.

I'm going to let it cool down and take it for another spin a little later today.
 
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