my jeep has me so confused with this starting issue

well my 93' xj is having issues. it wont run for long periods of time i can start it and itll idle every other time theres no pattern, but if it doesnt itll just crank, start and idle roughly for 2 seconds then die, continiously, over and over. then if i wait a little bit i can hop in and itll idle for 10 minutes perfect. like i said theres no pattern and i dont know wtf is going on. if i push the fuel pressure schraeder valve it squirts when the trucks on but when i crank it trinkles out. but if my fuel pumps bad then why the hell would it run every other time pretty good? its been like this since i bought it and the previous owner said the distributors bad so i replaced it because it wouldnt start AT ALL and now it does but its having these idling and staying running issues. any ideas?

It may be delivering enough fuel for idle but no more. Get a fuel pressur tester and check it.

hey a 4x4 shop owner and i were just talking about this same problem, exactly the same problem and he told me what it was and i forgot, e-mail me or pm me so i wont forget and i will talk to him and get back with you on monday, Todd

Instead of randomly throwing new parts at the problem, begin a logical and methodical process of troubleshooting and diagnostic testing. Start with the simplest and most basic possibilities, eliminate those, and work your way through the usual suspects.


Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. Jeeps do not tolerate low voltage or poor grounds. Disconnect, clean, and inspect all the wire harness and sensor plugs.

Gas in the tank ?
Unclogged fuel filter ?
Fresh tune up parts ?
Tested the battery and alternator ?

Once the basics are proven to be good and not the cause of the problem, test your Crank Shaft Position Sensor.

gas in the tank fuel filter fine fresh tune up parts and the battery and alternator are good. AND i put in a new crank shaft position sensor so..im confused. sometimes itll idle great for 20 mins on end, then stumble and die. then other times it wont keep an idle for more than 3 seconds until it stumbles and dies.

Ok, I've typed this a few times before, but it may bear repeating again:

DIFFERENT method of powering the fuel pump:

1. When you turn the key to the ON position, the fuel pump receives power through the ASD relay for 3 seconds, then the ECU/PCM will cut off the power if it hasn't received input from the CPS/CKP. The power supplied is a full 12 volts bypassing the ballast resistor.

2. When you turn the key to the START position, the fuel pump receives power through the starter relay. The power supplied is a full 12 volts bypassing the ballast resistor.

3. Engine running, from idle to just short of WOT, the fuel pump receives power through the fuel pump relay. The power supplied is reduced by the ballast resistor.

4. Engine running, at WOT, the fuel pump receives power through the oxygen heater relay. The power supplied is a full 12 volts bypassing the ballast resistor.

As suggested earlier you need to TEST the fuel pressure to see if it is within specs--31 psi w/vacuum to the regulator, 39 psi without vacuum to the regulator.

Your problem, if fuel related, could be not enough pressure OR the fuel pump is loosing power. I would start by bypassing the ballast resistor with a jumper wire, then attempt to determine the fuel pump power status when it stalls out. If you have power to the pump when stalled, then you need to determine if you have spark, and if the injectors are receiving a firing pulse--use a NOID light for checking the pulse.

how do i determine the fuel pumps power status? i mean i can test it for adequate fuel pressure, either with the ballast in stock setup or with a jumper wire. i think your just saying try it both ways and check the fuel pressure so ill do that

joe_peters said:

The power supplied is a full 12 volts bypassing the ballast resistor.

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Does a 93 have a ballast resistor? I thought that was a Renix only thing.

My '92 has one.

I'm pretty sure 93 has it, and I think even 94 had them? Not entirely sure. I know 91 does.

I guess you learn something new everyday! Anyway, the ASD relay would be a good place to start. Maybe swap it with another relay and see if the problem goes away.

i have swapped all the relays trying to fix it and havent been successful. i will try n jump the ballast resistor right now but i hear the fuel pump kick on for 2-3 seconds when keys gets turned on but the pressure at the fuel rail when i probe the valve with a screwdriver it trickles out, but then other times itll release a 2 footstream across the engine bay so im gonna check the fuel pressure regulator as soon as i find a fuel pressure gauge from a buddy

alright an update, i think i jumped the ballast incorrectly before but now theyre wired correctly bypassing the ballast all together, then i replaced the vacuum line for the fuel pressure regulator and it started up good and idled for about 20 minutes, drove it around the block paying attention to rpm's and gauges and stuff, this is an automatic by the way, and its going great except every time id come off the throttle sharply itd drop below 500 rpm and then come back up to 750 but the lights would dim and itd almost stumble but then keep going. then it was in my driveway idling and i started to stab the throttle up to 1500 quickly and letting it drop back to normal idle and it dropping lower and lower until it died, and now it wont restart! it just cranks no sign of catching and starting to run it just cranks and cranks. i dont have a fuel pressure gauge which is bugging me but im broke right now so im trying to diagnose myself. so what does this mean?? i hate how the jeep has no pattern whatsoever to running weird.

How low is your battery, from trying to start it?

scottmcneal said:

How low is your battery, from trying to start it?

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x2, any electronic controlled vehicle will crap out when the voltage drops below 9 volts.

Put a full, overnight (good) or 24 hours (best), charge on the battery.

EDIT: and don't be in a hurry to rule out fuel delivery problems yet, you NEED to put a gauge on the system to test. Get on your region's forum, there has to some one living close to you that will have a gauge.

the battery stayed at 14 volts while idling when i first fired her up this morning, it warmed n kept going great, i kept pulling sensors and itd die such as cps tps and iac and when reconnected it started right back up, drove it round the neighborhood for a while not going over 30mph, then take it back to my house park in the driveway and shut her down, sure enough i think to restart it and it cranks, starts, idles at 300 rpm for 3 seconds then dies, then when trying to restart right after this it would only crank over and over and over with not even a slight hint of attempting to start. this was all with the fuel ballast bypassed by the way and i fixed a corored vacuum line on the fuel pressure regulator at the fuel rail with a new one, these fixes were done BEFORE the epic trip around the neighborhood of the jeep running for easily a half hour (its longest time since buying it!:loveu:

Get it back into a no-start condition, then try un-plugging and plugging the CPS/CKP connector a few times and see if it will then start.