no start zj

[XJ-ARNIE]

Okay, a little back ground. I had no fuel pressure, and the jeep would crank but not start. I installed a new fuel pump, and now she starts but wont stay runnning at all. All the fuses are good, and the relay for the fuel pump is good. I put in new plugs after inspecting the old ones and realizeing that they were cashed out. Still the same result. I disconeccted the battery (which is an optima red top, 5 months old) and charged it and let the computer reset itself. She seems to be doing a little better, she'll start now, but run really rough for a few seconds and then die out. It wont stay running with any help from the right foot either. I threw a tested on the plug wires, and turned the jeep over, and my meter says I have spark to all 6 cylinders. What the hell do you think the culprit may be? Map sensor? bad cap/rotor/wires/coil? bad battery? I know its not an alternator becasue she would run fine with a charger hooked up if that was the case.

By the way, it is a 1998 Grand with a 4.0L. Any suggestions? thanks alot.

 

[imprezkid]

check the cps and tps

 

[birchlakeXJ]

Assuming no check engine light? If so, pull codes for guidance. If no codes, here are a few things to ponder. Basics first......always. Test your way to a solution.

Gotta verify electrical. Battery can be load tested and alternator output can be easily verified by putting a meter on the battery when running. At high idle, you should have approximately 14.4 volts.

If tuneup hardware is old, get it out of there. Plugs, cap, wires, rotor. It might be something else but I've seen guys chase their tails for weeks over a faulty piece of tuneup hardware.

Fuel pressure should be verified at the rail with a gauge

The ignition coil and many of your engine management sensors can be tested. Cam sensor and throttle position sensor would be a good place to start.

 

[XJ-ARNIE]

moving on to sensors then. thanks guys. I just plugged a new plugs/cap/rotor/wires/coil into it. same shit. no check engine light...and the battery is pretty much new, but im gonna load test it anyway. same goes for the alternator.

 

[XJ-ARNIE]

ARGGGHH!!!! im gonna scream! okay, heres an update on the situation. new cap/rotor/wires/plugs/coil, new fuel pump, new fuel pump relay/fuses, and a new crank pos sensor. Still no start, no fuel pressure, and there is no power to the fuel pump, i tried bypassing the ground and got nothing new.... any ideas?

 

[joe_peters]

I don't know about the ZJ, but why should that stop me from commenting!

On the XJ the fuel pump is powered in different ways at different times:

1. When the key is first turned to ON, the fuel pump is powered by the ASD relay, and if no signal is detected from the CKP/CPS the power is cut after 3 seconds.

2. When the key is in the START position, the fuel pump is powered by the starter relay.

3. When the engine is idling or in cruise, the fuel pump is powered by the fuel pump relay.

4. When at WOT, the fuel pump is powered by the oxygen sensor heater relay.

Almost sounds like you are not getting number 3.

 

[OverlandZJ]

My wife's ZJ had the same issue a few winters ago, it turned out to be the ECU.

Try this.. to me it seemed the colder it was outside the longer it took.

With all accesories off turn the key to on, and wait. Your waiting to hear a series of clicks.. this will be the fuel pump relay, then you'll hear the fuel pump prime the rail. It should start now.

Heres where i found my symptoms and the fix. I dont know if this happens with the 4slow ZJ's but it doesnt cost a cent to try.

http://www.jeepsunlimited.com/forums/showthread.php?t=418265

 

[XJ-ARNIE]

i tried waiting, as per the new fuel pump instructions instructed me to. Im begining to think that the computer isnt closing the ground...thus not completeing the circuit no matter which way you slice it. i replaced the fuel pump relay, and checked power right there, the relay is getting plenty of volts. The fuses to the relay are both IWO, but still no start. My next bet is to bypass the relay all together, so the computer doesnt have the chance to close the ground, and if it starts it means a blown computer right?

 

[joe_peters]

Or an open in the harness.

 

[JJacobs]

Power up the output leg of the fuel pump relay with a fused jumper wire. This should give immediate fuel pressure and allow the vehicle to run. If not, there is an issue with the fuel delivery system, either electrical or mechanical.