Hey guys,

I am hoping someone can help me figure out why my 98 Cherokee won't start. A buddy of mine (might even be a user on this forum) have been trying forever to figure this problem out.

A bit of history... There was a problem with the ignition, and instead of repairing the problem properly, the previous owner decided to bypass the ignition with a push button wired directly to the starter. Turning the key to start produced nothing but lighting the parking break light on the dash. The previous owner also told me he replaced the engine, however I have no documentation to back this up.

A few weeks after purchasing the Cherokee it developed a problem of not starting reliably with the push button. Initially, we thought this was the Crankshaft Position Sensor, so we installed a brand new one purchased from NAPA Auto Parts. Unfortunately, this did not solve the problem. Next we removed the hack job push button start and removed an after market security alarm, (I wanted these gone anyway). In the course of trying to identify the issue, we also replaced the ignition switch and the clock spring. Eventually, my buddy traced the problem to a bad relay.

I think the problem may have been a combination of a bad relay and something above, because we had tried rotating the relays before doing any of the above and still had the same result. After all that messing around the Cherokee would crank and start when you turned the key in the ignition.

Later that day, I was driving home and the Cherokee started to sputter and lose power (mechanical, not electrical) for a second, gain it back, and jerk around a bit. I made it home and pulled into the end of my driveway. I shut the Cherokee off, and immediately tried starting it again. It would crank, but would not start.

It has sat for a few months like that, with me occasionally going out and trying to start it. This weekend, my buddy came over and he and I tried to figure out why it won't start. We confirmed that the fuel pump has power by sticking a wire in where the relay normally is. We both could hear the fuel pump spinning. We also had fuel spraying out of the Schrader valve on the fuel rail when doing this. (removed the cap and pressed the center thing in) However, when we tried turning the ignition to on, the fuel pump does not respond. Neither of us hear it and no fuel ends up in the fuel rail.

Here is what we tried and had no success with:

• Replacing the wiring harness in the engine with one from obtained from a junk yard. The existing one was in rough shape.
• Replacing the Pedal Position Sensor. ODBII was throwing codes for this.
• Replacing the cam sensor (circular thing beneath the distributor cap)
• Removing the horn fuse to check for a bad Clock Spring.
• Tested voltage on the Crank Shaft Position sensor. That came back good.
• Checked fuses and relays.

The most logical thing I can conclude is that something in the ignition is not sending a signal to the fuel pump when the key is turned to start position.

98 Cherokee
2 Wheel Drive
152,xxx miles
78,xxx miles on engine (supposedly)
4.0 liter

Hopefully someone can tell me what is going on, because I am about ready to push this thing off a cliff.

 

Fuel pressure must be checked with a gauge. When you crank the engine to start have you checked for spark?

 

My buddy mentioned that we do have spark.

Could you elaborate on what you mean with checking the fuel pressure with a gauge? I did hook one up before and saw no pressure, but this we before we discovered that the fuel pump works.

Also, when there is fuel in the fuel rail from manually running the fuel pump via jumping the relay, the Cherokee sounds like it wants to start, but then goes back to cranking.

 

There is a Schrader valve located on the fuel rail, fuel pressure should be 49 +/-5 psi @ idle. Can you get it to start by dumping fuel in the throttle valve?

 

I haven't tried dumping fuel in the throttle valve to see if that will get it to start. I will give that a try when my buddy is around to help. If this gets it to start, what does that mean?

Now I know what thing on the fuel rail is called... Schrader valve.

 

I too had this same problem on my 98 it was the fuel pump. try dumping the fuel in the throttle valve. if it starts check the Schrader valve on the fuel rail if no fuel is in the rail check to see if the pump is getting power by the tank

 

Hi XjZack,

The fuel pump is getting power. I was able to verify this by jumping the pump from the relay socket in the engine compartment. Both me and my buddy were able to hear the pump spinning in the tank. Also, when plenty of fuel sprays out of the Schrader valve when doing this. (One of us was jumping the pump and the other was pressing in the Schrader valve)

When your pump went out, did you have power to it / fuel coming out of the Schrader valve?

 

I did have power to the pump but i did not have fuel coming out of the Schrader valve. did you try dumping the fuel in the throttle valve if not try that.

 

If you temporarily power up the fuel pump like that and leave it powered up while cranking, will the engine start?

 

Yes ^^^that, X2, although I gather that's not working. Also using starting fluid will provide "fuel". You checked the CPS voltage on an obdII in a 98? Yea, I've seen it can be done....not completely voodoo..but you are almost the only poster who has mentioned doing that. (there's a resistance check IIRC). I'm curious what voltage he measured on that CPS.

Anyway, Codes? Got anything there? And....Fuses, even the mini. If the sensor feed to ether, and including the rear 02 sensor shorts, the fuse that blows might cause issues. You might take a minute to take a good look at the post cat 02 wires down under there, as well as the fronts. Don't forget a relay get's power from one place, (for the relay coil), THEN connects power through from another, often when it's grounded. Googleing "SPDT relay", is always fun! (Single Pole Double Throw)

 

Hey guys, long day... no chance to work on the Cherokee. DFlinstone, I thought about doing that, but was wondering if run the risk of causing something to rupture. If the fuel pump is pumping fuel into the engine, but the engine isn't running, won't pressure start building up somewhere?

 

The pressure regulator will prevent that, it bypasses excess back into the tank.

 

Not to necro a thread, but I beleive I may have te answer to your problem. I also have a 98 GC 4.0 that did the EXACT same thing. Look at your ECM, if you are standing in front of your grill it is a black box on the upper on the left side of the firewall behind your cooland overflow tank. There should be 2 small screws on the outside of it facing you, back them off 1/4 to 1/2 turn and see if it starts. I did this to mine and it would run. If this is the case you need to replace the ECM, you can get one here http://www.autocomputerexchange.com/...-cherokee.html
it was approx 300ish when i bought mine last year. The jeep has been running like a champ since. Hope this helps.

 

Hey Fastpaws. Welcome to the forum 9-12, that's a a pretty old thread! Much thanks for the input . Power-train Control Module PCM 91 on, 87-90, ECU. CLEAN YOUR IAT!!!!!

 

The GC has the PCM at a different place than the Cherokee. According to dealership, it is the most common cause of GC not starting. (besides what does loosening and tightening have to do with it other than maybe twisting the case a little and making a broken connection)

AS for the cherokee, the PCM is driver side, front by the airbox and its aluminium with 3 connectors going to it.

As for things to check and things not to worry about:
If you have spark, All the essential sensors are ok.

As for the pump. here's the schematics for a 98 http://i615.photobucket.com/albums/t...umpcircuit.png

As you can see there are 4 things that have to happen for it to go
1-fuse 11
2-Fuse 21
3-Ground from the PCM
4-relay to close the connection

If you have power at D4, a ground a d6 When crancking(when ignition on, the ground stays there for 20s only), power at D2,
then jump d2 and d8. that will run your pump and it should start.

If the pump does not run this way, the wiring is damaged.