I'm in need of some help. My Jeep wont start sometimes. If I don't drive it for a day then try to start it the next day it won't starts. It will just crank but never fire. But in the afternoon it will fire right up. I did try replacing the ignition coil with no luck. I have head that sometimes replacing the cam sensor will help, but don't want to just throw parts at my baby. This is my first post and any answer is appreciated.

 

Welcome to the forum. When ever you make a new post always put the year, model and engine size. Anyways. Have you checked it for fuel and for spark? You may want to test you CPS. Here is a link on how you can test it. Just keep in mind, The test isn't always 100% accurate. You can have a bad cps test good and it still won't run.
https://www.cherokeeforum.com/f51/cr...x-tips-153657/

 

My jeep is a 1990 sport 4.0. I'm pretty sure I'm getting fuel. When i turn the key I hear the pump whirring away. Is the CPS temperature sensitive? Because when its 50 degrees in the morning the jeep doesn't work but later when its 70 or 80 it works. I don't see this link your talking about, could you re-post it?

 

It can be temp sensitive. But normally you will have that no start when it's at normal operating temp or hotter. Make sure that you have a bright blue spark. Any other color will cause problems with the 4.0. Also check the fuel pressure at the fuel rail your year should have 39psi +or- 5psi. Check it with a mechanical pressure gauge connected to your fuel rail.
Sorry about the link I took care of it, it should be there now.

 

Thanks for the link should be very helpful later. Ill pick up a new cps on the way home from work tonight then check the spark. before i replace the CPS of course. Wouldn't a bad CPS cause a "No Spark" sort of deal? When I was trying to figure this out the other day I wasn't getting spark at all, then in the afternoon I shocked my dad because he held the ignition wire while I cranked the engine.

 

When a cps is going out they can be work at time and not at other times. When mine was going bad it would act up at times and be perfectly fine at others. It ran like that for over a year before it completely went out. Also just because you dad got a unpleasant surprise. The spark can still be weak and not let the engine run. Just make sure that it is a bright blue and not white or orange.

 

We had same problem only in reverse. Jeep would shut off unexpectedly at a red light. Replaced the CPS (Crank Position Sensor) from the dealership and problem solved!

 

This sounds like the exact opposite of the problem I was having when I first got mine. I replaced the CPS and it starts everytime now. Its a pretty cheap part and relatively easy to install. I did the CPS test and it passed fine but still didn't start so don't put too much trust into that test.

Edit: I should ellaborate. My cherokee would start fine whenever it was cold, but once it got hot it would crank and crank and crank until it cooled back down. Those sensors are very finicky when it comes to temperatures.

 

Yeah I'm glad it doesn't do that. just problems getting it started.

 

The first time I tried this test the cps passe, But still didn't get it to start.

 

I would just get the sensor and install it. If it doesn't work then remove it, clean it, and go get your money back.

 

Should I get this part from the parts store or the dealership?

 

Lots of people will say the dealership. I got mine from the parts store and it has been fine since March. Ultimately do whatever you feel comfortable with.

 

Save yourself the headaches and get it from the dealer. The aftermarket ones have been known to be bad right out of the box and if they do work they have a short life span. Yes some have been lucky with an aftermarket ones. But the way I see it why take the chance.

 

Before you do any more testing which of Cruisers tips have you done? If you don't have good grounds your test results are worthless.

https://www.cherokeeforum.com/f51/cr...x-tips-153657/