mmj1111

Hi everyone, nice forum you have here! My 1990 Jeep Cherokee is not starting. I believe it's a 4.0L. I have ran a search thru google and the forums and haven't quite found what I was looking for. I am an absolutely newbie when it comes to mechanics but I Believe I can learn how to replace the starter if needed. The jeep just tries to start, but it doesn't actually start up. I had a problem last month where this happened and I got a jump start and it worked. Now it won't start at all. So I am asking the pro's, what do I need to do for a cheap DIY diagnostics and repair on my vehicle? Thanks!!!

F1Addict

When you say it "just tries to start", do you mean that the engine cranks over but it just doesn't fire or that your starter isn't turning the engine over.

If it the engine is turning when you engage the starter but it's not starting then you'll need to look at your fuel and ignition system. There are several easy things to check that are frequent failures.

If it the engine is not cranking then you've got a starter problem which could be the starter, the solenoid, your ignition switch, or any number of things. Give us some more specifics and we'll be able to offer better advice.

mmj1111

Thanks for the reply, I will be as thorough as I can. I can also provide pictures of anything if needed. I turn the key and hear it crank (the sound I usually hear before it starts) but it just doesn't start. It just cranks endlessly. After trying that for a while I gave up and began my research on how to fix this problem.

LeRoy90laredo

this narrows out the starter, check your plug wire coming off the distributor to the ignition coil.
check to see if there is pressure at the fuel rail.
if you can, get a chilton/haynes book (chilton is preferred) and do a complete look over of all your ignition system.

mmj1111

Thanks. I am not sure what the distributer is, or the ignition coil, or the fuel rail for that matter I will do some research and try and figure that out. Hopefully google has some a schematic or something.

LeRoy90laredo

fuel rail is off on the driver's side of the engine block. you can see 6 injectors that come off the rail and go into the block, the valve for a pressure check is at the very front of the rail.

the distributor, if you look has 7 wires on it.(6 go to the spark plugs on the passenger side of the block). and the middle one leads into the ignition coil.

mmj1111

OK So I looked those things up, went out and checked the connections nothing seems undone. I don't have a pressure guage so I can't check that myself. I tried turning it on again and it kind of almost fired up and gave off a puff of smoke then died?

LeRoy90laredo

okay, try your MAP sensor (manifold absolute pressure) its located at the back of the engine bay, dead center, has an electrical connector and a vacuum line.
look it up on a parts store website so you know what it looks like.

mmj1111

That is also connected.

LeRoy90laredo

its an electrical component. i know that when mine went out on me. it wouldnt start, it would crank but wouldnt start. or it would start for a second and puff black smoke out.

also check the crank position sensor. its on the top of the transmission bell housing.

mmj1111

OK, so what did you do to fix this? Is it worth trying to get a sensor myself and replacing or should I just take it to a mechanic?

F1Addict

Start with this... when you turn the key to the "run" position (before starting) listen for your fuel pump to prime. You should hear a hum coming from the fuel tank area when you turn the key. It will last between two and three seconds and then stop. Let us know if you hear that and we can begin to rule out your fuel pump/fuse as the source of your problem.

BTW, this is what your coil wire (green) looks like when viewed from the passenger side of the engine compartment. For reference, the battery is in the bottom right corner...

F1Addict

Based on some of the recent posts I'm thinking that it's most likely an electronic component. MAP, CPS, or ignition module. CPS (crank position sensor) being the most likely culprit. It's a fairly simple thing to replace and not terribly expensive but you'll be in for an adventure. You can test the CPS but it requires a multi-meter... do you have one of those?

mmj1111

I found a loose wire. Does anyone know where it attaches to and if this is the culprit? It is attached to the thing in the first picture.

mmj1111

Also when I turn the key before starting it, the hum that usually is there is not there at all.