Problem Starting, No Fire...

[Mix85]

I purchased an 88 Jeep Cherokee 4.0 in 2000 and it has ran fine for the most part since then. Last year I encountered a problem, I would be driving for a while and then when engine would get hot, it would shut off. After a while it would start back up again. However, not too long afterwards it wouldn't even start at all. Well I went and changed most of the electrical system. The pickup strator, the coil, everything in the distrubutor... but still it will not start. We then discovered that there was no fire coming through at all. I've been told that replacing the computer could fix it, but then again some say that that won't fix it. So I'm kind of in a rut here trying to figure out what is wrong. It is out of time, but I heard that the computer controls the timing on it so that is making me lean towards the computer... any help would be gladly appreciated!

[Saudade]

Check your crankshaft position sensor (CPS). You can search the forum and find lot's of info.

[baum430]

Originally Posted by Mix85

I purchased an 88 Jeep Cherokee 4.0 in 2000 and it has ran fine for the most part since then. Last year I encountered a problem, I would be driving for a while and then when engine would get hot, it would shut off. After a while it would start back up again. However, not too long afterwards it wouldn't even start at all. Well I went and changed most of the electrical system. The pickup strator, the coil, everything in the distrubutor... but still it will not start. We then discovered that there was no fire coming through at all. I've been told that replacing the computer could fix it, but then again some say that that won't fix it. So I'm kind of in a rut here trying to figure out what is wrong. It is out of time, but I heard that the computer controls the timing on it so that is making me lean towards the computer... any help would be gladly appreciated!

Hello, the computer is the brain of the system, it controls the spark and the fuel delivery to the engine, sensors just tell computer what engine
is doing they are built to last awhile, so if it does not start, then to test
if computer is bad , pour small amount of gas into trottle body, and
crank it over, if it starts the computer is bad.

[wwwildman]

Saudade is correct. It most likely is the CPS, but think of this:

The sensors tell the computer what is going on, but if the sensor is bad the computer will not fire because it does not know when to. Besides the computer costs mega $$$ and the CPS is only $40...guess which I would do first?

[Saudade]

Baum... How is pouring gas down the TB going to test the computer in this case? He's determined he has no spark.

Mix85 - Had the same problem. My '88 died when it got hot. Wouldn't start until it cooled off.

Check out: http://autorepair.about.com/library/faqs/bl077g.htm

[Dale Aeppli]

Originally Posted by Mix85

I purchased an 88 Jeep Cherokee 4.0 in 2000 and it has ran fine for the most part since then. Last year I encountered a problem, I would be driving for a while and then when engine would get hot, it would shut off. After a while it would start back up again. However, not too long afterwards it wouldn't even start at all. Well I went and changed most of the electrical system. The pickup strator, the coil, everything in the distrubutor... but still it will not start. We then discovered that there was no fire coming through at all. I've been told that replacing the computer could fix it, but then again some say that that won't fix it. So I'm kind of in a rut here trying to figure out what is wrong. It is out of time, but I heard that the computer controls the timing on it so that is making me lean towards the computer... any help would be gladly appreciated!

On passenger side shock tower you will see the ignition control module Disconnect connector marked A & B Using a ohms meter check terminals A & B ohms meter should read 125 - 275 ohms . Ifreadings are not as tested, replace crankshaft position sensor on bellhousing. Dale [email protected]

[Mix85]

Thanks guys, I replaced the CPS, still nothing... so waited til I got some extra cash to replace the computer... putting in a new computer still didn't fix anything, so I went and replaced the distributor since I only replaced the distributor cap last time... and alas, the jeep still will not start. I don't think it is in time, but I'm not exactly sure how to get it in time, or if that is the problem here =/

[Saudade]

Sorry you went through all this expense.

Once again, check for spark. If you still have no spark, you'll need to start testing all of the electrical omponents (even the ones you changed).

This link to Autozone's repair guides will give you the test procedues and specs to the various sensors.

http://www.autozone.com/servlet/UiBr...3d801522d5.jsp

This one is for the ignition components:

http://www.autozone.com/servlet/UiBr...raseCrumbs=YES

As for timing, you can't adjust it. It's controlled by the computer.

[wwwildman]

Originally Posted by Mix85

Thanks guys, I replaced the CPS, still nothing... so waited til I got some extra cash to replace the computer... putting in a new computer still didn't fix anything, so I went and replaced the distributor since I only replaced the distributor cap last time... and alas, the jeep still will not start. I don't think it is in time, but I'm not exactly sure how to get it in time, or if that is the problem here =/

Try this. At the ignition control module there are two connectors at the bottom. Disconnect both of them and them. Turn the key to the ON position and using a multimeter test for voltage at the yellow wire. If you have voltage at the yellow wire then you are getting power to the ICM.
If you are not getting the voltage then you have a bad ground, a gad ignition switch, or corrosion at a connector, either at the ignition switch or the computer.

If you are getting voltage, then you can remove the ICM. Seperate the ICM from the ignition coil. You can have the ICM tested at AutoZone. Normally this is free. You should also test the ignition coil by using the procedures in the HAYNES manual and the procedures from autozone.com.

It should be one of the items mentioned above.

Mike

[Mix85]

Thanks for the help guys, finally went and tested the ICM, we did get voltage to the ICM. We then tested the wire to the distributor, voltage was going in.. we tested the wire out at the pick up coil... and no voltage there.

So finally getting a voltmeter has helped a lot!

[Dale Aeppli]

check the ohms at the ignition control module on shock tower pass. side. On terminals A & B it should have 125--275 ohms. what reading did you get when checking voltage going into distributor. [email protected]

[Saudade]

Originally Posted by Mix85

So finally getting a voltmeter has helped a lot!

It's amazing how much easier it is when you have the right tools.