My Cherokee always ran fine and one day it just wouldn't start. I have been trying to figure out for some time now. No power to the fuel pump and no spark at the plugs. Turns over fine and the accessories work. I scanned for codes but the reading was no signal from the ECM. The check engine light does not come on. I would like to check to see if the ECM is getting any power or if it is bad. I hate to buy a new computer and then find out it was the ignition switch. Any ideas?
Thanks

 

When I get a trouble code my dash light does not come on either on my 96. A while back I was wondering if there was a way to check the operation of the PCM, I do not see any info in the manuals. What code was it throwing?

 

Thanks for the response. Actually, mine never shows a code which is what makes me think it is the computer. I have been trying to figure out if I am getting power to the computer. I assume it goes there first when you turn on the key. The fuel pump also doesn't come on so something is keeping those items from getting power.

 

I'm going to a birthday party, I'll try to touch base later, I'll look at my wiring diagrams.

 

I tried to check the power to the ECM by turning on the key, checking the voltage at the connector. I found a couple that read 12 volts so I guess it gets power at least at some locations. It doesn't have a reading with the key off so I assume the ignition is good. Still fuel and spark both shut down is a mystery unless the ECM is bad.

 

When you turn the key to on or start power flows from the ignition switch to one control terminal of the ASD and fuel pump relays. The other control terminal of the relays connect to the PCM. Pin C3, on PCM, for the ASD and C19 for the fuel pump. The PCM then provides a path to ground which then activates the relays.

On the relays the control pin numbers are 86 and 85. Normally 86 connects to the ignition switch and 85 the PCM but it could be reversed.

The power pins on the relays are 30 and 87. The socket for pin 30 should have contant battery voltage regardless of ignition switch position. The ASD relay gets voltage thru fuse 20 and is 20A. The fuel pump relay gets voltage thru fuse 8 30A. Check the fuses and also power at the socket for pin 30. Pin 87 supples power once the relay is activated.

The ASD powers the coil, alternator, injectors and a bunch of sensors.

It could be a bad PCM but check the electrics first. Check any PCM ground connections. If you want a wiring diagram PM me or post an email address and I will send one out.

 

Thanks ET.
I would like to see the diagram if not too much trouble.
sgaus50@gmail.com

 

I like a copy too, If I could. Thanks

addington.david@gmail.com

 

It could be the ignition switch inside the steering column. My 94 blew 2 in one year...It would turn the radio and all accessories but not crank the first time then the second time it would crank but nothing else worked...needless to say it was 2 different pins that shorted each time.

 

Thanks guys for your help. My issue turned out to be the computer. This is a great forum and was very helpful.

 

How much did cost for the PCM?