My buddy dropped off his 1999, 4.0 auto XJ for a no start for me to look at.
Cranks but does not start.
Turning the key i notice the volt gauge on the dash and the check engine light does not come on.
I look at the ASD relay and it and the fuel pump relay are not clicking.
All fuses check out good.
I go the PCM and back probe A22 on the black plug and it's got battery power, A31/32 both have ground.
I pull the connector to visually inspect, all looks ok, no loose pins on the PCM, no corrosion that I see.
While plugging it back in, I accidently left the key on, the relays all went nuts. The ASD and/or fuel pump started rapidly clicking like they do when they are low on voltage, but if I wiggled the plug just, not seated all the way into the retainer, the the ASD and fuel pump relay worked, the fuel pump primed, and pin A2 on the PCM had power, the volt gauge on the dash started working (The fuel gauge did not, not sure if it did before however). The check engine light now comes on with the key and I am able to pull codes.
p0113 - TPS
p0123 ECT
p0118 IAC
p1492 - Battery temp
None of those really meant anything to me for a no start, but I am a Ford tech, not a Jeep tech.
I put a noid light on the fuel injector, it is not pulsing/ no signal.
I did not check for spark, it was late...

Not really sure where to go from here.
I will check to see if those sensors are getting 5v reference.
See if fuel injectors are getting power.
See if the coil has power?
Any other ideas?
Does the CPS take away spark or fuel pulse?
If it was a Ford computer I could open it up and look for the brown stains, but I can't .
If feels like a PCM issue, but I want to be sure before I tell him to get that repaired, the whole not seating the connector all the way is strange, but I will clean it all tonight.

 

Probably the most common problem in a 4.0 that cranks and will not start is the "crankshaft position sensor" if a wire is broken or there is too big a gap or if it just went bad the engine will crank but not start.
Another common problem is the grounds need cleaning. You will find one on the fender by the battery but the more important one is on the block just forward of the distributor. The last thing is to double check the fuses.
Being as old as they are, they may check good but have slight corrosion or even be bad.
Good Luck and I am sure others will have more details/ideas to add!

 

As you are a tech, the same issues apply you would have encountered before on other vehicles

Yes to all above ideas

No CPS = No ASD = no fuel pump or injectors

You want to download the FSM

You can open the PCM to look for fried parts, search the archives for all

You may have a wiring harness issue, or a known issue is the PCM main solder connectors can crack, I believe this is quite repairable

archives !

 

Well the PCM connector working better with unknown wobbles doesn't help. That's the first problem. Inspect all male and female pins that none are pushed in or loose. I had to repin the DLC on my 4runner because of that. Grounds of course check. Make sure the block to firewall ground strap loom thing has full continuity. Also the crank position sensor on my XJ goes bad every couple of years like clockwork. It's the only thing that goes bad over the past 20 years. Does your tachometer needle wiggle around when you crank? Anyways you can check that at the PCM while cranking.