96 XJ 4.0 won't start

Okay, so my jeep just randomly died on me a couple months ago and I haven't been able to get it started. I'm hoping someone can point me in the right direction.

First off, I wasn't getting fuel. so I replaced the fuel filter, fuel pump, and fuel relay. I'm now getting fuel and it still wont start.

So now I changed the CPS, checked all the fuses, and still no go. I tried using an OBD2 code reader to see if it would give me any clues, but for some reason it won't connect / read anything. Works fine on my car, has worked fine on my jeep in the past.

So this is where I'm at:

I need to know the right way to check for power at the coil. ie, is it just key on positive side to vehicle ground with a 12v meter? or...

I also need to check the PCM, is there a good way to verify that is working or not working?

Any other ideas? I have fuel, so it seems to be a spark problem.

Thanks

TrailOfGears said:

Any other ideas? I have fuel, so it seems to be a spark problem.
Thanks

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You might have fuel pressure, but are the fuel injectors firing. Knowing that will tell you if the problem is just spark related. Either check with a meter or noid light, or look and see if the spark plugs are wet with fuel.

Unless you have put a pressure gauge on it you really don't know if you have fuel or not.

Random stall, no-start, and no connection to OBD-II trouble code suggests troubles with the CCD Bus data signals. Either damage to the wires, or one or more faulty engine sensors.

The most common and most likely sensor failure is the Crankshaft Position Sensor. It should tested and if necessary replaced with a genuine Jeep part. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.


The only DIY way to test the PCM is to replace it with a known good PCM, but they are numerous more common and lore logical cause for the symptoms describes that should be tested and eliminated before you can suspect a faulty PCM.

By far most common issue in a jeep is crank sensor. But, when a crank sensor is bad (going bad in the beginning), the jeep will shut down while driving/running usually amid traffic (ya fun!) then start again in 10 to 20 minutes, then repeat again and again (gets worse over time). So, in my experience, my crank sensor went bad at first, shutting me down in traffic at around 30 to 40 mph, ten minutes in, would start again and go, then repeat a few miles down the road. Few days in to this issue, the throttle position sensor went bad along with crank sensor. Now, when throttle sensor goes bad, jeep will shut down and not start again. So, you're probably looking at both are bad and need to be replaced. Its a good idea to regularly replace both as they do randomly go bad and I swear-- at the worst possible moments! just FYI

I disagree with replacing random parts in the hope of fixing an undiagnosed and unknown problem. A faulty CPS can just stop working, or it can begin to go bad with random stalling symptoms.

The CPS and the TPS can be tested. The CPS is much more likely to fail than the TPS. Cheap crappy Chinese parts are a fail waiting to happen, I only install genuine Jeep engine sensors. A genuine Jeep CPS should last about 150,000 miles and a TPS even longer.

I carry a spare CPS in each of my XJ's and only carry a spare TPS in my bin of repair stuff for off-road travels.

TrialLake said:

Now, when throttle sensor goes bad, jeep will shut down and not start again.

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Usually not, unless it's failed and telling the engine computer you're holding the pedal down, triggering the flood recovery mode when trying to start. You'll usually have shifting issues first if it's an automatic and not a renix era Jeep with the dual tps output.