Alright my brothers,

It started raining in the middle of my diag so I turn to the XJ family! Some of you know my XJ has been down for two months due to a dead fuel pump and I've recently just installed a new bosch unit last weekend but didn't have a chance to start it because the battery was shot. I threw a nice yellow top in her today and primed the system a few times. Pump primes nicely and plentyyyyy of pressure at the rail. Should fire up no problem right? Wrong! Cranked her over and over and over and got nothing. It would stumble a bit once I stopped cranking it but no life while cranking it. I'm not trying to kill this battery so I stopped cranking once it sounded a bit drained and put my charger on it.

I checked fuses and everything is fine. I plugged my scanner in and pulled a P0320 out of her. I know the case with this code is basically a 50/50 shot between cam or crank sensor (usually). I checked the wiring and connectors, all good. I have replaced both of these sensors about 2 years ago with Standard brand ones. That also doesn't mean squat because I have more faith in OEM sensors. Checked the cap and rotor, both good. I did manage to check spark and I saw an arc (pulled #2 plug) but seemed a bit weak IMO even though cranking amps are strong. Before the fuel pump died there were no issues. I cleared the code, cranked it a few times, no start and no code now.

So while it's raining I figured I'd pick some brains.

To catch some other members up to speed,

98 xj 4.0L AW4
73xxx original miles.

About two years ago I replaced the following as well.

Cap & Rotor
Plug wires
Plugs (champion)
Crank sensor
Cam sensor
Coolant temp sensor
TPS

 

If you have spark, the crank sensor is good. Did you change the fuel filter when you did the pump? Also, what is your fuel pressure at the rail?

 

I replaced the entire module so pump and everything which includes a new screen. I don't know what the pressure is at the rail but from my experience it's enough. I could rent a pressure gauge but seems unnecessary. I'm leaning more towards the cam position sensor being the culprit but that's speculation at this time until I can get in there and actually properly diagnose the cause. I want to double check spark again but fingers crossed the crank sensor is good because I don't want to do that one again lol.

 

Did you try holding the gas pedal down for 5-8 seconds while starting to bypass the computer? Just a thought, may or may not make a difference

 

I did try that at one point but made no difference. What I did notice is that after even after numerous cranking attempts, when I pulled the plug to check spark, it wasn't soaked in fuel like I was expecting. Maybe something is preventing the injectors from firing? ugh wish I still had my noid light kit! I'll pick up a set since they're relatively cheap and check it out

 

I believe the cam position sensor tells the injectors to fire so that could be the culprit as you said earlier

 

I actually saved my original pickup coil and crank sensor when I replaced them. They were never bad when I replaced them, just did it as more of a preventative maintenance kind of thing so I wasn't stranded on a trail. I keep them in my glovebox and just checked that they're in there. I'll swap the pickup coil and see what happens. I would like to thank my past self for saving these parts for my future self.

 

I wanted to return to this thread because I fixed my no-start problem. I'll give this a quick summary for anyone who may run into a similar problem.

Jeep died when fuel pump quit. Sat for about 2 months before I got around to installing a new Bosch unit. Installed new Optima yellow top and tried to start jeep. Strong crank but no start. Plenty of fuel pressure at the rail. I put a noid light on number one injector and the injector was pulsing during cranking. I then checked spark at the coil. There was spark but it really seemed weak. I could barely see an arc with very little gap in my spark tester. There was even less of an arc when I checked spark at number 2 plug wire.

Now, I was showing spark and fuel but still no fire. This shows that the CPS and coil-pickup were both working as they should despite the P0320 code I previously had but could not replicate. Based off the weak spark I saw, I went ahead and picked up a new coil and simply plugged it in without removing the other one just to check (if you haven't changed a coil on these, it's not very fun and super tight). I turned the key and the Jeep fired right up. I could have taken the coil off and tested it but it seemed more work than necessary when I could just plug a new one in and try.

I hope that this is helpful to others in the future if they run into a similar problem. This is a simple case of sticking with the major components an engine needs to run. Spark, Fuel, and compression. I ruled them out as I went. Experience is also helpful when dealing with these things. Some people may not realize that you should easily see spark especially when coming from the coil. I nice blue arc is what you want to see. A weak spark will only be "blown out" by the compression in the cylinders which is why the engine wouldn't start. I had to almost strain my eyes to see the spark on my tester. I worked up-stream to come to the conclusion of a bad coil.

Thanks guys! Happy Jeepin!