I've lurked around here for a few years or so when i needed technical advice and always found the solution. Unfortunately I am dealing with a bigger issue than the search function has netted. I'll give a brief background on the Jeep and issues, what I've checked, etc.

2000 xj with 150k. Engine got hot about three years ago, and took a nice chunk out of a piston. About a year later, me and a buddy pulled the engine and I had a reputable machine shop rebuild the longblock with all new parts minus the crank and rods. Me and a different buddy put the engine back in a few months later. I had clearance issues with an aftermarket header, and weather turned cold and lost interest in it. Fast forward a year and a half till now. I put the factory manifolds back on and tied everything back together. Had initial starting issues that ended up being a bad camshaft position sensor; installed a new one and jeep fired right up but with a really bad skip. The timing has been checked multiple times and snap on scan tool is saying it's dead on. Cylinder #2 and #6 seemed to be dead. If you pull the injector harness, there is no change on both cylinders. I have swapped injectors with a firing injector and no difference. I have not tracked the wiring back to the PCM but injectors themselves seem to be good. New coil boots and plugs (champions) and swapped plugs around similar to injectors with no change. My question is this; are cylinders #2 and #6 related in anyway as far as wiring, coil packs, etc? Anyone else had similar problems with just two cylinders dead? Any other insight would be appreciated as I am losing interest in the jeep yet again.

 

How did you go about installing the CPS?
Does this engine have a 0331 cylinder head?
What are the results of the compression test?
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Check the coil pack:

"Checking the resistance involves 2

parts

parts

:

1. primary resistance
-measuring the resistance between the two pins in the ignition coil connector
primary resistance between 0.6-0.9 ohms

2. secondary resistance
-measuring the resistance between one of the connector pins to the spring inside
secondary resistance at 6k to 9k ohms"

 

To be honest, not 100% sure on the crank sensor. My buddy was hooking up all the lower engine/trans harness.

It did and still does have the 0331 head.

Have not done any sort of compression test yet.

I do want to add that there is no check engine light or pending codes.

 

Unlikely. Cylinders 2 and 6 are on different coils. If you had a dead coil, you'd lose 1 & 6, 2 & 5 or 3 & 4 in those pairs. That's not to say you can't have a wiring issue inside the coil rail for single cylinders somewhere between the coil and plug contact, but considering how they're sealed up and self-contained, it's not all that likely. If you can find a known good coil rail you can borrow or buy for cheap, you could try swapping it in to rule out the rail. But if you can't easily get your hands on one, I would hold off on buying a new one until some other testing has been done.

Before doing anything else, I would dump the Champion plugs. I know they're the spec on the firewall and everyone always recommends them (correctly) for '99 and earlier, but the ignition system in the coil rail Jeeps actually likes the NGK ZFR5N plugs better, to the point that Chrysler added them to the firewall in later 4.0L vehicles. A 2000 in good repair should run okay on Champions, but personally I would give the motor every advantage in this situation just so I'd know it's not the plugs. And plugs are cheap.

Your best approach is to work the problem systematically. Based on what you already know, I would start by getting a noid light and testing the injector circuits to make sure you're actually getting a signal to the injectors. Auto Zone usually has a noid light kit for loan. Keep in mind the noid light will cause the computer to throw injector circuit codes, so be prepared to clear those and don't let them become a red herring. If the light isn't flashing steadily on those cylinders, you know you have an injector circuit issue or computer problem.

I would also buy or borrow a fuel pressure test kit and test the pressure at the rail. You should see 49 psi plus or minus 5 psi at idle. The fuel pump and filter are all one unit on your year. If the fuel pressure is low, you'll need to drop the tank to get to replace it.

Next, test compression. Again, you can borrow a compression test kit from an auto parts store if you don't have one.

The timing on these things is controlled by the computer, based on input from the camshaft position sensor and crankshaft position sensor. Regardless of what your scan tool is telling you, you might want to manually check the indexing on your oil pump drive to make sure the camshaft position sensor is reading correctly and your physical timing isn't outside what the computer can compensate for. Details on testing/reindexing the shaft/sensor are here:

http://www.jeepforum.com/forum/f11/h...ensor-1145301/

Your problem doesn't sound like the crank position sensor to me, but you can rule it out with a meter. A cheap $10 meter will do the job. Here's the procedure:

https://www.cherokeeforum.com/f51/testing-cps-5563/

There are some other things I would normally do, like pulling the valve cover off to visually inspect the springs and rockers, doing a leak down test, decarbonizing the combustion chambers, etc. But if this engine was rebuilt, logically I would save those things for later in the process.

Also, the 0331 doesn't seem like a likely cause. The cracking issue usually affects cylinder 3 and sometimes cylinder 4. Cylinders 2 & 6 shouldn't be affected by the known cracking issue at all.

 

Update.

-Checked all injector harnesses with a noid light. All were getting a signal.
-Checked coil rail with a spark tester and got a spark on every plug.
-Swapped old Camshaft sensor to rule out the new one being bad.
-Checked Crank sensor and checked good.

*Still has two dead cylinders on #2 and #6.

Did a compression test with these results. No major changes between dry and wet test on #2 and #6.

#1 - 145
#2 - 115
#3 - 150
#4 - 155
#5 - 155
#6 - 125

Being a rebuilt engine that sat for over a year, could those cylinders have been washed out and the rings just not seated yet?

 

Well I bit the bullet and bought the ngks and a new rail. Running like a new jeep. It has a low idle after warm but I had that before the rebuild so I probably have a TPS going bad.