Clayzer

Flexplate on my 2000 XJ cracked so I just replaced it with one from O’Reillys #FRA480. Now my XJ won’t start.

Square holes matched, torque converter holes matched, clocked correctly. CPS replaced. Old one registered 40 ohms, new was at 3 ohms.

I have fuel and spark. I have cleaned out every electrical connector.

any tricks to get my XJ running?

agreen

Put the old CPS back in?

Bryan Tift

It's turning over right? Starter works?

You need compression, fuel, spark, timing, and air to get an engine to run. If it was running before, you should have compression. Timing is computer controlled but make sure you installed the CPS, plugged it in, that's it's orientation is correct, and that it's the right CPS for the vehicle! Different years have different CPS part numbers. Air should be fine - confirm no blockages. Check that when the CPS is removed that you can see and feel the flexplate teeth.

Fuel and spark are last two. Confirm you have fuel pressure with a pressure gauge. Should be 45 +- 5psi at idle, key on engine off.

Confirm you have spark with a spark tester. I know you said you did but if everything else is fine and you have fuel and spark it should work.

Confirm your fuel injectors are firing with noid lights. This will ensure injectors are pulsing.

Clayzer

Starter turns the motor over. Took the inspection plate off the tranny and I can see tooth engagement. The engine will stutter and act like it is starting but it will quickly die.
spark is good, fuel is good, don’t have a compression tester.

Flexplate is mounted correctly and it’s the correct one. However, I just read that some aftermarket plates have a slightly smaller diameter CPS ring. This makes the CPS further away. Haven’t had a chance to check this but I will here in a few minutes.
I also might have picked up a bad CPS from the store. I need to test for continuity.

Bryan Tift

Is the CPS MOPAR brand or some cheap autozone/napa/oriellys crap?

Aftermarket CPS are known for being 100% bad out of the box.

Clayzer

Is one from Oreilly's. Discovered how faulty they are after buying it.

Did a bunch of electrical testing.
CPS have 3 terminals.
1= 12v
2= Ground
3= 5V power

I hooked up the negative side of the battery and probed Terminal 3 with the ACC power on and turned my Flexplate. I got 5V all the time. I verified the sensor was in a window with my fingers. I took the sensor off and it still roistered 5v. Touched it to my frame, still 5v. I plugged in my old CPS, stilll 5v at all times.

I then tested for ground. Hooked up my meter to the 12v battery terminal, turned the car to ACC power and probed the 2 terminal on the harness and didn't hear a beep on my continuity setting.

I Then tested for 12v power by hooking up to 12v battery, ACC on, Multimeter set to 12V setting, Red lead in the 1st Terminal and Black in the 2nd Terminal. I got .3 volts. I then touched the black lead to my frame, .3 volts.

Does this mean I have a busted power wire somewhere?

Clayzer

Still cant get my XJ to run. I think it doesn't have any spark
Flexplate replaced with correct flexplate. Everything matches up and in the right location.
CPS is good. Terminal 1 goes between 0 and 5 volts when the flexplate is turned. Terminal has a good 12 ground. Terminal 3 has a constant 5 reference volts from the PCM (Ive checked this with 2 jeep CPS and 1 oreilly's)
TPS has a good ground and 5 volts
MAP has a good ground and 5 volts
CamPS has a good ground and 5 volts
Took the CAM PS cap off and it looks ok inside.
Took the ignition coil off and tried getting a spark plug to light off when I turned the key but couldn't see any spark. Ran an ohm test between terminal 2 and the other 3 terminals on the ignition coil and got 1 ohm. Spec is .7-.8 ohms. Because mine is at 1ohm, could this be my gremlin?
Swapped the ASD relay with the one from the blower. I can hear the fuel pump turn on with each relay.
The Jeep will kind of start but it will quickly die and shoot air back through the intake. I also hear a thud from the rear.
What could be causing this. Is there another sensor I need to check?
Dumb question, I dont need my drive shaft in to get this thing to run do I? I left it out just incase I need to pull the tranny back out.

awg

* If you think it doesnt have any spark, buy an inline spark tester for a few $ and verify that for a fact and work backwards

* spray ether into the air intake with the air filter removed just to see if it wants to start that way

* If your model has a distributor, verify it rotates the rotor as it should when you crank the engine

* verify fuel pressure

cruiser54

My money is on the flexplate being defective.

awg

oh yeah, I thought for some reason he put his old flexplate back in

maybe it was some recent guy that fixed his by doing this

a junkyard flexplate from the same year XJ that isnt cracked, although clearly a somewhat undesirable option, may be one possible solution

if simpler solutions do not prevail

cruiser54

This happens all the time. The reverse engineered flexplates from overseas are made with the holes in the wrong place, the outer ring too far away from the CPS.

awg

I have learned the hard way to measure all critical dimensions with a vernier or some instrument of accuracy, new against old. Less than 1mm can make a world of difference

Assuming a new part will be right, and especially throwing away the old part before on is assured is a big mistake

Clayzer

Everything is the same and the CPS picks up the flexplate just fine. When I turn it by hand it fluxgates between 5 and 0 volts signaling that it see the windows.
I had it running yesterday but now it wont start again.

5-Speed

Don't quote me on this cause I am no expert on Jeep flexplates but those are not the same. See how the window on the oem flexplate goes all the way to the ring gear, the new one does not. That may be enough to throw the signal off depending on where the crank sensor is actually reading from.

Clayzer

I was going through my fuse box and noticed Fuse 21 and 18 were not completing a circuit.
FSM says
F21 is the PCM C3 (F142 18DG/WT) FUSED AUTOMATIC SHUT DOWN RELAY OUTPUT
F18 is the (A142 18DG/OR) which is the FUSED AUTOMATIC SHUT DOWN RELAY OUTPUT This guy runs through C107 (the big black rectangle on the passenger side of the engine up against the fire wall.
Do any of you know if these fuses are supposed to be hot when the key power is turned on? These might be causing my ignition problem.