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MikeBell81

2000 TJ 2.5L won’t start after rebuild

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I just helped a friend install a rebuilt engine into his son’s 2000 Jeep TJ with a 4 cylinder 2.5L, manual trans and 4WD. He got the engine as a long block so we only had to reuse the tin covers, ignition and fuel systems. He got it from a reputable nationwide rebuilder so we are not concerned with dumb mistakes like timing chain installed incorrectly issues etc.

We installed distributor as described in the service manual (TDC on 1 of compression stroke with 3/16 pin thru Camshaft Position Sensor and distributor housing etc.). The crankshaft position sensor is a two bolt type so no adjustment needed. I’m aware the PCM controls the timing so we can’t do anything with that. I’m assuming the CKP is working because we are getting flashes from the timing light.

When trying to start the engine it kicks and bucks with an occasional backfire thru the throttle body. We connected a timing light to number one and looked for the initial timing around the marks on the timing cover but it appears the mark on the balancer is showing up at about 50 degrees after TDC. We have triple checked everything (firing order, sensor connections etc.) but can’t figure out how to get it running. We tried putting the PCM in learning mode by disconnecting battery and holding positive and negative together for several hours to try to drain the capacitor that keep PCM memory alive.
We also did the ignition ON, headlights ON and then OFF, ignition OFF procedure. After putting in learning mode we disconnected the fuel pump fuse so we could crank the engine long enough for the CKP to figure out what is going on.

Does anyone have any ideas on where to look next?

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MikeBell81...You've been thorough.  There is obviously a spark timing error at 50 degrees ATDC.  Firing order is 1-3-4-2.  You have a distributor, not coil-on-plug, so this should be easier to trace down...I would take this approach:

1)  Remove the distributor cap and pull #1 spark plug.  With KEY OFF, rotate the crankshaft in its normal cranking direction and bring the #1 piston slowly to TDC on the compression stroke.  Use a sounding device or finger to confirm that you're coming up on the compression stroke and not the exhaust stroke.

2)  Stop at TDC on the damper.  Confirm that the #1 piston is at the top of the cylinder.

3)  See where the distributor rotor points to pinpoint whether that's close to #1 spark plug's terminal in the cap.  Recheck the camshaft position sensor if you suspect that the cam reference signal is misaligned.

If the distributor/rotor indexing looks right, test the Crankshaft Position Sensor resistance.  It is not uncommon for the sensor to become damaged during an engine installation.  A faulty crankshaft position sensor, or its wiring and engine grounds, can create the symptoms you describe.  This can also make the timing light flash erratically.

Note: One rebuilder lists this data and casting numbers for a 2000 Wrangler TJ.  Camshaft and casting details matter.  You can compare...

 2000 Jeep Wrangler

  • OHV; 8 Valve Eng.; Chrysler Engine; MFI; MPI Fuel System; In-Line Head Cast # 403, 117; Cam Cast # 53020495; Crank Cast # 904; Block Cast # 403, 474; Check Cam Cast, No Temp Sensor Head Rear; 1.125" Crank Snout, No Oil Pypass in Block; SEN; 249 

Also check the engine and body grounds.  Let us know what you find...

Moses

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Hi Moses,
Sorry for the delay, I had to go home and my friend lives 4 hours from me. I’m relaying messages to him and he is trying to find time for diagnostics.
 
We have verified the timing mark on the balancer is within an inch or so of TDC when the piston is on the compression stroke for #1. It’s hard to find exact TDC on #1 with the head on but we are close.
I’m working on a theory the balancer mark is off on the front pulley, which would cause the distributor to be in the wrong place. I had my friend monitor the location of the pulse generating notches on the flywheel compared to the harmonic balancer mark and the rotor in the cap. From what I’ve read there are 2 sets of 4 notches on the flywheel for the crank sensor and the coil fires on the training edge of the 4th notch, which is at 4 degrees before TDC.

“The notches cause a pulse to be generated when they pass under the sensor. The pulses are the input to the PCM. For each engine revolution there are two groups of four pulses generated on 2.5L 4-cylinder engines. The trailing edge of the fourth notch, which causes the pulse, is four degrees before top dead center (TDC) of the corresponding piston.”

I downloaded a photo of a Jeep flywheel and marked it up to show approximate locations of timing events. If you look at the table in the photo you can see by the time the 4th notch gets to the sensor we are way past TDC and the rotor can be firing either plug 1 or 3. The timing mark is about where I saw it when I was using the timing light on the number 1 plug. When my friend finds some time he is going to remove the balancer bolt to see where the crank keyway correlates to the timing mark on the outside edge of the pulley. I don’t know exactly how far apart they are supposed to be but from photos I’m guessing about 45 degrees. If it looks way off we can compare it to one at the auto parts store.

Lastly we did verify proper grounding and we will check the sensor resistance. I will let you know what we find.

Thanks,
Mike

JeepTiming.jpg

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I just spoke to my friend after he reviewed my last post. He said it felt like the notches were closer together (not 20 degrees apart) like in the photo but the timing events were accurate. He also mentioned he thought the CKS wires looked a little damaged so he is ordering another one and we will see what happens when the new one gets installed. No need to reply to my last lengthy post.

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We finally got it running; it wasn’t the CKS but rather the timing mark on the balancer. We removed the balancer bolt to expose the crank keyway and discovered the pulley timing mark was at least 100 degrees off from where it is supposed to be. We went to the auto parts and measured the correct spacing, about 2.25” from keyway to timing mark, and created a new mark on the old balancer.  We re-stabbed the distributor and it fired right up.

Moses, thanks for your help.
Mike

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Great, Mike...That's another good reason for placing #1 piston at actual TDC on its compression stroke.  I was thinking in terms of the distributor indexing, cap and rotor position. Your discovery about the damper ring slipping was right on.  Unusual to find this, but it does happen.  You'll have to see if there's any kind of imbalance with the defective damper.  As far as timing index goes, your measurement for the TDC mark provided the correct tooth alignment for the distributor.  The distributor housing has a fixed position, and the distributor shaft and rotor are now indexed properly with the camshaft and #1 TDC.  All spark timing is controlled at the PCM.  You obviously nailed it! 

You approached this academically, which is always great.  The flywheel only fits the crankshaft one way, so the notches would be correct if you used the original bellhousing and CKS location. You went to the other end of the engine and found the problem.

Moses

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