Engine Timing on a rebuilt 2008 JK 3.8l - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 5 Old 10-09-2017, 01:26 PM Thread Starter
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Engine Timing on a rebuilt 2008 JK 3.8l

New post yet related to my earlier posts on weird compression readings. Thanks all who posted to that thread. It turns out I had mid-timed the cam by nearly 20 degrees. Weird as this isn't my first rebuild. At any rate I carefully set the cam timing with #1 cylinder on TDC, the cam gear arrow pointing down and the blue links on their respective teeth. Everything lined up as one would expect on a new chain and gears. The engine starts hard and misfires back through the airbox. It is as if my sparkplug wires are wrong yet they are correct. Plugs are new. Once running the RPM will rev, yet very sluggish. Once the RPM drops below 2000, the misfires kill the engine. Their were two codes. Airbox inlet temperature too high and Mutiple Cylinder Misfires. The Airbox temp code repeated after code erasure. I even checked the visual timing on the cam by pulling the #1 spark plug and the right tappet cover. The sequencing on the valves looked appropriate. I'm stumped.
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post #2 of 5 Old 10-09-2017, 03:02 PM
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It does sound like some wires are crossed.

Double check the wires for proper routing. If they disappear behind the engine, making it hard to trace them, check each one for continuity with a multi-meter.

The coil pack has cylinder numbers on it.
Right engine bank, (passenger's side), is 1, 3, 5.
Left bank, (driver's side), is 2, 4, 6.

When you installed the cam position sensor, did it have a new paper spacer on its face, to ensure a proper gap between it and the cam sprocket?

The 3.8L is an interference engine.
After you re-timed the cam, did you perform another compression test?

2008 Unlimited Rubicon Automatic

Last edited by ronjenx; 10-09-2017 at 07:15 PM.
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post #3 of 5 Old 10-10-2017, 09:48 PM Thread Starter
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I completed another compression test. Same result as before I re-timed the cam. Long story short when I attempted to start the engine with the cam miss set the valves hit the pistons and several bent rods. The heads are off the jeep and at the machine shop. I'll post the results in a week and let you know how it cranks and runs with the rebuilt and shaved heads. I'm assuming I can just sand flat the small smiles in the pistons. Their new and it would be time and money to replace them.
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post #4 of 5 Old 10-24-2017, 08:32 PM Thread Starter
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I?m embarrassed to say the reason for the misfires were bent valves to to my prior misaligned Cam. After $375 for 6 intake and one exhaust valve all 6 cylinders are producing 175psi compression. The reassembled engine cranks yet is running lame. It revs to over 5k rpm yet is throwing a P300 Multiple misfires. My next step is to verify no intake or other vacuum leaks. Plugs and wires are new and I verified all are properly seated in their right slots.
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post #5 of 5 Old 01-09-2019, 08:31 AM
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Did this ever get resolved? Curious what the issue was.

'09 JKRU. 4" Teraflex long arm, Teraflex R44 housing, Teraflex / Fox Resis, Poly Performance skids, Nemesis Billy Rockers, Nemesis flares, 37" ATZ P3s on 17" 5x5.5" Trailready HDs, Spyntec hubs, Teraflex BBK, Mopar BBK master/booster, Superior front & Alloy USA rear axle shafts, CTMs, Reids, Synergy drag link & tie rod, WTOR hydro-boosted steering, 5.38s, TF Dual Rate front bar, TF bumpers, Warn Powerplant, Tom Woods shafts, AA xfer case cable, Kilby canister relo, RH4x4 cage.
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