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Unread 07-13-2013, 12:54 PM   #1
TrannySourceRex
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Runaway throttle 4.0L 2000 WJ – new timing chain and cam

I just finished installing new timing chain and sprockets, cam, and lifters into a 4.0L straight six in a 2000 WJ. I have rebuilt several different engines in the past, so I am familiar with the mechanical parts, and I believe I have everything back together and timed correctly. When I initially tried starting it, I got some backfiring, so I re-set the cam position sensor (CPS) by putting the engine at TDC and aligning the CPS with a drill bit in the alignment hole. The body of the CPS aligns with the engine, so it must be close. Since then, the engine will start right up, but acts like the throttle is held wide open. I can only start it momentarily as it will rev like the throttle is stuck. I have checked that nothing is interfering with the throttle or cables, and have removed the air intake to be sure. What could cause this? Massive air leak somewhere, acting like the throttle is open? But won’t the TPS control this regardless of a vacuum leak? What other things should I look for?

Any help would be greatly appreciated.

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Unread 07-13-2013, 01:00 PM   #2
TrannySourceRex
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I should add that the car ran great before I took it apart. There was a ticking noise that looks like it was a loose timing chain and broken chain ramp/snubber that caused me to tear into the engine.
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Unread 07-13-2013, 01:12 PM   #3
Mean Max
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Massive manifold leak. It won't rev up without air.

I suspect the intake manifold isn't seated properly on the alignment dowels.

Max
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Unread 07-13-2013, 01:18 PM   #4
TrannySourceRex
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Thanks Max - that may make sense, as during the brief running, it also sounds like there is an exhaust leak. I must not have the intake and exhaust fully seated. I'll check that.
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Unread 07-13-2013, 09:38 PM   #5
rjbruzan
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Or the seals around the injectors.
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Unread 07-14-2013, 08:36 AM   #6
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Massive manifold leak. It won't rev up without air.

I suspect the intake manifold isn't seated properly on the alignment dowels.

Max
This^^. Extremely common.
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Unread 07-14-2013, 02:58 PM   #7
TrannySourceRex
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Max and Cruiser54 had it correct. I remember now that the steering pump did not line up well with the bracket attached to the block and the bolts needing to screw into the intake manifold.

I loosened up the intake/exhaust bolts and jiggled the intake manifold until I found the alignment pins. Tightened it up and the steering pump now bolted up without any binding. The engine fired right up and ran normally. I completed the 20 minute cam break-in at 2000 RPM and changed the oil. I went for a brief drive around the block and everything appears to be working great. Thanks again for the help.
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Unread 07-14-2013, 02:59 PM   #8
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Glad to hear it.
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Unread 07-14-2013, 03:09 PM   #9
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Good to hear.

Congratulations on the successful resolution!

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