Odd Driveability issue , please advise - JeepForum.com
 
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post #1 of 4 Old 12-29-2012, 07:03 PM Thread Starter
lostone73
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Odd Driveability issue , please advise

My TJ has been running awful lately, it struggles accelerating past 3000 RPM or anything over half throttle it "pops" through the throttle body.

What Ive done so far:

Checked fuel pressure , result was 44 psi at all speeds and loads

checked exhaust and CAT for restrictions, none found.

Also this problem is not tripping any DTC's at all.

I have a decent pro type scan tool, here are some results

TPS seems ok .70vdc closed and 3.83 or so at WOT

MAP, CMP and O2 readings seem ok and within range

WHAT I DID NOTICE WAS THIS:

Crank Position Sensor (CKP) readings were a little odd, at a smooth idle(650 RPM) the CKP counts hold steady around 170-180counts, then will drop to 14 or 17 momentarily.

Has anyone seen this anomoly in the CKP counts or this driveability issue?


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post #2 of 4 Old 12-29-2012, 10:15 PM
hndswthtshdws
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I'd start with new plugs and wires. Then a compression test.

Could be a valve hanging open or loose clearance. Spark wires crossed. Blown head gasket. Dirty distributor cross sparking, except you don't have a distributor.

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post #3 of 4 Old 12-29-2012, 10:33 PM
Curly5759
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Depending on the update speed of your scan tool, the CKP readings are most likely normal. The CKP will count up to 250 (IIRC) then reset to 0 and count up again. Rinse, repeat. What you are probably seeing is the scan tool refresh rate catching a reset in the act. Try graphing the CKP if your scan tool can do that.

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post #4 of 4 Old 12-29-2012, 10:47 PM
Patrick H
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CKP count is normal. Just watched a data stream on an XJ 4.0 the other day after a CKP sensor replacement.

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