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Unread 08-13-2010, 01:56 PM   #1
keithert
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CPS adjustment and worsened gas mileage

I removed my camshaft position sensor (CPS) to check it for the wear that many 05-06 models are experiencing. I marked the gear position and took a photo of the position of the housing. When I put it back together it started immediately and has not turned on the check engine light or thrown a code at all. My gas mileage though has seemed to get worse. Before this on the road it would get 20-21 mpg and around town 16-18. Overall it seems to be getting 2-3 mpg worse than before. On a road trip I just completed it only got 16.5 and 17.3. On similar trips in the past it's gotten 18-21. What I wonder is if the housing for the CPS is rotated even slightly could it affect the timing enough to cause worsened gas mileage. From what I've read of the electronic system this should not be possible without it throwing codes. But I know on an old distributor system a slight turn of the housing would throw the timing off 2-3 degrees. I have not done a "cam/crank relearn" using a DRB scan tool.

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Unread 08-13-2010, 02:26 PM   #2
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I pulled today too mine had the abnormal wear, as far as fuel mileage my highway was always 15 and in town about 13... sorry can't help...
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Unread 08-13-2010, 02:49 PM   #3
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I pulled mine put it back on with marks but didn't get it lined up "just right" ran fine no codes but my exhaust was glowing and now I have partially plugged cat according to the dealer. took it in for the exhaust glowing and had them check the timing, was off 9 degrees
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Unread 08-13-2010, 02:54 PM   #4
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You have affected your fuel synchronization, not timing.It has to go back in at the exact same position as it came out!The camshaft or crank can not be moved during re installation of oil pump drive gear.I didn't have a DRB scan tool... after a few attempts I towed it to the dealer and they reset it for me.I learned this when installing my stroker.I know better the next time!Good luck!
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Unread 08-13-2010, 05:23 PM   #5
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Quote:
Originally Posted by GOLENJEEPTJ View Post
You have affected your fuel synchronization, not timing.It has to go back in at the exact same position as it came out!The camshaft or crank can not be moved during re installation of oil pump drive gear.I didn't have a DRB scan tool... after a few attempts I towed it to the dealer and they reset it for me.I learned this when installing my stroker.I know better the next time!Good luck!
I didn't turn my engine over at all while the CPS was out. The crank and cam stayed in the same position. I think if something is off it just may be the timing by some rotation of the CPS housing. Other than the gas mileage I have had no driveability issues. I'll probably take it to the dealer for the CPS wear issue on Monday.

EDIT, I've done some reading about fuel synchronization and it sounds like that might be the issue.
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Last edited by keithert; 08-13-2010 at 06:06 PM..
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Unread 08-13-2010, 06:51 PM   #6
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What do people do if they replace an engine? Have to drag it to the dealer to get that thing timed?
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Unread 08-13-2010, 08:00 PM   #7
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Originally Posted by chris142 View Post
What do people do if they replace an engine? Have to drag it to the dealer to get that thing timed?
There is a procedure to get it set up, but to fine tune it you need the DRB scanner.
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Unread 08-13-2010, 09:31 PM   #8
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If you read my previous post, it should explain.Timing is adjusted through the CKP it has nothing to do with the CPS.Forget about the distributor era!You didn't use a toothpick or such for alignment when you removed the oil pump driveshaft correct?You need to now re-establish the correct positioning with a DRB scan tool! You would understand this if you had a FSM!
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Unread 08-13-2010, 09:32 PM   #9
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Quote:
Originally Posted by chris142 View Post
What do people do if they replace an engine? Have to drag it to the dealer to get that thing timed?
If you don't follow the proper procedures,yes.Read an FSM and it will explain the procedure and what your options are.
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Unread 08-13-2010, 09:34 PM   #10
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Quote:
Originally Posted by keithert View Post
I didn't turn my engine over at all while the CPS was out. The crank and cam stayed in the same position. I think if something is off it just may be the timing by some rotation of the CPS housing. Other than the gas mileage I have had no driveability issues. I'll probably take it to the dealer for the CPS wear issue on Monday.

EDIT, I've done some reading about fuel synchronization and it sounds like that might be the issue.
The CPS is not the problem.That is a simple procedure to replace.The fact is you pulled the oil pump drive gear out on top of this!
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Unread 08-13-2010, 09:38 PM   #11
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You must have not marked it very well. I did the same thing as you and it went back exactly how it came out after playing with it for 30 mins.
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Unread 08-13-2010, 11:25 PM   #12
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I've said it numerous times in the other camshaft position sensor thread, but I guess I will repeat it here.

Don't try and make pen marks so you can realign your CPS assembly because you will never get it right back where it was.

The only way to insure that it will be put back in the EXACT same timing location is to use the timing alignment hole.

To do this you undo the two torx screws and remove the cover from the top of the CPS assembly. Once inside you will see the reluctance wheel that is spun around by the camshaft. On the wheel is a small hole about 1/8" in diameter on the edge of the wheel. This is the alignment hole and on the bottom of the housing there is matching hole roughly in the 7 o'clock position.

To use the alignment pin you have to either turn the crankshaft with a wrench on the crank pulley or if you have a manual transmission put it in 5 or 6 gear. With the Jeep in gear have someone slowly push it till the hole in the ring lines up with the hole in the bottom of the housing. Once they are lined up slide the tightest fitting allen wrench or similar object in the holes to lock the rotor.

Now that the rotor is locked you can pull the housing and inspect it. Once your done slide the housing back in and reinstalled the clamp that holds the housing down. Then all you have to do is remove the allen wrench, put the cover back on and your ready to roll.


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Unread 08-14-2010, 12:01 PM   #13
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Quote:
Originally Posted by GOLENJEEPTJ View Post
If you don't follow the proper procedures,yes.Read an FSM and it will explain the procedure and what your options are.
THX. Fortunatly I've never had to replace a 4.0. Done tons of Chevys and ford v8's though.
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Unread 08-19-2010, 07:11 AM   #14
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I had the dealer remove and check my CPS for wear and redo the crank/cam relearn. The gas mileage is still down. I'm now getting 15 commuting and only 16-17 on the road. It had gotten as high as 21 on the road a month ago.
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