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How to reindex the camshaft position sensor

177K views 58 replies 30 participants last post by  aprilkaelber 
#1 ·
From what I've read, the timing chain stretches out as you rack up the miles on your Cherokee with a coil rail and at some point it gets outside of the range the computer can correct for it. Mine got there right after I installed a new crank position sensor and hit 130,000 miles.

The process is easy. You need a helper, a toothpick or small drill bit, some basic hand tools and a "mirror on a stick" so you can see the timing marks on the bottom of the cover.

Remove the coil rail, the first spark plug and the camshaft position sensor.
Carefully place a finger of the spark plug hole.
Have your helper bump the starter a little at a time until you feel pressure.
Break out your mirror and check your timing marks.
Use a ratchet or wrench, 19mm I think, to turn the crank forwards to the zero mark.
Remove the camshaft position sensor from the camshaft synchronizer.
Loosen the retaining fork that holds in the camshaft synchronizer.
Find the small hole in the outside of the housing for the oil pump drive shaft.
Find the small hole on the magnet inside that indicates camshaft position.
Carefully turn the housing on the camshaft synchronizer until you can align those two holes and insert a toothpick or drill bit straight through them.
Tighten down the retaining fork, reinstall the camshaft position sensor, spark plug and coil rail.
Enjoy quicker starts and having avoided the problems that this stupid sensor causes when it gets even further out of spec.

The NAXJA guys finally found my problem and provided me this link to learn what the fix was. The process for finding top dead center and zeroing the timing came from my dad although I performed the work myself. It's basically the modern iteration of setting the timing on something you're led to believe you don't have to set the timing on.

Also, this is just the shade tree mechanic version of the fix. Alternately you can take it to a shop with a DRB scan tool and they can reprogram the computer to compensate the difference without ever having to open the hood or turn a wrench. A JF member in a thread I don't recall posted that the shop he went to wanted over $100 to do this. A guy in my Jeep club said he'd do it for free for me. Like anything else, YMMV.

(This may still be edited for terminology and additional accuracy.)

To illustrate the location
 
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#4 ·
The DRB will reprogram your computer to compensate for the stretched timing chain without actually fixing the condition causing the problem. The instructions about allow you to physically adjust the CPS for the condition. The DRB might be good for fine tuning but short of replacing a timing chain simply because it stretched some, this is indeed a proper repair. Also I am not 100% certain, but I believe if you perform a factory reset on the computer, you will loose any aftermarket DRB reprogramming.

How do you think a "professional repair" would be different?
 
#21 ·
#6 ·
When I get a chance I would like to add the codes and symptoms I was having along with more pics and the verified socket sizes for everything.
 
#12 ·
If it was daylight, you probably could have seen the timing marks in the mirror in this pic. Mine are a little greasy. Yours probably are as well. This is the area you need to look for them in.

 
#15 ·
NEVER turn a motor backwards. Especially when you're trying to adjust for timing chain slack.



The dealer doesn't program your computer for the fuel synch, they use the tool to monitor the dwell while turning the oil pump drive/cam sensor assembly into the correct window.


The cam sensor has nothing at all to do with what is traditionally called timing, which is spark advance. Spark advance is read from the crank sensor only.

Anyway, if you have chain stretch the proper solution is to spend 75$ on the chain and gasket set and fix it properly.
 
#20 ·
Runs like new

Wow! I finally got around to realigning my cam position sensor today. It was off by about 10 degrees. Huge difference in throttle response and smoother idle. Now just have to wait a few run cycles to see if the P0300 problem goes away. Reminds me of improvements made with earlier distributor models when adjusting distributor timing.
 
#24 ·
timing chain

You're right about that, it can be a pain to get to but I've had a little experience with them. I've put a new one in the last three XJs I've owned and rebuilt the engine in two of them. Getting everything else out of the way is the biggest part of the job. I may slip a performance cam and a new set of lifters in it while I'm there.
 
#25 ·
You're right about that, it can be a pain to get to but I've had a little experience with them. I've put a new one in the last three XJs I've owned and rebuilt the engine in two of them. Getting everything else out of the way is the biggest part of the job. I may slip a performance cam and a new set of lifters in it while I'm there.
What performance cams are offered for the 4.0 that dont really require any other mods?

~Nate
 
#30 ·
mileage



I haven't driven it enough since reindexing it to be able to get a concrete average, but just from the couple of fill ups so far it appears I have gained at least a mile or two per gallon. Anything is better than nothing but I was mainly after that pesky random misfire issue and it doesn't appear to have fixed that. What it has done is give me a better indication that I have injectors that aren't closing completely and are bleeding fuel into the cylinders after shutdown. I have a set on the way from painjectors, I'll let you know how it goes once I get them installed.
 
#32 ·
I reindexed my cam sensor last year and I definitely felt an improvement. With that said I just rebuilt the motor on mine and comparing the old timing chain to the new one I found almost no difference in length between the two, that's with 170,000 miles on it. I'm talking less than 1/4" if that. The amount of stretch needed to throw off the timing must be very small since the chain I took out was completely usable still. I'm thinking now it may be a result of overall wear on the valve train as a whole because I found more significant wear on the cam lobes, .005.-.007, than anywhere else. If I didn't have the new chain and gears already I would have definitely reused the set I took out, no questions asked.

Also about cam selection, unless you plan to use your jeep for racing, WOT, what has been said already is right. The stock cam grind will be the best you can find for what most of us want from our jeeps, low end torque. Increasing the lift or duration may increase top end HP but will also move the torque curve peak higher in the RPM range, not something most people want or can honestly benefit from. Just my .02.
 
#33 ·
I reindexed my cam sensor last year and I definitely felt an improvement. With that said I just rebuilt the motor on mine and comparing the old timing chain to the new one I found almost no difference in length between the two, that's with 170,000 miles on it. I'm talking less than 1/4" if that. The amount of stretch needed to throw off the timing must be very small since the chain I took out was completely usable still. I'm thinking now it may be a result of overall wear on the valve train as a whole because I found more significant wear on the cam lobes, .005.-.007, than anywhere else. If I didn't have the new chain and gears already I would have definitely reused the set I took out, no questions asked.
Your old timing chain has 1/4" of slop in it and you would be okay with using it on a rebuild? :nono: The whole idea of "reindexing the CamPS" is to save the trouble of tearing into the front of the motor. It's just a quick fix. I haven't ever heard of someone using an old timing chain after rebuilding a motor. Why not reuse the same air filter and spark plugs too? I know it's not a super cheap part set, but it's common sense to replace them even after 30K-50K miles if they are accessible for some reason during any project.
 
#34 ·
As a matter of fact yes I did reuse the same air filter and spark plugs, nothing wrong with them so I put them back in. If I was to follow your line of reasoning I might as well just get a whole new jeep to put my rebuilt motor in, I mean it does have 170,000 miles on it, I can't reuse that again, right? :nuts:
 
#35 ·
My 01 4.0 wrangler has 111K on it and the engine light is on and it reads cam position sensor. and it has had very good oil changes and is one clean engine and is NOT beat on. surely not a bad timein chain at 111K? heck I have had several Fords with 300k engines that started and ran OK but weaker in power.
I can disconect the battery and it goes out for maybe 100miles then will come back on while on the interstate runnin like 60mph. that just seems odd for some reason. jeep starts and runs and picks up great just the light comes on. has done it like 4 times like this. I hate to fool with something when it runs this good. kinda like the ol sayin dont fix what aint broke ya know...
 
#36 ·
JBA111 said:
My 01 4.0 wrangler has 111K on it and the engine light is on and it reads cam position sensor. and it has had very good oil changes and is one clean engine and is NOT beat on. surely not a bad timein chain at 111K? heck I have had several Fords with 300k engines that started and ran OK but weaker in power.
I can disconect the battery and it goes out for maybe 100miles then will come back on while on the interstate runnin like 60mph. that just seems odd for some reason. jeep starts and runs and picks up great just the light comes on. has done it like 4 times like this. I hate to fool with something when it runs this good. kinda like the ol sayin dont fix what aint broke ya know...
Sounds like your sensor is getting weak but just hasn't quit on you yet.
 
#37 ·
From what I've read, the timing chain stretches out as you rack up the miles on your Cherokee with a coil rail and at some point it gets outside of the range the computer can correct for it. Mine got there right after I installed a new crank position sensor and hit 130,000 miles.

The process is easy. You need a helper, a toothpick or small drill bit, some basic hand tools and a "mirror on a stick" so you can see the timing marks on the bottom of the cover.

Remove the coil rail, the first spark plug and the camshaft position sensor.
Carefully place a finger of the spark plug hole.
Have your helper bump the starter a little at a time until you feel pressure.
Break out your mirror and check your timing marks.
Use a ratchet or wrench, 19mm I think, to turn the crank forwards to the zero mark.
Remove the camshaft position sensor from the camshaft synchronizer.
Loosen the retaining fork that holds in the camshaft synchronizer.
Find the small hole in the outside of the housing for the oil pump drive shaft.
Find the small hole on the magnet inside that indicates camshaft position.
Carefully turn the housing on the camshaft synchronizer until you can align those two holes and insert a toothpick or drill bit straight through them.
Tighten down the retaining fork, reinstall the camshaft position sensor, spark plug and coil rail.
Enjoy quicker starts and having avoided

I am going to do this to my jeep tomorrow and found the 0 on the timing marks but not sure what im looking for on the crank, is there a mark or something. thanks and great write up!
 
#43 ·
Its giving me a p0304, cylinder 4 misfire, and sometimes one about an very small evap leak. I have a big write up on here about it call "Need help, cylinder 4 misfire in a 2000 XJ". Basicly it misses and runs real bad when its cold, within a mile from where I leave from then if I shut it off and restart it will run fine. I changed the plugs ( copper core) coil rail, cam sensor, crank sensor, TPS, the ECM, swapped injectors around, did a compression and fuel pressure test, ran seafoam through it and lastly checked the index of the cam sensor
 
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