sync sensor

[90xj06]

is there a way to maybe fix the cam sensor instead of buying a new one? i think this is why my jeep takes longer than normal to start. but should i replace the cps first? and can it just be dirty?

[Matthew Currie]

I don't think there's anything in the cam sensor that can get dirty. It's a magnetic device. Bad connections to it might play a part, but otherwise not mcuh you can do about it except replace. Long starts are more likely the crank position sensor or something else. Have you checked to see if the fuel rail is losing pressure when it sits?

[langer1]

There both magnetic pickups so don't need cleaning.
Slow starting is more ofter caused by a slow turning starter or low fuel pressure.

[90xj06]

i have a normal start speed. as for the fuel pressure i have tried turning the key on and off a couple times to bring pressure up but that doesn't help. so i will try the cps sometime soon. but if its magnetic how would it go bad besides the wires.

[87manche]

umm, it lives it's life in a very harsh enviroment, and it generates a signal based on magnetic fields. it doesn't take a whole lot to upset that signal generation, could have developed a hairline crack that's let in moisture, could have broken conductors inside.

[langer1]

Sometimes they become magnetized much like the heads of a tape recorder.

I had a classic CPS problem, sometimes a good start sometimes no start.
Unplugging and reconnecting the CPS started it every time, Ohm check showed good.
I took a tape head degaussing tool and degaussed it and that was two years ago.

[90xj06]

well if it just takes long to start but once running it runs fine would that still leave the cps in the equation?

[8Mud]

I've had numerous CPS's refuse to start or starting would be a sometimes thing or starting would require excessive revolutions, but when the motor did start, it would run just fine. When the CPS got flacky, temperature seemed to play a roll. Some CPS's wouldn't start cold, some wouldn't start hot. I guess the temp. differences, took it out of the resisitance envelope it was designed to work in (as will dirty connectors and grounds). 200 ohms, plus or minus 75 is a pretty large resistance envelope, I've got a CPS in my 88 now that test 278 ohms hot, time for a change. I've also had them test perfect and still not work reliably.
You need fuel and air, in the proper mix and spark to get it going.
Low fuel (or pressure) will mess you up. The IAC not parking in the proper position, will mess with the air mix. *Weak spark* can cause problems (corroded cap or cable ends). The Renix seems to need a certain number of revolutions and/or starter RPM to spark/fuel the motor correctly for a start. The CPS tells the ECU, that the motor is turning over, a fresh battery and good starter seem to help it get to the RPM's it needs for it start well. The CPS signal and other sensor processing, during start (typically low voltage in the whole system anyway), can get flacky, low voltage and/or excessive resisitance.
Cleaning all the connectors and grounds, is usually a good place to begin. Inspect the CPS wire to make sure it isn't cooking on the manifold. Battery in good shape, so it turns over fast enough.
I found the coil connections to the ignition module on mine (split the coil from the module), pretty dirty and corroded. After a cleaning them, my spark seemed a lot sharper and bluer.
Hard starting is often a lot of little things that just add up.
I once ran my Renix for a couple of weeks without the SYNC sensor connected, I never noticed any difference in the way it ran. I'm guessing if I had disconnected the battery and reconnected it, I may have had some problems. They say the Renix ECU doesn't have a memory, mine seems to remember which position the cam is in, without the Sync sensor input at every start.

[5-90]

If your CPS is totally shot, you won't start.

Here's a quick test to see if it's your SYNC sensor tho - unplug it, and try to start the engine. It should start without the SYNC sensor, but it's going to buck a bit (like the timing's off - it's guessing...) and take longer than normal to start. The SYNC sensor signal is useful, the CPS is mandatory.

The SYNC sensor can be replaced - you have to pull the distributor to do it.

5-90

[Matthew Currie]

If your CPS is totally shot, you won't start.

Here's a quick test to see if it's your SYNC sensor tho - unplug it, and try to start the engine. It should start without the SYNC sensor, but it's going to buck a bit (like the timing's off - it's guessing...) and take longer than normal to start. The SYNC sensor signal is useful, the CPS is mandatory.

The SYNC sensor can be replaced - you have to pull the distributor to do it.

5-90

Note, please, that this does not work on Chrysler (91-up) systems. If you unplug the sync sensor it will fail to start and throw a code 54. It is, however, possible under some circumstances at least, to start one of these with a bad sync sensor by first turning the ignition on, unplugging and replugging the distributor, then starting. It will run, but not restart unless you do it again. Why this works I do not know, but it did for me when the sync sensor on a 93 failed.

[5-90]

Note, please, that this does not work on Chrysler (91-up) systems. If you unplug the sync sensor it will fail to start and throw a code 54. It is, however, possible under some circumstances at least, to start one of these with a bad sync sensor by first turning the ignition on, unplugging and replugging the distributor, then starting. It will run, but not restart unless you do it again. Why this works I do not know, but it did for me when the sync sensor on a 93 failed.

Thank you - more information for the notebooks... I'm just too used to working on RENIX...

5-90

[90xj06]

i will try that. im guessing that if it makes no difference. then it would be bad.

[5-90]

i will try that. im guessing that if it makes no difference. then it would be bad.

Yeah, pretty much. Considering you've got a 1990 (going from your moniker - but it's always handy to let us know what you're working on...) you should therefore be RENIX, and that test will work for you.

The CPS reads the speed of the crankshaft, while the SYNC sensor tells the ECU which cylinders are coming up next. The ECU can "guess" at cylinders until it hits something that runs (that's why the stumble,) but if you can unplug your SYNC sensor (3-wire connector from dizzy) and the starting doesn't change, then the SYNC is probably shot. I've not known them to fail very often, tho - while the CPS has a useful service life of 150Kmiles or so. However, if you have a blown CPS, you will not start.

Helpful Hint - when posting anything that's a tech question, it's really useful to give us "baseline" information (like this - 88XJ, 4.0, BA-10 for instance - that's 1988 Cherokee/Wagoneer w/4.0L I6 and Peugeot manual gearbox - just condensed...) so we don't have to guess. My most useful expertise and advice will be on RENIX systems - if you've got a 1991 and up, that tells me that I'll need to open a manual to translate what I know into ChryCo OBD-talk.

I've actually been trying (slowly...) to get a "standard format" for the tech line - so far, unsuccessfully... However, it's easy to read on its own, and would be a HUGE help with information for tech questions. There were some changes over the years, and it helps to tell us what you've got (and what, if any, changes you've made...)

5-90

[90xj06]

ok. i have a 1990 xj 2dr with 4wd with the command-trac it has the aw-4 with the I6 power in it. this sounds kind of sarcastic the way i worded it but its not.

[90xj06]

and i also have visited your web site. which is nice i might add. you could consider adding in this if you haven't already done so. it is an electrical contact "sealant" and improver it has little metal bits that grab the connector and make it a better connection. its made by ideal. bought at home depot. and its name is NOALOX. on the bottle it says its an anti-oxidant joint compound. so far it works great. I've seen improvement in speed in starter motor.

[5-90]

I use Gardner-Bender Ox-Gard - which is probably similar. Non-conductive, non-hardening, water displacing, and doesn't crap things up like that OEM garbage does (but the OEM stuff probably costs less - by an order of magnitude...)

I am thinking of expanding my line - and I do thank you for the suggestion. If I can find a wholesaler that will allow me small quantities of Ox-Gard, I'll probably carry that as well (I don't carry it unless and until I use it. I'm funny that way...)

Without knowing more in detail, I'd probably try cleaning the CPS connectors (you can get Delphi Weatherpack tools from most auto parts houses - they'll let you take the contacts out and reinsert them. Hot water and cheap toothpaste can work wonders...) and try DX-ing the SYNC sensor to see if anything changes. Try solutions ONE AT A TIME - otherwise, you won't know what you did to solve the problem. It takes a little longer, but you'll learn more...

5-90

[90xj06]

im open to the trial and error learning. also i will let you know what happens tomorrow when i try it. also if the cps sensor is just "magnitized" is there a home avalable solution?

[5-90]

Not that I know of - I haven't had that problem yet. I've just dealt with sensor failures (due to age) and shorts (due to wiring lying on the exhuast header.) Fortunately, you can cut-and-splice the wiring, if it get melted thru...

5-90

[90xj06]

i unplugged the sync sensor and it had no effect on starting or running. so is that a bad thing?

[87manche]

unplugging the sync sensor should have made it worse than before.
if there wasn't any change then it seems to me that the sync sensor wasn't doing it's job in the first place.

[5-90]

unplugging the sync sensor should have made it worse than before.
if there wasn't any change then it seems to me that the sync sensor wasn't doing it's job in the first place.

Concur. It would be the first one I've heard of failing, but it's a possibility.

If you disconnect a sensor, and it doesn't change anything, the sensor was shot to begin with - you'll end up replacing.

To replace the SYNC sensor, you need to pull the distributor. There's a roll pin that holds the gear on - drive it out, pull the gear off the bottom, and pull the shaft out the top. There are, I believe, two screws that hold the SYNC sensor down - remove those, change the sensor, and replace.

NOTE - make a "match mark" on the dizzy gear and shaft. Also:

When you remove the cap, make two marks where the rotor is pointing. Pull the dizzy, DO NOT move the rotor, and make a SINGLE mark where the rotor points after you get the thing out.

When you put it back in, make sure the gear is lined up with the match-mark on the shaft, align the rotor with the SINGLE mark you made, and install. Make sure the rotor lines up with the DOUBLE mark you made after it's fully seated... (Can you tell I've pulled a few distributors before?)

I find a Sharpie pen good for the rotor marks, and use a scribe for the gear marks. Reason for the Sharpie up top? If I ever have to pull the dizzy again, it's a cinch that the rotor won't be in the same place, and I can't be arsed with turning the engine - easier to sand the marks off and make new ones...

5-90

[87manche]

they also make different colored sharpies now, I've found that the metallic ones are brilliant for marking on these sorts of things, much easier to see in low light conditions often found under the hood.

[90xj06]

will try that. i will start with the cps it seems easier. and taking the dizzy off sounds. complicated but i will get around to it. can you buy the sensor at autozone or is it a dealer thing?

[5-90]

The CPS is pretty much OEMR only or mail-order, I haven't found one locally. The cam sensor? Haven't had to get one yet... And, I haven't converted by Borg-Warner catalogue to HTML - I'm still working on torque tables...

5-90

[langer1]

Worst come to worst a reman Distributer comes with a new one installed.

[90xj06]

is there some kind of sealer around the cps sensor. when i put a new starter in today i when up and felt around where it is and it felt like there was stuff moving in there. the jeep was sitting for 2yrs and im wondering if something made a nest. i might pull it off and see what happens. and i just noticed when i did my cam sensor test. i had a vacuum line disconnected. this may be why i didn't see any difference.

[5-90]

A vacuum leak will cause either a "wandering" or "hunting" idle, or a high idle. The engine should still start just fine.

As far as the CPS goes, some have reported a rubber plug around the sensor body, closing the bellhousing hole. I finally saw one on the AX-15 I pulled to repalce my Peugeot (and I've seen a bunch of XJ gearboxes by now!) so it probably falls out or doesn't get replaced.

5-90

[90xj06]

im wondering if its sort of stuck under the sensor not making a full strength signal. seeing that no one has replaced the cam sensor. i will work with the cps knowing that it has the potential to go bad. i will try to just "clean it" and see what i can do.

[90xj06]

is there a way to make a "demagnetizer"?

[5-90]

A tape head degausser should work, but I don't know if they can be had anymore. I'm not sure how to build one - I've probably got instructions somewhere, but if I do, I haven't seen them in 10 years or so.

Have you tried Google? "Degausser" or "demagnetizer" should yield results...

5-90

[87manche]

might want to search for "bulk eraser"

[5-90]

Nope - a "bulk eraser" is a different animal. It's meant to take the semi-ordered magnetic patterns on recorded media and effectively realign them in a single direction, erasing the information.

A "degausser" is used to take a device with is not supposed to have a magnetic field, but picked one up anyhow, and randomise the orientation of the "magnetic" particles (usually iron salts,) in an effort to destroy the magnetic field.

5-90

[90xj06]

well im just going to pop it out and check the hole. i have one at my school somewhere but its a matter of finding it. and i hope it is big enough. i think its for screwdrivers.

[5-90]

well im just going to pop it out and check the hole. i have one at my school somewhere but its a matter of finding it. and i hope it is big enough. i think its for screwdrivers.

Should be plenty. Degaussers for magnetic media heads are necessarily not very large - you don't want to depolarise the drive motor, if it's a permanent magnet motor. That would suck.

[90xj06]

what drive motor?

[5-90]

Sorry, I lapsed into thinking about tape drives again. The drive motor is usually somewhere near the read heads, and you want to "scramble" the field on the read head without screwing up the magnets in the drive motor.

5-90

[90xj06]

i was going to say. i waiting for music to come out of the motor.

[cumorglas]

I hate to be the one to ask this question, but when you say it takes a long time to start. How long? renix motors take a little longer than others to start, They won't fire till the cps shows 300 rpm. They will, however, fire without the sync sensor. The compuer just selects a random sequence and goes on with it. if this is happening it will add a few seconds to your start time.

I bring this up because while I definitely encourage you to spend quality time going over all your underhood electrical connections, i think you may be trying to fix something that isn't broke.

You should also keep in mind that this long crank time is also partially responsible for the renix xj's longevity. the extra time to get oil pressure up before dealing with actual combustion definitely helps these motors lat longer. I have three renix xj's tw 4.0's and a 2.46ish four cylinder. all of them have over 200,000 miles on them. and all of them still run nicely. two of them have REALLY rough bodies, but they all run nicely.

[90xj06]

i have 220,196 miles on it and the sensor has never been replaced. to my guessing.

[Matthew Currie]

A vacuum leak will cause either a "wandering" or "hunting" idle, or a high idle. The engine should still start just fine.

As far as the CPS goes, some have reported a rubber plug around the sensor body, closing the bellhousing hole. I finally saw one on the AX-15 I pulled to repalce my Peugeot (and I've seen a bunch of XJ gearboxes by now!) so it probably falls out or doesn't get replaced.

5-90

The sensors I've bought have always come with a stiff plastic shield that snaps in. As far as I recall that includes both the two Renix ones I've done and one for the 93. I found it very handy, because the shield holds the sensor in place somewhat, allowing one to place it from above, then crawl underneath to put in the bolts.

[cumorglas]

The sensors I've bought have always come with a stiff plastic shield that snaps in. As far as I recall that includes both the two Renix ones I've done and one for the 93. I found it very handy, because the shield holds the sensor in place somewhat, allowing one to place it from above, then crawl underneath to put in the bolts.

That would be handy!!!
where did you get them like that? the ones i have bought from napa or autozone certainly did not come with the shield. my four cylinder has never been replaced and I am going to do it before winter because i just don't feel like worrying about it in the cold. The last eight years this jeep has just been a toy for teaching kids to drive stick in the field here but gas being at three plus dollars a gallon i put floor pans into it and am gonna put it back on the road.

[5-90]

The sensors I've bought have always come with a stiff plastic shield that snaps in. As far as I recall that includes both the two Renix ones I've done and one for the 93. I found it very handy, because the shield holds the sensor in place somewhat, allowing one to place it from above, then crawl underneath to put in the bolts.

'S funny, because the last half-dozen or so I've bought didn't come with that.

Fortunately, I figured out how to "notch" the first one, and now I don't have to pull the screws all the way out anymore. Just loosen them, pull out the old sensor, set the new on in place, and tighten...

5-90

[cumorglas]

Fortunately, I figured out how to "notch" the first one, and now I don't have to pull the screws all the way out anymore. Just loosen them, pull out the old sensor, set the new on in place, and tighten...

5-90

one of those moments when somebody shows you something so simple and obvious that you just can't believe how many times you did it the hard way and feel like a fool for having done so.

Thank you for adding this to the list.

[Pioneer84]

You can still get them on ebay .

http://cgi.ebay.com/New-head-demagnetizer-all-tape-recorders-FREE-SHIPPING_W0QQitemZ170024569944QQihZ007QQcategoryZ1 5000QQssPageNameZWD7VQQrdZ1QQcmdZViewItem