sync sensor

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?

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?

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

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.

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.

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.

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

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.

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

5-90 said:

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

Click to expand...

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.

Matthew Currie said:

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.

Click to expand...

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

5-90

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

90xj06 said:

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

Click to expand...

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

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.

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.

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

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?

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

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

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.