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View Full Version : what is cps and where is it


bradmoody
July 13th, 2006, 18:34
I have a 98 xj w/ 4.0 it shut down on me and wont start, will turn over fine
could it be cps?

87manche
July 13th, 2006, 18:49
cps is the crank position sensor. It tells the ECU what the position of the crank is.
Without it the ECU won't fire the coil, and you won't get any spark.
Check to see if you have spark while cranking. If you don't then the CPS is a good bet.
It is located at the 11 O clock position on the bellhousing, looking toward the front. It's a PITA to get at, you'll need an assortment of extensions and some u-joints.
You should also check the CPS connector for corrosion, sometimes replugging it will fix it.

jeepdude10000
July 13th, 2006, 18:50
CPS - crankshaft position sensor, its on the back of engine

tealcherokee
July 13th, 2006, 18:54
CPS is the mistaken abbrv for CKP, which yes, is the crankshaft position sensor

bradmoody
July 13th, 2006, 19:07
is it located between the fire wall and the back of the motor? a pic would be great.

87manche
July 13th, 2006, 19:12
the CPS is mounted at the front of the bellhousing for the transmission, drivers side.

bradmoody
July 13th, 2006, 19:27
whats the best way to check this and would this keep it from starting? do you suggest checking something else the valve stem on the fuel bar spays gas when i push it, it bleeds out then i crank it over again check the valve stem again and can make it spray with pressure again, so i think maybe the fuel pump works.

jeepdude10000
July 13th, 2006, 20:20
ya fuel pump works , but how much pressure?

and yes the CPS will stop from starting., it sends a signal to the computer.

87manche
July 13th, 2006, 20:41
see my first post. Check for spark.

bradmoody
July 14th, 2006, 12:41
Is the valve stem on the fuel bar where you check fuel pressure? How much should it have? what tells it whether it has enough pressure or not.

87manche
July 14th, 2006, 13:56
yes that's where you check pressure.
You need a fuel pressure guage that reads up to about 50 PSI.
My 87 is supposed to be 31 PSI with the fuel pressure regulator vac line attached, 39 PSI without. I don't have numbers for your HO, but that should put you in the ballpark.

bradmoody
July 14th, 2006, 14:07
would the fuel pump quit all at once? seem like when I started it that morning it reved up pretty high untill I put it in gear, then it seemed normal no other warnings. I did notice it rev up which I thought was abnormal but paid it no mined and drove on to work, or at leased I tryed.

87manche
July 14th, 2006, 14:12
possible. have you checked all the fuses?
I think that you need to elaborate what happened when it died. And what you've checked.
Check all the fuses and relays first.
Make sure that the CPS connector isn't nasty, in fact just unplug and replug all the wires connected to the engine.
Check that the CPS harness hasn't fallen against the exhaust and melted.
Verify that the motor is getting fuel.
Verify that you've got spark.
If it has spark and fuel it will start. You need to figure out which one of the triangle of fire you're mising to diagnose further. Spark is the easiest one to determine. Find out if the coil is firing spark plugs and report back. I'm willing to bet you've got no spark, and if that's the case the CPS has likely failed. It is known that the CPS can just die, and when that happens the motor will quite just as if you turned the key off.

bradmoody
July 14th, 2006, 14:24
can I jump or bypass the cps to see if thats the problem. this rig just shut off driving down the road at55 mph, I've had no problems at all with this. I think I have located the cps and there really is a good way to get to it, I can get my hand on it from the bottom side bearly. I did unpug the plug and pluged it back to check for bad connection.

drewkeen
July 14th, 2006, 14:24
I had the same problem. Popped the hood and I instantly saw that the wire from the coil to the distributor had come off the coil and was just sitting on top of it. Not trying to insult your intelligence, just reminding you to check the simple things first.

Nixt
July 14th, 2006, 14:55
My '96 has 49 PSI at the fuel rail. Don't know when it changed from the 31/39 that 87manche posted, but I'd call a dealer/garage to check.

Just replaced CKS/CPS on mine today chasing random rough run & misfires. Took care of most of it. Starting new thread related to your thread, subject will be:
Crankshaft End-Play?

langer1
July 14th, 2006, 15:13
A 98 will through a code, so start there.

guther66
July 14th, 2006, 15:29
When changing the CPS, remove the front driveshaft, it'll make it a whole lot easier to get at. I used a 20" extension from craftsman and a u-joint.

apsdad
July 14th, 2006, 18:36
I just replaced my CPS. My 96 just flat out quit a couple times after about 45 minutes of operation. After waiting about 30 minutes it would start and run for another 7 hours with no problem. Another thread said the CPS can put out a marginal signal which will kill the spark, but not show on the OBD-II as a check engine signal.

I got it out and back in using a 12 inch extension with a swivel end. Putting the bolts back was easy. I forced the heads into the sockets with a piece of typing paper to hold the bolt head in the socket. Removed and replaced the CPS in less than 20 minutes.

bradmoody
July 14th, 2006, 19:23
my rig has set for over 2 days and still wont fire, so what ever it is it's dead. I've tried the turn key for 10 sec trick and that didn't work also I've checked connections at the coil and several other places. I was hoping someone would know how to jump or bypass the cps so I could try that.

Saudade
July 14th, 2006, 20:01
I was hoping someone would know how to jump or bypass the cps so I could try that.

You can't. But you can test it.

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/15/24/5f/0900823d8015245f.jsp

87manche
July 14th, 2006, 20:08
my rig has set for over 2 days and still wont fire, so what ever it is it's dead. I've tried the turn key for 10 sec trick and that didn't work also I've checked connections at the coil and several other places. I was hoping someone would know how to jump or bypass the cps so I could try that.
have you checked any of the basics yet?
you ask many questions, we give nwers and suggestions but you never post back with results.
This entire thread is conjecture until you post back with conclusive troubleshooting results. I could guess all day at why your XJ won't start, but until you actually check some of the things suggested and post back the results no one will be able to help you.

langer1
July 15th, 2006, 05:00
Another thread said the CPS can put out a marginal signal which will kill the spark, but not show on the OBD-II as a check engine signal.


This is true of most DIY scanners that only read code but the real good professional scanners can do their own diagnostics and will show a weak signal from a sensor before it sets a OBD II code.

bradmoody
July 15th, 2006, 14:40
Well I finally got a chance to mess with my rig and as far as I can tell I'm not getting a spark. I took a plug out and grounded the side while trying to start it and never seen a spark. I can smell gas so I figure I'm getting gas. I can also unplug the connector for the cps while the key is on and by doing that I can hear the relays clicking on and off also a zap noise like a sparking sound around my injectors but I do not see a spark. A new cps is $39 at autozone but its a booger to get to on my rig, looks like I'll have to drop the front driveshaft to get to it if thats the problem. But with unpluging and pluging it back up causing the relays to click I almost think it could be working.

89xj
July 16th, 2006, 10:27
Well I finally got a chance to mess with my rig and as far as I can tell I'm not getting a spark. I took a plug out and grounded the side while trying to start it and never seen a spark. I can smell gas so I figure I'm getting gas. I can also unplug the connector for the cps while the key is on and by doing that I can hear the relays clicking on and off also a zap noise like a sparking sound around my injectors but I do not see a spark. A new cps is $39 at autozone but its a booger to get to on my rig, looks like I'll have to drop the front driveshaft to get to it if thats the problem. But with unpluging and pluging it back up causing the relays to click I almost think it could be working.

just put in a new cps for heavens sake.

if you think its working, then test it.

RedHeep
July 16th, 2006, 11:28
just put in a new cps for heavens sake.

if you think its working, then test it.

x2. Several guys have suggested it on two different threads because you have classic symptoms of a failed CPS. It takes longer to fire up the ole computer and post about what the jeep doesn't do than it does to spend $39 and change the damn thing.

bradmoody
July 18th, 2006, 13:01
I put my jeep in the shop and yes the mechanic thinks the cps is bad but there is not one in town so he'll have to order one because my trans is a jeep instead of a dodge whatever that means.

89xj
July 19th, 2006, 14:38
why not put it in yourself and save some money.

yes, its difficult to get to, but not impossible.

Yucca-Man
July 19th, 2006, 14:44
What's a CPS and what's it do??
http://www.yuccaman.com/jeep/cps.html

http://www.yuccaman.com/jeep/pics/cps_2.jpg
There ya go - those are the bolts holding it in place. Imagine yourself looking at the tranny bellhousing from the transfer case, looking forward.

bradmoody
July 19th, 2006, 14:47
Thanks for the pics, bad part is I ran out of patience and took it to the garage. They had to order the part and it takes 2 days.

Yucca-Man
July 19th, 2006, 15:02
Sorry to hear you're getting jacked around...2 days to get a part that Jeep dealers stock? If I recall correctly I even picked one up from NAPA once..

IslanderOffRoad
August 3rd, 2006, 17:25
x2. Several guys have suggested it on two different threads because you have classic symptoms of a failed CPS. It takes longer to fire up the ole computer and post about what the jeep doesn't do than it does to spend $39 and change the damn thing.

Sorry to bump an old topic, but I'm curious where you got a CPS for $39. I can't seem to get one for under $100.

Saudade
August 3rd, 2006, 18:03
One for my '88 is $32 at Autozone.

87manche
August 3rd, 2006, 19:25
GP sorenson for $33 at the local advance, in stock, 87.
THe 97 cherokee I have listed for my front axle parts reports that the same part is 108 for a 97, so I guess you're hosed if it's an HO.

IslanderOffRoad
August 3rd, 2006, 19:35
i guess i'm hosed.