Ignition problem... any help with some codes?

[FLpilot]

Hi guys,
I've had no problems or anything like this since i bought my grand cherokee in '97, and it showed no sign of problems today... However tonight when i went to start it turns over but will not fire. the fuel pump is working, all the fuzes under the hood seem to be ok... i flashed the computer and get a 12 and 11... i am guessing the 11 is because i pulled out the alt. fuze and it thinks i disconnected the battery... i can't seem to find the code list anywhere as i haven't had to use it before. Any help would be greatly appreciated... its a 95 ZJ with a 4.0.

btw, from what i'm gathering so far from the previous posts i dug up, i'm seeing a lot about the crankshaft position sensor... if thats what any of you suggest, could you give me a little more info about where i can find it and how you change it??

Thanks in advance!
-Nathan [addsig]

[MudderChuck]

My code list (95) says 11 is "no crank reference signal detected during engine cranking. 12 "direct battery imput to PCM was disconnected within the last fifty cycles.
The list is supposed to work until 98 model year. WWW.obi-wan@jedi.com
I´ve never changed a crank position sensor, on a newer XJ (post 91).[addsig]

[FLpilot]

ok, thanks! i haven't figured out how to refer back to to that other post... but from you know do you think that the cps would just go out like that without showing any signs of problems prior to its failure? I have been looking around and i'm not even real sure where the thing is... there doesn't appear to be a lot of sensors around the crankshaft pulley on the front of the engine, but i did find a sensor on the left side of the tranny bell housing just on the other side of where it is connected to the engine... the sensor is in the tranny tho... thats not the cps, right? I haven't crawled under it yet to get a better look but any advice on where the cps might be located would be appreciated as well as any advice on whether or not anyone thinks that the cps would actually be the guilty party...

Thanks!
-Nathan
[addsig]

[dingus]

cps is located on the tranny... it signals the computer when and how fast the engine is turning. i believe it is located on the bellhousing. my jeep had its CPS die too... the stupid thing wouldn't start!

-nate[addsig]

[bluebelle]

The CPS is a very subtle sensor located on the bell housing pointing down on the flywheel.

My bluebelle 92 4L CPS is mounted with two bolts on the upper driver's side of the bell housing with two (or three?) wires about a foot long routed up to the top of the intake manifold where it quick-disconnects to the main wiring harness. Very easy to access and change as well as reasonably priced from the dealer ($40 ish).

It 'counts' the number of 'tabs' on the flywheel as a measure of engine rpm. If that puppy dies, your engine is useless because it's like the computer thinks the engine isn't rotating, so why signal any ignition of fuel?

Most i've talked to about the CPS carry a spare (it's small and less than a tow) in their jeep. I do.

I'm not aware of a functionality test to determine if your CPS unit is operational, but there is a history alive and well that they go out more often then most other sensors.

Hope this helps.

blue
[addsig]

[remember5]

My Haynes manual says:
Beofre checking the crankshaft position sensor, check the voltage supply and ground circuits from the PCM. On all except 4.7L V8 models, follow the wiring harness up from the crankshaft position sensor to locate the narness connector. Disconnect the connector and connect the positive lead of a voltmeter to the white/black (1998 and earlier) or orange (99 and later) wire terminal tne the negative lead to the black/light blue terminal of the harness connector. Turn the ignition key on - the voltage should read approx. 8 volts. If the voltage is incorrect, check the wiring from the CPS to the Power Control Module.
To check the CPS operation, reconnect the connector to the CPS and backprobe the orange/light green wire terminal of the CPS connector. Connect the pos lead of the Voltmeter to the probe and the neg. to a ground point. Turn the key on. Rotate the engine slowly with a breaker bar and socket attached to the crank pulley center bolt while watching the meter. The voltage should fluctuate from approximately 5volts to 0 volts as the notches in the flywheel pass the sensor. If the results are incorrect, replace the CPS. *NOTE... Rotate through one complete revolution. The notches are equally spaced on v8 models but on 6cyl. models they are 120 degrees apart. Removing the plugs will make the engine easier to turn.

Now that my fingers are tired from typing, I'm going for some coffee. I hope this helps.[addsig]

[bluebelle]

5,

Thanks for the technique. I'll test the 'old' one I pulled out. Maybe it's still good. I wonder if the test you outlined would indicate an intermittent sensor? Did the manual get into that?

blue
[addsig]

[FLpilot]

well, after trying to figure out the best angle to get in there and change the cps, i determined the best angle was sitting in the waiting area of a local garage while a mechanic turned the wrench... the cps definitely fixed the problem... but just for fun i flashed the codes again once i got it home and it is still giving me the same codes (11 and 12)... i'm speculating that as MudderChuck said with the 12, that it applies to the last 50 cycles or so... is this the same for the 11 code? they just stay in the computer for the next 50 cycles or something???

While i had it in there, i figured i'd have that left motor mount replaced.... the rubber was all broken and chunks were starting to fall out... now you can barely tell she's running when you're sitting at a redlight...
everything seems have been put back together correctly, except for the air box which i noticed had a few clips just dangling... i tried to put them back on and the filter wasn't in right and then i noticed the hole air box was just laying in there... after telling the mechanic and him playing dumb for a few minutes saying he didn't know what it attatched too... when their are 3 bolts just dangling from the bottom of it, he eventually said he'd go see if he can find somethign that fits it.. and mysteriously on the first try he comes out to the parking lot with 3 bolts that were the correct size... oh well everything is all good again.

Thanks for all the help guys! gotta love the loyalty and knowledge base that can only be found amongst the Jeep guys!!

Thanks again!!
-Nathan[addsig]