Odd situation

[Jason L Williams]

For the last couple of days, I've been driving the YJ to work since my wife's car is down and she is using the Mustang to get to fro work. So, Monday I'm heading to work and the Heep hiccups while driving. Uh????? Kind of like a miss. Keep driving, and it doesn't happen again. Out of sight, out of mind. Go to lunch. Sitting in the drive-thru and the engine dies. Start, idle, sit a few, and die. Get my food, drive back to work, all the while keeping a foot on the gas while at any stoplights.
Fastforward to Tuesday and the driving experience to work was the same. So, I asked myself, "Self, when is the last time you did a tune up?" Down to the auto parts store I go. Plugs, wires, cap, rotor, air filter.....
Here's the strange part. I'm removing the #1 spark plup and it doesn't look right. By that I mean, it's an Autolite brand. I only use Champions. Out come 2 through 4 and all Champions. Call me crazy but I don't mix and match Sparkplugs. I don't know of any adverse effects if you do, but I never have. So, who would do such a thing?
The only time I can think of when this happened was when the heep was down for the count with smog troubles and the Mechanic kept it for a couple of days. I guess he must have changed it after hooking up the OBDII and determined #1 needed replacing. But after changing everything, all seems well. So...I don't know. That just seemed rather odd to me.
Thanks for listening.
I'm Jason Williams

[Robert J. Yates]

Maybe the mechanic broke the sparkplug and replaced it with whatever he had lying around? Thats probably not the cause of your problem though - possibly the plug for the CPS is corroded or loose - seems to be a common problem and can cause the symptoms you described Jason.

[Jerry Bransford]

Originally posted by Robert J. Yates
Maybe the mechanic broke the sparkplug

A mechanic break a spark plug? Nah, never happens... just like I didn't break the ceramic part of 4 of the 8 spark plugs I talked my dad into letting me install in his '62 Olds Starfire when I was 15 heheh.

[John]

I'm with Robert on this sounding like a CPS issue. Pretty much how mine acted when it died.

[Robert J. Yates]

Originally posted by Jerry Bransford
just like I didn't break the ceramic part of 4 of the 8 spark

....I've never broke a spark plug either jerry

[Jason L Williams]

Thanks for the CPS suggestion. I'll look tonight. But, the drive in this morning was flawless. We'll see what happens on the way home.

[Jerry Bransford]

Originally posted by Jason L Williams
But, the drive in this morning was flawless.

If it's the CPS, it's going to wait to go bad until you're 50 miles out in the middle of the boondocks. (and is why I carry a spare CPS )

[Jason L Williams]

How does one test a CPS? Or are they just as disposable as VCR's are now? I recall reading from another post that no error codes show up for a malfunctioning CPS. I'm starting to think that the older the YJ gets, it may behoove me to purchase a OBDII computer.

[Jason L Williams]

After looking at the CPS last night, other than it looking alittle dusty, I can't tell if anything is wrong. If I'm correct, the CPS tracks the spining flywheel. How does it do this? If there is a window of sorts and if it's dirty, then faulty readings?

[John]

It's a magnetic pick up IIRC. When they go, there's no external clues.

[Daless2]

Hi Jason,

The Crank Positioning Sensor is a Hall Effects device which uses a built in magnet to sense the groves on the flywheel or torque converter plate.

Basically, as the grove passes the magnet, the magnetic field changes and causes the hall effect device to go "high" or go "Low". In other words, it either passes +5 volts (high) or it doesn't (Low).

That said you can test it with an Ohm Meter, either digital or analog.

Here is how.

Unplug the CPS from the Jeeps wiring harness.

You will see three pins in the plug going to the CPS.

One pin supplies +5 volts to the CPS Sensor,

One pin is Ground

and the last pin is the CPS Signal pin which is returned to the Computer.

The problem is I can't tell you which pin is which on the YJ.

On the TJ, when you are looking into the connector WITH the connector Lock on top, the pins are wired this way from left to right,

1. (Left) +5 volts
2. (Center) Ground
3. (Right) Signal back to Computer

To test this on the TJ, (Maybe yours are wired to the same pin configuration, I just don't know.) you need an Ohm Meter.

Set the meter to the 1K to 10K meter scale
Connect the meter probes to pin 2. (Center) Ground AND pin 3. (Right) Signal back to Computer

You should read an "Open" circuit, meaning very high resistance.

If you read low resistance (like a short would read) on this scale the hall effect device inside the sensor is bleeding to ground and is defective and the CPS should be replaced.


If someone here has a FSM for your YJ they should be able to tell you if the pin-outs for this connector are in the same positions as the TJ.


That said, your problem is Hmmmmm............................................ .............

Could be anything Jason, including something as simple as a carbon trace inside the old distributor cap you replaced.

Please understand, your YJ is not OBD-II compliant. It is Jeeps proprietary OBD I system. In truth not even all TJ are OBD-II compliant. That didn't start until well inside the 1998 model year.

I say this so you understand OBD-I DID NOT record all error codes in the PCM (Computer) like OBD-II requires. The only error codes recorded in OBD-I are those that would cause a pollution failure if the event happened three times within 25 warm up cycles. (ODB-II records the similair way, PLUS it records DTC codes.)

If you can take it to an auto parts store like Auto Zone they will put the proper scanner on it and tell you want you have. If you do the Ohm Meter test above and it looks good I doubt very much the problem is CPS related.

ALSO, if you buy your own scanner make sure it can read the YJ codes. Not all ODB-II scanners can read the old codes. Most can, but not all.

I'd be cleaning all my underhood electrical connectors and filling them with dielectric grease. I would also be checking all the engine grounds.

I might also put a fuel pressure gauge on the fuel rail and watch to see if the pressure varies by more then 2 PSI while I varied the throttle.

Hope this is helpful for you.

Frank

[Jason L Williams]

Thanks Frank. I did do some reading last night about checking the CPS with an Ohm meter. It was late last night and I was tired. I have had no problems since doing my tune up so I guess I can tinker with it now.
I curse the CPS, MPS, TPS, and all the other S's that come in cars now. I long for the day with gap points and the ability to Time an engine just by listening to it and rotating the Distributor. Well, almost. There are some nice things about EFI and the other computer driven devices in today's cars.
Now on another note, this type of response is the very reason I enjoy posting here. Lots of good and useful information.
Thank you everyone.

[Robert J. Yates]

Originally posted by Jason L Williams
I curse the CPS, MPS, TPS, and all the other S's that come in cars now. I long for the day with gap points and the ability to Time an engine just by listening to it and rotating the Distributor.

I do not miss gapping points in the least, particularly that Mallory dual point distributor I had in my 69 Mustang. I can say though that I miss the distributor and regular plugs in my daughters Cherokee because now I have to learn something new in order to tune it up