would you buy a '99 4.0 4x4 140k?

[hubs97xj]

If you're sure you're testing correctly, and it's out of spec, it should be replaced.

CKP, not CPM. CranKshaft Position sensor. Not to be confused with the CMP, CaM Position sensor. A lot of people refer to both generically as the CPS, which gets confusing quickly.

edit- if you're not familiar with it, add "site:naxja.org" to Google searches. In this case, "99 P1391 site:naxja.org", "P1391 ckp site:naxja.org", etc. There are many ckp/cmp/p1391 threads, and there is bound to be some useful info somewhere (especially if you're not convinced and ready to throw money at it yet), and it might save you a few bucks/hours/gray hairs, etc.

 

[Mediaslave]

If you're sure you're testing correctly, and it's out of spec, it should be replaced.

CKP, not CPM. CranKshaft Position sensor. Not to be confused with the CMP, CaM Position sensor. A lot of people refer to both generically as the CPS, which gets confusing quickly.

edit- if you're not familiar with it, add "site:naxja.org" to Google searches. In this case, "99 P1391 site:naxja.org", "P1391 ckp site:naxja.org", etc. There are many ckp/cmp/p1391 threads, and there is bound to be some useful info somewhere (especially if you're not convinced and ready to throw money at it yet), and it might save you a few bucks/hours/gray hairs, etc.

Thanks! What a great tip! I have been reading thread after thread tying to discern what pertains to my situation. Done more reading than wrenching lol!

I will do a little more research with your tip before I run out. Here I thought they (CKP-CPM) were the same thing! this really is confusing but hopefully I'll figure it out.

So correction The CKP sensor is testing at 45ohms which I belive, from what I've found and been told ^^^, that it should test "infinate". so I'm pretty sure it's bad.

The CPM is the sensor connected to the bottom of the distributor "right" ? Well that little guy is covered in oil. I sprayed it with electrical parts cleaner and can't get it off. Also noticed I can turn it all the way around and is leaking "junk" around where the plastic meet the metal "cylinder" part.

 

[Mediaslave]

Wow this is confusing???

Correction again. I was not looking at the CMP. Aparantly the CMP is located inside the distributor, as stated above ^^^^.

I was looking at the Oil pressure sending unit which is located directly under the Distributor and is leaking like crazy.... I know it's not my misfire problem but it's only $22 at Napa so I might as well replace it too.

I guess I'm gonna have to drop about $100 or so and go from there!

Thanks everyone for your Help.

 

[JeepCherokeeGuy99]

I'd pull the sensor from the junkyard. Its a "freebie"

 

[ehall]

You probably ought to put yourself on a cash timeout until you know what you're replacing.

 

[Mediaslave]

You probably ought to put yourself on a cash timeout until you know what you're replacing.

My wife would agree. Great Advise. All starting to come together now.

CKP- crankshaft position sensor - located on upper bell-housing. Tested resistance at 45 ohms which is low. Should Test "infinite resistance".

CMP- camshaft position sensor - also known as "pick-up assembly" located inside distributor. gonna wait on this one. May have to replace entire distributor - yet to be determined.

CPS apparently refers to both above.

Oil Pressure Sending Unit - located directly below distributor and above oil filter "Release Red-clip to remove" Leaking all over. replacing

Learning to discern who knows what their talking about - located on internet "use and spend at your own risk"

gradon - Found your reply on another thread on this issue and your link to article. If the ckp crankshaft position sensor doesn't work out I'll be syncing that cmp camshaft position sensor on the "Dizzy???"

 

[ehall]

P1391 CMP sensor

that's not the crank sensor

 

[Mediaslave]

Decided to go to Napa in south austin to get the parts. Brought the multimeter with me and the.crankshaft p s. I pulled. Asked if I could see and test the new one. Well it tested with about a 20ohm resistance. So I did not buy the new sensor.

Just so happened to be JEEP MASTERS garage next door. Went in and talked to a guy behind the desk there. He doubted me on the camshaft sensor says they hardly ever go bad. Pointed me in the direction of timing. So now I'm just slowing down, saving what little money I have and gonna get my hands real dirty.

I don't give up very easily. I will learn by digging in.

 

[DanMan2k06]

How on earth could it be the timing?

 

[birchlakeXJ]

How on earth could it be the timing?

Base timing for the 4.0 is controlled by the computer.

 

[gradon]

Camshaft sensors(CMP) do not fail often; Crankshaft sensors do fail often(CKP), and are responsible for most of the "cranks, but doesn't start" issues. I have a fluke 77 and the values of good CKPs I've measured range from 4.6-6.4mega(million) ohms. You did right by not buying the 20ohm one. How many ohms does your meter register when you touch the leads together? Timing is generated by the CKP, so you indeed have a timing issue.

 

[Mediaslave]

My multimeter reads below 0 when touched together.

 

[Mediaslave]

Should clarify my above statement. Basicly at zero after slight adjustment.

 

[Matthew Currie]

If you were looking at a new crank position sensor that tested at 20 ohms, that's the right value for the older Renix (87-90) system, so that's likely the one you were handed. No good for a 99.

Cam position sensors may not fail often, but I've had two of them go, while I've never had a crank position sensor go bad. I'm probably tempting fate, and will go out tomorrow and find my Jeep doesn't start, and have to eat crow.

 

[ehall]

The code points to the cam sensor, it probly ought to be tested. outrageous I know

 

[Mediaslave]

Put her back together with the same crankshaft position sensor for now. Added a new oid pressure sending unit cause the oil one was cracked and leaking. Going to play with the distributor tomorrow to see if i can dial her in. the wire running to it is pretty tight seems fishy to me.

If I have to take this whole thing apart I will. Gonna look more into testing the camshaft position before I just replace it.

Lot's to learn and re-learn... haven't wrenched on a vehicle in a decade. Been sitting behind a computer for a long time now. I forgot how much I love getting my hands dirty. Even went to a couple junk yards today on the way to Napa. Found the one interior trim piece I needed and the guy just gave it to me... Pretty cool. No 99's at eithor yard though.

 

[Matthew Currie]

As others have mentioned here, you cannot adjust timing on this setup. However, there is the possibility that a previous owner indexed the distributor wrong. This might put the distributor far enough off to go beyond the ability of the engine management system to compensate. Even though the computer can manage spark timing, it cannot, obviously, manage rotor timing to the plug wires. That's a very coarse and forgiving bit of timing, but if it's far enough off, you may get spark failure and high speed miss similar to what you see with a bad cap and rotor or bad plugs.

I haven't experimented with the 99, but the old Renix XJ would run pretty well with the distributor one tooth advanced. It started very hard, though. With one tooth retarded it would start fine but couldn't accelerate. So if you have mysterious running problems and no obvious sensor issues, you might try moving the distributor back a tooth. Make very sure that you do this with the engine at TDC by the timing mark, and carefully mark the position of the rotor as it is now. The rotor will rotate a little when you insert the distributor. If it's well marked, you'll be able to put it back the way you found it.

However, I do think that if you have a clear cam sensor code, that's probably your clue. The cam sensor sets the timing for the injectors. With a faulty or non-running cam sensor, the engine will start fine if it starts at all, and will run, but it will tend to stumble and may run hot at the exhaust.

Archive note: untested on Renix and post-96, but this trick works on 93-95 at least. If you have a bad cam sensor the engine will not start. If you turn on the ignition, then unplug and replug the distributor connector, the engine will start (once) and allow you to drive at least a few miles. You must do that for every start.

 

[Mediaslave]

Found a great article if anyone is interested.

http://www.asashop.org/autoinc/feb99/techtotech.htm

gradon you are the man! I believe you told me this a day or so ago.

Got to figure out how to index the distributor. Found this: http://www.angelfire.com/my/fan/dist_index.html & "gradon" this http://motorage.search-autoparts.co...estandard//motorage/292005/169830/article.pdf

Going to try to test the camshaft position sensor first. Found This: http://www.lunghd.com/Tech_Articles/Engine/Cam_Position_Sensor_and_Sync_Pulse_Stator.htm
Looks like this^ is for Renix.

 

[Mediaslave]

So as I stare at the distributor and try to visualize the procedure I'm about to attempt. I'm still curious as to why the the wiring harness is so tight around it. So I pulled on the harness a bit to access the connector and find that it is wrapped around the backside. Followed the wire to the ignition coil where I noticed something not right.

The wire sheathing "insulator" attached to the connector on the Ignition coil right at the plastic connector are brittle damaged and have exposed wire showing at both connections. Detached the connector, Released the ground connections, pulled the harness up to get a better view. Sure enough both wires exposed right at the end of the connector. Broke off the rest of the brittle insulator sheathing, cleaned it all off with electrical cleaner and wrapped each in an electrical tape cast.

Could this be "arcing" shorting to the Ignition coil and causing a domino effect???

We will find out. I put it all back together, put the testing/indexing on hold and am going for a little drive soon.

Also Rebooting the ECU/PCM to erase memory and put the PCM into Fast Learn Mode.

 

[ehall]

If the wires are exposed then there is probably some corrosion on the pins preventing solid contact. I'm not sure what part you're talking about though.

FWIW the cam sensor is officially called the sync generator on my 91 (dunno about the 99), but sometimes called a stator (NAPA), a pickup coil (Autozone), or an ignition pickup (rockauto). It's basically just a hall effect sensor that monitors rise and fall of a magnetic pulse to inform the computer on injector timing--if it goes bad or comes loose the computer will misfire the injectors. I don't have a 99 FSM and my 91 set does not include the group 8 ignition tests, so I'll leave it to somebody else to tell you how to test the part.