crank sensor

S

snowman313

NAXJA Forum User
Location
wyoming
i just purchased a 2001 xj and the original owner swaped in a short block from a earlier comanche pickup (not sure of the year) and was never able to make it start it sat for 2 year and i bought it for dirt cheap it has no crank signal to the coil pack and i think the problem is the wrong tone ring on the flex plate. how do i tell the difference if there is any the one on it now has 4 square holes spaced about an inch apart in 3 locations on the flex plate and the pic in the manual looks like 3 holes spaced close together autozone says they all take the same one and my local jeep dealer says they are different.any experts out there on the subject
ps the original motor has already gone to scrap.
 
thanks do you no what they look like because i don't know if they switched it when they changed the short block so i have no way of knowing which one i have
 
After reading everything i can find i think it has the correct flexplate. The pic from rockauto never shows the tone ring very well. But based on what i read in the factory manual i have the right one. If you have more info on this project i would love to hear it is the older short block completly wrong or can i make it work.
 
on a wim i changed the crank sensor and still no signal to the coil i reindexted the cam sensor again still in the right place i tested the 5 volt refrence at the cam and crank sensor also checked the ground at both sensors i don't no how to test the signal from the 2 sensors anyone no how to do this without a osiloscope also the odometer says no bus and everything says bad crank sensor or bad conn. at instrament cluster and since i have a nostart i ass/u/me i have a crank sensor circiut problem.
 
You probably already know all this stuff but just entering it all for clarification.

Engine speed and crankshaft position are provided through the CKP sensor. ( Crank Position Sensor) The sensor generates pulses that are the input sent to the Powertrain Control Module (PCM). The PCM interprets the sensor input to determine the crankshaft position. The PCM then uses this position, along with other inputs, to determine injector sequence and ignition timing.The sensor is a hall effect device combined with an internal magnet. It is also sensitive to steel within acertain distance from it.
The flywheel/drive plate has groups of four notches at its outer edge. On 2.5L 4-cylinder engines there
are two sets of notches. On 4.0L 6-cylinder engines there are three sets of notches .
The notches cause a pulse to be generated when they pass under the sensor. The pulses are the input
to the PCM. For each engine revolution there are two groups of four pulses generated on 2.5L 4-cylinder
engines. There are 3 groups of four pulses generated on 4.0L 6-cylinder engines.
The trailing edge of the fourth notch, which causes the pulse, is four degrees before top dead center (TDC) of the corresponding piston.
The engine will not operate if the PCM does not receive a CKP sensor input.

So yes, you are on the right track. You need to determine if a signal is getting from the CKP to the PCM.
If I were you I would be checking the continuity of the wiring between CKP and PCM, and checking to see if signal line is possibly shorted to ground. Also checking that PCM is getting power and is properly grounded. You can try to check for a DC pulse coming off the CKP at the PCM input with a meter while trying to start the motor. I do it with a scope but I would think you would get some indication depending on the type of meter you have...maybe see a a pulse to 4 volts hopefully.​
 
ok last night i got my hands on a otc Pegisys scan tool there are no engine codes this scanner has a scope feature that give me some information that i don't know what to do with, at the pcm connector the crank sensor signal wire give one sign wave that goes clear off the 5 volt scale when i crank the engine over but only one signal each time i crank it over the cam sensor does the same thing so i checked the 5 volt reference wire at the pcm and have 5 volts until i start cranking it over then it goes to battery voltage 12.6 is this normal or could this be my problem and this much voltage just overwelms the pcm and it shuts down?
 
The 5 volt reference should not change. It should stay at a nice clean steady 5 volt level. The PCM generates the 5 volt reference voltage and supplies it to various sensors that use it in a 2001 xJ. Doublecheck yourself by measuring this voltage with a DVM, and check it while cranking the motor over, to see what you get.

Whenver I see scope signals shooting off the scale I look for ground problems.

The Powertrain Control Module (PCM) has 2 main grounds. Both of these grounds are referred to as power grounds. All of the high-current, noisy, electrical devices are connected to these grounds as well as all of the sensor returns. The sensor return comes into the sensor return circuit, passes through noise suppression, and is then connected to the power ground.The power ground is used to control ground circuits for the following PCM loads:
Generator field winding
Fuel injectors
Ignition coil(s)
Certain relays/solenoids
Certain sensors
The Sensor Return circuits are internal to the Powertrain Control Module (PCM).
Sensor Return provides a low–noise ground reference for all engine control system sensors.

Something seems messed up with this PCM to me... but I would be hesistant to swap in another one. I would have to be absolutely sure things are wired up right. You don't want to try a different PCM and blow it up.
​
 
Here is a scope picture of a crank posistion sensor signal on a 01 XJ running at idle speed, one revolution of the motor...signal amplitude is approx 4.8v... you can see the pulse for each notch in the flywheel.

jeep015.jpg
 
again thanks for helping out i did check the 5 volt referance at the pcm and i have 5.2 volt with the key in the run position but as soon as i have someone crank it over it goes to battery voltage. I agree it sound like a ground issue and it is entirely possible do to the fact someone has changed this engine and not been able to make it run. I have searched for ground lugs that are not hooked up and haven't found any do you know where i should look for these ground locations I have hooked a large jumper between the engine and body to check the body ground but know change was seen also both grounds in the pcm conn. have good continuity to ground, but i did not check for ground while cranking. Also on the scope i was using i had one spike that looked like a heart beat that happened ever time i cranked it over but only one. Also something i find odd the crank sensor connector is down by the trans linkage and the factory manual shows it up by the intake and there is not enough slack in the harness to get it back up there and the pigtail on the sensor is also to short any thoughts on this.
 
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yea thats where they put crank sensor connector on 01 xj's... thats normal...
Your scope may be triggering on the first pulse, generating a sweep across the screen, but if you get the trigger on the scope set right, you should see the pulse train repeating if you keep the motor turning over. Your scope may be in single sweep mode which will only show the first pulse. I am more concerned with the 5 volt reference changing... I will do some measurements in the morning on my running 01xj and get back to you.
 
Well, no surprises here.... checked the +5 volt primary and secondary outputs from the PCM and read exactly 5.1 volts D.C. on both of them with the key in the Start position, Crank posistion and Engine running mode. the Voltage measure ment stayed constant, steady 5.1 volts D.C., as to be expected on a running 01XJ.
If I were you I would look for a shorted circuit and do some resistance checks on sensor/circuits by doing the following:
Disconnect Battery !!!
Disconnect Connectors C1, C2, C3 at PCM and thoroughly inspect both the PCM connectors, and the Harness Plug pins and wiring to the pins.
Measure resistance checks ON THE HARNESS PLUG (NOT THE PCM!)

12 volt input to PCM is C1 pin 22 wire DG/BK
C1 is black PCM connector pin 4 is sensor ground BR/YL wire, pin 17 is 5 volt primary supply ORange wire
C2 is white PCM connector pin 31 is 5 volt secondary supply VT/OR wire
Primary 5–volt supply:
supplies the required 5 volt power source to the Crankshaft Position (CKP) sensor. (signal input line to PCM is C1 pin 8 wire GY/BK)
supplies the required 5 volt power source to the Camshaft Position (CMP) sensor. (signal input line to PCM is C1 pin 18 wire TN/YL)
supplies a reference voltage for the Manifold Absolute Pressure (MAP) sensor. (signal input line to PCM is C1 pin 27 wire DG/RD)
supplies a reference voltage for the Throttle Position Sensor (TPS) sensor. (signal input line to PCM is C1 pin 23 wire OR/DB)
Make resistance checks looking for short circuit between signal lines and ground.
Make resistance checks looking for short between signal lines and 5 volt reference pin
Make resistance check looking for short between 12 volt supply and signal lines.
Make resistance check looking for a short between 12 voly supply and 5 volt supply.
　
Secondary 5–volt supply:
supplies the required 5 volt power source to the oil pressure sensor.
supplies the required 5 volt power source for the Vehicle Speed Sensor (VSS) (if equipped).
supplies the 5 volt power source to the transmission pressure sensor (if equipped with an RE automatic transmission).
If all looks good reconnect PCM... reconnect Battery...leave sensor plugs disconnected...
Put key in Start position and check 5 volt reference at PCM output
Crank motor and check 5 volt reference at PCM output
Hpefully this process will give us some info to work with.
 
Well this is good news now i have a lead to follow instead of shooting in the dark since the last post i have been looking at a wireing diagram and I'm thinking mabe I could have a problem in the heated o2 sensor wireing because if I'm right that circuit has a 12 volt lead that i fed by relay while cranking and running and that wireing and those sensors would be easily damaged while changing a engine. Let me know if you have any thoughts on that and I will let you know when I can check into it what I find. Thanks again for all your help my 77 cj5 is so much easier to work on especialy with the D.U.I. ignition I even considered just throwing one of those in the cherokee but EFI and is nice when it works.
 
hastawell I found the source of the trouble finally, and boy i feel dumb the person that changed this motor had hooked the pcm grounds to the starter not only one but both one on the battery hot stud and the other one on the starter motor stud which is why things went nuts when cranking these pcm must br double tough to take that kind of abuse and still work.
Now I have a whole new issue it started right up and idles at 4500 rpm with the throttle plate closed and it has a major exhaust leak. Near as i can tell so far is the older block has a wider deck and the intake and exhaust man. are hitting the block instead of sealing on the head because i can see where each exhaust port is leaking underneath the manifold so here we go again i ass/u/me the intake has the same leak giving it all the air it neads t run away like that since it looks like all the vacum ports have a hose on them.hasta
Does anyone have any info on this and should i make a new thread for this issue i'm new to this forum stuff and thanks again for all your help.
 
Note from DJ
This was my post# 5 on 8-25-2011
I hope you realize there is more to this project then just changing the flex plate.
Keep us posted please!

Now on to the present; first congregations on you solving the firs problem.

I think you need to find exactly what you are working with regarding the engine change out. The 2000XJ had a head installed on it that that developed a hairline crack in between the #2 &#3 cylinders that in some cases was visible if you removed the oil filing plug. This is probable why the PO attempted a home repair job.

First bit of information;

Extensive survey on 0331 cracked heads by year and millage by Dino Savva 03-25-2006
I frequent 3 XJ forums. Here is the longest, most comprehensive thread I've run into on the infamous 0331 head.
http://www.jeepsunlimited.com/forums...d.php?t=391831

With this information you will see that your Jeep was not the only on with this problem.

Now most of the postings that I happened to look at with this problem only the head was changed out, not the block that you claimed was changed.

So my advice is to establish exactly what you are working on.

What head do you have?
Head casting number by years
Look hear for a lot more info
Information from: Scribd-Jeep Engine and Cam-Tech Specs
http://www.scribd.com/doc/15418414/jeep-Engine-and-Cam-specs

Head casting number by years
It is easy to determine what head you have. On the driver’s side, about halfway down the cylinder head between #3 & #4 fuel injector but below the valve cover clean the lip of the head with a rag or solvent if really greasy. With a good light, you can read the casting number of the head.

Head casting number by years
Casting numbers are as follows:
Year............Casting No
1987-90......2686
1991-95......7120
1996-99......0630
2000-01......0331

And what block do you have?
Block Casting Numbers by Years
Information from: Scribd-Jeep Engine and Cam-Tech Specs
http://www.scribd.com/doc/15418414/jeep-Engine-and-Cam-specs

Block casting no location can be found hear in post # 2 by CJ7-Tim
http://www.jeepforum.com/forum/f11/4-0l-serial-number-location-995174/

Year Casting No.
1987 53005535 (8933002665)
1988-90 53005535 (8933002665)
1991 53008405
1992 53008405
1993 53008405
1994-95 53008405
1996-99 53020569
2000-01 53010449AA

After this information is available more information can be gathered on how to correct the poor fits.

Just my thoughts.
 
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well at least it starts now! Sounds like the previous owner didn't know what he was doing.

What casting number head is on it?

EDIT: apparently I am wrong, dj posted the right head casting numbers.
 
well I got home late last night from work but i had to check and sure enough 0331 head and i can see coolant sitting ontop of a head bolt under the oil filler cap so the head is junk. and the block has a 53005535 casting so it looks like i have a 88-90 block that i don't have any history on so given the fact i bought this jeep to give to my 79 year old mother that still live 10 miles from town on her ranch sounds like i may be better off with a reman. i hope all the junk 0331 are out of the system so i don't get another one with the reman. if i try and make a pre coil pack head work will a 630 head work with that block or do i need to find something different.
 
I'm sure with all the other botch ups done during this swap that the po didn't put sealant on the one headbolt that goes through the coolant passage(driver's side front corner). I'd pull off the valve cover and look for the infamous crack b/t 3 and 4. High idle probably due to the intake manifold not sitting in the two locating tabs correctly.
 
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