Crank sensor? - JeepForum.com
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post #1 of 22 Old 08-23-2018, 10:24 AM Thread Starter
broncoguy80125
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Crank sensor?

Hello-

2003 4.0, randomly dies while driving. Not a sputter and stall, but dies like the key has been turned off. Sometimes as I am coasting to a stop, it will re-start by itself, sometimes not. When it dies, it will always start right back up. No codes are being thrown except for an emissions leak code that I know about. From what I have read, there are a couple things mentioned- one is the crank position sensor, and the other is a short/melted wire harness from the back of the engine- something about rubbing on the valve cover bolt and then shorting out. I would think that a crank sensor would throw a code, but I'm not getting one. Any thoughts on this?

Thanks.

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post #2 of 22 Old 08-23-2018, 11:03 AM
Uniblurb
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A bad crank sensor doesn't always throw a code. Sometimes the gas gauge or voltage gauge will quit working if a crank sensor is about to cause a stall. On the other thing you mentioned it should be easy enough to check to see if the wires next to the back of the valve cover have worn through insulation or shorted by a bolt.

Below is a crank sensor resistance test you can use if you have a multi-meter. Best to test it when the problems occur. But a bad crank sensor will often show resistance between power & ground pins in the connector all the time when there should be absolutely none.

If you do have a bad crank sensor don't install any other brand other than OE/Mopar or you'll be sorry since aftermarket ones fail almost always. Good luck.

Here's the crank sensor resistance test.
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2004 4.7L WJ Limited, 96 4.0 ZJ


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post #3 of 22 Old 08-23-2018, 11:21 AM Thread Starter
broncoguy80125
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Thanks for the info, Uniblurb. Haven't had a chance to check the harness yet, and I will definitely test the crank sensor per your instructions. Appreciate it..
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post #4 of 22 Old 08-23-2018, 11:45 AM
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You're welcome broncoguy, let us know what you find, and good luck.

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post #5 of 22 Old 08-26-2018, 09:32 AM Thread Starter
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Well, when I turn my meter to 200 ohms (lowest setting), the screen shows a "1" on the far left before I do anything. Touching the leads together, I get a different reading, so I guess the meters are working... When I make the connections above, it still says "1". Tried this on 2 different meters, so can I assume that means no resistance?
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post #6 of 22 Old 08-26-2018, 09:54 AM
2oldjeeps
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no resistance can be open wires/connector
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post #7 of 22 Old 08-26-2018, 12:02 PM
Eddatree
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I couldn't swear to it for sure, but I believe my tachometer on dash wouldn't move when cranking after my cps died. Easy to check. Also search for the shortcut to r&r the cps through the little hatch above the gas pedal, much easier.
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post #8 of 22 Old 08-26-2018, 12:20 PM
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Also forgot about the thin cardboard on end of the new cps needs to be left on to get the gap setting right and wears off after the first crank. Use grease or a bit of paper to hold the tiny bolt in socket on a wobble extension to re-install and don't cross-thread it by turning by hand at first.
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post #9 of 22 Old 08-26-2018, 12:32 PM
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Quote:
Originally Posted by broncoguy80125 View Post
Well, when I turn my meter to 200 ohms (lowest setting), the screen shows a "1" on the far left before I do anything. Touching the leads together, I get a different reading, so I guess the meters are working... When I make the connections above, it still says "1". Tried this on 2 different meters, so can I assume that means no resistance?
Sound like you did the test correctly and your crank sensor is testing good; no resistance same as if probes are touching nothing or 'open'. This test is just for checking to make sure the crank sensor is not shorted internally or have power/ground bleeding together which can happen. I once moved a crank sensor connector on my 96 4.0 ZJ over to the other side of the engine for easier access for testing. The sensor tested good on the passenger side but bad on the driver's side. Turned out the wires were shorted out internally where they go into the sensor.

Believe I'd still be checking for any wires with insulation rubbed or melted around the engine. Good luck.

2004 4.7L WJ Limited, 96 4.0 ZJ


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post #10 of 22 Old 08-26-2018, 05:21 PM Thread Starter
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Quote:
Originally Posted by Uniblurb View Post
Sound like you did the test correctly and your crank sensor is testing good; no resistance same as if probes are touching nothing or 'open'. This test is just for checking to make sure the crank sensor is not shorted internally or have power/ground bleeding together which can happen. I once moved a crank sensor connector on my 96 4.0 ZJ over to the other side of the engine for easier access for testing. The sensor tested good on the passenger side but bad on the driver's side. Turned out the wires were shorted out internally where they go into the sensor.

Believe I'd still be checking for any wires with insulation rubbed or melted around the engine. Good luck.
Thanks for the confirmation on the test. I checked the harness that I think is in question from the other info I read- Pretty thick one that runs close to the top and around the back of the valve cover. It's already wrapped with a thick wire loom and I saw no evidence of any melting. Maybe the crank sensor wire itself may be the culprit? It runs around the back of the engine too.

BTW, I drove the jeep quite a bit today and did not have any instances of dying. But the wife tells me she could go a couple days with no issues, and then it would die.
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post #11 of 22 Old 08-26-2018, 11:11 PM
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Quote:
Originally Posted by broncoguy80125 View Post
Thanks for the confirmation on the test. I checked the harness that I think is in question from the other info I read- Pretty thick one that runs close to the top and around the back of the valve cover. It's already wrapped with a thick wire loom and I saw no evidence of any melting. Maybe the crank sensor wire itself may be the culprit? It runs around the back of the engine too.

BTW, I drove the jeep quite a bit today and did not have any instances of dying. But the wife tells me she could go a couple days with no issues, and then it would die.
Those intermittent type engine dying problems are some of the most difficult to figure out. Every bad crank sensor I've had/tested showed some resistance when there should be none. The true test would be testing it right when the engine has died. But on the other hand you say sometimes the engine will start right back up.

In looking at the schematics from the 04 FSM the wire routing from crank sensor connector to PCM connector should be as follows. And all 3 wires from the crank sensor connector connect to the C1 (Black) PCM connector.

1. Gray/black wire, sensor signal, to PCM #8 (C1).
2. Black/lite blue, sensor ground (middle cavity), to PCM #4 (C1).
3. Orange, 5V sensor power, to PCM #17 (C1)

Note the bottom row of C1 receptacles is 1-11, middle row is 12-21, and top row is 22-32.

Have you ever cleaned any of your grounds? Below is a ground write-up I did and you may want to at least clean that G103 ground on the passenger side of the block. It's the ground location for both PCM grounds on both the 4.0 and 4.7.

While the photos in the 'edit/addition' section are for the 4.7 below the 4.0 should be around the same location for G103.

https://www.jeepforum.com/forum/f310.../#post39199354

Believe I'd be cleaning the grounds before you check/trace the crank sensor wires to PCM connector to make sure you have full continuity. Also I'm not sure I'd blow off that emissions code and what is it? If it involves a vacuum leak those can also create havoc. Good luck.

2004 4.7L WJ Limited, 96 4.0 ZJ


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post #12 of 22 Old 08-27-2018, 09:36 AM Thread Starter
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Thanks Uniblurb. Almost right after I made that last post, I went out to take it to the grocery and it died almost immediately in the driveway. This time, however, it didn't start right back up- first time that has happened. Had to crank it once with a no-start, turned off the key, and then the next time I cranked it it started. Any chance this might be an ignition switch problem?

Have not cleaned the grounds on it. Seems like that might make a difference. I've got an appointment to take it in to the shop for some diagnosis help tomorrow. It's the wife's daily and I'm running out of time to tinker with it. I hate taking it to the shop though..
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post #13 of 22 Old 08-27-2018, 11:47 AM
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You're welcome broncoguy and had thought about your ignition switch could be the problem.

The 2 PCM grounds on G103 on passenger side of the engine are critical to be good/clean. And from what I've seen the crank sensor will be the 1st sensor to fail w/o a good ground from the PCM. Plus the PCM and crank sensor can be damaged w/o a good ground.

Lets just hope that shop actually hunts down the problem quickly since they're known to throw parts at the problem rather than diagnosing/testing. Good luck and let us know how it goes.

2004 4.7L WJ Limited, 96 4.0 ZJ


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post #14 of 22 Old 08-27-2018, 12:40 PM Thread Starter
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Quote:
Originally Posted by Uniblurb View Post
You're welcome broncoguy and had thought about your ignition switch could be the problem.

The 2 PCM grounds on G103 on passenger side of the engine are critical to be good/clean. And from what I've seen the crank sensor will be the 1st sensor to fail w/o a good ground from the PCM. Plus the PCM and crank sensor can be damaged w/o a good ground.

Lets just hope that shop actually hunts down the problem quickly since they're known to throw parts at the problem rather than diagnosing/testing. Good luck and let us know how it goes.
Definitely agree on throwing parts at it, which is one of the reasons I am reluctant to take it anywhere. Been working on my own cars a long time, and I always hate the few times I have had to take them in. These days it's a lot better with forums like this where you can bounce stuff off other folks. So I appreciate everyone's input, and I will post the findings once I get them..

Thanks again-
Brady
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post #15 of 22 Old 08-27-2018, 02:27 PM
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Check the grounds and make sure the crank position sensor is OK, but the next thing is to consider the PCM. https://www.jeepforum.com/forum/f310.../#post40277927


When it dies next time try to notice if the gauges work at all or if everything is gone including the fuel level. That indicates complete loss of communication between the instrument cluster and the PCM. Then pull the connector on the cam and crank sensors. If you still don't get gauges it's highly possible/probable it's a bad PCM.

If you're interested, PM me, I can likely get you a used PCM programmed to your VIN that's more likely to work than the hit and miss "remans"...
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