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Unread 07-28-2013, 03:41 PM   #1
cfatrat
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P1391 CKP or CPS issue Not the usual Issue

I just purchased a 98 Cherokee and have a unusual issue with my crank position signal. I have replaced the sensor with one from NAPA and to my surprise, it had already been replaced before. I have owned many Jeeps in the past, this one has me puzzled to the max. When checking the reference signal, it has the 5 volts on the orange wire, but it also shows 5 volts on the signal side. This is with it unplugged and checking at the plug from the PCM. I am not sure how the CKP can send a signal if it is getting a steady 5 volts across the signal circuit without turning the engine over.

When trying to start, it will turn over forever on the first try and then on the second attempt, it will fire right off. It will do this religiously. There is the seldom case it will start on the first try but mostly on the second. It was setting the P0320 code and the p1391 before replacing the CKP for the second time but now it only sets the 1391. This is really strange, especially since it has 5 volts on two of the three terminals. In addition, there is about 9 ohms if you check pin A&B, but 0 when crossing B&C.

Any help you can provide would be a blessing. I am leaning towards the PCM but not there yet. As a matter of fact, the Cam Position sensor and the MAP have 5 volts constant on their signal wire also.


Last edited by cfatrat; 07-28-2013 at 03:47 PM.. Reason: Mistakenly hit the enter button before completing the post.
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Unread 07-28-2013, 07:20 PM   #2
CJ7-Tim
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Measuring 5 volts on both the A and C wire is normal.


P1391 Jeep - CMP or CKP Signal Intermittent Condition

Possible causes

- Faulty Camshaft Position (CMP) Sensor
- Camshaft Position (CMP) Sensor wire harness is open or shorted
- Camshaft Position (CMP) Sensor circuit poor electrical connection.

The camshaft sensor is inside the distributor ( or the camshaft synchronizer housing on a 2000-01 ).

When your 1997 to 2001 Cherokee won’t start on the first try day after day, the first thing to suspect is a failed check valve on the fuel pump. The fuel pump check valve is supposed to hold pressure in the fuel line while the engine is off. The check valve is located on the fuel pump and located in the gas tank. A failed check valve allows the fuel to drain back to the tank. This results in one or more of the following symptoms:

SYMPTOMS

• Longer than normal cranking times
Never starts on first try, almost always starts on the second try
• Rough idle for a few moments of idling
• Rough running for first ½ block of driving
• Little or no fuel pressure at the fuel rail test valve similar to this -

1- Key in on position; fuel pump primes for 2 seconds then stops. 0 PSI
2- Cranking over the engine. 2-3 PSI
3- Engine starts and idles for 20 seconds. < 5 PSI
4- Engine idles and fuel pressure creeps up to 45-50 PSI.


POSSIBLE CAUSES

• Failed check valve on the fuel pump in the gas tank.
• Leaky fuel injector(s) may be the true cause of your problem, but more likely they are simply contributing to the check valve issue.

Testing of the fuel injectors should show if any are faulty and are allowing fuel to drain into the cylinder. Either problem can allow heat soak to vaporize the remaining fuel in the fuel rail, and you may be dealing with a bit of vapor lock as well, especially in warmer weather.

1. Connect the gauge at the fuel rail and start the engine. The gage should read 49 psi plus or minus 5 psi.

2. Turn the engine off and immediately clamp the fuel line just ahead of the fuel tank. Watch the pressure gage and see how long it takes to loose pressure.

If the pressure remains at 49 psi for an extended period of time then the problem is in the tank - probably the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky injector.

There are a few solutions to the problem –

1. Turn the key to ON for 5 seconds and let the fuel pump prime. Turn the key to OFF, turn the key back to ON for 5 seconds, start the engine.

2. Crank the engine for 3-5 seconds, pause, and crank the engine again. It will almost always start on the second try.

3. Replace the fuel pump assembly in the gas tank. The check valve is not a separate part and cannot be serviced. This is both expensive and time consuming because you have to remove any hitches and skid plates and then remove the gas tank from the vehicle.

You can use solutions 1 or 2 for as long as you want to, they do not harm anything and the fuel pump will continue to function for many more years.


If you do replace the fuel pump assembly, purchase a high quality OEM style pump assembly such as Bosch or Carter. Some cheap aftermarket fuel pump assemblies, like Airtex, don’t hold up and fail completely within 12-18 months.
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Unread 07-28-2013, 07:31 PM   #3
cfatrat
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It seems you're saying there is two separate issues. The P1391 code should be the Cam Position sensor since the Crank sensor has already been replaced, and the delay start is either the injectors or Fuel pump. It that fair to say?

Thanks a ton for spending your time with the last reply. This gives a lot of insight.
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Unread 07-28-2013, 07:36 PM   #4
CJ7-Tim
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The 2 issues are probably separate and unrelated. 1997-2001 check valve failure is very common.
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Unread 07-28-2013, 07:45 PM   #5
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Thanks! I'll dig into it next weekend and let you know how it goes
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Unread 08-01-2013, 06:45 PM   #6
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OK, replaced the Crank and cam sensor and light still comes on with P1391 code. Checked the fuel pressure and it was just as you described. It went up to 50 psi running and then fell off pretty steady when shut off.

I am at a loss with the CKP code. It has 5v signal and reference voltage. it has actually set P0320 and P1391 before. Now it just seems to set one or the other. When it stalled on me before, the voltage gauge stopped working and then the jeep died. when the voltage gauge came back to life it would start.

I guess we need to start over.
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Unread 08-01-2013, 06:53 PM   #7
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Quote:
Originally Posted by cfatrat View Post
... When it stalled on me before, the voltage gauge stopped working and then the jeep died. when the voltage gauge came back to life it would start.
Usually this symptom is related to CPS problems.


Did you buy genuine Jeep sensors or cheap crappy "Lifetime Warranty" parts ?

Did you inspect the CPS and CMP wire harness and wire plugs for damage or corrosion ? An OBD-II code can help focus your troubleshooting, but a sensor that cannot send data, looks to the computer exactly like sensor that has failed.
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Unread 08-01-2013, 07:14 PM   #8
cfatrat
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The crank sensor came from NAPA and the Cam sensor came from MOPAR. I have OHM'ed the signal wires between the sensor and the bulkhead connector and no issues.
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Unread 08-05-2013, 07:45 PM   #9
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Did everyone give up? Puzzling huh?
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Unread 08-11-2013, 06:32 AM   #10
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OK, All the signal wires were verified good. So, the CKP has been changed twice, the CMP once, and all the wiring checked. I still get an intermittent loss of CMP or CKP signal (codes 1391-0320). I even checked to see all the cylinders were firing by using an infrared probe. There's only a couple things left that could possibly be checked or swapped. The Distributor, ECM, or could it be a misfire?

THOUGHTS??????
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Unread 08-11-2013, 09:36 AM   #11
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Voltmeter went to 0!!. There is your clue, you have a bad connection somewhere, it could be either the red or black lead.
1) Remove black lead from battery and follow to all of its connection points.
Clean all of them to shiny bright and replace as necessary, I would install SS or Bronze star washers of the appropriate sizes.
2) Remove red battery cable and perform the same procedure, also check the cable for swollen areas, these indicate water intrusion, replace as necessary.
3) Don't forget the alternator cable and PDC cables/connections.
4) If the cables need replacing, get good quality cables. If you have no accessories, you can use the appropriate pre-made ones from your favorite store. Try and verify the wire is silver, indicating it is tinned as opposed to copper. In any event, if you see copper wire, tape it and apply liquid tape to seal it. Otherwise check this forum, there is a fellow who makes cables to order.
5) Reconnect the battery leads red first, black last.

Regards,

Jim W
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Unread 08-11-2013, 12:15 PM   #12
cfatrat
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I never have been able to verify the voltmeter goes to 0. However, I can tell when it is getting ready to set a code because the idle will change and you can hear a slight miss. Then the scanner will show a pending code of 1391 or 0320. A while after that, it will show a check engine light.
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Unread 08-31-2013, 06:53 AM   #13
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OK, we can put this one to bed. I was getting the crank and cam codes from a half dead cylinder. It was showing heat with an infrared, but after inspecting the plug and plug wire, the wire was horribly corroded and the plug was half fouled. once those were changed, no codes and no pending codes.
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Unread 09-15-2013, 09:07 AM   #14
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I hate to say it but this issue won't go away. It ran fine for a couple days then... here comes the CEL. I did fix the problem where it wouldn't start on the first tray. Apparently the distributor shaft had some wear and let the base time be too far off. I replaced the distributor and no more issues with that. However, the P0320 and P1391 codes are back. At this time I have replaced the following


[*]Engine harness has been replaced. The one that encompasses the Crank and cam sensor connectors, injectors Idle air, speed sensor, O2, etc... This harness connects directly to the computer but doesn't contain the relay center. It is in a different harness. Not sure if there is anything in there that would be doing this.
  1. crank position sensor (Napa brand) twice
  2. Cam Sensor... Twice
  3. Cleaned every ground
  4. checked all signals with meter and no issues
  5. Plugs, wires, cap, button, distributor
I am at the end of my rope. what else could it be. This just won't go away.
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Unread 09-15-2013, 10:55 AM   #15
CJ7-Tim
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Read this -> http://jeep.blackonyx.net/pdfs/jcss.pdf
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