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  #1  
Old May 14th, 2019, 07:19
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Hard start; replaced CPS; CEL back on; won't start

About a week ago, the CHECK ENGINE light came on at the beginning of a 90-mile drive. The engine seemed to run fine for the entire drive until the end of the day when I had to start it to return home. It cranked for longer than normal before firing up, then I shut down again after moving the Jeep to load it for home. A few minutes later (in the rain) it wouldn't start. It cranked strong and forever, but took over a dozen tries and ten minutes before it finally fired up and ran fine all the way back home.

I managed to start it the next day with no problems at all (other than the still-illuminated CEL) and took it to the local AutoZone to have them check the codes for me. It came back as Crankshaft Position Sensor (I don't know the actual code number).

I've changed the CPS twice in the past. The first one lasted about 20K miles and the current one lasted about 25K miles. I did the first one myself with an aftermarket part. The second time, I was injured and needed the car, so I had a shop fix it and they apparently also used an aftermarket part (and charged me a HEFTY parts fee for that crap).

A few days ago I bought a Mopar CPS and installed it the next day. At first, the CEL was off and the engine started strong every time, but yesterday it wouldn't start again and the CEL is back on. I drained the battery trying to start it (it's on a charger now) and I tested the new CPS with an ohmmeter after reading on this site how to do that. It tests OK as far as I can tell.

I found a video describing a method of getting the odometer to display engine codes by holding the trip reset button and then turning the key to RUN, but this produces no codes of any kind after the full display check.

Here we are:
Battery is fine and fully charged;
Starter is nearly new and cranks very strong;
Crankshaft Position Sensor is new (Mopar part);
CHECK ENGINE light is ON;
Engine cranks all day but will not fire.


What should I check next?
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  #2  
Old May 14th, 2019, 07:29
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Re: Hard start; replaced CPS; CEL back on; won't start

The exact Check Engine Light trouble code number is your guide for troubleshooting. Buy, rent, or borrow a trouble code reader and post the code numbers here.

Always use genuine Jeep OBD sensors, the auto parts stores only sell cheap crappy Chinese clone sensors that are often out of specification.
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  #3  
Old May 14th, 2019, 07:45
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Re: Hard start; replaced CPS; CEL back on; won't start

Quote:
Originally Posted by Tim_MN View Post
The exact Check Engine Light trouble code number is your guide for troubleshooting. Buy, rent, or borrow a trouble code reader and post the code numbers here.

Always use genuine Jeep OBD sensors, the auto parts stores only sell cheap crappy Chinese clone sensors that are often out of specification.
By "Jeep OBD sensors," do you mean the thing that plugs into the OBD2 port?
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Old May 14th, 2019, 07:52
lawsoncl lawsoncl is offline
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Re: Hard start; replaced CPS; CEL back on; won't start

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Originally Posted by PDBreske View Post
By "Jeep OBD sensors," do you mean the thing that plugs into the OBD2 port?

I think he's referring to the poor quality of aftermarket sensors. It seems like it's a crap shoot ometimes, but I usually have good luck with Napa and lousy luck with autozone "lifetime warranty" stuff which I have about a 50/50 shot of it lasting more than a year.


If you can beg or borrow an OBD code reader that would be helpful. Keep in mind a bad CPS may not throw a code. Have a good look at the wiring to it and make sure it's not damaged or up against the exhaust. If you have a means to check for spark or fuel, that would help as well.
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Old May 14th, 2019, 07:54
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Re: Hard start; replaced CPS; CEL back on; won't start

Remember to include the year model. Things are different over the years.
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  #6  
Old May 14th, 2019, 08:06
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Re: Hard start; replaced CPS; CEL back on; won't start

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Remember to include the year model. Things are different over the years.
Sorry. It’s a 99 Cherokee, 4.0 auto.

Is there a way to edit previous posts?
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Old May 14th, 2019, 08:07
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Re: Hard start; replaced CPS; CEL back on; won't start

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Originally Posted by lawsoncl View Post
I think he's referring to the poor quality of aftermarket sensors. It seems like it's a crap shoot ometimes, but I usually have good luck with Napa and lousy luck with autozone "lifetime warranty" stuff which I have about a 50/50 shot of it lasting more than a year.


If you can beg or borrow an OBD code reader that would be helpful. Keep in mind a bad CPS may not throw a code. Have a good look at the wiring to it and make sure it's not damaged or up against the exhaust. If you have a means to check for spark or fuel, that would help as well.
Ok. I did replace the CPS with a genuine Chrysler part.
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Old May 14th, 2019, 10:13
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Re: Hard start; replaced CPS; CEL back on; won't start

You might want to test the orange wire going to the CPS for five volts. Both with the key in the run position and while cranking. Numerous sensors share that voltage, if another sensor is partially shorted in can affect and code the CPS first before showing a true code for the failing sensor.
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Old May 14th, 2019, 10:18
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Re: Hard start; replaced CPS; CEL back on; won't start

Further troubleshooting requires the CEL trouble codes to narrow down the list of suspects and help focus your diagmostics.


The OBD sensors provide data to the ECM which uses the data to change the adjustable engine operating parameters. If the sensor is faulty, or is providing incorrect data to the ECM, the ECM will make incorrect adjustments that will cause drivability issues, rough running, stalling, or a no-start. Some of the OBD sensors are TPS, IAC, IAT, CTS, Cam sensor, Crank Sensor, O2 sensor.

Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a " Lifetime Warranty ". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.
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Quote:
Originally Posted by bimmerjeeper

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Last edited by Tim_MN; May 14th, 2019 at 16:15.
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  #10  
Old May 14th, 2019, 10:41
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Re: Hard start; replaced CPS; CEL back on; won't start

Quote:
Originally Posted by 8Mud View Post
You might want to test the orange wire going to the CPS for five volts. Both with the key in the run position and while cranking. Numerous sensors share that voltage, if another sensor is partially shorted in can affect and code the CPS first before showing a true code for the failing sensor.
I’ll try that next. Thanks.

Ordered an OBD scanner that is supposed to arrive tomorrow.
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  #11  
Old May 15th, 2019, 07:49
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Re: Hard start; replaced CPS; CEL back on; won't start

OBD2 scanner arrived. Scanned the Jeep and got this:

Confirmed code: P0340 Camshaft Position Sensor "A" Circuit
Pending: P1391
Permanent: NONE
Additional Information: Malfunction Indicator Lamp (MIL) status ON; Freeze frame DTC P0340

I replaced the camshaft position sensor once before, but I believe I replaced the entire distributor to do it. In researching this issue the other day, I think I saw an article about replacing just a part inside the distributor. Does that sound correct?
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  #12  
Old May 15th, 2019, 07:57
RCP Phx RCP Phx is online now
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Re: Hard start; replaced CPS; CEL back on; won't start

Sounds very similar to mine, my part won't be in till tomorrow so I can't tell you the results.
https://naxja.org/forum/showthread.php?t=1154226
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  #13  
Old May 15th, 2019, 10:19
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Re: Hard start; replaced CPS; CEL back on; won't start

I would troubleshoot for the P0340, and then look into troubleshooting for the P1391. Notice that the possible causes for both codes are somewhat similar.



P0340 JEEP - Camshaft Position Sensor Circuit

Possible causes
•Faulty Camshaft Position Sensor
•Camshaft Position Sensor wire harness is open or shorted
•Camshaft Position Sensor wire plug poor electrical connection
•Weak battery

Tech notes
Sometimes and in some models, low battery voltage can trigger a Camshaft Position Sensor code.
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I'm starting to realize people on the Jeep forums are highly expert mechanics .....
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  #14  
Old May 16th, 2019, 06:46
Fatlip671 Fatlip671 is offline
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Re: Hard start; replaced CPS; CEL back on; won't start

My jeep is doing this exact same thing. I replaced the cam and crank sensors. It started and ran fine for 15mins. Then when it was put into drive it died and wouldnt start. The guys working on it cant figure it out.
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Old May 16th, 2019, 07:32
lawsoncl lawsoncl is offline
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Re: Hard start; replaced CPS; CEL back on; won't start

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Originally Posted by Fatlip671 View Post
My jeep is doing this exact same thing. I replaced the cam and crank sensors. It started and ran fine for 15mins. Then when it was put into drive it died and wouldnt start. The guys working on it cant figure it out.

Have a good look at the wiring. Make sure the CPS sensor wiring didn't get up against the exhaust or otherwise damaged. Look at the ground strap at the back of the block to the firewall. I you get it running again, shake all the wiring harnesses to see if you can make it die. Check the fuses in case something blew. The thought is that you have an intermittent connection or short and putting the trans into drive moves things around a bit. If you have an older Jeep, Cruiser54 has some great tips at cruiser54.com that you should do regardless.


Also a long shot, but make sure the transmission bellhousing to engine block bolts are tight and you don't see any gaps. I have see a few cases where those become loose and in addition to causing odd noises cause CPS sensor issues.
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