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Fuel Pump or CPS Issue?

EWatauga

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Feb 8, 2021
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Mills River NC
After working on upgrading some suspension components all last week I took the TJ (2005 X model with 6M 143k miles) for a test drive yesterday and everything was great. Tried to start it a couple hours later and it turns over freely but doesn't start, there is no sputtering or anything resembling it catching. Then i turn it to the On position i hear (what I only assume is) the fuel pump turn on for a second or two, and again for a second or two when I turn the key off. There is no scent of gas at all. Also the Jeep had been running great and there are currently no error codes. The PO has replaced the fuel pump a year or two ago.

From what I have read it seems that when a CPS goes out there is some sputtering an missing, could the CPS cause the Jeep to abruptly stop running? It currently has over 3/4 tank of gas and I have dropped the tank before (with 1/8 tank of gas) it seems like it would be really difficult with the added 100lbs of fuel so I am hoping that maybe the CPS could be the issue but wanted to get some opinions before I start throwing $ at stuff. Again it drove perfectly for about 15 minutes, then when starting it a while later won't start.

FYI I also replaced the stereo receiver and added a Sound Ordinance 8" powered sub in the center console (all from forum recommendations, so thanks!) but I dont see how that or the suspension changes would effect it, with the exception of maybe the rear adj tracbar since that's in the neighborhood of the fuel lines.

Any feedback is much appreciated.
 

CharlesHS

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I would do a look thru the PDC in the engine compartment and the fuse block behind the glove compartment to see IF any of the fuses are blown.
Then move on to the CPS and CMPS troubleshooting.

 

rasband

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As far as I remember CPS isn’t used in closed loop mode (when a Jeep first starts it runs on pre-configured values until it starts using sensor provided values when it’s closer to temp), so the CPS alone shouldn’t keep it from catching I don’t think.

I’d expect something fuel or ignition related. I wish they didn’t drop the shrader valve on the fuel rail on our later models to make the fuel pressure check simple.
 
OP
EWatauga

EWatauga

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Feb 8, 2021
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Mills River NC
As far as I remember CPS isn’t used in closed loop mode (when a Jeep first starts it runs on pre-configured values until it starts using sensor provided values when it’s closer to temp), so the CPS alone shouldn’t keep it from catching I don’t think.

I’d expect something fuel or ignition related. I wish they didn’t drop the shrader valve on the fuel rail on our later models to make the fuel pressure check simple.
Thanks, that makes sense.
 

CharlesHS

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As far as I remember CPS isn’t used in closed loop mode (when a Jeep first starts it runs on pre-configured values until it starts using sensor provided values when it’s closer to temp), so the CPS alone shouldn’t keep it from catching I don’t think.

I’d expect something fuel or ignition related. I wish they didn’t drop the shrader valve on the fuel rail on our later models to make the fuel pressure check simple.
You are incorrect.... The Crank Position Sensor is used in both Closed and Open Loop conditions....
The CPS and CMPS send signals to the ECU letting the computer know when to pulse the fuel injectors and when to pulse the igniter coils. Without the sensors; the computer wouldnt know what was going on and while the engine might briefly start; the engine would stall again....
 

mrblaine

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Nov 20, 2015
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Quail Valley, CA
You are incorrect.... The Crank Position Sensor is used in both Closed and Open Loop conditions....
The CPS and CMPS send signals to the ECU letting the computer know when to pulse the fuel injectors and when to pulse the igniter coils. Without the sensors; the computer wouldnt know what was going on and while the engine might briefly start; the engine would stall again....
The 05-06 4.0 will start and run with the CPS unplugged or bad. The 97-04 will not even try to start with a bad CPS.
 

mrblaine

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Thats right it has that different style flywheel.... Thanks for the clarification......
And there are two different 42RLE flex plates, one for the 03-04 and one for the 05-06. The CPS is in the same spot for both. The CPS is not in the same spot for the 03-04 manual and 05-06 manual. 03-04 has it the same as 97-02 manual or auto, 05-06 has it the same as the 42RLE.
 
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EWatauga

EWatauga

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Feb 8, 2021
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Mills River NC
I ordered a Bosch fuel pump, the PO replaced it not long ago but I image he put in a cheap one. Hopefully this works. I sprayed some starter fluid in it and it started and ran for a second, so pretty confident its not a spark issue.