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Chris, Shop Foreman
Category: Jeep
Satisfied Customers: 3369
Experience:  Jeep Certified Master Tech
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I was having problems with a 2003 Jeep Liberty, miss-firing

Customer Question

I was having problems with a 2003 Jeep Liberty, miss-firing and generally have ignition timing issues. The interm loss of cmp or ckp came up on my code reader. P1391 was the code. It also threw a bunch of other codes related to coil failures, such P0356 355 354 352 etc. I replaced the cam and crankshaft sensors. It ran perfectly. Until it was well warmed up and then had exactly the same issue with the new sensors installed. By the way, the exhaust sensor is not very friendly to remove, but got it done. Hope you have some suggestions. Thanks.
Submitted: 9 months ago.
Category: Jeep
Expert:  david craig replied 9 months ago.

Hi Im David, please allow me a moment to look up some information

Customer: replied 9 months ago.
Expert:  david craig replied 9 months ago.

so all of these codes went away while it was running good after the sensors were replaced? did the check engine light ever go out?

Expert:  david craig replied 9 months ago.

P1391 JEEP - CMP or CKP Signal Intermittent Condition Possible causes - Timing belt or chain stretched or jumped - - Camshaft Position (CMP) Sensor harness is open or shorted - Camshaft Position (CMP) Sensor circuit poor electrical connection. plus all of the coil need to do a compression test and check the timing at #1 tdc

Customer: replied 9 months ago.
I checked one dead centre. It's Ok. When the engine is cold it runs like a top.
Customer: replied 9 months ago.
I cleared the codes and they stayed away until the engine had run for about a half an hour. Then little by little it got worse until if started missing badly.
Customer: replied 9 months ago.
I reconnected the wiring plugs and to no avail.
Expert:  david craig replied 9 months ago.

ignition components, i.e. coils, crank sensors,cam sensors,ignition switches tend to be very vulnerable under heat. theres a thermal breakdown of a component since it runs good when cold. do you have a scan tool that can read live data? also when you turn the key to the on position (not start)does the check engine light come on?

Customer: replied 9 months ago.
Thanks David, I have replaced the crank and cam sensors and the wiring from those appears to be sound with no Obvious heat deterioration. When I have cleared the codes, when the engine is cold, the check engine light does not come on until until the engine is fully warmed up and beginning to show signs of ignition failures. The check engine light comes on when I'd like the ignition switch into the running but not starting position before starting the engine each time, so as to check that all of the dash lights are working.
Expert:  david craig replied 9 months ago.

ok. good. what i want you to do next is a back pressure test to determine if the catalytic converter is clogged. you will also need to remove all of the ignition coils and compare resistance readings from all of them.

Expert:  david craig replied 9 months ago.

if you find a coil with a fairly different resistance reading form the rest, this very well may be the source of the problem as it will continue to get worse under load or heat.

Customer: replied 9 months ago.
Ok, I won't get to it until Wednesday as I am away on business for a few days. Thanks for the help so far.
Expert:  david craig replied 9 months ago.

you're welcome

Expert:  david craig replied 9 months ago.

were you able to do anything as of yet?