# 08 Grand Cherokee 4.7 misfiring

**URL:** <https://community.cartalk.com/t/08-grand-cherokee-4-7-misfiring/136348>\
**Category:** Maintenance/Repairs\
**Created:** [March 12, 2019, 1:09pm UTC](https://community.cartalk.com/t/08-grand-cherokee-4-7-misfiring/136348 "2019-03-12T13:09:35Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![toomuchhayday\_149368](https://avatars.discourse-cdn.com/v4/letter/t/c57346/32.png) [@toomuchhayday\_149368](https://community.cartalk.com/u/toomuchhayday_149368)\
**Post date:** [March 26, 2019, 6:55pm UTC](https://community.cartalk.com/t/08-grand-cherokee-4-7-misfiring/136348/21 "2019-03-26T18:55:15Z")

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Vehicle owner kept clearing code (ugh) so my freeze frame for the code never had LT

I had battery unplugged during the intake replacement which took 5 days due to them wanting to supply the parts. I normally don’t allow that but needed a break due to the flu!

I relearned throttle and cam/crank sensors (Owner told me he had done the ckp on his own before towing it here.)

Issue is not present right now so gave it back to them to drive and have asked them not to clear any codes.

I’m left wondering if the pcm had somehow learned improper firing?? And the long duration of no battery reset memory? Or if I had tried relearn from day 1 if it would have fixed it??

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**Author:** ![tcmichnorth](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tcmichnorth/32/25126_2.png) [@tcmichnorth](https://community.cartalk.com/u/tcmichnorth)\
**Post date:** [March 26, 2019, 9:11pm UTC](https://community.cartalk.com/t/08-grand-cherokee-4-7-misfiring/136348/22 "2019-03-26T21:11:06Z")

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I want to learn. Why would you concentrate on long term. Isn’t short term more real time? Would it be because of an intermittent problem that long term is looked at in this case?

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**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\
**Post date:** [March 27, 2019, 1:40am UTC](https://community.cartalk.com/t/08-grand-cherokee-4-7-misfiring/136348/23 "2019-03-27T01:40:01Z")

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> [@tcmichnorth](#):
>
> Why would you concentrate on long term. Isn’t short term more real time?

The short term ft is what the computer is currently doing to try to keep up w/the o2 sensors, and changes as rapidly as the o2 sensors change; i.e. more than once per second. Short term ft can reflect a response to transient changes in the throttle position, engine load, the sensor’s time response, etc. The long term ft is just the calculated average of the history of the short term fuel trims. I don’t know which formula the engineers use for that calculation, probably varies by manufacturer, but I’d guess the average is over an hour of driving or more. This makes the long term fuel trim more diagnostic of a systematic problem involving the engine fuel management.

> **[What are fuel trims all about?](https://www.obd-codes.com/faq/fuel-trims.php)**
>
> Everything you wanted to know about fuel trims in terms of modern OBD-II equipped vehicles. Fully explained with scan tool screenshots.

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**Author:** ![tcmichnorth](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tcmichnorth/32/25126_2.png) [@tcmichnorth](https://community.cartalk.com/u/tcmichnorth)\
**Post date:** [March 27, 2019, 9:11am UTC](https://community.cartalk.com/t/08-grand-cherokee-4-7-misfiring/136348/24 "2019-03-27T09:11:08Z")

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Thank you.

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