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Unread 05-06-2012, 08:06 PM   #1
jeep04
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Won't downshift at full throttle?

OK so here's the issue,,, I had installed a cheap DIY cold air intake and a classic chambered power stick exhaust and it seemed to run great, but then I noticed when I floored it the trans wouldn't down shift.

So I figured at 75k maybe time for my third tune up, I changed the plugs, fuel filter, PCV valve and every fluid the jeep has. I also put the factory intake back on, but still wouldn't kick down.

Could this be related to the open style exhaust causing a loss of back pressure?, its coming off anyway as soon as I get a super 44 as the power stick sounds good but way to loud.

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Unread 05-06-2012, 10:14 PM   #2
pinky2252s
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Quote:
Originally Posted by jeep04
OK so here's the issue,,, I had installed a cheap DIY cold air intake and a classic chambered power stick exhaust and it seemed to run great, but then I noticed when I floored it the trans wouldn't down shift.

So I figured at 75k maybe time for my third tune up, I changed the plugs, fuel filter, PCV valve and every fluid the jeep has. I also put the factory intake back on, but still wouldn't kick down.

Could this be related to the open style exhaust causing a loss of back pressure?, its coming off anyway as soon as I get a super 44 as the power stick sounds good but way to loud.
Do you have the I6 or V8? (Im on my phone so no profile details). I have a CAI, and no muffler. It hasnt affected my shifting. But, it could be a back pressure problem. Im just not sure where. Is everything tight and secure for the CAI?
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Unread 05-06-2012, 10:15 PM   #3
McCloudsZJ
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The Jeep will still downshift at full throttle with open headers... Just don't ask how I know So I don't think back pressure is your problem.
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Unread 05-06-2012, 10:32 PM   #4
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I have headers, no catalytic converter with a flowmaster 44 and I'm have the same trouble so maybe it is open exhaust. Time to put cats back on!
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Unread 05-06-2012, 10:34 PM   #5
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Quote:
Originally Posted by Jeepgcl9947
I have headers, no catalytic converter with a flowmaster 44 and I'm have the same trouble so maybe it is open exhaust. Time to put cats back on!
Agreed, the engine has to have some back pressure. As a suggestion, get a flow master free flowing cat. I dunno if you need the pre cats, but having a big cat will create some back pressure.
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Unread 05-06-2012, 10:36 PM   #6
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Quote:
Originally Posted by pinky2252s

Agreed, the engine has to have some back pressure. As a suggestion, get a flow master free flowing cat. I dunno if you need the pre cats, but having a big cat will create some back pressure.
Can I add a cat but keep it loud? I love how loud it is now and I think adding a cat will quiet it up a bit.
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Unread 05-06-2012, 11:28 PM   #7
pinky2252s
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Quote:
Originally Posted by Jeepgcl9947

Can I add a cat but keep it loud? I love how loud it is now and I think adding a cat will quiet it up a bit.
It might quiet it some, but its the least restrictive that you can get and still retain some back pressure. Honestly, I have all 3 stock cats, no muffler and a CAI, and my exhaust is pretty darn loud. Backfires some too.
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Unread 05-07-2012, 03:28 AM   #8
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Quote:
Originally Posted by McCloudsWJ View Post
The Jeep will still downshift at full throttle with open headers... Just don't ask how I know So I don't think back pressure is your problem.
spot on.

maybe rather have a look at a throttle position sensor and it wiring for reason for not down shifting

cats have no influence on the down shift


good luck

maybe also disconnect and recollect the battery to give every thing a reset
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Unread 05-07-2012, 07:07 AM   #9
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I still have the factory pre cats, mine never had the big cat and as said above the cai is off.

So either the powerstick or the tps sensor as kfxnando suggested, i dunno i do know its annoying when merging.

Thanks for everyones help so far
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Unread 05-07-2012, 07:56 AM   #10
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what about the kick down cable?
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Unread 05-07-2012, 09:10 AM   #11
jeep04
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Originally Posted by narnwv View Post
what about the kick down cable?
is this located on the trans somewhere, could it have failed somehow or stretched?
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Unread 05-07-2012, 09:36 AM   #12
kfxnando
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was thinking about this, and remembered that there is a earth strap on the exhaust close to the cat at the bottom, that earth also goes to the gearbox, seeing that someone worked on the exhaust, maybe that is missing or loose or damaged

apparently these jeeps are very sensitive to minor electrical issues

good luck
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Unread 05-07-2012, 09:49 AM   #13
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Quote:
Originally Posted by jeep04

is this located on the trans somewhere, could it have failed somehow or stretched?
I don't exactly where on the 4.7 but it should be attached to the throttle body and the adjustment should be up top near where it connects. Again I'm not 100% sure this is the case for the 4.7.
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Unread 05-07-2012, 10:24 AM   #14
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self am under the impression that these jeep don't have kickdown cables, me thought that it all happens electronically
depending on signals from the map sensor and tps, rev and speeds

could be wrong

.
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Unread 05-07-2012, 10:37 AM   #15
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Quote:
Originally Posted by kfxnando View Post
self am under the impression that these jeep don't have kickdown cables, me thought that it all happens electronically
depending on signals from the map sensor and tps, rev and speeds

could be wrong

.
You are right, the 42re trans have the kickdown cable but the 545rfe is controlled electronically.
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