CJK

Not sure if this is Hypertech related, bad gas, or a computer issue. Recently I've noticed a intermittent slight stumble at idle. I have the auto trans and Hypertech programmer set for regular fuel. While sitting at traffic lights every so often I feel the engine stumble, the rpm drops from approx 700 to 500 and then recovers. Has anyone else experienced this and found a cure?

spartan99

There are several threads that you can find with the search option. People have found their Jeeps to have vacuum leaks. Mine also stumbles a bit and I'll be having Chrysler look at it soon.

TeraFlex

Have you done a update to your Hypertech then reflashed your JK? I updated mine everytime I change my oil.

Mark Doiron

This sounds like a good idea. Is it necessary to uninstall the Hypertech firmware before doing the online update, or can it just be done by connecting the Hypertech up to the Internet (with it stowing the stock firmware) after the initial install into the JK?

TeraFlex

You have to flash the JK back to stock first, then update the programmer then flash the JK.

CJK

I'll give it a try.

JPop

While you've set back to stock, see if the stumble still exists. Easy enough way to sort out if the problem lies elsewhere or with the Hypertech.

Also, if you have any exhaust or intake upgrades the Hypertech may not be playing well with them. Additional airflow probably won't be detected or corrected for with their programs. With Just an air temperature and the O2 sensors on the JK there isn't much to go on and you could be leaning out your A/F mixture.

Keep us posted.

captjay

this happen to me before the hypertech, i now run premium fuel with the programmer and every once in a while, it still happens, so prob nothing to do with hypertech IMO. only happens at idle the drops below idle speed. i know on other vehickles u can manually adjust idle speed under the hood but i have not looked to see if can be done on the jk

foxcasper

Good advice - eliminate the variable, go back to stock.

Other thing to llok for is nicely switching O2 sensor signals in a nice slow sine wave.

Bad fuel or bad fuel blends are a good culprit - you live in AL - weather in the winter is normally mild there and the fuel is blended accordingly. I know when I was there a few weeks back it was unusually cold. Fuel blends change throughout the year. More volatile in the winter to promote good vaporization and hence good combustion in cold temps, less volatile in the summer for the opposite reasons. My "other car" is very sensitive at change over times between summer winter and winter summer. I wonder if jeep is also sensitive- especially when the weather differs significanly from the norm like you probably experienced. (i.e. you have a tank of warm weather fuel in a sudden cold climate).
->Try a good fuel blend with good detergents like shell/bp.

Last thought -did you check your spark plugs for gaps and cleanliness ? One of my cars is quite sensitive to spark plugs.
-> if you take them out you may as well exchange them with (properly gapped) new ones - a cheap trial.

Stuka

My bone stock JK does this. Has since day one. And there are many threads on it. I was considering a hypertech for the extra power (how is yours BTW?) and I was hoping it would fix the issue.

But I am still thinking the issue is because its a V6 without balance shafts.