just went back and looked at my previous dyno results on some of my cars and not a one changed the afr's enough (when headers were added) to cause a noticeble lean condition. most of my lean condition were either a timing problem or lack of fuel.

 

I disagree with JPop on mostly everything. However, after years of tuning mainly high end european sports cars, long tube headers do require quite an addition of fuel, this was also of course with the installation of a full exhaust that was to work with the headers. Obviously, not as much with just headers and stock exhaust though.

the long tubes change the power band. since the stock headers are shortys, the stock programming is for shortys. if our jeeps came stock with long tubes, and we switched to shortys the same situation would occur, the powerband would be changed.

 

not every car needs tuning though, that was kinda my point in my post. you have needed to add fuel on previous cars and i havent. its really a matter of how well the stock computer can learn and adjust. from what i know of the stock computer in the jk, i think it has the ability to learn and adjust to minor mods.

O.T.

i do however find it odd how some cars computers will adjust to just about anything, short of a turbo, but others will throw a hissy fit with the addition of a CAI and exhaust.

-shaun h

 

I continue to mention headers because the only product I am aware of that replaces the Y pipe is the Borla long tubes. I am only aware of one person on this forum that has replaced his Y Pipe after crushing it, and he did so without cats. It did throw plenty of DTCs and no one was able to present him with a solution. The last solution I recall being thrown out there was a wideband O2 controller, but the OP never presented what his final solution was.

If your intent is just to replace the Y pipe with a fabricated one, it will also include replacing the cats unless you plan to cut them out and re-weld them into your new Y pipe. If the plans include high flow cats, I have no idea if they would work, but if they didn't it wouldn't be the first time I heard of after market cats creating issues with a PCM.

What wasn't mentioned prior to this post was the intent to use a tuning product, which is going to allow you to present different data to the PCM. That is certainly a workable solution, but not for the faint of heart.

 

My JK was definitely running lean after the installation of headers as revealed by both the plugs and an Aeroforce Interceptor. I was running a Hypertech Max Energy at the same time and returning to stock didn't correct the issue. I tried running colder plugs to no avail and finally straightened things out running 94 Octane with Hypertech's 91 setting. Didn't feel that I was getting any additional power, but I wasn't running lean anymore.

I'm unsure of what exactly caused the lean condition, but I wasn't alone as other people with headers stated the same lean issue. My only guess is that the headers were better evacuating exhaust gas from the cylinders enabling more and cleaner air in on the intake stroke.

 

Headers can assuredly change timing and fuel needs. Easy to take care of when you don't have a computer in the middle of things, but requires some serious intervention when you do.

 

I followed nearly the exact same trek on my JK as my Hemi Ram. They both use essentially the same PCM. Headers, exhaust, CAI and no issues on the Ram. The JK never responded as well to upgrades, and the relearn time could be several tankfuls. I also added a cam and 6.1 heads to my Ram which upped the flow and compression ratio and it still runs fine with the SC Flashpaq. The JK never faired as well with the stock PCM or the Hypertech, but with the Flashpaq I seemingly don't have the same issues.

 

That's kinda what I was getting at. Most of the time
on minor mods, if there is a problem, it's with the computer.

I've seen plently of times that an 02 sensor reads something
and the computer translates it different, that's why when tuning it's always best to tune w/wide band as far up the exhaust as possible.

Are you sure it wasn't hypertec programming that caused
you to run lean, off the shelf maps in my opinion are not the best. No two cars are the same.

I seriously doubt that going from 91 to 94 octane changed
your lean condition as well. Usually it takes a lot higher octane rating to richen the vehicle up enough. Unless ofcourse you have FI. Even then 3 octane point higher is not much of a change. Not saying it didn't happen, it's just not the norm.......maybe your computer is on the slow side

 

It could have very well been the Hypertech. I did go back and forth between the Hypertech and Stock PCM without resolve. As I had a few hundred bucks invested into the Hypertech it was my intent to get the thing to work. The Hypertech tunes are based off of a stock engine without exhaust or intake modifications. Others have experienced similar lean conditions with just a CAI and the Hypertech, while I had exhaust, headers and a CAI.

Upping the Octane was a suggestion from Hypertech, and it wasn't something I came up with on my own. It definitely helped and I'm assuming the slower burning fuel left some unburned fuel in the cylinders. There also could have been less percentage of ethanol in the premium fuel which also would change how things were effected.

It wasn't that long into the process after upping the octane levels for use with the Hypertech that the Flashpaq came along. It was also fairly cold here still and it's a little difficult to do testing when it might take as long as 10 minutes to get to operating temperatures. Water under the bridge at this point as I no longer have the Hypertech and haven't had issues with the Flashpaq.