Long Term Fuel Trim Adjustments

bandersson · Post by **bandersson** » Thu Jun 21, 2007 8:31 pm

Ok, so I installed a BBK CAI on my '03 Mustang GT and the Diablo performance tune, no other mods.

At idle, LONGFT1 & 2 is in the -12% to -14% range and, unless I have this totally backwards, that means that the PCM is adjusting for a rich condition. At speed it leans out and LONGFTs are in the -3% to -4% which I am ok with and at WOT between -2% and 2%. Now, if the fuel adjustments that the Predator can affect is at WOT only, how can I adjust the fuel delivery at lower RPMs down to idle? I am also a little surprised at the numbers because if the CAI truly increased air flow, then shouldn't I expect that the PCM would be adjusting for a lean condition? More oxygen, same amount of fuel = lean and expect LONGFTs in the positive range adjusting for the lean condition. Am I off on my assessment? If so, please correct my assumptions.

Thanks,
Bjorn

LightningMike03 · Post by **LightningMike03** » Thu Jun 21, 2007 8:47 pm

Did you do any data logging before installing the CAI? If not, I would go back and do that to get a baseline for comparison. The numbers you have don’t mean much unless they are compared to the stock numbers.

BTW generally there is way too much hype about the benefits of most CAI’s. You will probably see that over a couple weeks normal driving that the ECM will correct for most of the benefits, though they do sound good.

bandersson · Post by **bandersson** » Thu Jun 21, 2007 9:06 pm

I sure did. With just the performance tune and original AI the LONGFTs were @ -3% to 2% at idle and around -5% to -2% @ 55 MPH. I know there is more hype than actual gains to CAI alone, however I am planning additional mods in the future that should benefit from increased breathing that I'm not so sure I'm even seeing right now. I may have to install the original AI again and monitor the MAF voltages for a baseline and then try the CAI again. Thanks for the suggestions.

LightningMike03 · Post by **LightningMike03** » Thu Jun 21, 2007 10:22 pm

Did you run both tests with the engine at the same temperature? Was the ambient air temp the same?

Since the whole idea of the CAI is to keep the intake air colder, “I believe” the ECM will try to add fuel for the cold engine (open loop?). After the ECM goes to closed loop (warm engine or a preset number of seconds), sorry I can never keep the two straight, the tune will take over and the numbers should look better.

Sorry if this does not make much since and I may also have it ass-backward.

Bottom line: engine and ambient air temps will have a lot to say about the fuel and timing, so they really need to be as close to the same for each test as possible. Also don't run tests under variable weather conditions or altitudes. Atmospheric pressure will screw the results too.

Post by **mikel** » Fri Jun 22, 2007 1:33 pm

bandersson wrote:I sure did. With just the performance tune and original AI the LONGFTs were @ -3% to 2% at idle and around -5% to -2% @ 55 MPH. I know there is more hype than actual gains to CAI alone, however I am planning additional mods in the future that should benefit from increased breathing that I'm not so sure I'm even seeing right now. I may have to install the original AI again and monitor the MAF voltages for a baseline and then try the CAI again. Thanks for the suggestions.

I think you just hit the nail on the head.
Issue with most CAIs is they alter the MAF voltage, mainly at low engine speeds, as a result of all the bends before the MAF.
This can be corrected in a custom tune, but it is not hurting anything as of now.

Thanks