CONFUSED - PLEASE HELP Lean or Rich after Cold Air Intake?????

[John Youngblood]

Please help, I am totally confused. With a completely stock 2002 Z, will the addition of a cold air intake, WITHOUT tune, cause a lean or a rich condition? Will the condition (lean or rich) be the same throughout the entire power band? I put an MTI true ram air CAI on my Z and althought I don't see a SOTP increase below 50 MPH, I do see a difference above 50. Also, I am not throwing any codes. Thanks for clearing this up for me.
John

[ZO6/Les]

Adding a cold air intake .. ANY cold air intake, should not throw codes or cause a lean condition. Lean conditions/codes happen when unmetered air "leaks" into the sysytem after the Mass Air Flow sensor - and before the T/B. The unmetered air can cause a lean condition, plus unmetered air is not filtered so it is important to get the system air-tight.

There will be, with most systems, a 10-12 RWHP increase - especially initially, as the stock PCM runs a little rich - and the extra metered air will/should lean the A/F out SLIGHTLY after install. Many (me included) believe that affect is short lived as the MAF "learns" from the increased airflow and changes the A/F back to the factory setting. At that point the cooler, denser air is what is increasing power, not the A/F ratio. The only way to maintain an improvement in the stock (read rich) factory AF ratio is through tuning.

There are also some systems that create a slightly positive pressure at the T/B at speed (Vararam for example) which has a positive affect on cylinder fill rates. This positive atmosphere (also called "Ram" air) is a subject of much debate, some of it even informative - use the search function if that discussion interests you ....

Just my .02....

Les

Originally Posted by John Youngblood

Please help, I am totally confused. With a completely stock 2002 Z, will the addition of a cold air intake, WITHOUT tune, cause a lean or a rich condition? Will the condition (lean or rich) be the same throughout the entire power band? I put an MTI true ram air CAI on my Z and althought I don't see a SOTP increase below 50 MPH, I do see a difference above 50. Also, I am not throwing any codes. Thanks for clearing this up for me.
John

[John Youngblood]

Thanks Les, your explanation is very informative. Anybody else want to chime in? I can't get enough info.

[POWERTOWEIGHT]

I put a Vortech cold air system on. The car didn't benefit at the track until I did a dyno tune. I've also done headers, themostat, etc. If your not going to tune it I would leave the stock intake system alone. The good after market cold air and header systems increase flow if done successfully. If they are too sucessful, your computer will enrich the mixture to keep from burning a valve. This will, in effect, make your car slower than stock and depress your fuel economy (I assume you don't care about the latter or we would be on the Honda Civic forum). This is why a good dyno tune, and I mean real life not guess work, is the best way to truly realize a gain from your modification. Good luck.

[FRC Tom]

In most cases you will not get a lean condition. The computer will make adjustments for the increase in air by adding more fuel but at the same time your LTFTs are going to go on the positive side. What this does is make your car run rich at WOT or openloop.
This is why it is important to get the LTFTs as close to 0 as possible in closed loop.
The LTFTs keep track of the fuel being used in closed loop and refer to them when you go in to open loop or WOT.
So as you will not be running lean because the PCM is dumping fuel to make up for the increased air, the computer will also dump fuel at WOT if you don't reduce your LTFTs.
When you go into open loop the PCM refers to the PE table for the AFR. You might have the PE table scaled for a AFR of 12.8 but if the LTFTs says add fuel it could drop as low as 10.

The PCM will always relearn the conditions and keep the car at it's preset stoich value in closed loop but the AFR in open loop is reached by the scaling of the PE table plus the fuel added from the recorded LTFTs.

To answer your question, you will be at 14.7 or so in closed loop and most likely rich when you step on it.