Lean Codes with the T-1:

There have been a few folks that have seen lean codes with our T-1, but only in the cases where the MAF screen has been removed by the customer or on the 2002 by GM.

The honeycomb screen was initially put there to keep the airflow straight, which allows more accurate airflow sensing. None of our intakes ever coded on the 2001 C5s, since they all came with the screen.

We have received reports of lean codes on maybe 5 of our T-1 customers, no more. That is out of 600 customers. The coding may be an installation issue where the hose clamps have cracked the carbon fiber, or simply a small leak somewhere.

The code P0171 and or P0174 is a lean code bank 1 and 2, but here's what it really means:

The MAF sensor is the front guard. It "sees" the mass of air and reports it to the PCM. The computer automatically adjusts the fuel trims by increasing or decreasing the pulse width.

The rear guard are the first O2 sensors. They dial in the pulse width to bring all 19 fuel cells back to stoichiometric, or 14.6:1 in the case of GM. The delta between how much air the front guard sees and reports to the PCM and how much trim the O2s must make up, is called the Long Term Fuel Trim. Each of the cells in the closed loop system have a LTF.

Your car cannot run lean. What the code means, is that the delta between the MAF air {estimated air} and the O2 air (air or fuel left over after the combustion process) have exceeded a built in PCM threshold of 23% unexpected oxygen. It is set at 10% for fuel.

When the MAF has a screen in, it records the mass much more accurately. Without the screen, it has a more random estimate, and misses much of the actual air. The stock Z06 airbox, does not provide enough airflow to cause the estimated/actual delta to go beyond 23% LTFs in any cell, so it passed GMs standards.

Since the stock GM 2001 Mass Airflow Sensor flows over 800 cfm (screened) it is the easiest method of correcting a PCM problem with new intakes.

Other options:

1) The MAFT (Mass Airflow Translator) Works very well
2) The AFR1 by Halltech-Works very well
4) Programming
3) Larger injectors
4) Making sure there are no hairline cracks or leaks_This should be first.
5) Disconnect the battery overnight and redo the idle learn procedure.
6) Go back to stock

The Long Term Trims are simply an average of the corrections made by the Short Term Trims over time. It takes only one trim that sees 23% LTFs for more than 6 seconds to trip the code.

Bottom line: You cannot run lean or rich, since the PCM always returns the trims to 14.6:1. The lean codes mearly express the amount of additional fuel trim the O2 sensors have had to correct in closed loop.

Why then is it important to get the LTFs close to baseline? WOT or fuel cell 22 takes a snapshot of the last trim you were in, just before WOT. The computer looks at the correction and either adds or deletes fuel based on that fuel table. Very complex, but simply stated, you end up with fuel on fuel in WOT and very rich a/f ratios, which if below say 12.5:1, fuel is leftover in the combustion chamber, which makes for less than ideal combustion and a loss of power. Your torque will be high, but the HP low.

[Modified by Jim Hall, 10:16 PM 4/18/2002]


[Modified by Jim Hall, 10:20 PM 4/18/2002]

 

Jim,

Thanks for the writeup. Is the AFR1 or the MAFT really required for all airbox replacements, or is it just just to correct problems? Does the writeup on this page sound correct to you:
http://www.zz0066vette.com/faq.php?q...c=31&sn=Engine

Please replace "zz0066" with "z06" in the above URL

The author of that writeup claims the MAFT is used to LEAN out the WOT mixture. That does not sound correct to me. I figured that the additional airflow provided by the new air intake system would cause the MAF to correctly read additional airflow, and then tell the PCM to enrichen the A/F ratio to get close to 14.6:1. If you need more fuel in closed loop to get 14.6:1 then it makes sense that you would also need more fuel to get the correct A/F ratio when WOT.

If the MAFT is used to fake out the PCM into thinking that the MAF is flowing a different amount of air than it really is wont that mess up the A/F ratio?




[Modified by rbartick, 10:47 PM 4/18/2002]

 

Jim
I am a moron.. so in simple terms do I need the AFR or not with an 02 Z than is dynoing at 360 RWHP... in stock trim.. :)


[Modified by Afy, 12:16 AM 4/19/2002]

 

The best way to determine what your LTFs are is the AutoTap program. Then the AFR1 can dial in a perfect a/f ratio.

Otherwise you're guessing. Chances are your WOT is slightly rich. The best pull I have seen was 369.9 RWHP with just the T-1 Intake. His WOT a/f ratio was 12.8:1, which is a sweet spot in my book. Good balance between strong HP throughout the curve and strong torque. The peak numbers are really not as important as the average HP and Torque.

For instance, Borla's new headers made only 2.5 peak torque over the stock 02 headers on a Halltech STinger package car. At 2500 rpm the delta was 20 ft. lbs over stock and declined until 4800 rpm where it hit the 2.5. The peak HP was 4.6 with similar numbers at low rpm (8 RWHP @ 2500 rpm).

Jim