View Full Version : Adjusting A/F

10-14-2005, 11:40 PM
I'm still learning the ins and outs of TRs, so bear with me. DirectScan tells me that I'm running 14.7 or 14.8:1 very consistently under a variety of load/throttle conditions. Is there a way to adjust A/F mechanically, or am I looking at two different brains for the ECM?

From lburou's inj duty cycle calcs I see:
Air/Fuel Ratio Limits
6.0:1 Rich run limit
9.0:1Low power, black smoke
11.5:1Rich best torque at WOT
12.5:1Safe best power at WOT
13.2:1Lean best torque at WOT
14.7:1Chemically ideal
15.5:1 Lean light load, part throttle
16.2:1 Best economy, part throttle
18-22:1Lean run limit

The long and the short of it is this:
--Can I run 16:1 for my 4 miles at 30 mph to work, then change to 12.5:1 when I want to go play?
--Is stoich just the best balance between power and economy?

PT52 w/50# injectors, chip unknown


10-15-2005, 02:53 AM
Is there a way to adjust A/F mechanically, or am I looking at two different brains for the ECM?

http://www.stealth316.com/2-calc-idc.htm is what you're referring to. Lot's of good info there.

Mechanical adjustment? Well...uh...sure. Let's look at some examples.

You could adjust the fuel pressure. If you adjust it enough, you can overcome the amount of adjustment ability the ECM has programmed into it. (which is quite a bit) Now doing this on the fly...that is another story. Not really designed into any gizmos I'm aware of.

You could adjust the air. At least the amount of air under boost. Actually, adjust the amont of boost. That is pretty easy. Doing it from within the car...not impossible. However, this won't do much for creating a leaner cruise to help gas mileage, etc. Only be able to tweak the amount of air when your right foot is down.

The right way to adjust things is to have the air/fuel curves and such in the chip set to the parameters you wish. Something like the Thrasher chip is known for having a leaner cruise that aids in improving gas mileage. If you want multiple options at your disposal, get a blank Ultrachip from Caspers Electronics and burn all of your favorite chip images into it. Then switch to what you want/need at that time.

10-16-2005, 12:50 PM
So, the Ultrachip allows multiple maps to run without physically changing chips? Does a signal from the TPS tell it which 'program' to run?

10-16-2005, 02:07 PM
Just to be clear ...

DirectScan is just telling what the COMMANDED A/F ratio is (according to the cal in the chip and corrected for trims and sensor readings). It doesn't tell you WHAT the A/F is.

You need a wideband O2 for that ...

Most of the adjustable chips either have a thumbwheel that selects the map you want or they have you do some sequence with the TPS, A/C controls, etc. (ala TurboTweak or Max Effort). The Extender chips work with adjustments you can make with the Translator.