JNorris

iTrader: (4)

I have a 98 Z28 and neither AutoTap for DOS or Windows has the option to display the A/F ratio. Is there a way to calculate it by using the MAF, IPW, or other data AutoTap can collect?

Thanks

John

<small>[ June 11, 2002, 07:49 PM: Message edited by: JNorris ]</small>

JNorris

iTrader: (4)

ttt

Bear

iTrader: (1)

TTT, I just ordered this for this purpose. I hope it an be done. Help please.

Dave F

It displays all 4 O2's for the Corvette, so I don't understand why it would not fror your car. Are you sure you have gone through all of the menus?

I follow no 1

iTrader: (6)

Not sure how accurate it is but I found a menu that says A/F ratio.It logs as 11.1 or 12.5 and so on.Not sure where it is though.

NoGo

iTrader: (2)

looks like I am going to jump on the TTT band-wagon as well. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

JNorris

iTrader: (4)

Thanks for the replies. I have looked in the DOS and Windows versions of AutoTap and I have not found it anywhere. In the 98 GM Service Manual it says that the A/F ratio is only displayed if the Freeze Frame data snapshot and in the FR data snapshot when a DTC (SES) is set. The customer support guy for AutoTap said that GM did not make the A/F ratio available for continuous display for all years. This statement is supported by the GM Service Manual for the 98 Fbody.

I would think that if you knew the injector pulse width, injector flow rate, MAF data, air density, and maybe a few more variables then it should be possible to calculate the A/F ratio if you know the formula.

John

DolfanZ28

Well I want zero knock retard so I went base 10% rich and WOT 4% rich and that did it. I will tune more agressively at the track.

JNorris

iTrader: (4)

Somebody has to know how to do this!

John

red ws6 99

Since this has not been answered. First off autotap is not a good choice for a scanner, to slow.

you want to caculate air flow in lb/min or lb/s whatever does not really matter, you get this from the maf of course.

then you need fuel, you have your injector flow rate at 100% in lb/min and you need injector pulse width.

Then make sure the units are the same lb/s or lb/min

Divide air flow by fuel flow.

I dont think the number would be accurate at all, one of the reason why is autotap, but even with something like EASE it aint that simple. Your best bet would be to use a wideband, but that costs <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Gary

The Dragon

iTrader: (6)

It's in there Dude <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Connect to your car's PCM via Autotap. Go to gauges and set up the # of parameters you want to monitor (I always use 8), Click setup beneath one of the gauge windows and choose "display all".

A/F ratio will be on that list somewhere <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

If not, return your Atap cable and get it replaced.

QuickSilver2002

The value in auto tap is not the actual a/f ratio being produced. It what the computer thinks it is giving to the motor in terms of air and fuel based on MAF and fuel injector mass flow. Think of it as a value based only on what is being measured on the input side of the equation and the devices measuring the values are not extremely accurate, especially when you have modified the system for more efficiency.

If you want accurate a/f ratios at WOT you need a wideband o2. For normal driving conditions, the onboard 02s will give you fairly accurate info, but who really cares about that.

gwj

You're not going to get a real accurate number w/o a wideband O2.
What you can do is monitor your front O2 sensors @ WOT and average the numbers. You can monitor the TPS to make sure you're close to 100% and/or in fuel cell #22. A general rule of thumb is .880 - .910 or thereabouts is "normal". <.880 getting leaner, >.910 getting richer.

JNorris

iTrader: (4)

The Dragon – I wish you were correct. The 98 PCM only shows the A/F ratio in the Freeze Frame data.

red ws6 99 – It seems that you are correct. Your suggested method is how we had calculated the A/F and the result was 33.54:1!!! Talk about lean.

A/F calculations

I guess if I really want to know it is time to go the wideband O2 route.

Thanks for the replies.

John

Trevor @ Texas Speed & Perf.

iTrader: (3)

John - I'd recommend that you put the car on a wideband O2 and monitor the front O2's during the run so you'll have some data to compare. This will give you an idea as to what the true a/f ratio is given whatever values you obtain from the O2's. When I showed a 12.5:1 a/f ratio on the wideband, my O2's were reading in the .930 range.