Please enlighten dyno and a/f meter

bcollid · 02-26-2010, 02:18 AM

I have a new 383 in my 1989 corvette.

I have been data logging with DataMasters which shows the engine running on the rich side. BLMs of around 120 at part throttle

So I take it to the Dyno today and they put an air/fuel meter in the tail pipe. They're air/fuel meter says I am running lean at part throttle.

How can this be???
Question, does the catalytic converter change the mix?
The dyno A/F sniffer was picking up exhaust after the cat while the data logging is taking info off the narrow band o2 senor on the head before the cat.

The engine developed abut 335 hp at the wheels. which is about what I expected.

Rohn · 02-26-2010, 01:44 PM

120 BLM is not rich. All that means is that the ECU is pulling fuel and placing A/F at stoich. Conversely 136 is not lean, adding fuel to place at stoich. the dyno uses a WB sensor that is most likely very accurrate. My Innovate WB sensor is about 16 inches after header collector with no cats. For me 14.7 is stoich and at part throttle I see 15.0-15.3/1. I have decell entean and hyway criuse disabled. What A/F did dyno show at part throttle? You can tweek stoich A/F if you like and enrichen it a bit. You need to move the 02 swing points up a little(10%) and reset the stoich value in .bin.

bcollid · 02-26-2010, 02:58 PM

Quote:

Originally Posted by Rohn

120 BLM is not rich. All that means is that the ECU is pulling fuel and placing A/F at stoich. Conversely 136 is not lean, adding fuel to place at stoich. the dyno uses a WB sensor that is most likely very accurrate. My Innovate WB sensor is about 16 inches after header collector with no cats. For me 14.7 is stoich and at part throttle I see 15.0-15.3/1. I have decell entean and hyway criuse disabled. What A/F did dyno show at part throttle? You can tweek stoich A/F if you like and enrichen it a bit. You need to move the 02 swing points up a little(10%) and reset the stoich value in .bin.

Thanks for your comment

I'm get more confused every day. Just when I think I have a handle on it. I learn what I don't know!

With Datamasters I almost always see 120 BLM and I see the O2 sensor swing back and forth across between .9 and .3 volts. at part throttle steady cruise. I made the assumption that I probably have too much fuel being delivered.

The Dyno showed me running 16.5 to 17/1 at part throttle around 2000 to 2300 rpm. then when the throttle was punched the A/F went way rich like 9/1 before levelling off at about 12/1

The dyno shows a nice level rise in horse power but the torque curve shows an initial drop when going to WOT.

Regarding the catalytic converter, I've got to think that it messes up the A/F ration coming out the tail pipe. The 1989 has an air pump feeding the converter. To me that means there is more air being introduced into the tail pipe after the combusion. Does that make sense.

your help and knowledge is greatly appreciated