Just playing around last night I noticed that the air/fuel jumps from the rich zone at WOT back to stoich for a moment when the engine goes into VTEC. It stays rich all the time if you shift below VTEC or above VTEC; it's only at the x-over that it leans out. It's all stock internally, the ECU is stock, so is this normal? If not what could be the reason for this?

 

because when u go into vtec, it requires more fuel. probably not a big deal as the huge jump you are seeing in your gauge can be attributed to autometer's complete worthlessness (a/f gauge)

mike

 

^what he said...

it could also be that the computer cuts fuel to the engine while it switches.

I saw a friend of mines a/f autometer guage the other day... it looked like a gay disco... how you supposed to derive ANY reliable info from that is beyond me.

 

A/F gauges work properly in open loop. On stock unchiped computers when you let off the gass ecu goes into closed loop. This is when the ECU does not read the 02 signal. Its all predetermined programed fuel in the ECU. If your computer runs in open loop constantly the A/F guge is very accurate once the engine is up to temp. Open loop uses the 02s signal to lean or add fuel as required.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Phat_Optimo &raquo;</TD></TR><TR><TD CLASS="quote">A/F gauges work properly in open loop. On stock unchiped computers when you let off the gass ecu goes into closed loop. This is when the ECU does not read the 02 signal. Its all predetermined programed fuel in the ECU. If your computer runs in open loop constantly the A/F guge is very accurate once the engine is up to temp. Open loop uses the 02s signal to lean or add fuel as required. </TD></TR></TABLE>

I thought in closed-loop is when it runs off the O2 sensor, and in open-loop is when it runs off the ecu.

 

Closed loop: It uses the ECU fule map with small adjustments from the O2 sensor.

Open Loop: It uses the ECU fule map with no adjusstments from the O2 sensor.

At WOT it goes into Open loop, under normal driving it's in closed loop. Also the A/F ratio that you read with the stock O2 sensor does NOT tell you the A/F ratio it only lets you know if it's more than 14.7:1 or less than 14.7:1 (lean or rich, but no info on how lean or how rich). It can not tell you any more than that. The sensor is such that it will read about zero volts when A/F is less than 14.7:1 and will read 1v when A/F is more than 14.7:1. There is no slope to the Voltage Vs A/F graph for the stock sesor. It's zero volts then jumps right up to 1 volt at 14.7:1. You would need a wide band O2 sensor if you want to know what the A/F ratio really is.

I'm not sure but, the ECU might cut fule off for a slpit second as the VTEC cams kick in, this might be why you read on the lean side at this point.

 

mine tells the ecu the actuall af...