[Gmecm] Closed loop

[David Haggard]

I'd much rather see the O2 reading fluctuating between, say, 0.2 and 0.7. I thought that was more the normal range. But then, I can be wrong.
 
David


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From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On Behalf Of David Cooley
Sent: Sunday, May 15, 2005 9:59 AM
To: gmecm at diy-efi.org
Subject: RE: [Gmecm] Closed loop


your O2 readings are perfectly normal.  The ECM get's to it's "target" range by going lean then rich over and over... those are called O2 crosscounts.  Believe it or not, a standard narrow band O2, .07 volts can be 16:1 and .9 can be 13:1 A/F not a wide range.
Look at any stock vehicle and you'll see the exact same thing.
 


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From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On Behalf Of David Haggard
Sent: Saturday, May 14, 2005 7:10 PM
To: gmecm at diy-efi.org
Subject: [Gmecm] Closed loop


I've got my 1227747 real close to "perfect" after a few hundred chips. But I have two questions. The car has a moderately-cammed 305 with 650 cfm TBI throttle body and Holley/Weiand TBI intake. 
 
1. The one problem I have left is unstable idle and widely varying O2 readings.
    In closed loop, it will idle nicely for up to half a minute, then either surge or stall. Then it will correct itself, idle nice for a few seconds, then surge or stall.
    If I force it to idle in open loop (by setting the closed loop idle thresholds higher than target idle), it idles smooth as glass. However, in open loop idle it can be stalled out and die easily by turning the wheels hard to the side (power steering load), or when coming to a stop after highway speeds.
    In closed loop, idle or cruise, the O2 sensor voltage will vary from 0.07 volts to 0.97 volts. This seems like an awfully wide range to me. I think it's this wide O2 range that causes the unstable idle in closed loop.
    When I force it to open loop idle, the O2 sensor reading stays absolutely steady.
    I think the ECM is making injector pulse corrections in closed loop that are too large / too fast, causing the unstable closed loop idle. Probably not helping fuel economy, either.
 
    Is there a set of parameters for the 1227747 that adjust how much and how quickly the ECM makes injector pulse corrections?
 
 
2. I understand that the '747 has a set of parameters for "highway mode fuel" that are disabled by default. Can anyone tell me where these settings are, and how to enable them?
 
Thanks. You guys are always great help. My flat spot problem was a stripped TBI mounting bolt that was allowing a vacuum leak.
 
David Haggard


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