Cold Start AFR
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Supreme Member
Joined: Jan 2003
Posts: 2,133
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From: Houston, Texas
Car: 88' IROCZ
Engine: 388 TPI Motown 350 Race block
Transmission: 700R4
Axle/Gears: 2.77
Cold Start AFR
Is it normal for the AFR to go as high as 38:1 until the O2 warms up?
mine did this for about 3 minutes.
Hope I get a better response from this post than my last one which is currently zero responses
mine did this for about 3 minutes.
Hope I get a better response from this post than my last one which is currently zero responses
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Joined: Jul 1999
Posts: 10,907
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From: The Bone Yard
Car: Death Mobile
Engine: 666 c.i.
Re: Cold Start AFR
Is this from the stock O2 sensor or a WB?
If it is the O2 sensor, that is entirely possible as the stock sensor is strictly a "switching" device and you may be getting a false reading while the O2 sensor is still "warming up" and it's stuck at a lower O2 value (until it warms up).
FYI, a cold engine typically requires a "richer" fuel mixture initially. This is why the ECM only uses the "tables" when the engine is first started and not the O2 sensor for a period of time until the engine warms up. The specific time delay is set inside the BIN and the length depends on "how cold" the engine was when it was first started). There is a seperate time for a cold, warm & hot engine.
If it is the O2 sensor, that is entirely possible as the stock sensor is strictly a "switching" device and you may be getting a false reading while the O2 sensor is still "warming up" and it's stuck at a lower O2 value (until it warms up).
FYI, a cold engine typically requires a "richer" fuel mixture initially. This is why the ECM only uses the "tables" when the engine is first started and not the O2 sensor for a period of time until the engine warms up. The specific time delay is set inside the BIN and the length depends on "how cold" the engine was when it was first started). There is a seperate time for a cold, warm & hot engine.
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From: Chasing Electrons
Car: check
Engine: check
Transmission: check
Re: Cold Start AFR
Well, it took me a few days of staring at your graph to figure out what I was looking at. May be why the response rate is low, not enough information as to what the graph respresents. Grim, same as you I thought I was looking at a WB AFR.
Nope, it is the ECM commanded AFR. Along with the NB O2 & injector PW from the ALDL stream.
rgarcia63, what you are seeing for the COMMANDED AFR is normal (the high & low spikes). The ECM is making calculations to come up with the final commanded AFR. During that time the ALDL stream is spitting this AFR out. However, the ALDL is not synchronized to the ECM internal logic. So it is picking up the AFR value in the middle of the calc's.
Once the ECM goes closed loop the AFR is a set 14.7:1, no other calculations are done. So you see the steady line at that commanded AFR.
The commanded AFR in the graph is interesting. Immediately at startup the AFR is commanded rich, which slowly decays out. This is called choke or after start fuel. Then as the engine warms up the AFR slowly increases, and is commanded leaner then stoich.
Suddenly, boom, closed loop, and the AFR is commanded to 14.7:1 (or what ever the stoich value is in the BIN). And the commanded AFR stays flat.
RBob.
Nope, it is the ECM commanded AFR. Along with the NB O2 & injector PW from the ALDL stream.
rgarcia63, what you are seeing for the COMMANDED AFR is normal (the high & low spikes). The ECM is making calculations to come up with the final commanded AFR. During that time the ALDL stream is spitting this AFR out. However, the ALDL is not synchronized to the ECM internal logic. So it is picking up the AFR value in the middle of the calc's.
Once the ECM goes closed loop the AFR is a set 14.7:1, no other calculations are done. So you see the steady line at that commanded AFR.
The commanded AFR in the graph is interesting. Immediately at startup the AFR is commanded rich, which slowly decays out. This is called choke or after start fuel. Then as the engine warms up the AFR slowly increases, and is commanded leaner then stoich.
Suddenly, boom, closed loop, and the AFR is commanded to 14.7:1 (or what ever the stoich value is in the BIN). And the commanded AFR stays flat.
RBob.
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