Going Lean
Thread Starter
Pro
Joined: Apr 2001
Posts: 744
Likes: 13
From: Lenoir City TN
Going Lean
I've have my stock O2 located in the collector of my long tube header. I've started doing some data logs using an LM-1. I put the WB O2 for it in the other header collector.
What I found is at around 3500 RPM at 38 MAP the tune goes lean, from 15.5 target AFR to almost 16 AFR to up around 4700 RPMs. During that same time the stock O2 stops cross counts and the MV drops very low.
The bin has Highway Mode programed in which leans it out at cruise based on MAP 30 to 60 above 55 MPH. I don't think thats it.
Could it be that the O2 is getting to hot and shutting down?
I post the excel file for the data log but I don't know how to do it.
Thanks for any help
Chuck
What I found is at around 3500 RPM at 38 MAP the tune goes lean, from 15.5 target AFR to almost 16 AFR to up around 4700 RPMs. During that same time the stock O2 stops cross counts and the MV drops very low.
The bin has Highway Mode programed in which leans it out at cruise based on MAP 30 to 60 above 55 MPH. I don't think thats it.
Could it be that the O2 is getting to hot and shutting down?
I post the excel file for the data log but I don't know how to do it.
Thanks for any help
Chuck
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Probably the opposite. There is a reason it's located as close as possible to the engine in the stock exhaust pipe. The output voltage increases with temperature. The ECM waits until it sees a minimum O2 sensor voltage before it switches to closed loop mode. If the O2 sensor never gets hot enough the ECM will stay in open loop mode.
The O2 sensor should be heated if it's located in a header collector, especially with long tube headers.
The O2 sensor should be heated if it's located in a header collector, especially with long tube headers.
Thread Starter
Pro
Joined: Apr 2001
Posts: 744
Likes: 13
From: Lenoir City TN
Probably the opposite. There is a reason it's located as close as possible to the engine in the stock exhaust pipe. The output voltage increases with temperature. The ECM waits until it sees a minimum O2 sensor voltage before it switches to closed loop mode. If the O2 sensor never gets hot enough the ECM will stay in open loop mode.
The O2 sensor should be heated if it's located in a header collector, especially with long tube headers.
The O2 sensor should be heated if it's located in a header collector, especially with long tube headers.
It is working fine other times. It only does this when I bring the rpms ups slowly for scanning.
Thread Starter
Pro
Joined: Apr 2001
Posts: 744
Likes: 13
From: Lenoir City TN
OK I found the problem. When I had the last mail order tune changed due to new heads and intake the tuner programmed in the Highway mode. When data logging above 3k in a lower gear it was going into highway mode and leaning out the engine. When I deactivated highway mode the issue went away. After I adjust the tune in that area I'll reactivate highway mode. I didn notice a nice emprovement in fuel milage
Thread Starter
Pro
Joined: Apr 2001
Posts: 744
Likes: 13
From: Lenoir City TN
Believe it or not the factory Bin does not have it programed in. I did notice I got better fuel milage after that last mail order tune. I called the tuner and asked him if he thought that was it and he said no. And gaged on where the engine is map wise etc at that RPM it shouldn't effect it, but it does. I just set the min. mph to 255, like the factory setting, and it doesn't come in. After I set the VE for fuel map in that area I reactivate it so I can keep getting better mileage.
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
Hiway mode was disabled in the constants using unattainable parameters as a concession to the EPA. I use it on roadtrips and see over 10% better mileage! I think reactivating it is worth looking into!
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