BLM's on LT1 with mods...Help Needed..
Thread Starter
Burning Brakes
Joined: Apr 2001
Posts: 1,209
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From: Toronto Ontario
St. Jude Donor '13
BLM's on LT1 with mods...Help Needed..
Im using a scanner that provides real time info. Two of the two parameters are: STFTB-Short Term Fuel Trim Table
LTFTB-Long Term Fuel Trim Table
Under these catagories is shows -/+ percentages and BLM values. Can someone help me understand how to interpret these better to understand how my car is running.
A typical reading for the short term would be +3% 130
A typical reading for the long term would be +16% 146
Thanks,
Victor
LTFTB-Long Term Fuel Trim Table
Under these catagories is shows -/+ percentages and BLM values. Can someone help me understand how to interpret these better to understand how my car is running.
A typical reading for the short term would be +3% 130
A typical reading for the long term would be +16% 146
Thanks,
Victor
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Re: BLM's on LT1 with mods...Help Needed.. (89'Bowtie)
Your short term fuel trims are immediate adjustments that the ECM/PCM to maintain stoichmetric based on feed back from the O2 sensors.
The long term fuel trims are also based on the 02 feed back but is calculated on how much time the O2 sensors voltage is over or below 450mV. You can say this value is what the PCM is using to predict it will have to trim the fuel in order to maintain stoich. The long term trim value is a learned value over time hence the term "long term"
Your trim numbers indicate that the ECM or PCM is seeing that the engine is running a bit lean so its correcting by adding fuel. A number of 128 means that its happy at its theoretical stoichmetric point of 14.7:1 or 450mV from the O2 sensor.
[Modified by tjwong, 12:16 AM 6/2/2003]
The long term fuel trims are also based on the 02 feed back but is calculated on how much time the O2 sensors voltage is over or below 450mV. You can say this value is what the PCM is using to predict it will have to trim the fuel in order to maintain stoich. The long term trim value is a learned value over time hence the term "long term"
Your trim numbers indicate that the ECM or PCM is seeing that the engine is running a bit lean so its correcting by adding fuel. A number of 128 means that its happy at its theoretical stoichmetric point of 14.7:1 or 450mV from the O2 sensor.
[Modified by tjwong, 12:16 AM 6/2/2003]
Thread Starter
Burning Brakes
Joined: Apr 2001
Posts: 1,209
Likes: 0
From: Toronto Ontario
St. Jude Donor '13
Re: BLM's on LT1 with mods...Help Needed.. (tjwong)
Thanks for the reply, very helpful and informative...
So under WOT/Full load where would I want my BLMS and 02 volts to be.
Thanks,
Vic
So under WOT/Full load where would I want my BLMS and 02 volts to be.
Thanks,
Vic
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
Re: BLM's on LT1 with mods...Help Needed.. (89'Bowtie)
Thanks for the reply, very helpful and informative...
So under WOT/Full load where would I want my BLMS and 02 volts to be.
Thanks,
Vic
So under WOT/Full load where would I want my BLMS and 02 volts to be.
Thanks,
Vic
O2 voltage means nothing at WOT. They're only good for idle and part throttle cruise when the PCM is aiming for 14.7:1 afr. You need a wide band o2 sensor to tune WOT. Here's an example why. At WOT, my o2s were 900mV. On the dyno, my afr was 11.6:1 and I was at 12.0 before my laptop crapped out :( My o2s were still reading 900mV. I've made some changes based on the wide band data that should put my afr around 12.8 the next time I test. My o2s still show 900mV yet all the other logged data indicates the engine is now running leaner.
