Explain BLM's
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,471
Likes: 2
From: 1993 Quasar Blue 'vert Scottsdale AZ
Explain BLM's
Put my '93 on the scanner yesterday to double-check that the new heated O2 sensor was working (it was). Everything else seemed to be in the correct range too, except the BLM's. As I understand, they should be about 128. One of mine read 130-135 and the other side read 117-122. Can someone explain to me what this means?
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
BLMs=block learn mode, it's actually the long term fuel trim (long term in computer lingo equals a few seconds). 128 is a target, in other words most cars differ some and vary up or down. I can't explain one side from the other, seems like my l98 only has one side, one 02. But, I don't think your readings are out of whack, might be just a difference in the 02s.
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
BLM / INT numbers can be thought of as fuel multipliers, with 128 being the target. Readings higher than 128 indicate that the ECM is picking up a lean condition and is trying to correct it by adding more fuel. Numbers in the 130-135 range would be a little more fuel added, 150-160 would be a LOT more fuel added. Readings lower than 128 indicate that the ECM is picking up a rich condition and is trying to correct it by taking away fuel. Numbers in the 126-122 range would be a smaller amount of fuel taken away, 118-108 would be a larger amount taken away.
I am not as familiar with split BLMs like that since my car only has one O2 sensor. If one sensor is brand new and the other is fairly old, readings might be affected. But it is interesting that one side is reading a bit lean while the other side shows rich. This thread might help: http://forums.corvetteforum.com/show...ght=split+blms As posted by TJ, a small exhaust leak could definitely cause the split BLM issue.
I am not as familiar with split BLMs like that since my car only has one O2 sensor. If one sensor is brand new and the other is fairly old, readings might be affected. But it is interesting that one side is reading a bit lean while the other side shows rich. This thread might help: http://forums.corvetteforum.com/show...ght=split+blms As posted by TJ, a small exhaust leak could definitely cause the split BLM issue.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Clearly one side is running richer, try swapping O2 sensors.
If the problem doesn't follow the sensor swap, look for a leak at the exhaust header gasket.
You could pull the spark plugs to see if a cylinder is misfiring.
If the problem doesn't follow the sensor swap, look for a leak at the exhaust header gasket.
You could pull the spark plugs to see if a cylinder is misfiring.
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,471
Likes: 2
From: 1993 Quasar Blue 'vert Scottsdale AZ
The O2 sensor idea makes sense. Last week, we switched the left one to the right (the right one ended up being dead), and installed a new one on the left. I need to blow out the carbon that accumulated from the bad sensor. I'll try that and re-scan. Thanks guys.
Melting Slicks
Joined: Jul 2004
Posts: 2,695
Likes: 0
From: Chicago Illinois
Put my '93 on the scanner yesterday to double-check that the new heated O2 sensor was working (it was). Everything else seemed to be in the correct range too, except the BLM's. As I understand, they should be about 128. One of mine read 130-135 and the other side read 117-122. Can someone explain to me what this means?
Drifting
Joined: May 2003
Posts: 1,730
Likes: 1
From: Charlotte NC
St. Jude Donor '05
Actually those numbers aren't bad at all. They will swing from bank to bank quite a bit especially if the car has a cam
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