The ole split BLM issue
Thread Starter
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
The ole split BLM issue
My scans show a split of between 8-14 points lean on my left side. I have done a search for vacuum leaks and find none. My left O2 sensor is flakey and I am going to replace it with one I got from Superior for $34 Cris was great told him I was a member here and he saved me $25 from my local dealer they wanted $115 installed $59 for the sensor. Didn't figure it would take them over an hour to do it told em that is outragous. Anyway could the flakey O2 cause the split? It would seem to me if it was the O2 it would be rich not lean as my scan shows it reading lower than the right side. Any other ideas on what could cause this?
Melting Slicks
Joined: Dec 2000
Posts: 2,719
Likes: 60
From: Fremont Oh
hey redeasy...
I have a simular situation many others as well, my left side is also leaner that the right. I've been chasing other "bigger" gremlins", but the split blms can be a couple things, it could be the cylinder balance settings, where the ECM is programed to meter a different amount between the different cylinders, also it could have to do with the throttle body settings. There are a quite a few posts dealing with these issues.
Mo
I have a simular situation many others as well, my left side is also leaner that the right. I've been chasing other "bigger" gremlins", but the split blms can be a couple things, it could be the cylinder balance settings, where the ECM is programed to meter a different amount between the different cylinders, also it could have to do with the throttle body settings. There are a quite a few posts dealing with these issues.
Mo
Thread Starter
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
Thanks Mo I have been reading them but I did not see any saying O2 was the cause although I got a PM saying it could be so I guess I will see whats up when I get the O2 replaced and if it doesn't go away gonna have to look elsewhere.
Le Mans Master
Joined: Sep 2001
Posts: 7,928
Likes: 1
From: More cowbell...
St. Jude Donor '04
Redeasysport-
A bad O2 sensor could definitely cause a split blm. If the O2 sensor isnt reading correctly, it thinks it is more rich or lean than it really is, and you will get a split BLM.
I am going through a similar problem, but I happen to know both my O2 sensors are fine. I suspect I have a partially clogged cat which could be causing my problem.
A bad O2 sensor could definitely cause a split blm. If the O2 sensor isnt reading correctly, it thinks it is more rich or lean than it really is, and you will get a split BLM.
I am going through a similar problem, but I happen to know both my O2 sensors are fine. I suspect I have a partially clogged cat which could be causing my problem.
Drifting
Joined: May 2003
Posts: 1,730
Likes: 1
From: Charlotte NC
St. Jude Donor '05
The split blms are usefull in diagnosing several worse problems.
Like
a burnt plug wire will make one side read lower
A burnt or baked O2 wire will cause one side to read lower
Lazy o2's (pretty obvious on that one)
locked up injectors
exhaust leaks
the list goes on an on.. I can't tell you how many small burnt plug wires i've found with split BLM's
Like
a burnt plug wire will make one side read lower
A burnt or baked O2 wire will cause one side to read lower
Lazy o2's (pretty obvious on that one)
locked up injectors
exhaust leaks
the list goes on an on.. I can't tell you how many small burnt plug wires i've found with split BLM's
Le Mans Master
Joined: Sep 2001
Posts: 7,928
Likes: 1
From: More cowbell...
St. Jude Donor '04
Would a partially clogged cat be on that list? (seems to be that would mean I have a different back pressure on the two sides, and all bets would be off). Guess I wont know until I fix it..
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Le Mans Master
Joined: Sep 2001
Posts: 7,928
Likes: 1
From: More cowbell...
St. Jude Donor '04
BLM is how much fuel the computer is adding or taking away from the injectors in order to reach stoich.
The problem with split blms is that one side is tending to run rich, while the other is lean- and your tune affects both sides equally. Thus if the driver side is running lean, and the passenger side rich- if we get the passenger side to lean out, the driver side will be even more lean than it was before.
The problem with split blms is that one side is tending to run rich, while the other is lean- and your tune affects both sides equally. Thus if the driver side is running lean, and the passenger side rich- if we get the passenger side to lean out, the driver side will be even more lean than it was before.
Melting Slicks
Joined: Dec 2004
Posts: 2,137
Likes: 5
From: Howard PA
Originally Posted by MarkLT1
BLM is how much fuel the computer is adding or taking away from the injectors in order to reach stoich.
The problem with split blms is that one side is tending to run rich, while the other is lean- and your tune affects both sides equally. Thus if the driver side is running lean, and the passenger side rich- if we get the passenger side to lean out, the driver side will be even more lean than it was before.
The problem with split blms is that one side is tending to run rich, while the other is lean- and your tune affects both sides equally. Thus if the driver side is running lean, and the passenger side rich- if we get the passenger side to lean out, the driver side will be even more lean than it was before.
If you have access to an infrared thermal imager (such as I do) could you point it at each individual exhaust port and get some insight as to whether it's one particular cyl. or all on one bank?
I'm a former TV repairman and I've "got an awesome set of tools man"
Le Mans Master
Joined: Sep 2001
Posts: 7,928
Likes: 1
From: More cowbell...
St. Jude Donor '04
Yes- the BLMs are based on how much fuel the computer has to add or take away, in order to keep the exhaust moving past the O2 sensors at the right A/F ratio.
I'm not sure what a thermal imager could do- possibly find an exhaust leak- but as long as the blms are in a range in which the computer can compensate, you are having a correct A/F mixture, thus the temps for each cylinder *should* be the same.
I'm not sure what a thermal imager could do- possibly find an exhaust leak- but as long as the blms are in a range in which the computer can compensate, you are having a correct A/F mixture, thus the temps for each cylinder *should* be the same.
Thread Starter
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
Originally Posted by Alvin
The split blms are usefull in diagnosing several worse problems.
Like
a burnt plug wire will make one side read lower
A burnt or baked O2 wire will cause one side to read lower
Lazy o2's (pretty obvious on that one)
locked up injectors
exhaust leaks
the list goes on an on.. I can't tell you how many small burnt plug wires i've found with split BLM's
Like
a burnt plug wire will make one side read lower
A burnt or baked O2 wire will cause one side to read lower
Lazy o2's (pretty obvious on that one)
locked up injectors
exhaust leaks
the list goes on an on.. I can't tell you how many small burnt plug wires i've found with split BLM's
2 check the wire Ok there
3 Gonna replace the O2 with Delco on Sat(Hope it is it)
4 New injectors
5 New exhaust
6 No vacuum leak that I can find I use starting fluid at every jucnction I coud find.
I just got a like new set of OEM injectors may replace the FMS 24's with them if it does not go away. ( I got them for $56 with under 4k on them look like new
)I am also getting the Opti cap and rotor replaced and got a new GM water pump for $65 from my mechanic gotta love this guy he is only charging me $125 to replace them and he has done it before so he knows what he is getting into he is definatly a keeper.
Last edited by Redeasysport; Mar 25, 2005 at 01:35 AM.
Thread Starter
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
Originally Posted by ALLT4
Is it true the only common sampling device would be the O2 sensor(s)?
If you have access to an infrared thermal imager (such as I do) could you point it at each individual exhaust port and get some insight as to whether it's one particular cyl. or all on one bank?
I'm a former TV repairman and I've "got an awesome set of tools man"
If you have access to an infrared thermal imager (such as I do) could you point it at each individual exhaust port and get some insight as to whether it's one particular cyl. or all on one bank?
I'm a former TV repairman and I've "got an awesome set of tools man"
Le Mans Master
Joined: Feb 1999
Posts: 9,947
Likes: 39
From: South Carolina
St. Jude Donor '03 & '05
I had my stock LT1 . no mods whatsoever done, and there were split BLMs. Formato and Ed Wright said exhasut leak. Well after several mods, form bolt on to new engines, they are still there. Our 93 LT1 are batch fire also, and supposedly the BLM issue is the idle circuitry, you know where the vaccum loss on a big cam causes #1 cylinder to read lean so it adds fuel causing the split. Youcan see the idle holes drilled into the manifold that the factory throttle body allows air to get to. I have had different T Bodes, wires, plugs, exhaust manifolds, shorty headers, and now long tubes, different injectors, chips, manifolds ,ECM, sensors, cams and the list goes on, and the BLM split is still there.
I honestly dont think it is a big issue to stress out on. Once I get this last motor done, tuned via mail order (just kidding), using Datamaster and a dyno, if the split is gone great, if not, I personnaly got tired of chasing it.,
http://www.chipsbyal.com/frameset1.html go to LT1/LT4 , impove idle and it explains a little on the BLM
http://para.noid.org/~lj/ pcm turorial for BLM fix
I honestly dont think it is a big issue to stress out on. Once I get this last motor done, tuned via mail order (just kidding), using Datamaster and a dyno, if the split is gone great, if not, I personnaly got tired of chasing it.,
http://www.chipsbyal.com/frameset1.html go to LT1/LT4 , impove idle and it explains a little on the BLM
http://para.noid.org/~lj/ pcm turorial for BLM fix
Melting Slicks
Joined: Oct 2000
Posts: 2,158
Likes: 9
From: N.E. WA
I'm with Steve. You should try to fix it, but don't get hung up on it. If you doubt one of the O2 sensors, swap it with the other side. If the split follows that O2, then you found your problem. I have spent countless hours with my scanner and tweeking my TB and playing with the IAC and checking for exhaust/vacuum leaks. Damn near everything under my hood is new and I still have a split. I've lost count of how many chips I've burned changing timing and fuel. Nothing has really helped all that much. In my case, there is a correlation between the IAC and the throttle plate opening, but by the time I get the splits to settle, my IAC is open so far and the plates shut that the car can't compensate for things like the A/C and cold starting. I hope that you are more succesful than I was. Good luck!
Le Mans Master
Joined: Sep 2001
Posts: 7,928
Likes: 1
From: More cowbell...
St. Jude Donor '04
ANTI VENOM-
Does your split go away above light throttle/idle?
Not sure about the original poster, but my split blm goes all the way up through the RPM range, and I dont have a radical enough cam to cause the overlap in the intake at idle, so there is definitely something amiss. (I just hope it is that semi-clogged cat!)
Does your split go away above light throttle/idle?
Not sure about the original poster, but my split blm goes all the way up through the RPM range, and I dont have a radical enough cam to cause the overlap in the intake at idle, so there is definitely something amiss. (I just hope it is that semi-clogged cat!)
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Originally Posted by Redeasysport
Would night vision goggles work on this idea?
Melting Slicks
Joined: Dec 2004
Posts: 2,137
Likes: 5
From: Howard PA
Originally Posted by Morley
Doubtful. Nightvision gear just amplifies ambient lighting to make things more visable. What you need would be an IR vision device.
Image enhancement - This works by collecting the tiny amounts of light, including the lower portion of the infrared light spectrum, that are present but may be imperceptible to our eyes, and amplifying it to the point that we can easily observe the image.
Thermal imaging - This technology operates by capturing the upper portion of the infrared light spectrum, which is emitted as heat by objects instead of simply reflected as light. Hotter objects, such as warm bodies, emit more of this light than cooler objects like trees or buildings.
Thermal imaging - This technology operates by capturing the upper portion of the infrared light spectrum, which is emitted as heat by objects instead of simply reflected as light. Hotter objects, such as warm bodies, emit more of this light than cooler objects like trees or buildings.