BLM issues, pulling hair out and need help!!!
BLM issues, pulling hair out and need help!!! Ok guys, I have been going round and round with this split BLM issue where the passenger side is showing lean in datamaster and the driverside rich. The weird part is it only seems to be split quite a bit at low RPMs or at idle and when I drive the car it practically levels out on both sides. I know that an exhaust leak can introduce O2 into the stream tricking the O2 on that side causing the computer to enter a false lean condition and in response the PCM richens the mixture. Now I have checked/double checked and am not seeing any exhuast leaks and even spent the past day replacing the header gaskets with the Percy aluminum crush gaskets and locking all the header bolts down. I also replaced the O2s recently with Bosh (I KNOW I KNOW - most people hate them) and haven't seen any major issues with them and had the injectors flow checked, cleaned and matched. I have double checked every vacuum and don't see any leaks there either, replaced the spark plugs, and checked/triple checked all the sp wires/coils (delteq setup). No major intake leaks I can find (using the tb cleaner method), and EGR is all sealed up and cycles normally during driving. Could this be just bad 02s and is there any way to check them or check to make sure the PCM is getting the proper signal, also could it be a wire harness issue (injector or o2s)? My cam is pretty mild (CC305) and I should not be having this split BLM issue. Any suggestions are much appreciated and I have attached a datamaster recording so you can see what I am talking about. Please help and chime in as I am really getting frustrated/confused with this issue.
TECH Fanatic
Joined: Jan 2005
Posts: 1,162
Likes: 0
From: St. Augustine, FL
First off your IAC is reading 100+. Ideally it should be 40-50 or so. You can adjust this with the set screw governing the blades on the throttle body. My tuner tweaked mine which was reading high too, and after that the splits improved. You might try that first and possibly consider going to a GM TB or reinstalling your 48mm for diagnostic purposes.
Also I have read time after time where aftermarket TB's cause strange problems. I am running a bored to 52mm GM TB and my BLM's at idle are very much in check.
I have also read where a leaky intake valve will cause the idle BLM's to go to pieces.
I saw the link about the copper tubing in the IAC outlet on the back of the TB. Not saying that wont work, but I don't see how it could help.
Also I am personally no fan of the Bosch O2 sensors. I had them and they crapped out in months. AC's are the best. Also might try swapping the O2's to see if the problem reverses.
Also I have read time after time where aftermarket TB's cause strange problems. I am running a bored to 52mm GM TB and my BLM's at idle are very much in check.
I have also read where a leaky intake valve will cause the idle BLM's to go to pieces.
I saw the link about the copper tubing in the IAC outlet on the back of the TB. Not saying that wont work, but I don't see how it could help.
Also I am personally no fan of the Bosch O2 sensors. I had them and they crapped out in months. AC's are the best. Also might try swapping the O2's to see if the problem reverses.
TECH Senior Member
iTrader: (3)
Joined: Oct 2006
Posts: 7,564
Likes: 4
From: Decatur, TN (N-W of Athens)
First off your IAC is reading 100+. Ideally it should be 40-50 or so. You can adjust this with the set screw governing the blades on the throttle body. My tuner tweaked mine which was reading high too, and after that the splits improved. You might try that first and possibly consider going to a GM TB or reinstalling your 48mm for diagnostic purposes.
Also I have read time after time where aftermarket TB's cause strange problems. I am running a bored to 52mm GM TB and my BLM's at idle are very much in check.
I have also read where a leaky intake valve will cause the idle BLM's to go to pieces.
I saw the link about the copper tubing in the IAC outlet on the back of the TB. Not saying that wont work, but I don't see how it could help.
Also I am personally no fan of the Bosch O2 sensors. I had them and they crapped out in months. AC's are the best. Also might try swapping the O2's to see if the problem reverses.
Also I have read time after time where aftermarket TB's cause strange problems. I am running a bored to 52mm GM TB and my BLM's at idle are very much in check.
I have also read where a leaky intake valve will cause the idle BLM's to go to pieces.
I saw the link about the copper tubing in the IAC outlet on the back of the TB. Not saying that wont work, but I don't see how it could help.
Also I am personally no fan of the Bosch O2 sensors. I had them and they crapped out in months. AC's are the best. Also might try swapping the O2's to see if the problem reverses.
closed throttle timing? I run around 31* degreess in the 800-1200 rpm to take care of converter caused surge.
Generally IAC counts should be in the 25-30 range in neutral at HOT idle.
Do you have the stock fresh air hose assembly on the passenger side or a breather and the TB capped off?
I have split BLMS at idle, but not sure if they're caused by the leaky inline breather I have on the TB, the possible EGR tube leak at the header was the only other thing i can think of.
Generally IAC counts should be in the 25-30 range in neutral at HOT idle.
Do you have the stock fresh air hose assembly on the passenger side or a breather and the TB capped off?
I have split BLMS at idle, but not sure if they're caused by the leaky inline breather I have on the TB, the possible EGR tube leak at the header was the only other thing i can think of.
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closed throttle timing? I run around 31* degreess in the 800-1200 rpm to take care of converter caused surge.
Generally IAC counts should be in the 25-30 range in neutral at HOT idle.
Do you have the stock fresh air hose assembly on the passenger side or a breather and the TB capped off?
I have split BLMS at idle, but not sure if they're caused by the leaky inline breather I have on the TB, the possible EGR tube leak at the header was the only other thing i can think of.
Generally IAC counts should be in the 25-30 range in neutral at HOT idle.
Do you have the stock fresh air hose assembly on the passenger side or a breather and the TB capped off?
I have split BLMS at idle, but not sure if they're caused by the leaky inline breather I have on the TB, the possible EGR tube leak at the header was the only other thing i can think of.
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Staging Lane
Joined: Nov 2006
Posts: 70
Likes: 0
Sorry to hear you are having the same issues, but I havn't figured it out yet. I have tried the throttle screw, new IAC and cleaned out the IAC ports as well - to no avail. It only happens at idle and she levels out under normal driving (see thread above). I decided not to drill out the IAC port as it looks perfictly fine and also not to go with the tube method some mention to help the air go straight into the plenum as the BBK TB's don't have the same cross overs as the ASM's and it should be sealed up tight. Any other suggestions you come up with I'd deff entertain as I am pretty much tired of trying to figure it out. Let me know what you find
