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 can send you my datamaster recording if you PM me your email so you can see what I am talking about. Please help and chime in as I am really getting frustrated/confused with this issue.

 

might check out this thread and see if any of this applies to you

https://www.camaroz28.com/forums/sho...ight=split+blm

 

What are the O2s doing during the problem?

Are you sure the left harness is plugged into the left O2 and the right harness is plugged into the right O2? Saw the same problem you have when this was the case once.

 

Yup positive they are all plugged up right and the harnesses checkout ok (IE: no burns, corrosion etc...) and in the logs the O2's look to be cycling quite normally (occolating very fast - mV from 50ish to 900ish).

 

Not true. I would expect you to have this issue unless you have made sure all your idle air is going through the idle air plenum. Please look at the thread that DelSoto posted for you.

 

Thanks, a quick question, if it was just the IAC causing the BLM issue would I see surging or hard idle, as it is idleing just fine?

FYI - I will try the IAC/tube method as it is also mentioned here:
http://para.noid.org/~lj/PCM%20Tutor...litBLMinfo.htm

 

Looking at your datalog you rpm's are dropping very low while driving but stay steady and higher when just idling. so if you fix that it might help your problem. Make sure if you reset the pcm to drive it for a couple hours before datalogging if you want the fuel trims to be accurate. I replaced my O2 sensors with AC Delco because of all the bad things I have read.

 

http://www.noid.org/~lj/

click on pcm tutorial and find the split blms section for a possible fix

 

You are confusing IAC with split BLM's. IAC controls the air going into the idle plenum normally but in your case, you are dumping the air into the intake plenum which is excacerbating your BLM issue. There are 2 reasons for this: one, pretty sure the BBK TB bypasses the idle plenum and dumps into the main plenum; second, most likely you have not closed off your TB blades as much as possible to try and get all possible idle air going through the idle plenum.

Do the fix as you posted and I think you will be very happy.

 

Ok, I'm gonna pull the TB tomorrow and work on it this week and I'll scan it next weekend and let you guys know. I am also, gonna go ahead and replace the IAC as well while I am at it.

 

Thanks for the input and I'm gonna give that a shot this week, and can't hurt to try the tubing trick as well. Also, I've heard that adding a bit of timing at idle can help. Anyone know anything about this as I am running around 27 before 1200 and was thinking of bumping it to 28-29 do you think this would help any?

 

bump timing and check your vacuum then repeat process. You are going down the right road if your vac. increases. FYI, I am idling at 1000 rpm and 40 degrees timing. Further, I may be bumping it more to test for further vac increases. I don't think you will be using so much yourself since your cam is not as radical. You will definitely do better with more timing. most likely in the 30's somewhere.

FYI, questions like this are more tuning related. You will get more responses in that section.

 

DAVE00:

A little off topic but I'm sorry to hear that getting your injectors serviced didn't fix your problem. I've been following your threads for quite some time, because I am having the exact same problem as you are, and I'm actually a few steps behind you in the trouble shooting process. Next up for me is using TB cleaner to test for leaks. The tb/iac discussion that was brought up is very interesting. I will be trying this before I send my injectors off for servicing. BTW, I know you said you replaced your spark plugs, but did you happen to note if any of the plugs happened to look a little bit different then the others. This might be able to allow you to narrow in on the problem more. I say this is because I pulled the plugs on the drivers side (the side with the rich problem) and noticed that cylinder 1 seemed to be getting a lot more tan/brown then the others. That is why I am leaning towards an injector problem on my car anyway...

 

Sorry, I havn't responded sooner, but still without power at the house and finally can get on the computer from work. I was gonna try the IAC thing but havn't had the time since the storm hit us here in Houston, so I am hoping maybe this weekend if my power is back on. As to my spark plugs the driverside did look darker or fouled from being rich so much but nothing other than that. I am really hoping this IAC thing will work and I'll keep you posted.

 

What still has me baffled is the fact that I have this issue to begin with. The Hotcam is supposed to be mild enough that split BLM's aren't an issue. I don't think the IAC trick is going to solve my problem but I'm going to try it anyway as soon as I get more time.