So I just finished up my new build and have been going through some break in driving. Car is running very strong but for some reason I have high BLMs at idle (over 145). When driving around they drop into the 130s.

I have exhausted looking for vacuum leaks and cannot find any. EGR is good. No misfires, plugs look fine and all injectors are pulsing. Checked each ignition wire and they are all firing. MAP readings are normal. IAC counts seem normal as well. TPS voltage is .69. Idles pretty well at 850 rpm.

I had an exhaust leak on the #1 primary and a very small leak at one collector flange. Fixed those this weekend and the car is running great. But I still have high BLMs although not as high as before. They used to be steady at 155-160. Both banks are equally high and my integrators hover around 125-128. Do you think I need to reset the PCM since I fixed the exhaust leaks? How long does it take for the computer to relearn the BLMs?

Car currently has a mail order tune and I will be getting dyno tuned next week.

Cam is mild 216/225 112LSA .575/.575 so this shouldnt be an excessive overlap problem.

Fuel pressure at idle with the vacuum line off is 42psi. At idle with the vacuum on, pressure is 30psi.

Any thoughts as to what else might be causing my high blms? I will add that the exhaust smells a little rich but that might not be a very good indicator.

I just installed new O2s (Delco) and will be putting in a new stock MAF tonight.

Maybe the dyno tuner can fix it?

Thanks for your help!

 

It takes very little time for the PCM to "sync" up and set the BLM's.

High BLM's mean the PCM is adding fuel to make 14.7. In the case of a bad split, it is almost always a header flange gasket leak or in your case maybe the right side collector gasket leak since you have the RK's. Also misfires as a result of damaged wires or plugs will cause high BLMs. Even the smallest exhast gasket leak will screw the BLMs up.

In your case since they seem to be balanced, it may be as simple as adjusting the MAF tables assuming you have no exhaust leaks that are causing them to inflate. If you have a datalogger and Tunercat or something similar, you can rather safely tweak on the MAF tables to see how the BLMs respond.

Most likely it is nothing from the intake forward through the intake track to the filter.

 

I thought high BLMs meant the PCM was compensating for a lean condition and is adding fuel. So if its not an exhaust leak, you think its in the tuning?

 

If your fuel pressure actually drops 12psi when you reattach the vacuum line, there is something wrong. The vacuum compensation line should pull the fuel pressure down proportional to intake manifold vacuum. A 6 to 8psi drop from the "no vacuum" reading would be expected with a stock cam. Less drop with a more aggressive than stock cam.

Correct, high BLM's (above 128) indicate the PCM is adding fuel to compensate for a lean condition - real or "false". If it smells rich (and that's very subjective) it may be pointing to a false lean. Before you start tweaking your MAF tables, check for problems that can cause a false lean condition.

You've already picked up on the impact of exhaust leaks before the O2 sensors. Misfires, or tight valves can put air in the exhaust causing a false lean. Faulty O2 sensors or extensions with leakage to ground can reduce O2 sensor voltage and cause a false lean.

With regard to the MAF - have you cleaned it? If its dirty, its going to report less than actual flow, the PCM doesn't add enough fuel, and the BLM's go up (= a true lean conditon, corrected by the BLM's).

 

Whoops.
Fixed.

 

Thank You both very much for your responses. When I adjusted the valves, I did 1/2 turn past zero lash. This is what comp recommended in their instructions. I am using GM LS lifters and comp ultra pro mag NSA rockers (7/16 studs). Do you think that is too tight? They are very quiet right now. (I actually expected a little more noise from hearing other setups)

I havent cleaned the MAF recently but will be installing a new one that I received yesterday since my original is 16 years old anyway. Once I install that, I will check the BLMs again to see if I need to move on to the valves. Installed new Delco 02s with no extensions. Didnt see any change after that.

Injuneer, if I read your post correctly, if the valves are too tight that will cause excessive vacuum at idle and reduce the fuel pressure right? In addition to putting more fresh air into the exhaust?

With the reduced fuel pressure, the PCM will need to compensate by increasing the BLMs right?

Thanks Again!

 

Does anyone know what the correct idle fuel pressure is? I have a feeling my pump is getting weak and causing my high BLMs.

 

Mine is around 38# IIRC.
WOT was around 44#.