I am working with a 92 Corvette LT1 using $DA2 files. I have run a few data logs, and created a few history tables. I notice I have split in the BLM's from the left and right side. Not a big slit, most of the time at lower RPMs, they are closer at higher RPMs. It is the left side that is running richer.
I guess my question is how to tune for this. Should I average the left and right BLM, and then plug into the VE table spreadsheet, or use the leaner or richer side?
Thanks for your help.
I'm wondering if you can post a log file (.xdl), and the .adx you are using?Originally Posted by trmccarty
dave w
try closing your throttle plate just a bit (if its not closed already) to raise IAC counts, that usually helps blm splits at low rpm a lot.
also check for exhaust leaks
is the engine fairly stock?
you should never tune an engine that isnt running perfectly, so make sure
if you're sure it's a blm split you can't fix, tune it on the lean bank's info... always better to start rich than lean and let the trims fix it.
Dave, Thanks for your reply. I will try and upload the files you asked for.
Thanks for your reply. The motor is not stock. I have installed a Comp Cams CC503 cam with 1.6 rocker arms, valve springs, retainers, push rods, new chain and gears, GM LS7 Lifters, Long tube headers, no cats, custom exhaust, new plugs, wires, Opti-Spark. The heads, intake and block are still stock. I did install a BBK 52mm throttle body. I have the IAC counts adjusted to 25-30 at idle. I also changed the O2 sensors over to heated sensors when I installed the long tube headers. This is a 6 speed car with 4.10 gears.
I do not hear any exhausts leaks, I did have a small one at the center cross over after I changed out the rear axle gears but I run it back over to the exhaust shop that installed the system and they fixed it.
I have posted a data log in a reply above, in that file the split is only about 8-10 from side to side. I have read that the throttle body may cause this if the IAC passage does not feed directly into the intake idle passages.
I know the throttle blades are open some. I will look into closing the throttle blades and raising the IAC counts. What IAC count are you thinking 40 - 50?
Thanks again for your help.
I looked at the files you posted. I exported an Excel spreadsheet from the .xdl, see attached .zip file.
I don't have an answer for the Left Bank / Right Bank BLM's. I don't know what the $DA2 computer does with the Left Bank / Right Bank BLM's.
PRO's vs. CON's if the Left Bank / Right Bank BLM's are averaged?
My first thought was averaging will move the Rich Bank to the Lean and the Lean Bank to the Rich, which in theory will "balance" the BLM's?
If one bank is 122 (Rich) and the other bank is 131 (Lean) the Average = 126.5. The BLM correction for 126.5 is 0.98 which removes fuel from the VE table.
Removing fuel from the Rich side is good, but removing fuel from the Lean side is not good. Seems averaging will not "Balance" the BLM's.
As an experiment, only add fuel to lean cells. Keep track of the changed cells and see if a trend happens. I'm thinking the $DA2 computer has a learn routine that will add / subtract for each bank. I'm thinking if you correct the VE table for Lean only (either bank), the learn routine will actually lean the rich bank?
dave w
Steveo,
I have made some of the changes you mentioned in your reply. I removed the throttle body and drilled a 1/8 inch hole into the idle passage. I also made a filler block to put into the two openings feeding into the throttle bores. I closed the throttle blades. Now all the idle air goes into the idle passage in the intake. Reset the TPS and started it up, let it warm up and the BLM are allot closer now, most of the time even. The IAC counts are a little high at 68, but I think I will drive it a day or so and see if stays there. If it does I may open the blades a bit and see what happens to the IAC count.
When I get this set I will run a data log and see how even they are running and make adjustments from there.
Thanks for your help!
great to hear that helped.
your 68 hot iac counts is totally acceptable, but i'd rather see you shave a tiny bit more off that idle passage just so cold weather starts dont run out of IAC or whatever.
some people have noticed you can 'tune' the blm splits a bit just by jacking around with the throttle plates slightly... but...
a bit of a split (even stuff like like 122/130) is alright especially on your car; and might not be fixable.
you have to realize that with later sequential LT1s, they alleviated this problem at lower rpm and idle by trimming individual cylinders to match airflow charactoristics in the plenum
yours being batch fire, this type of trimming is impossible, so it'll never be right on the mark, and a bit of reversion from the cam or whatever just makes it a bit worse
is it a full twin exhaust fitting a balance pipe will help a lot with cylinder distribution.ive pulled plugs and found all different kinds of colours with full twin exhausts fitted a balance pipe of smaller diameter than the main pipes and now all plugs are the same colour and left to right bank fueling is a hell of a lot closer
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