Split in BLM (LT Fuel Trims) with new cam
Split in BLM (LT Fuel Trims) with new cam How much split in the LT BLM's is normal with say a 226/226 110 LSA cam? Right now I have a MadZ28.com tune and I've tweaked the injector constant to get close to 128 LT BLM, but I still get a split, showing >128 left and <128 right. Seems to be less split at higher TPS%, but low and cruising, it is split.
How much split is normal, and anyway to lessen the split?
Also, in closed loop, my wideband shows lean (14.8-15.7) at low throttle. I thought closed
Loop tried to keep the A/F at stoich 14.7?
How much split is normal, and anyway to lessen the split?
Also, in closed loop, my wideband shows lean (14.8-15.7) at low throttle. I thought closed
Loop tried to keep the A/F at stoich 14.7?
Your wideband is also picking up on that residual oxygen and reporting leaner than the combustion process is actually seeing.
No, I stated they are showing over 128 on left and less than 128 on the right, for the most part. Occasionally they will both go over 128, but the left is always higher than right at low throttle openings.
He said greater than 128 left and less than 128 right. kgkern, tell us how much. I wouldn't be concerned about a few points. With cam overlap, you're always gonna get misfires at idle and low speed (thus the lopey sound), so the O2's are gonna see all that un-used oxygen from a misfire, misinterpret it as lean, and jack the BLM up.
Your wideband is also picking up on that residual oxygen and reporting leaner than the combustion process is actually seeing.
Your wideband is also picking up on that residual oxygen and reporting leaner than the combustion process is actually seeing.
What TB are you running? If you are running an aftermarket TB, thats part of the problem. I modded my TB to force all the idle air into the small port on the front of the intake like GM intended. Aftermarket TB's allow the idle air into the plenum which causes imbalance. Bad or open plug wires will casue the BLMs to go to Hell too. I have pics in another post of my TB mod.
Also FWI, Adjusting the individual fuel trims, will not fix the problem. It will only make the numbers look better. Same goes for O2 threshhold.
With the TB mod and repairing a couple of wires, I have 128/128 in cell 16 better than 95% of the time. The idle is better and the MPG's got better too. If you are 128/128 +/- 7 points, I would try to resolve the problem. Up to +/-3 points, IMHO is acceptable. Also no amount of tuning will fix a split. It has to be determined what is causing it in the motor. Also my cam has more overlap than yours so that should have nothing to do with it.
Good luck.
Also FWI, Adjusting the individual fuel trims, will not fix the problem. It will only make the numbers look better. Same goes for O2 threshhold.
With the TB mod and repairing a couple of wires, I have 128/128 in cell 16 better than 95% of the time. The idle is better and the MPG's got better too. If you are 128/128 +/- 7 points, I would try to resolve the problem. Up to +/-3 points, IMHO is acceptable. Also no amount of tuning will fix a split. It has to be determined what is causing it in the motor. Also my cam has more overlap than yours so that should have nothing to do with it.
Good luck.
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I'm still running stock TB, but I'll pull it and see how well it seals the idle air away from the plenum. Hopefully doing the 'idle air mod' to mine will help as well.
BTW, I checked my tune yesterday, and turns out the O2 threshold values were set to a 4% lean .425v instead of .450 which is stoich. Just changing this to .450v seems to have gotten the A/F closer to 14.7 on the wideband, although still seems to average about 15.3. I DataMaster logged it on the way to work and will look over the scan tomorrow.
BTW, I checked my tune yesterday, and turns out the O2 threshold values were set to a 4% lean .425v instead of .450 which is stoich. Just changing this to .450v seems to have gotten the A/F closer to 14.7 on the wideband, although still seems to average about 15.3. I DataMaster logged it on the way to work and will look over the scan tomorrow.
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Verdad Gallardo Doubt the air foil is doing anything. There is no need to tweak a OEM TB for a BLM split. I am betting you have a bad plug wire. Get a multimeter and OHM check all 8 wires. Also the smallest header gasket leak will screw them up too and I do mean the smallest.
i have a spare set of new Autozone wires I'll try putting on to see if that helps.
I also have the Hooker LT's with the slip fit #1 primary, that I suspect may be causing the left bank to show lean? I will put some Copper RTV in to help try to seal it up.
I also have the Hooker LT's with the slip fit #1 primary, that I suspect may be causing the left bank to show lean? I will put some Copper RTV in to help try to seal it up.
Last edited by kgkern01; Aug 23, 2010 at 04:17 PM.
I revised my tune with the injector constant at 44.31# (for the 60# injectors on E85) as well as checking the header bolts (all tight, and am using Percy's dead soft aluminum gaskets) and sealing the Hooker LT slip fit primary with Copper RTV, and also noticed in the tune that the target idle O2 voltage was 405 in closed loop, so I adjusted it to 450. After all of this, it is now sitting at an even BLM at idle cell 16, but is at 134/134, and showing lean on the wideband as well. I wonder if this has to do with the cam reversion at an 850 RPM idle and the 110 LSA? Now every open throttle fuel cell shows no more than 1-4 BLM split, and the range in BLM's across all cells being 126-129, with the 4 BLM split being at cell 11 (128/124). I assume that the biggest effect on the split was possibly some very minor leakage in the slip fit primary, which is now sealed up.
I would think that it is pretty much dialed in as far as fueling in idle-part throttle, correct?
Finally did a few WOT runs as well after this scan to check my WOT A/F, and was pretty spot on at my goal of 11.7 (.79 lambda). Highest MAP I got was once hitting 96 out of about 5 WOT runs, so it may be time for a 52mm TB? Can't wait to get it to a track now and see what it will run, and dyno it as well.
I would think that it is pretty much dialed in as far as fueling in idle-part throttle, correct?
Finally did a few WOT runs as well after this scan to check my WOT A/F, and was pretty spot on at my goal of 11.7 (.79 lambda). Highest MAP I got was once hitting 96 out of about 5 WOT runs, so it may be time for a 52mm TB? Can't wait to get it to a track now and see what it will run, and dyno it as well.
