When the cold start idle is nearly pegged, it starts dropping to 120's in about 20 seconds and is down in the 50's in less than a minute or two tops. I dont see a problem with this.

I really do appreciate your help. Thanks.

If you dont mind, please look at my individual cylinder trims and comment. When the left cell 16 BLM is < than 128, do the 1,3,5,7, individual fuel trim numbers need to be slightly increased or decreased to try to force them closer to 128?

My assumption is they should be slightly decreased. If this is correct, I might try reducing 1,3,5,7, by 5% each and see what the left BLM does. Hopefully, it moves from 113 and goes higher, or closer to 128 or so.

 

5 and 7 are probably running fat. 7 really gets screwed on airflow because 6 and especially 5 swallow up anything available in that area of the plenum before 7 gets a chance at it. Also cylinder 2 goes before 1 and thats why the oem trim is fatter on 2 than 1.

Everything will be even more complicated now that you've added a cam and reversion to the mix. What I posted before is generic and usually gets good results. If the blm is below 128, then its pulling fuel from that side and thats what you would do to correct it. If you do go with your plan of removing 5% from each one start from the back and go forward.

What you're trying to tune around is a complicated issue. Some of it is cross talk between cylinders, some of it is injectors that leak a little more than others or non-linearity in the injectors showing its face etc, basically a bunch of junk that will drive you nuts. You don't really have the info you need to fix it properly.. you have the average air fuel trim per cylinder bank according to a narrow band sensor, and what you need is the wideband or gas bench reading from each cylinder at steady state. For all you know that one bank has one injector that is particularly crappy and that cylinder is making the rest of them look rich but the average is correct.

Iac behavior you described sounds normal enough, leave it.

 

Finally getting some good results now.

I have 129/128 on cell 16 by adjusting the individual cylinder trims. This is driving around the block several times and they stayed rock solid. I then turned the motor off, waited five minutes, started it back up and drove again.

The BLMs were 130/134 and remained very steady. This is a huge improvement at least from looking at the cell 16 BLM's. I am confident I can jack with them just a little more and get them closer to 128/128. One day later and after some more driving they are still running 130/134 at full operating temps. During cold start and warm up their still have some split but not near as bad as before.

My current (tweaked) individual cylinder trims are:
1 - 0.97
8 - 0.95
4 - 0.95
3 - 0.90
6 - 0.98
5 - 0.85
7 - 0.84
2 - 1.08

The 2,4,6,8, are actually stock GM values. The 1,3,5,7, had to change to get the left bank in check.

WS6T3RROR, please look at the above numbers and "polish" them the way you think they should be to ensure balance on each bank and I will try them in the tune.
If the BLMs being where they are now, is there any harm running with this? Am I creating any other problems?

 

I already posted numbers I think you should at least try and work from. Something else I will mention just because the right side is at 128 does not make it correct. A likely scenario is that cylinder 2 is getting too much fuel and the rest are running lean for that to happen. Do not make the mistake of assuming that just because the blm is 128 that everything over there is just peachy.

I have attached a picture here of your trims with the cylinders numbered as they are in the engine along with the ones i suggested previously and the bank average trim.



I think overall you have not done enough with the even bank and too much cutting on the odd bank. The maf values where you idle may need a bit of work to get everything centered back around 128 when you get 'done'. If you look at the average the only thing you have really accomplished is to pull fuel out of the left side instead of the blm doing it. In essence you have gained nothing but prettier numbers. I am not trying to be harsh but that is the facts when you take a more analytical view of it. You cannot hurt anything with an engine at idle, the worst you can do is make a cylinder so lean as to misfire and that will screw up your blms and idle quality, or the car will die and that will be the extent of it. Imo, splits of 5 or less at any point except wot are doing excellent in a non stock engine.

Having said all that you will likely not be able to make the sensors agree during warmup and open loop no matter what you do. Also if the car idles and drives well... run it. Most people do not realize this when it comes to both efi and carb tuning 90% of the results are had from 10% of the effort. Do not give yourself brain damage over something that runs very well but does not give the sexiest logs you have ever seen, they are only numbers.

 

I think I see what you are saying about overdoing the ICFT's and soley using those settings to get the left/right banks balanced AND to get them both to 128/128.

I should focus on just making them match using the ICFT's with as little butchering as much as possible like maybe get 120/120 or 140/140. Then use the MAF tables to move the balanced numbers toward
128/128.

Is this understanding correct?

I will load your numbers ASAP and see what the BLMs do and tweak on them.

Thanks for the help and no you are not being harsh, your getting directly to the point. This is the kind of information I have been waiting on for years to resolve split BLM's.

 

Yeah, now you're beginning to frame the problem correctly I think. Don't get too worked up if its never perfect. Even if it was perfect, once they change the fuels again for summer time and the distillation curves and additive packages change it will be off again to some extent. Its a good thing for us that engines are very forgiving when it comes to acceptable fueling.

 

WS6T3RROR,
I loaded your ICFT's and got consistant 110/140 cell 16 BLM's.

I then lowered the left bank settings .05 and raised the right bank settings by .05 and the new cell 16 BLM's are 119/129. Left average=0.94 and the right average=1.03. Clearly a bit better.

I am going to now lower the left bank settings another .02 and raise the right bank settigs another .02 and the BLMs should balance out around 125/125. These new averages would be left=0.92 and right=1.05. Then use the MAF settings to bring the numbers up closer to 128/128.

Is this what you would reccomend? Or something else?

 

If I were you I would drive the car a day or so between changes. It can take awhile for the blm's to stabilize for idle and other areas as well. Which is one reason people end up chasing their tails while tuning.

Other thought is that if your average on the trims on each side are not about 1.00 or at least close to equal to one another then you are just jacking the numbers around manually instead of the blms doing it and you have gained nothing because the fuel on each side is still just as far out of whack it just is not shown in the long term fuel trims. The goal here is not pretty numbers its fixing why they are split not just splitting them somewhere else that doesn't show up in the trims.

A possibility may be that your injectors are just not fantastically linear and while they may be inside the tolerance may be at the outer limits of it. If that happens to be the case then you may end up with numbers that do not make sense. With the equipment and data available to you it may not be possible for you to get it right.

 

Thanks again for the help.
I just made another datalog and now the BLMs are now 127/124 so I slightly over shot my target. That is with .07 under on the left and .07 over on the right numbers.

I have now tried .06 over and under just to see what it does. I got 125/125 on the cell 16 BLM's. This now gives me the complete picture with the understanding that I only conducted short drives between changes. Even that said, there appears to be consistent and predictable behaviors going on here and not any random crap or weirdness between changes.

Many have suggested that the real reason I have the splits is my 107 LSA cam. If thats the case, I will have to find the happy medium with the ICFT averages cause I ain't pulling any more cams.

On a side note. Even with the current settings, the exhaust is not nearly as smelly as before and unless its my imagination, some of my 1500-2000 RPM cam surge problem is bit better.

I will do what you say and reload your original settings then drive it more in depth between changes to see how it does.

As far as my injectors. I have rather new condition 37# Racetronix but they are not specially matched as far as I know. It might be worth looking into.

I understand your point on the averages being more balanced. What tolerance do you think would be acceptable if I decide to not have them exactly equal but rather "close" to equal like you stated above?

 

I would probably try to keep everything +-5%, but if what you have is working to your satisfaction then use it.

Something else you could also try if you have a lot of spare time and don't mind messing with it, is to try and vary one cylinder at a time and note the effects on the trims.

 

Good deal.
I am going to more extensive testing like what you have suggested but there is a snow storm on the way so it might not be till next week.

Some have suggested an IR gun on the header primaries to ensure the temps are balanced. Might look into that.

 

From your experience, would a 10% difference (as exemplified by the averages of his first attempt) between left and right banks be realistic? Is there so much maldistribution due to cam and intake manifold charcteristics that this could occur? Seems to me that the data suggests that there is either too little fuel, or too much air on one side.

If the huge maldistribution at idle is not typical of the characteristic of the cam and the manifold, it would make more sense to find out why the BLM's are "off" by so much, and differ so much from each other. And I guess that's what he's been trying to do over all these months, without success.

I see this in the posts on the "Computer Diagnostics.... " forum. People have bad BLM's and the first thing they want to do is alter the MAF calibration table to make the BLM's 128. Again, might make more sense to analyze why they are high or low, rather than just (possibly) cover the problem up with a program tweek.

Just thinking out loud, recognizing that I have no experience whatsoever tuning an LT1 PCM.

 

Agreed that the root cause should be investigated.

This is what I have done:
Checked for vacuum leaks between the MAF and the intake. None found.
Checked fro vacuum leaks at hoses and fittings. None found.
Checked for exhaust leaks betwwen the header flanges and O2's. None found.
Switched the O2's side to side. Numbers remained rather the same. O2's are good.
Modded the TB idle air curcuit back to stock. That helped and made BLM's much more consistant and less wild.
Had similar splits with OEM ported TB too.
Raised idle. That helped some.
Closed TB blades. That helped some.
Checked the valve preloads. All good.
Adjusted the ICFT's @ idle. Split fixed as described by my recent posts.

Again the other cells are not nearly as split as the idle cell 16. Only thing really left on the table must be the 107 LSA cam reversion. It appears that my adjustments have not affected any other cells. The intake was ported by LE too, not sure if that is impacting anything. Dont know how one could tell without trying an unmodified intake and logging.

 

How about a small vacuum leak on the intake gaskets, on the lifter valley side? That one would be hard to check. Is it possible the little pinholes in the manifold for the idle air are clogged up?

Maybe the 107 LSA could cause the 10% difference in flow at idle... I don't know. That's why I was asking WS6T3RROR, because he obviously has more experience in this area.

 

I thought about the gasket too. Might be a nice summer project to just pull it and put it back on to rule that out.

I did try the ether trick and never found a smoking gun.