I find that actually running something just a bit leaner than 128BLM appears to make my motor run smoother/quieter. Exhaust note was smoother and more mellow. Responsiveness was very good. Overall the motor just seemed to be happy. And no KCs.
Anyone w similar experiences?
My car is a 92 ZR-1 w the LT5 that has been modified w 454rwhp/402rlbft.

 

When you're higher than 128, the ECM is erring on the side of adding fuel. So counterintuitivelty, you may actually be getting a little richer. The engine may like that.

Do you have dual O2's? I noticed that when my NB side is running higher BLMs, the WB side AFR is a little richer than stoich.

For that reason I try to target my BLMs to 128 or above, not below.

 

ULT,

Yes the LT5 has dual NB O2s. And yes I definitely get the “split” blm issue which is very marked at idle but straddles 128 +/- 3 in most other instances

 

If you have dual O2s you can't adjust each bank individually to overcome that?

 

Don’t I wish. Earlier somewhere I wished that someone could come up w a hack allowing adjustments of the O2 mv windows on a bank to bank basis.
My passenger side bank is the richer bank, w the left being on the lean side. This is exaggerated in idling conditions.

 

Each bank fires separately I take it?

 

You don't want to adjust the O2 INT window to correct split BLMs. You want to adjust the injector PW on either an individual basis or a bank - bank basis.

RBob.

 

LT5 is SFI. Thanks RBob for chiming in. Always look forward to ur input. Could u explain further as to why that would not be a good strategy? With 2 O2s I know that the O2 input does modify the PW on a bank to bank basis. But the base VE however is global. So ur starting w a compromised basis for PW calc that doesn’t accurately represent even each bank let alone each cylinder.

 

When the O2 INT window values are changed, it is changing the actual targeted AFR.

The main cause of split BLMs is air flow issues. Both sides aren't flowing the same. It can also be caused by differences in compression ratio, or exhaust flow.

So the cure is to adjust the injector PW to match, and provide the same AFR for both banks.

RBob.

 

If we really want to have some fun, we can talk/discuss the injector closing angle... Being SFI, it can make a big difference.

RBob.

 

Lol... yep.

On my late-Jurassic era 7730, after I put that idle air manifold on the Miniram way back when, that solved about ~85% of the split BLM problem. I basically then found that if I went open loop at <1000 rpm, I could then essentially split the difference on AFR between the two sides and keep everybody happy. About the best I could do with batch fire unfortunately.

Its interesting though, in the context of this thread title... after my discovery last week about the additional ignition timing, I actually found that the additional 5 deg of idle timing allowed me to dial in about 1/2 point leaner on the AFR and still maintain the same smoothness, while still maintaining the 1/2" Hg of vacuum increase I initially realized after the timing adjustment. So rather than needing about 13.75:1 for a smooth idle, I'm actually much closer to stoich at 14.25:1... and that definitely helped in the smell department. Even with cats, you still get a bit of musclecar-ish exhaust smell unfortunately. I haven't swapped sides on the WB to see what the driver side is doing (WB is currently on the pass side), but as good as it's running, my guess is it has to be pretty close.

I tried closed loop idle again as well with the added timing and it does ok, but the Miniram still does seem to prefer open loop idle for optimum idle quality.

 

Thanks guys. I’m happy to have begun a discussion even if only it results in further educating me and hopefully some others.
My operating premise was that the O2 on each side provides the ECM w the data to modify PW for that bank based on what the O2 reading is.
Now a thought occurs regarding the injector constant. If u r able to have 2 inj constants. Using a larger inj constant on the rich side, then the PW calc for that side would be reduced and so bring BLM closer to 128. Thoughts?

 

I suppose one option for folks with short runner intakes like the Miniram could be to run larger injectors on the front 4 cylinders.

If you look at the fuel trims on the SFI 4th gen LT1's, you can see how they trimmed the fuel richer up front since it's getting significantly more air than the rear.

Now that I'm looking at this again (even the off idle is adjusted), I'm thinking about possibly trying that.

 

So ULT, what exactly are u adjusting w these trims? Is this a factor applied to PW? Even something along these lines applied to the primary injectors. Don’t need to be concerned w the secondaries as their PW is dictated by the primary injector PW they are paired w. IOW the ECM calcs the correct PW, then multiplies it by .51, w both injectors firing concurrently. If I could get a table like this even if only for bank to bank.

 

These values are out of the $EE mask for SFI 4th gen LT1s, for reference on how GM dealt with fuel/air distribution issues.

I obtained the 4th gen stuff as it greatly helped me on the Miniram like with accelerator enrichment.

 

So GM was modifying the PW for each injector.

 

Do tell RBob!

 

there used to be an injector box, I believe accel made it. was for using low z injectors with high ohm injector ecm's but it also allowed you to adjust each injector trim. it would. probably have worked pretty good this on batch fire.

does anyone even run low z injectors anymore? seems they have figured out big flow numbers out of high ohm injectors these days.

 

I was actually going to post a question about something like this... whether there was something you could wire into the circuit that would allow you to "artificially" trim certain injectors richer.

Would be more convenient than having to buy different injectors. I contacted FIC for these 33 lb/hr injectors they sell... I figured I could increase the fronts by effectively 10% over the rears. All my injectors are currently 30 lb/hr.

When I pull my spark plugs out, it's clear the rears are running richer than the fronts.

 

The more obvious indicator for me is bank to bank rather than front to back w the D/S bank being the “lean” side. Now I have wondered if there isn’t an FP drop from left to right bank given that the duel fuel lines enter the fuel plenum/regulator from the P/S and then into eash dide rail. For many years, I’d owned an 84 Xfire which I upgraded to something akin to what Grumpy had done to a Firebird. There he used a Y block with separate feeds to the twin TBIs. The Xfire had two single barrel TBIs and fuel was routed to the front, where the regulator was(IIRC) and sending fuel to the rear TBI. At one point, I put a FP meter in between those two TBIs and measured a FP drop of .5#. That correlated well with the stock setup of using a 63# injector up front and a 65# injector in back. And I have always wondered if this was not at lesst a contributo to the disparity between L&R given that the fuel needs to travel an extra distance to the left side rail after the regulator.

 

seems it has disappeared from the internet on a quick search. I'm sure they are discontinued at this point.

fuel tech might be the only hope for something like that at this point.

 

What do they have that you're thinking of? Quick look at their website and they're selling complete EFI systems...

 

Injector closing angle... Short version is that it can make a big improvement in driveability. The engine just runs better in part throttle situations. Likely due to large injectors.

Bruce and I started with controlling the injector opening angle. But that entailed compensating for load and RPM. Just didn't work out.

So looking the data, it hit me, we are adjusting to the injector closing angle. That is what matters. Changed the code to do just that and bam, The entire table of values ended up being the same (injector closing angle versus load & RPM)..

So ended up with a single parameter to do the trick.

RBob.

 

RBob,

Not totally familiar w Injector Closing Angle. If u could expound on that, thank u. I’m certain I have a Compensation Load v RPM table. Never really looked at that before. Did u modify the code for the table or create something separately? Again, that looks like it modifies things globally. Hiw could it address changes on a cyl x cyl or bank2bank basis?

 

It's difficult without individual cylinder control, even CNC parts don't flow exactly the same as the smallest difference in the runner alone, let alone the valve angle will make a giant difference in a cylinder's air/fuel ratio. Even with sequential, if you can't monitor and read the individual primary... even if you were able to get lucky, you'll be chasing your tail as guides, rings and seats inevitably wear down, you'll always be chasing your tune. I remember a Grand National owner once telling me it'd be easier if we just welded an O2 bung in each primary, datalogged each cylinder, and used an injector that came with individual pressure control, then adjust accordingly. He was definitely onto something decades back, but then individual cylinder control was introduced, and that was that...

- Rob

 

It is the angle in crankshaft degrees of where the injector closes. On an SFI engine this makes a difference. The injector opening point is changed to get the proper closing point, as RPM and injector PW affect it.

I can't see it making much difference on a batch fire system. But never tried it to tell.

With SFI an injector fires once per two engine revolutions. So is it on an open, or opening, or closed, or closing intake valve? Does it make a difference if it is injecting fuel on the back of an intake value. Which then when it opens reversion atomizes that fuel?

We never did get into the wheres & whys, just something we played with and dang if it didn't make a difference.

Note that this was code that was added, not in the stock GM stuff.

RBob.

 

Let’s see if I understand. And I am very appreciative of ur indulgence, The valve closing angle is a fixed point in terms of when it occurs during the crank revolution. The calc’d PW is accommodated by opening the injector sooner or later relative to crank degrees. But in the end, closing angle will take place at a certain point in the crank revolution full stop. W an 8cyl, if I identify the closing valve crank angle, I can identify the cylinder it is for. Then the table can show the Cyl# and I can apply a certain correction factor to be included in its PW calculation, letting the ECM concern itself re compensation w load and rpm. Ur injector closing angle factor is the final? consideration regarding the PW calc. This allows adjustment for each cylinder individually.

 

I am not quite sure what you are saying. But the injector closing angle is across the board, but at the same time is for each individual injector.

In sequence an injector fires according to its DRP. So 4 injectors with 4 DRPs every engine revolution (8-cyl). Each injector in turn will close at X number of degrees past its DRP. Same for the next revolution of 4 cylinders.

Note that the injector PW that is used is the basic PW. Prior to individual cylinder trims. The cylinder trims are minor so no need to take them into account. Besides, it would entail cam & DRP syncing and cylinder counting. Not worth the effort.

RBob.

 

RBob,

I believe that I understand the closing valve angle to be a fixed point, ie does not change w PW. What does change is the starting point of the injector opening based on the duration of the calc’d PW. If DRP for injector firing is 45*, the closing valve angle is say an additional 5* of crank rotation or at 50* of crank rotation which is a fixed # for that particular cylinder. It could be 90* DRP for the next the closing angle would be 95* crank rotation angle but still 5* beyond the injector DRP. And that the closing valve angle will always be a constant number of degrees beyond its DRP. for all cylinders. The factor u apply to each cylinder modifies the base PW calculated. Any other inputs to the PW calc, u ignore as being minor.
Am I closer to understanding?
Is it possible to see the kind of table u used for this in the calibration?

 

Yes.

No table is used, the closing angle is a single value/parameter.

RBob.

 

So RBob, in ur instance the value used for the parameter was what? And it represented what?
Or was it simply an option that u checked or unchecked?

 

A value that is the number of degrees after the DRP that the injector closes. From 0 to 575° with a resolution of 2.25°

RBob.

 

So by varying the closed valve angle, ur using the "tail to wag the dog" so to speak. Changes to the CVA, affect injector timing overall in terms at what degree the injector begins and ends operating. Your comment regarding SFI as being an area CVA could show significant benefits, would that include improving bank to bank variation in BLM, ie Split BLM? What other benefits have u experienced?

 

Bank to bank variations on an SFI system is best dealt with via injector trims.

We only looked for improved drive-ability, nothing more.

RBob.

 

Thanks RBob. Sound like CVA may not be relevant to what I am trying to address but its always educational to hear about one of “rabbitholes” you and Grumpy have explored.