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Discussion Starter #1
I am using DST for my tuning after Chasing my tail with LT1 Edit.

But anyways got closed loop about as close to 14.7 as I could get it. But wanted to lean it out for highway. And just couldn't get it to lean out anymore that 14.5-14.7. My question is there anyway to get it to lean out in closed loop?

I've tried to use the right and left fast o2 rich/lean threshold vs cl mode vs rpm. Is there some other table? I know in the lsx ecm's there is a table you can tell it what stoich is.

Just think for a 10:1 cr 383 auto 3.23 with 224/230 114+4 cam that I should get better than 16 mpg on the highway and really babying it with no boost adder on right now.
 

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you misunderstand how closed loop works

running a different AFR requires you run open loop, period.

the o2 sensor is inaccurate outside of stoich.

o2 sensors dont read AFR, they only read three things:

- kinda close to stoich
- richer than stoich
- leaner than stoich

thats why o2 sensors switch.

the sensor becomes innacurate very quickly outside the narrow band around stoich; that's why it's called a narrowband

changing what the ecm thinks is stoich AFR (not that the variable is known for your ecm anyway) will only affect how far off your trims are. it will correct for it and force you back to stoich or whatever

you might screw with the o2 voltage midpoints to force it up to 14.9:1 or something, but that's about it, and that wont make a difference for you.

if you go too far, it'll just lose all accuracy and it'll wildly swing between rich and lean aagain.

you dont have enough real control over things so you can effectively switch between open and closed loop when load increases. you could end up hurting something.

some other ECMs have a 'lean cruise' mode for that purpose that throws it into open loop and leans it out under some conditions; yours doesn't have that. it could be hacked in, but hasn't been done.
 

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Discussion Starter #3
I do understand how close loop works and how the O2's constantly moves back and forth in frequency to try and keep in the int 14.7 range, and that once you get over your set Kpa it goes into PE for WOT.

Just thought I would ask just to make sure I wasn't missing something. But thanks for the explaining how the lean cruise works.... didn't know that is puts into Open loop for the lean cruise. Since it is most accurate at 14.7 for closed loop it must not use closed loop for E85 and different type of ethanol fuels then either because of the imitating factor of the O2's.

My 04 Silverado SS is next, nice to have heads up on that.
 

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I do understand how close loop works and how the O2's constantly moves back and forth in frequency to try and keep in the int 14.7 range, and that once you get over your set Kpa it goes into PE for WOT.

Just thought I would ask just to make sure I wasn't missing something. But thanks for the explaining how the lean cruise works.... didn't know that is puts into Open loop for the lean cruise. Since it is most accurate at 14.7 for closed loop it must not use closed loop for E85 and different type of ethanol fuels then either because of the imitating factor of the O2's.

My 04 Silverado SS is next, nice to have heads up on that.
you're close, but thing is, an o2 sensor doesn't know what 14.7:1 is. it knows what stoich is.

it measures in lambada, which is fuel agnostic, since it's just measuring oxygen to determine how complete the burn is, it'll determine something approximating stoich AFR for pretty much any fuel you throw at it.

regular o2 sensors work just fine with E15, E85, propane, whatever.
 

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Discussion Starter #5
I get what your saying......I need to get more use to looking at lambada and quite referring to it as 14.7

Thanks
 

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This use to be a bit confusing for me as well. lambada stoich is always 1.0 That could be a different afr depending on what type of fuel you are using. Gasoline is 14.7:1 CNG is 17.2:1 ethanol is 9:1 etc.
 

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Discussion Starter #7
Thanks got that figured out now..... was hoping there was a way around it but if the computer is reading lambada there is just no way of getting around it.


This use to be a bit confusing for me as well. lambada stoich is always 1.0 That could be a different afr depending on what type of fuel you are using. Gasoline is 14.7:1 CNG is 17.2:1 ethanol is 9:1 etc.
 

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well, there is to a point, i managed to get a pretty stable 14.5:1 out of closed loop with ordinary gas. any further and it got really unstable, jumping around everywhere.
 

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Discussion Starter #9
I was able to get it to run 14.5-14.8 in closed loop but not getting to good of mpg's though. Getting 15-16 mpg's and with the cam I have I should be in the low to mid 20's.

Better be looking for some vac leaks I'm thinking. But I'm pulling 14 vac but must be loosing some if Im only at 16mpg with 224/230 .496/.502 114+4 with 3.23 gears :eek:
 

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leaning it out isn't generally how you milk fuel economy out of an engine like an LT1 anyway.

you generally try to dump the right amount of fuel and burn as completely as possible with a bunch o' timing in cruise range

14 vac? is that 14" of mercury or 14kpa? neither one seems right for that cam.

you will never get awesome fuel economy from a cam like that...

lets see some logs
 

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Discussion Starter #11
14" of vac......And have to look at the timing....Solomon did the base tune and I haven't got to the timing part yet. And Im going to check for vac leaks also. With that cam muti people have said it should be in the low 20's. I'd be happy with 20 mpg and bonus if more. I have to get my data logger wiring figured out not picking up the IAT and CLT data so I can cross reference that info vs rpm vs kpa.
 

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Discussion Starter #12
what kind of timing should I be seeing for cruise?
 

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that depends on a LOT of factors.

timing is a tricky thing. compression ratio, cam design, temperature, head efficiency, spark plug choice, bunch of other stuff.

you want to try to increase timing slowly and do a bunch of datalogs.

as you increase timing in a particular range, generally it'll act something like this.

first it starts pulling more vacuum (good). note that this can push you into a different timing cell.

then vacuum kinda levels off. sometimes this is the point that you get a bunch of cam surge (it'll start feeling a bit rough..)

then vacuum starts to drop. this is a bad thing.

shortly after you'll hit pre-ignition and it'll start knocking, and something is going to break.

typically LT1s tolerate quite a bit of timing, but if you arent' getting more vacuum by increasing it, dont bother.

usually once you've found your target timing, most people back off 1 degree or so.

but a short answer is, during cruise with mild to moderate compression usually lands around 40 degrees of timing during light cruise range, +/- a few degrees.

i've seen a lot of tune by mail guys rack up 45+ degrees, i find that unnecessary, and it usually get smoother if you back it off a little bit...
 

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This is a lot of good info. Steveo really knows his stuff when it comes to the lt1.
 

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i'm no master of timing maps, mine sure isn't perfect, but it's better than the sketchy tune-by-mail one i started with.....

my gripe is how long it takes to fine tune it; flash after flash.. im jealous of the earlier gm ecms with emulators.
 

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Discussion Starter #16
I'll have to work with that timing a little then also. Most of it is 41 or less except for the lower Kpa vs RPM's like you said is 44-48 degree's advanced in the 25-50 Kpa cells. I got a lot going on right now putting air ride in my Silverado ss so I can get in and out of it. When I get that wrapped up I'll take a look at a few things and get back to working on the tune once again. Want to make sure that I'm not chasing my tail with vac leak and or bad vac lines. FIrst of the month going to order new silicone vac line for everything under the hood.

And thanks for your input.
 
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