RedWS6 00

I know the holden PCM's are allowed to run the lean cruise and its not enabled in the USA/Canadian PCM as running lean produces the NOX gas.

Anyway, when forcing open loop by uping the enable tem[perature to a temperature it will never reach then it will never enter closed loop. Therefore using the Open Loop EQ Ratio Table, by setting point of this table to less than 1 you can get leaner running than 14.6. I have also disabled my fuel trims.

The question is what is a safe lean cruise AFR, looking on other forums they talk of 20:1, but they was on a 4 cylinder engine, I think the Holdens can run 17:1 but not sure. Certainly is the MAP increased then it goes to 14.6:1 AFR, and over 50kps for examples its rich.

Does anyone know the lean cruise AFR other V8's use?

Rolemodel

15.8-16.3:1 is something reasonable. Your throttle response won't be as nice though. Make sure your wot is not in the 13.0 & leaner range

ChrisS@sdpc

What's safe vs best mileage just might end up being two different values.
You may find that you can easily run 17:1 with the right timing at cruise, but that you have to give more throttle that it is not as efficient as say 15.5:1 and less throttle.

Might check out this thread for some other mileage tuning ideas.

RedWS6 00

Thanks I'll shoot for 15.8 - 16.3 AFR at cruise. Not too worried about throttle response, from what I have tried by accelerator striaght down I'm quickly at 12.5 AFR and seems to pick up quick. I spend most of my driving at 1600 RPM and < 40 kpa so I may aswell lean them cells to lean cruise AFR's.

I'll run a few tests looking at the injector duty cycle and throttle position and MAP, you're probably right, going too lean you will require more throttle therefore you may could stay richer for the same performance.

TAQuickness

iTrader: (28)

DFCO is a good way to pick up some mileage as well.

RedWS6 00

Thanks, I'll try playing with DFCO too.
I do have it enabled but the parameters are as stock.

After about 3 seconds of decelleration it cuts of the injectors to almost nothing so my AFR goes way over 17.3:1, I dont know what it goes to as my WB only goes to 17.3.


I have completed all the WOT tuning and WOT spark timing. Was just looking for something else to tinker with, its a little addictive toying with the cars parameters. went on a couple of 25 mile trips over the weekend, so was an ideal time to do some logs. Gas prices are now $8.33 per gallon in this area so thought that will be my next challange to increase the MPG's. However Heads/Cam and forced induction is still on my list of things to do in future.

tici

iTrader: (1)

Could you please explain that more in detail?

thanks!

horist

see
http://www.hptuners.com/help/vcm_edi...uel_cutoff.htm


it's enabled in stock vehicles, you can tweak some of the settings to help more... it basically reduces fueling (to the point of no fuel) when you're decelerating

ggk

iTrader: (1)

question by lean cruise do you mean when you turn on cruise it turns on or do you mean it will happen if you are at a constant speed.

can this be achived on an lt1car?
i was looking at it and it said it was gm parameters on hpt's site.

foff667

iTrader: (2)

yes


its probably not in the code or not turned on so probably no.

infinitebird

iTrader: (11)

Incorrect. All he did was disable closed loop and set his cruise AFR using the open loop table. You can easily do the same thing on an lt1.

txhorns281

iTrader: (12)

lean cruise operation is definitely not LT1 inclusive, what you are describing nets the same effect, but is not what is defined as "lean cruise mode"

ggk

iTrader: (1)

Is this a yes or a no?
cause my car is going to become my dd and i want to get the most gas mileage i can because where i live gas prices are higher then anywhere else near me.

tici

iTrader: (1)

Thanks! What are considered good settings? For racing? for better mileage?

I looked at the Corvette vs F-Body settings (both 98 cars, like mine): the Corvette needs higher RPM to enable DFCO and activates it with 1 sec delay vs 3 sec of the F-Body.
Is there a reason for that?

Can I mess something using wrong settings? like burn the cats?

Is there a driveability drawback?

Thanks - Stefano

infinitebird

iTrader: (11)

I never said it was. ggk asked if "this could be done" on his lt1. I assumed he meant what the original poster said he did. The original poster did not enable "lean cruise mode" he merely disabled closed loop and set the AFR with the open loop table as I mentioned. That can be done just as easily on the lt1, that's what I was saying.

yes

RedWS6 00

Yep thats right, I cant enable the true 'lean cruise' as the code isn't in my PCM. So what I have done is forced open loop constantly by uping the close loop ECT threshold to somethnig that wont be reached. Therefore while in open loop it uses the EQ ratio table, have made it about 16 AFR up to 20kpa, 14.6AFR up to 50kpa then richer above.
The thing is with runnine lean, or even rich for that matter is that it woundt [pass the emmision test, too lean I think produces NOx gas. When I'm due for an emmision test I'll put it back in closed loop and put the cats back on.

My next thing is to work on DFCO to reduce the entry time. Looks like its the 'Entry Blending vs RPM' table if you double them values it will enter DFCO twice as quick by the looks of it.

Quick question, when in Open Loop is the MAF used in any calculations at all?

tici

iTrader: (1)

I'm also interested! I was thinking MAF was important to calculate torque and G/cyl for timing. But if SD is possible (and it is!) timing and torque have to be calculated in another way.

RedWS6 00

g/cyl is caculated though the VE table without using the MAF, there is a fall back routine which does that. Not sure of all the calcs to achievle g/cyl, but I am running SD mode at the moment and its picking out the correct spark advance numbers.

Once I finished my open loop tuning I'm probably going to reconnect the MAF although I know its not needed its always nice to see it plugged in when I lift the hood at car shows.

infinitebird

iTrader: (11)

The MAF is still used to measure incoming air.

While in open loop the pcm uses a stored formula to calculate what it thinks is the current AFR (since it can't measure it directly with the O2s), the mount of incoming air is still definitely one variable of that formula.

The MAF's function is the same in open loop as it is in closed loop. The only difference is that in closed loop the computer has feedback from the O2s to know whether the AFR it calculated was accurate. Ideally it is usually close and the O2s are only used to make small adjustments.

RedWS6 00

My car is in open loop all the time now I beleie which I what I want to achieve, have raised my ECT level for close loop so it shouldn't ever go in closed loop. The EQ Ratio works on the MAP. Therefore at 20 kpa when driving it commands 15.6 AFR, gets richer the higher the KPA, I can see the commanded AFR changing to the way I want it to be.

But this is my question, when in Idle it always commands 14.6 AFR, how do I get it to command higher, has it somehow gone to closed loop even though I thought it was disabled from the high ECT threshold?