Can someone please advise on these fuel tables

tw2

New member
I am slowly getting ready to take my car to get dyno tuned properly. I would like to get my fuel tables configured and do some low load, low rpm street tuning to get the car reliably mobile first.

I have been reading a few recent EFI tuning books which have helped a lot.
- How do the rpm and load spacings for my AFR and VE tables look?
- Does the target AFR table have appropriate values in it?
I would like to make sure these are as good as they should be before spending a lot of time tuning them.

VE fuel table
VEtable.jpg


Target AFR value table for auto-tune function
AFRtable.jpg
 

MWP

New member
Target AFR table looks good.

Not sure about the VE table though.
Really need to get on the dyno to tweak that as every engine is different.
 

tw2

New member
Thanks, I have changed a couple of things in the AFR table, 15.7 is probably too lean to cruise. I have lowered it to about 15.0-15.2 and changed some other low load areas closer to 14.7.

The VE table numbers themselves are not very accurate and need a lot of futher tuning. It will be thrown on the dyno before too long. Do the rpm and load spacings look ok? I tried to give it a lot of low-mid rpm resolution since this is where things will be changing the most.
 

Simba

New member
tw2":2z9dv17t said:
15.7 is probably too lean to cruise.

It's very lean and will lead to bad things happening, especially in a tip-in WOT situation from those AFRs. 15:0-15:2 is safe enough for lean cruise, after that you're risking a lot for a tiny increase in economy.
 

sleeper

New member
Looks ok,
Not really shure what ems you have, but i think you have to many load points in the of boost area..
20-40-60-80-100 will do.. no need to have one every 10..
 

tw2

New member
Thanks for the help. It is megasquirt 2 extra. Those load points are vacuum, 100 is 0psi. Boost is 100 to 250kPa.
 

MWP

New member
Meh, i lean cruise at 16:1 with no problems.
As long as the engine doesnt ping with rapid throttle increase from cruise, youll be fine.
Going lean for a fraction of a second on transition isnt going to melt a piston.
 

Simba

New member
MWP":g5vnon2k said:
Meh, i lean cruise at 16:1 with no problems.
As long as the engine doesnt ping with rapid throttle increase from cruise, youll be fine.

Frankly, that's a hack of a standard and has no place in a proper EFI tuning discussion. "I do it and it hasn't blown up or melted yet" is generally the sort of advice to be wary of.

$2-3,000 for an engine rebuild buys a lot of gas, and the difference between a 15:1 and a 16:1 cruise is around 1-2 mpg at most. You're stressing the engine and running it much hotter than it needs to be run in order to realize a minuscule fuel savings and range increase. That is a ridiculous thing to suggest anyone replicate.
 

sleeper

New member
Simba":38owfrgd said:
MWP":38owfrgd said:
Meh, i lean cruise at 16:1 with no problems.
As long as the engine doesnt ping with rapid throttle increase from cruise, youll be fine.

Frankly, that's a hack of a standard and has no place in a proper EFI tuning discussion. "I do it and it hasn't blown up or melted yet" is generally the sort of advice to be wary of.

$2-3,000 for an engine rebuild buys a lot of gas, and the difference between a 15:1 and a 16:1 cruise is around 1-2 mpg at most. You're stressing the engine and running it much hotter than it needs to be run in order to realize a minuscule fuel savings and range increase. That is a ridiculous thing to suggest anyone replicate.


well, combustion temps are not higher at 16:1 than 15:1, they will actually be higher at 15:1 than 16:1... ( exhaust temp normaly is at top at about 14.2afr.. and get`s lower the more you lean it out due to lack of energy... ( fuel)
 

MWP

New member
sleeper":1ux5r5uz said:
well, combustion temps are not higher at 16:1 than 15:1, they will actually be higher at 15:1 than 16:1... ( exhaust temp normaly is at top at about 14.2afr.. and get`s lower the more you lean it out due to lack of energy... ( fuel)

... this is true.
 

___Scott___

Active member
NOx formation correlates with combustion temperatures, so in the graph below you can get a general idea of what the combustion temperatures are going to do as a function of AFR by looking at the NOx curve:
AFR_Emissions_Graph.jpg
 

tw2

New member
Exactly, oxides of nitrogen only form in very high temperatures which is why most new cars run 14.7, some running that ALL the time (at a loss of WOT power obviously) to have optimum emissions, and reasonable (ie not the best absolutely possible) economy. Fuel has a cooling effect. The leaner you go the higher the combustion temperature and the more sporadic and non-uniform the burn is. The fewer and further between the fuel molecules are the more the mixture burns in little pockets one at a time = detonation. The question really is how high is safe, I am not going above 15.2. I want to try and get good economy but I also want excellent reliability and margin for error.
 

Simba

New member
sleeper":3s111qpe said:
well, combustion temps are not higher at 16:1 than 15:1, they will actually be higher at 15:1 than 16:1... ( exhaust temp normaly is at top at about 14.2afr.. and get`s lower the more you lean it out due to lack of energy... ( fuel)

The issue I was referring to is not EGT at lean AFR cruise. It's what happens when you transition from a very lean cruise to a tip-in WOT condition. Potentially very bad things.

There are a number of things to consider-- how much cam overlap exists? Is there a cat in the exhaust? What, exactly are the EGT and CHT temps in a particular application? How quickly does the fuel system and EMS in use react to load changes? Those metrics, and many more decide if a given lean cruise AFR is safe. "I do it all the time so it's safe for you" is irresponsible.
 

MWP

New member
So what bad things exactly?
I want to know what can happen that's that bad in the fraction of a second (ie, one or less rpm's) before tps pump enrichment kicks in.
If it's not knocking or getting high egt's, what's going to cause damage?
 

cozmic512

New member
I have a few questions here. Is the lean cruise based solely on throttle position?
which translates to load? or is it simply rpm. Im not familiar with the way megasquirt is tuned.
I know you have afr's tuned for each cell based on rpm. what is fuel load %?
because the scale goes up to 250, and that makes no sense to me.
how can you have 250%. sorry about that, I think Im missing something.
 

MWP

New member
To enter closed-loop (EGO) mode:
- RPM must be over 1000, and under 3000
- Load must be less than 10"Hg
- Throttle position must be less than 25%
- Throttle position must have been in the same place (+- a few %) for last 5sec
- Coolant temp must be above 70degC

When in closed-loop, fueling is based on EGO reading alone.
Oh, maybe with one or two correction maps like batt voltage.

Thats a rough example.
 

tw2

New member
Load is based on volumetric efficiency. So in the case of megasquirt: 100 means atmospheric ie 0 boost, everything below that is in vacuum. 200 means 1 bar of boost ie 14.7psi and 250 is around the highest boost i would ever run ie 22psi.

Lean cruise is based on load (and rpm to a degree). In my setup low load will put you into fuel cells which are fairly lean but it will get slightly richer if you are at low load and high rpm (ie waiting to waste some asshole going 20 below the speed limit), the fuel helps keep temperatures down at the higher rpm. It is not based on throttle position directly but obviously if the TB is open then you will no longer be at low load. Hope that helps. I am not using closed loop because I want to run leaner than 14.7 in places but otherwise as described above.
 

cozmic512

New member
Thanks, that helped a lot. I think I have a pretty good understanding of the table.
after checking it against a couple other tables (non MS) it looks ok
and nothing stands out as wrong or too far off.
I think that before a proper dyno tune, you really dont want to go too lean at any point.
because if there is a cell thats off, or the progression isnt gradual
theres the possibility of knock
or even having the cyl temps have a drastic change instantly.
because shit always happens on the road.
I personally run fairly rich over 25% throttle.
and lean cruise between 14.5-15.0 with a tune.
 
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