Fuel Tuning Basics - Fuel Tuning 101 -

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Fuel Tuning Basics - Fuel Tuning 101 -

Postby loxxrider » Sun Sep 14, 2014 1:16 am

Basic Fuel Tuning 101

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**Notes**

I thought this might be useful to have in an easy-to-find place. This was originally posted in another thread, but I always had a hard time finding it and have re-written it several times in the past. I would also like to add a PID closed loop boost control one as well (whenever I find it).

EDIGREG made a very nice fuel tuning post on quattroworld. It goes into a lot of detail on getting started with tuning fuel, specifically in VEMS and may be just what you're looking for. http://forums.quattroworld.com/s4s6/msgs/112142.phtml This post here on the project pad is more geared toward the general concept of tuning fuel.

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Alright then, let's get started. You will be sent a base tune with your ECU based on what your setup is like (big turbo, small turbo, injector size, etc.). If you do not have a base tune, we can go into that more later. You can always ask here too! Someone is bound to have something that will work for you. The timing map will be pretty good and you should not mess with this unless you really know what you are doing, and even then you should preferably tune timing on a dyno. What you are left with then, is tuning fuel. You can start tuning fuel without really knowing much. You just have to know a few basic rules.

Since you are pretty new to this whole thing, I'll start with the basics. For gasoline, the ratio at which the fuel burns completely is 14.7:1 (14.7 parts air to 1 part fuel). More air than that (above 14.7) means the car is running lean(er) and less air than that (and thus more fuel in relative terms) means the car is running rich(er). You will adjust the AFR (or lambda... I'll expand on that later) in VEMS by pulling up the VE (volumetric efficiency... its stupid I know, just think of it as the fuel table) table in the tuning drop-down menu. The VE table is set up with manifold pressure on the y-axis (in kPa rather than psi.. get used to it!) and RPM on the x-axis. You will see various values in each cell which correspond to how much fuel the injectors will deliver to the cylinders in that particular load cell. If you want the car to run richer, you simply increase the value in that cell. If you want it to run leaner, you just decrease the value. That is pretty easy while just cruising or idling where you can hold the engine at a specific RPM and MAP pressure, but it takes some practice to track the path of the engine across the map at wide open throttle and then make adjustments to the map accordingly. So now that we have the basics out of the way, lets move on to how much fuel you really need in any given situation.

As a rule of thumb, you should tune idle, cruising, and anything light load at 14.7:1 air to fuel ratio since that is the ratio at which the fuel burns the most efficiently. It'd be great if we could keep the mixture that lean under all conditions, but that just isn't the case for various reasons (mostly to do with heat).

Now... before we go much further, lets switch over to talking about lambda rather than air to fuel ratio because that is what you are going to see while tuning with almost any standalone engine management systems. The conversion to lambda is xxx AFR/14.7 = lambda. So if your current AFR is 14.7, then lambda is 1 (14.7/14.7). If your current AFR is 10, then lambda is 0.68.

So as I was saying before, tune your light load, cruising, and idle to run at 14.7:1 AFR or 1 lambda. Just increase or decrease the value for the cell (on the VE map) in which the car is currently operating, and watch to see how your lambda reading changes. It should go down as you increase the fuel you are providing the engine (less air and more fuel = richer... richer = lower lambda value). Now, as you increase manifold pressure, you will have to fatten (make richer) the mixture up. Use the following as rules of thumb:

-Anything below 120 kPa, keep lambda around 1
-Between 120 and 200 kPa (15 psi), shoot for 0.9 lambda
-between 200 kPa and 250 kPa (22 psi), shoot for 0.85 lambda
-above 250 kPa, start to fatten up to 0.8, continuing to as rich as maybe 0.78 or even richer as you approach 300 kPa (29 psi) and above

That should keep you in a pretty safe place, yet still make decent power. Others, feel free to comment on my numbers there... it's been a while since I have tuned anything unfortunately :( I guess it has been less than a year, but it feels like forever!

So basically, you are going to go out and make a bunch of wide open throttle pulls, watch your wideband 02 sensor, and make adjustments accordingly. If you start going too lean, let out of the throttle and add more fuel immediately. Don't keep beating on it while it is lean ;)

There is a lot more to learn than just this... you will have to know how to increase boost, set limits on boost and fuel, etc., etc... it might seem a bit daunting at first, but don't worry! It will come with time. There is a lot of of great help available on this forum, so ask away and I'm sure there will be people willing to remote tune for you or talk you through some of the steps involved in starting to tune for yourself, recording logs, reading those logs, etc.

Good luck, and I hope you have fun with it!



-Chris
Last edited by loxxrider on Thu Apr 28, 2016 7:50 am, edited 2 times in total.
-Chris

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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby PRY4SNO » Mon Sep 15, 2014 6:20 am

All of this is right in line with the texts on tuning EFI that I've been reading.

Nice work.
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby 88a5tq » Sun Nov 02, 2014 10:05 pm

This is great stuff. Chris, thanks, I was just thinking about general fueling rules concerning the AFR. Now I just need an integrated VEMS AFR readout in true HUD fashion from EFIexpress. I'm really enjoying this DIY section!
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby ChrisAudi80 » Tue Sep 08, 2015 2:23 am

Chris, does the same count for E85? 0.9 lambda up to 15psi?
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby loxxrider » Tue Sep 08, 2015 4:28 am

I'm no e85 expert but yes I believe so. Just tune the same way based on lambda.
-Chris

'91 Audi 200 20v - Revver/BAT project
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby pilihp2 » Tue Sep 08, 2015 10:12 am

lambda is wonderous in the sense that stoich is always 1. A couple local tuners go off AFR and I never understood why they would even bother. Such a pain.
e85 is the same when it comes to lambda levels. Up at higher boost levels you can even go a tiny bit leaner, like .80 instead of .79 at the higher levels.
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby mushasho » Tue Sep 08, 2015 12:32 pm

because I'm a newbie, and mostly do tweaks on the street I stay .77-.78 max under boost
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby Mcstiff » Tue Sep 08, 2015 1:03 pm

Yeah, E85 is pretty tolerant to being lean...

viewtopic.php?t=206&p=39434
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby ChrisAudi80 » Tue Sep 08, 2015 11:25 pm

Mcstiff wrote:Yeah, E85 is pretty tolerant to being lean...

viewtopic.php?t=206&p=39434


Thanks, good read. I did notice today the AEB likes 0.9 lambda (13.0-13.2 AFR) under boost to 14psi.
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby loxxrider » Wed Sep 09, 2015 3:09 am

Just like gasoline :)
-Chris

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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby ChrisAudi80 » Wed Apr 27, 2016 10:17 pm

Any chance you could do a write up on (VEMS) tuning ignition timing with EGT?
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby loxxrider » Thu Apr 28, 2016 7:48 am

ChrisAudi80 wrote:Any chance you could do a write up on (VEMS) tuning ignition timing with EGT?


No, sorry. It's becuase I don't think you should tune timing away from the dyno unless you have significant seat time doing it by ear/egt/knock phones/butt dyno on the street.
-Chris

'91 Audi 200 20v - Revver/BAT project
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Re: Fuel Tuning Basics - Fuel Tuning 101 -

Postby ChrisAudi80 » Thu Mar 23, 2017 2:34 am

I know you are a busy guy, but if you could write something similar for acceleration enrichment, it would be good.

I figured out the dTPS enrichment a while ago and FINALLY understood that the acceleration RPM table is like a weight table.
More accel enrich at lower RPMs is needed with the same dTPS. I could not find this information anywhere.
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