Author Topic: Base Fuel Tables  (Read 19327 times)

Offline antonch

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Base Fuel Tables
« on: December 16, 2007, 03:03:14 am »
I've been meaning to write a guide of how I setup my fuel tables when I first start the car. A lot of information I found over the internet which worked well for me. Many will disagree on using "base" numbers. But in my opinion it is much easier to get a car started using ball park figure that will get you 80% there. Fine tuning will be much easier once the car runs.

The first thing I do is set up my Lambda table:


Lambda=1 at P/T is good for emissions and makes tuning easier. Lambda=0.8 will provide the necessary cooling once in boost.

Then I setup my VE table to look like this:


You can use the built in VE table builder. But since it is so inaccurate as it largely depends on the injectors I just build it from scratch.

Coolant bins need to be setup as follows for most installations:


I found that the following warmup enrichment settings work surprisingly well. I haven't had to tweak these yet. Colder fuel has more difficulty vaporizing, so more fuel needs to be injected to compensate.


Acceleration enrichments and cranking PW depend on the req_fuel parameter. So it is best to give an example. My engine has req_fuel of 5.1ms.


For cranking, I found that 50% of req_fuel for warm engine and 150% of req_fuel cold engine always gets the engine started:

These values are actually from a running car. As you can see, the base numbers are very close to the final cranking parameters. IC engines have a relatively narrow window of operation as far as AFRs are concerned.  You don't want to be too lean or too rich. But richer is always easier, and smoother. Tuning cranking PWs is easy. First warm the car up and tune the warm parameter, then tune the cold parameter with engine cold.
I usually don't bother with priming the fuel injectors. Priming is unnecessary and just wastes fuel.

Acceleration enrichment is usually turned off during the tuning stage. Unfortunately if you do not have access to a dyno, the car will be undrivable with AE off. Use the following base numbers:
dV %ofReq_fuel
2 0%
5 10%
10 20%
40 40%


To accurately inject the proper amount of fuel the ECU needs to have an accurate model of the fuel injector. Unfortunately, VEMs carried over a linear battery voltage correction model over from MS. Here is approximately how VEMS deals with battery correction and how other ECU.


Batt_fac is the main variable the determines how much the injector opening time varies with battery voltage. This value must be determined empirically. It is easiest to tune this variable at idle by increasing the battery load and watching the AFR.
Image coming soon...

Ideally you would send send injectors in to a vendor and the vendor would test them and provide you with calibrations. It seems that VEMS does not have provisions for this. This makes tuning fuel more difficult than it should be.

Offline dnb

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Re: Base Fuel Tables
« Reply #1 on: December 17, 2007, 12:04:08 am »
Very good writeup :) 

The VEMS battfac model isn't totally linear - it plateaus at 7v and 19v IIRC.  Still not ideal, but better than it being totally linear.

I'm working on a way of using datalogs to estimate some of the more tricky parameters at the moment, so I'll add some stuff when I have tested it.


Offline miniminor63

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Re: Base Fuel Tables
« Reply #2 on: May 19, 2008, 03:57:57 pm »
have you got a chance to do this yet dnb?

Offline dnb

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Re: Base Fuel Tables
« Reply #3 on: May 19, 2008, 05:34:44 pm »
Yes - I've done a fair bit of work now.  It's far from perfect, and there's too many variables to pin each one down in isolation, but my method does give an overall picture of which way parameters should be changed.

Offline Anden83

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Re: Base Fuel Tables
« Reply #4 on: March 01, 2017, 08:05:43 am »
Could you upload the pictures one more time?
« Last Edit: March 01, 2017, 07:19:50 pm by Anden83 »