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Thread: Someone explain lost fuel to me.

  1. #1
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    Someone explain lost fuel to me.

    Now my guess of what these tables are for is due to the low cylinder head temperature we get incomplete combustion, this would make the car run rich when cold? Is this right?

    What does the ECU use this table for, to inject less fuel to get stoich?

    Eg you want 1.0 AFR however you actually get 0.9 AFR due to incomplete combustion, the ECU then uses the map to add the 0.1 lost fuel ontop of the requested AFR and request 1.1 AFR so that the resultant AFR comes to 1.0

    Is this how it works?

  2. #2
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    You get a wall wetting / puddling affect and you typically need to add fuel to account for this loss.

  3. #3
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    Right so if I'm getting rich tip out when cold this is not where to look.

    Any suggestions on where to start with rich tip out on cold start? My injector pulse width goes to minimum (0.2ms with ID1000) however I still record a rich event around 12.8:1 AFR

  4. #4
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    How rich we talking. You may have too much deadtime adder. What's your batt offset at operating voltage?

  5. #5
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    I should add that these tables are an adder accounting for lost fuel, but it adds via subtraction from the commanded base fuel (be it base cold or base proper depending on the modifier table). The values are obviously lambda.

    Where you need to be careful is if you have values in cells where if the stabilised temp of the donk is. Ie after installing cooler thermostats for example.

  6. #6
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    Quote Originally Posted by IH8TOADS View Post
    How rich we talking. You may have too much deadtime adder. What's your batt offset at operating voltage?
    Offset is 0.00117 at 14V

    The reason I didn't believe it was an offset problem is it only really occurs when cold/car is started when warm it is still happens but is much better (more like 13.8:1). It also only happens on tip out, if you are on deaccel (with DFCO disabled) the AFR is at stoich it is just for 1-2 seconds after tip out it occurs.

    It goes down to about 13-12.8:1 AFR (98 octane) on tip out when stone cold.

    Normal cruise and everything is is pretty much spot on between 14.5 to 15 AFR at cruise in all cam angle vs rpm cells if you average it out so I dont believe it is a problem with the speed density maps either. It seems to occur in all cells but only on tip out transient conditions.

    I've left closed loop disabled and run the car permanently in open loop to rule out issues with the closed loop oscillating etc however the result is fairly similar.
    Last edited by rolls; 08-03-2016 at 09:59 PM.

  7. #7
    HPT Employee Eric@HPTuners's Avatar
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    Lost Fuel is the fuel that gets injected and not burned. The units on these tables are in lambda. If you see a vehicle crank and the trims are way off, but as the car gets warmer the trims are ok, then you would compensate for this in the lost fuel tables (assuming the rest of the tune is setup properly).
    Eric Brooks
    HP Tuners, LLC

  8. #8
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    so is this used across all ba/bf/fg pcm?

  9. #9
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    Hptuners have only mapped it for fg but I believe it is in bf as well (haven't checked)

  10. #10
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    Quote Originally Posted by misk View Post
    so is this used across all ba/bf/fg pcm?
    There are 2 tables in my BF calibration (one for cold start) but not defined in the Editor, have not checked a BA yet. Have a look at an FG calibration to see what they are.