The best way to standardise tables

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Marek
Master MS/Extra'er
Posts: 573
Joined: Sun May 10, 2009 1:20 am
Location: Guildford UK

The best way to standardise tables

Post by Marek »

Dear all,

I have been looking at my tune today on account of not being able to start the car and it occurred to me that the cranking tool tip hinted at a way to make basic tunes more easily comparable.

The tool tip suggested that the last entry on the cranking pulse table ought to correspond to a VE of 100 and that a cold engine may need twice as much fuel to start it.

Does this suggest that we should rescale our Reqfuel numbers and our VE tables such that they take over from a cranking table which has been itself scaled by the reciprocal of that factor such that the cranking table ends at 100?

The reason I find this appealing is that I am a dual fuel user, so assuming I do this for both petrol and lpg with the correct AFRtarget and alternative AFR values inserted, ought I not find that I have identical VE tables for both fuel types if the dead time is set correctly for each injector type?

Put another way, if the tables appear to diverge from each other with increasing pulse width, does that not suggest that the injector dead times are mismatched against each other?

(Most LPG conversions use a piggy-back ECU to intercept the commanded petrol pulsewidths and these are repurposed by a scale factor which varies with rpm. The implication is that separate VE tables and cranking tables aren't necessary to run a dual fuel car.)

If everyone ran cranking tables which ended at 100 and VE tables to suit, would it not make for easier comparison and mutual assistance in the MS community?

kind regards
Marek
billr
Super MS/Extra'er
Posts: 6828
Joined: Sun May 15, 2011 11:41 am
Location: Walnut Creek, Calif. USA

Re: The best way to standardise tables

Post by billr »

Yes, your logic is correct in all that.

That is why we always harp on setting req_fuel correctly and leaving it alone; and using a timing light to get the crank to agree with what MS sets. It is perfectly possible to have a well-running engine with "bad" req_fuel and spark reference, but then the tables will be rather weird and unintelligible to most of us.
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