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Main Fuel - too low values in VE Tables


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i am not familiar with tuning LINK Ecus but have some experience with other brands (megasquirt ecumaster). I try to help a friend with an issue he has on his tune. The Car is a e34 535i with itb and turbo and is equipped with a G4+ ECU. The car runs, but tuning the fuel makes some trouble. The ECU is set for traditional Speed Density fuel calculation. But tuning the VE Table makes some trouble. Especially the part of the Fuel Main value.

As far as i understand, the Fuel Main Value is a factor for scaling the whole fuel table (same as "req fuel" on megasquirt), so with the correct Fuel Main we should get well tunable VE numbers to be able to tune idle areas as good as the high RPM/Load areas. So decreasing Fuel Main will result in higher values in the VE table. The Manual sais that the Fuel Main should be set so that you get an average of 50 in the middle of the table. But thats where we run into issues. The Fuel Main value is already set to the smallest possible value (4ms). But the VE Values are still so small that we cant get a good tunable values. A change of 1% in the cruise area will get the AFR from too rich into very lean. On idle the VE values are at about 16 and on cruise (3000rpm/100kpa) about 20 and on high load (6000rpm/300kpa) the ve value is at about 55. With these values it is not posssible to get a stoich muxture on idle or low cruise areas.

The Setup of the car is:

3,5l Engine (12V) with M5 ITB, 1000ccm high-z injectors with fuel pressure set to 3bar, wasted spark (timing verified with timing light) ECU is a Link G4+.

The dead times are at just under 1ms@14V. The Injectors are fired in two groups (rate set to 1/2 engine cycle)


I attached the config file. I don't have a log now but i am going to get one.

I would appreciate some help! Thank you and best regards







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Can you try once per engine cycle? Should allow doubling the master fuel and you could work from there to see if there are other issues.

Or re-wire to semi-sequential as per help file if you have a cam sync.

(edit - have also noticed you have 30% trim on the master fuel - that should be 0% unless there is good reason to fine tune the master fuel from a whole number. As it is, I believe 4ms + 30% is the same as 5ms and 4% trim)

Edited by CamB
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Hi you mention the engine is on ITBs generally these are best tuned using TPS for the load axis on the main fuel table

I would certainly upgrade the firmware as the first step. Generally 1/cycle injection rate is used for multi point applications 1/2 cycle is generally for single point applications.




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Thanks for the replies, i also thought of injecting only once per cycle, maybe that will help. If i upgrade the firmware i think i'll have to retune a lot of parts, there will be a lot of changes i think. It would not be a problem if he wasn't 400km away haha :) Ok what i'll try is to inject only once per cycle and set the Trim to 0%. If that helps he will have to get away with this solution until he gets the car to me. I'll report if that will help.


i apperciate you help!




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