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Questions regarding master fuel - Link G4

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I've just recently road tuned my 4age powered starlet, basically standard motor with quad throttles from a 20v 4age. I wired in a Link G4 atom and tried my hand at road tuning (my first effort at EFI tuning) after doing the road tuning course. I really struggled at the start with the master fuel figure. I had no real injector data but figured i couldn't go to far wrong with using typical numbers.

I started with 12ms as seemed to be a good starting point, got to around 3500rpm and ran out of resolution, slowly but surely as i kept tuning further up the rpm/tps range I had to keep adjusting the master fuel number (and scaling the whole map to suit) just to keep the table within the maximum numbers. I got the car tuned in a slight hurry before an event and it seemed to be pretty sorted through out the bulk of the map but I think i ended up with a Master Fuel number of 23ms, the values in the map range from 6 up to around 140 (i'd upload the map but they are on a different laptop)

Am I doing something wrong? being so far above average numbers seems odd to me but then in the end the the engine runs fine and I had no issues getting all load points to my desired Lambda targets.



That is a massive change from 6 to 140. What is your load equation set to? and what are you using as load on your axis tp or map?

Do you have a map sensor connected?

Almost sounds like to me either, you have your load equation set to map and don't have a map sensor connected or you're tuning in Modelled mode and don't have a Map sensor connected or you have run out of injector/fuel pump and keep raising your MS number because you're trying to add more fuel which the injectors can't, what is your injector duty cycle at high rpm?

hey chris,

set to BAP and TPS main on load axis, no map sensor connected. Set to traditional.

I wouldn't have thought i'd be running out of injector being a near factory motor, fuel pump may be a cause as i'm having issues with the setup but it did tune up fine in the end and AFR is fine right through the rpm range. one thought was to plumb up a Fuel pressure gauge that i could see while driving to see if i was loosing pressure. I will have to get back to you on duty cycle

If you don't have injector data how have you filled in your injector dead times?

the ECU had default dead time values, they seemed comparable to other values i had seen floating around, I figured some values (although not right) were better then none. I've also seen write ups from people who have accurately measured dead time and it has differed from specified values anyway. If you have any leads as to where I would find data for factory smallport 4age injectors i'm all ears!

If you're using the Load = BAP then you'll naturally have a larger spread in your fuel table numbers as the final requested injector pulse width won't be modified by the background fuel equation as the manifold pressure drops at light load/low TPS. That being said, the spread is still larger than I'd expect to see. Essentially what it means is that you're getting a minimum pulse width of 1.38 ms being delivered (6% of 23 ms) and a maximum pulse width of 32 ms (140% of 23 ms). What you need to consider is whether that maximum pulse width in particular is realistic - For example if you're seeing a 32 ms pulse width at 6000 rpm for example, then cycle time is only 20 ms which means that you're at about 160% IDC which obviously isn't possible. I'd check your actual injector duty cycle to see what this is showing. It's possible you're compensating for a fuel system that is dropping in pressure and just barely able to achieve sufficient fuel flow.

Even on an itb setup I still run a MAP sensor into a balance pipe and then use the Load = MAP equation. This tidies up the inconsistent AFR you'll see as you drive an itb car on the road and the load varies as you go up and down hills. The only exception is if you've got very large cams that result in an erratic vacuum signal.

Thanks Andre, I think what your saying is most likely the cause as i've been quite dubious of the fuel system (was in the car when I got it). It had a very crude surge tank setup in the spare wheel well which I removed to regain a spare wheel, used the pump it had in place already as an inline pump and ever since it's operated loudly. The current fuel setup I've been regarding as temporary until I have some time to modify the fuel tank with an intank swirl pot. Now that the event i was hurrying to get the car done for is over (not the best way to do things!) I will go back and address those issues and see if I can get some more reasonable figures.

So if i add in a map sensor, I change to LOAD=MAP, but still use TPS as the load axis?

If you fit a map sensor then yes you change the load to MAP and still use TP for load axis.

The MAP calculation is a background calculation on your main fuel table

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