Thread: STI injectors @ 4 bar fuel pressure. Anyone have any knowledge??

This is the common go-to solution*. Get things the way they should be for normal operating temp with your injectors by tuning the fuel table and other things at operating temp.
Then adjust the ECT enrichment at colder temps (you will want less enrichment now that you've tuned the fuel table properly) until it matches your goals well.

The initial reaction is to add fuel using the ECT enrichment so idle behaves. This is not the right way to do it and you'll find yourself chasing your tail. Reduce the ECT enrichment in the colder regions to make up for the weird injector behavior. Adjust the fuel table all over while warm.


*If injector flow rate and assumed injector dead-time values can't be manipulated directly.

This might be your best option. Being able to control the assumed injector dead-time directly is the proper solution to this problem. Getting those specs is the hard part though.


@Boostlee it is possible you'll need to use both solutions to get things right. Get the injector dead-time based on battery voltage curve sorted properly, then work on the warm-up enrichment and fuel map(s).

Thank you @BenFenner! That's what I figured would be the best bet considering the conditions.

As far as the injector dead time (or latency) specs, they are available online, with the caveat being for the 4 bar unmodified yellow tops (510-520cc). There is a mathematical equation which can get you in the ballbark however.


I would like to put forth another suggestion:
Scaling the injectors lower and run them @ 3 bar, but scale injectors to ~700cc (as an example) instead of the 800 (812, 811, 810, 812 ccs are the EXACT flow rates at 3 bar respectively from Witch Hunter) and going from there. I should have enough headroom in the fuel table to not reach the "ceiling" of the injector multiplier. Or terrible idea??

NOTE: The turbo is capable of ~440 lbs (so roughly 400 WHP), but won't be hitting near those numbers on the skreeet, so regardless of the scaling factor, I will run out of turbo before I run out of injectors.

@gomba: It seems the problems are related to modified yellow tops.

The latency (based on battery voltage; the higher the voltage, the less time it takes to open the injector) is always added to the calculated injector pulse width. It is NOT part of the pulse width calculation, as suggested above.

Thanks for the input! I waiting for either your or John to chime in!

What would you suggest at this point?

Generally, increasing fuel pressure increases latency, but I'll defer to John for more details.

Thanks! I will tag John.

@JKTUNING, any input??

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What injector latency are you using?

You will absolutely need to increase the latency as fuel pressure rises. If you are trying to use the OEM latency values at 4 bar and the modified injector, that is likely your issue.

John, I am using whatever latency values are scaled after inputting 940cc injectors (what they flow at 4 bar).

Current setup is 0.85 from 10.0 Volts to 16.4 Volts

"Well there's your problem."