fuel cut logic for boost control

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rac
Posts: 13
Joined: Tue Aug 14, 2018 5:06 am

fuel cut logic for boost control

Post by rac » Tue Jan 15, 2019 5:17 am

Seeking clarification on this.

Running 1.87 n54 pnp kit.

I've been having fuel cut kick in to manage manifold pressure where the manifold pressure exceeds manifold target (Wastegate Control -> Manifold Pressure Target) and as modified (reduced) by target adjustment for gear (Calibrations -> Boost Control).

The relevant fuel cut severity appears to be determined under "Limiters -> Manifold Pressure Limiter". However this section also includes its own Pressure Limit maps.
Original I thought the fuel cut strategy under "Limiters -> Manifold Pressure Limiter" was only relevant to the “Pressure Limit Base”.

I feel like “Pressure Limit Base” figures and an aggressive fuel cut strategy were intended to be used as a global safety cap to prevent exceeding MAP sensor range or other safety considerations, but then it seems I am also having this same fuel cut strategy apply to the lower pressure target specified elsewhere.

So would I be right in assuming the "Limiters -> Manifold Pressure Limiter -> Fuel Cut Severity" table applies to both “Pressure Limit Base” OR “Target Limit” (and as modified for gear), whichever is lesser?

Thanks.

rac
Posts: 13
Joined: Tue Aug 14, 2018 5:06 am

Re: fuel cut logic for boost control

Post by rac » Sun Jan 20, 2019 5:44 am

think I eliminated MAP limit related fuel cutting, still have fuel cuts on me and seems to be more correlated to total fuel flow / fuel supply pressure might not be up to it.

stevieturbo
Posts: 834
Joined: Sun Dec 07, 2008 2:04 pm

Re: fuel cut logic for boost control

Post by stevieturbo » Sun Jan 20, 2019 10:08 am

If you log trqfuelsev it should state the amount of fuel cut and trqfuelsevsrc the reason.

And maplimitbase should indicate the cut threshold at that time ? ( boost cut anyway )

Not sure where the wgmaplimit plays into the above if at all....that's just the actual target stuff, rather than cuts ?

As for fuel pressure etc....is it and relFP behaving ? What are the trips set at ? Again the warning flags for amount of fuel cut should indicate if a trip is doing anything ( including limpmode )

So log all those items to see

Pressure Limit Base should indicate the total cut pressure....scaling up to this as per Fuel Cut severity, so if this has a range of 100mbar then trqfuelsev should start to show cuts 100mbar prior to pressure limit base ( scaling up from 0% to 100% at pressure limit base )

At least that's how things seem to behave on mine.

Would be interested to hear how you get on with the N54, as a friend recently got a 1M and wants to do his.

rac
Posts: 13
Joined: Tue Aug 14, 2018 5:06 am

Re: fuel cut logic for boost control

Post by rac » Sun Jan 20, 2019 1:57 pm

yeah I will pick up more of the fuel logging parameters. Initially the fuel cuts just coincidently happened near the map target. I since ran lower map targets and everything ran happily.
The HPFP is nowhere near target when this happens so I'm going to log its parameters and also change the split to more port injection and see if that helps.

But my LPFP is also going erratic when this happens, which means its underdone or its a side effect of the fuel getting cut.
I havent hit the low fuel pressure limp, double checked that many times. car doesnt go into limp, just sounds like antilag which i presume was a bunch of fresh air going through a few cylinders and igniting unburnt fuel in the manifold.

thanks for this suggestion, logging trqfuelsevsrc.

as far as the n54 goes, it's nice to have my widebands post turbo (I have a single turbo on a RHD car), no space in there.
the sequential injector split from DI to PI also works really well.

the only PITA so far for a novice like me is tuning cold start/hot start, AFR for an engine warming up. I previously under appreciated how much difference engine temperature makes....
I didn't like tuning against TPS either. I switched to MAP base for load and its made life much easier.

rac
Posts: 13
Joined: Tue Aug 14, 2018 5:06 am

Re: fuel cut logic for boost control

Post by rac » Sun Jan 20, 2019 2:21 pm

actually, I've seen so many logs now I've forget what I have already logged...

trqfuelsev = 0 during the event, and then goes to 30 when i let off the pedal. looking back at that log, its possible the sample rate was too low. i'll check that out.
Last edited by rac on Sun Jan 20, 2019 2:37 pm, edited 1 time in total.

stevieturbo
Posts: 834
Joined: Sun Dec 07, 2008 2:04 pm

Re: fuel cut logic for boost control

Post by stevieturbo » Sun Jan 20, 2019 2:23 pm

trqfuelsev will cover all fuel cuts. So letting off pedal it could cover the overfun fuel cut. It's just the percentage of cut at any given time.

not the reason for the cut.

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