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Title: Med9 Fuelling Post by: littco on April 07, 2016, 08:57:02 AM Looking at an S3 in particular with stock pumps IE No HPFP and stock FPV
Just trying to get a better understanding of the fuelling on these cars LPFP feeds HPFP, and then we have the FPV to vent pressure above the max of the valve. Requested fuel pressure maps and the sensor regulate the rail pressure and then the injectors opening times control AFR as requested by the ECU. So for any 1 AFR request we could have 2 injector MS. Ie low Rail pressure and high injector MS or high rail pressure and lower injector Ms giving the same fuel flow. in much the same way the 1,8t could have a 3 or 4 bar FPR with the same injectors and get differing flows . So my question is how much can you push the stock HPFP/rail pressure maps and what is an acceptable Ms for the s3 injectors before you need to upgrade to a Larger HPFP? Obviously the answer is to run the car up with increasing load/boost and then increase in the rail pressure to try and maintain the required AFR and MS to the point where requested and actual start seperating or InjMS gets to high/maxed but does anyone have info on where you can start to expect this? Title: Re: Med9 Fuelling Post by: gman86 on April 07, 2016, 04:57:38 PM Your summary is pretty much on the money.
Stock pump will safely do ~340lbft in the midrange and ~350bhp top end. It's midrange limited due to the fact it's cam driven (3 lobe cam, actuates 1.5 times per engine RPM). Facelift S3 (CDL engine) has a slightly longer stroke on the pump (extra 0.3mm) which doesn't seem much, but it's enough to make a difference. If the actual rail pressure deviates too far from requested, there is a specific map that specifies load on E_hdr. Injection time ideally needs to stay 10ms or less. Any more and you'll start to see fuel trims heading towards 25% and start missing your AFR target. Title: Re: Med9 Fuelling Post by: littco on April 07, 2016, 11:37:59 PM Your summary is pretty much on the money. Stock pump will safely do ~340lbft in the midrange and ~350bhp top end. It's midrange limited due to the fact it's cam driven (3 lobe cam, actuates 1.5 times per engine RPM). Facelift S3 (CDL engine) has a slightly longer stroke on the pump (extra 0.3mm) which doesn't seem much, but it's enough to make a difference. If the actual rail pressure deviates too far from requested, there is a specific map that specifies load on E_hdr. Injection time ideally needs to stay 10ms or less. Any more and you'll start to see fuel trims heading towards 25% and start missing your AFR target. Thanks Gman, Gives me something to work with.. Finally the figures here are BAR? Title: Re: Med9 Fuelling Post by: Beaviz on April 08, 2016, 02:29:58 AM Title: Re: Med9 Fuelling Post by: gman86 on April 08, 2016, 03:49:34 AM MPa ;) Yep. Set the factor to 0.005 if you want to express in bar. Title: Re: Med9 Fuelling Post by: SB_GLI on April 08, 2016, 04:25:45 AM Thanks for posting this topic. If only all threads were questions with answers in the first post!
Title: Re: Med9 Fuelling Post by: littco on April 08, 2016, 05:53:09 AM MPa ;) I've already set the conversion to 0.005 so just confirming that is bar. Thank you.. Title: Re: Med9 Fuelling Post by: littco on April 08, 2016, 05:57:16 AM Thanks for posting this topic. If only all threads were questions with answers in the first post! There's is some good info on here already but it is a bit sporadic and very much like the Me7 was 5 years ago before s4wiki appeared. So, I will hopefully add so more as it goes on. Maybe a MED9 Wiki is needed... I'll post up the stuff on the fuelling in due course and also uprated HPFP stuff, again there is some info on Nef about it but it's not complete and spread over 2-3 posts. |