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Direct injection pressure fails at low RPM


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Firmware, software, though I didn't see anything in the notes for about GDI changes.

I have a weird issue where the fuel pressure tracks just fine at 6k RPM, up to 0.0696 g fuel/cyl with a 5.188ms injector duty cycle at 200 bar, but it won't track at 3k RPM, above 0.055 g fuel/cyl with a 4.070ms injector duty cycle.  It's a Bosch HDP5.  It seems that it should be able to handle the same fuel flow rate per cycle in either case.  Interestingly, it looks like the GDI Pump Control makes no attempt to make up for the fact the fuel pressure is falling (see log).

I will admit most of my GDI parameters are guesses, but it seems the GDI Pump Compensation table can (crudely) mask deadtime (at one voltage) and pump calibration.  I have tried other lobe TDC angles to no avail (usually makes it worse).  I also tried other maximum cc/lobe values (thinking perhaps I was exceeding a the upper limit on duty cycle) but it didn't help either.  As it is, the cc/lobe * # of lobes * fuel g/cc is well above the required numbers above.

If it matters, the pump is driven by the exhaust cam, which is trigger #2 and VVT.  However there are VVT changes on the 6k RPM run and pump control is relatively steady there.

Attached is a log where RPM was held at 3k RPM while throttle was progressively fed in.

Also, what is "Spill valve on angle?" Is it a minimum amount of time to energize the pump?  In which case why is it different than "Minimum pump angle?"



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Can you attach the tune too please.  Certainly looks like it might be related to cam position in that log.  If you set the exhaust cam target to 0 (or disable the VVt sol) as a test does pressure then control any better?

1 hour ago, Scott33 said:

Also, what is "Spill valve on angle?" Is it a minimum amount of time to energize the pump?  In which case why is it different than "Minimum pump angle?"

"Minimum pump angle" is the threshold below which the pump solenoid wont be activated.  So for instance if the volume calculation determines the spill valve needs to be activated for 9° to correct the fuel pressure on the next stroke, and you have a minimum of 10° set, then the solenoid wont be activated for that stroke.

"Spill valve on angle" is how long the solenoid is held energised for.   With a normally open pump like yours, once you have energised the solenoid, the pressure in the pump instantly builds and as soon as piston pressure exceeds the rail pressure that pressure holds the valve closed all by itself - you dont need to keep power on the solenoid to keep it closed.  It will stay closed until the pump reaches the top of the stroke and pressure under the valve reduces.   

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I emailed that along with a 6k rpm run to tech support.  Hopefully it reaches you.

I can really only test this on a dyno or race track, and I don't easily have access to either right now.  I think the VVT is a red herring.  I have tried lobe angles at -10 and +10 relative to what is in that tune (which is how far the exhaust VVT moves at 3k RPM), and it still drops off at the same point.  Also, the 6k rpm run has VVT movement and works fine.

I'll repeat what I said before - the GDI Pump Control is actually DECREASING while the pump pressure is dropping.  It's almost like it's being forced down by some clamp.

Thank you for the description on Spill Valve On Angle.  I didn't realize the pressure keeps is closed until it isn't needed.

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