When using a cam with an oversize fuel pump lobe are people adjusting the fuel pump start angle table? Seems like if I understand how things work it would take less start angle when the stroke is increased by an oversized fuel pump lobe.
When using a cam with an oversize fuel pump lobe are people adjusting the fuel pump start angle table? Seems like if I understand how things work it would take less start angle when the stroke is increased by an oversized fuel pump lobe.
I believe you edit the row axis on the leading edge angle. Multiply whatever percent fuel lobe you have to the entire row. This will edit both leading and trailing edge angles.
Could you share a little more about the leading edge angle? I'm not seeing it anywhere in the tune.Quote:
Originally Posted by SILV
Under fuel system tab
This is the table I am talking about. It seems to me that the table would need some sort of update based on a factor related to the fuel pump lobe. I don't see much in the scanner related to the pump control though.
Attachment 99660
That tables does need to be calibrated for larger cam lobe, info came from an OEM calibrator to do so
Yes that's the table. I dont know your application but it looks like the row has already been modified.Quote:
Originally Posted by DanLeeWatson
So how do I go about doing that with HPTuners? I don't see much in the way of pump channels in the scanner.Quote:
Originally Posted by Ben Charles
You just update/edit the row axis values to reflect the percentage of increase in the pump’s output volume.
Click on the row axis title to edit it.
How are you determining the pumps new output volume? are you just assuming it is the same as the % called out on the fuel pump lobe?Quote:
Originally Posted by crankz1
Yes. Like SILV said above.
Ok, but how are people verifying this actually works properly? I can't find anything in the scanner that shows error or correction for pump pressure. I would think this table is the primary means to correct under and overshoot in the rail pressure but I never see it talked about.Quote:
Originally Posted by crankz1
When I put in my 32% fuel lobe I never really noticed many fuel pressure issues, it appeared the commanded and desired behaved like stock. Anyway I multiplied the entire row axis by my new fuel lobe cam value (1.32) like SLIV said. I didn't notice any difference though but I feel better that its now "fixed" at least.
I have a 38% fuel lobe and previously was using the stock Leading Edge Angle settings. In an attempt to reduce pressure spikes when quickly transitioning from high fuel demand to low fuel demand, I modified this the fuel volume axis. In my case, it messed up the fuel trims at idle where no matter what I changed, I couldn't get them dialed back in (20%+ error at idle). I tried multiplying by 1.38. I also tried an interpolated multiplier from 1 to 1.38 at the highest flow. Each test resulted in seemingly uncorrectable fueling. If I change it back to stock, it's fine. If I multiply by a lesser value, say 1.10, it introduces a smaller amount of error. Whether the table is modified or unmodified, the rail pressures stay really close to commanded (aside from the spikes when fuel demand rapidly drops).
Has anyone experienced this? I have no idea why this messes up fueling, but it does in my application (2017 Camaro ZL1 M6).
Any ideas on reducing momentary rail pressure spikes (5,000+ psi) with a large fuel lobe?
I hope it's OK if I jump in with a question also because I'll soon install a cam with larger fuel lobes. (I know it's an old thread)Quote:
Originally Posted by travislambert
Fundamentally, the larger fuel lobe strokes the positive displacement HPFP more, so it pumps more fuel, and it is fixed to the engine RPM (unless I'm missing something) - so the pump creates the pressure; my question is, what relieves the pressure to maintain desired pressure? It doesn't make sense to me that it would just be fuel injectors to relieve pressure because they need to deliver the rate of fuel the engine needs, which is different than the amount of fuel pressure needed to be relieved to control fuel pressure. So how is pressure controlled?
Did you ever figure this out? I am seeing the same exact thing with a 38% lobe. When I lift off after a pull I am seeing spikes of 4000-5000psi. Is this acceptable? Or is there a fix?Quote:
Originally Posted by travislambert
One thing that was never mentioned in this thread was the pump type. You should start with the stock leading edge table that the HPFP in use was designed for. If running a LT1 hpfp pump, then you need to start with a LT1 table. If running a LT4 pump, then you need the LT4 table. If running a LPE big bore, you need to use the LT1 table. Then you multiply the row axis buy the fuel lobe percentage. I only mention this because many have upgraded from a LT1 hpfp to a LT4 or LPE. Or went from a LT4 to LPE. So, you need to make sure to start with the correct base table then modify it per the fuel lobe percent.
Did the guys having spike problems and not seeing expected results with this table, find that they were starting with wrong table? Or still doing the odd stuff regardless?
Starting with the wrong data in the angle table and then multiplying the axis by the fuel lobe can cause excessive spikes.
LT4 pump supposedly, lt4 injectors, cam with 34% lobe on it, with all the LT4 info in it and axis mult by 34% Im still seeing a spike after letting off from commanded 2600psi to @4000psi? This is on that car with the weak power in other threadQuote:
Originally Posted by TriPinTaZ
The pressure spikes are inherent to the larger fuel lobes. The orifice in the pump simply cannot return enough fuel back out of the piston bore and the fuel backs up and causes the pressure to go high. I discovered it on road race applications years ago. Causes stumbling at light throttle high rpm mid corner. Have since gone away from the 32% and 38% lobes. You can still max out lt4 injectors with a 27% lobe and the pressure will only spike to upper 3000's.