Fuel pressure issues

[zfgracing]

So I'm pretty far as long in my 93 tune. I'm noticing an issue those. On my tip in I'm seeing these large fuel pressure drops. Enough that I'm tripping the insufficient fuel flow in the ddsl. It's wired because I only see it in tip ins. I don't think I'm out of fuel yet my turbo mass flows are in the 30lbs/min area in the location of the fuel pressure dip. Keep in mind I have no problem flowing 44lbs/min on the big end. I've got the little ko3s tapped out. I still feel like I have a lot gain in the 2500k to 4500k rpm range where my mass flow rate is in the low to mid 30s.
I'm not sure what would cuz such a sudden drop and then instant recovery like shown.



Fuel system wise I've targeted 2400 psi and increased the injection widow by 20* I'm also targeting afrs in the .81 range they are looking great. I've also turn up the voltage on the lift pump on the 2 highest flows.

I feel like I'm missing something.

[metroplex]

Am I reading that injector pulsewidth correctly?? I normally never see over 6 ms or so with my SHO.
Are you hitting any limits?

[zfgracing]

Am I reading that injector pulsewidth correctly?? I normally never see over 6 ms or so with my SHO.
Are you hitting any limits?

No, like I said I'm pretty far into it and have all the limits removed, or raised. It's likely the injector pw is so high because the fuel pressure is low in that spot so it's compensating once the fuel pressure recoveres the ipw returns to about 5-6ms like you say.

The big issue is that dip. I'll post up a few more examples it's always on the tip in. Even sometimes in spots where otherwise it wouldn't normally have a problem.

[zfgracing]

The only limit is insufficient fuel flow that comes on when the pressure drops enough to max out the injection window.

[zfgracing]

The drop is pretty much always right after a shift or right after tip in in the 3-3500 rpm range

[zfgracing]

So I think I figured out my issue. I look up the mass flow rate curve of the fuel pump (although I?m not sure on the credibility of the source, working with RTR to get the actual) and I did some math. Basically at the lamba I?m running at (.8) I generated the maximum air flow that could be supported based on engine RPM. It looks like I am indeed out of fuel pump at the places I?m having fuel pressure issues. I?m having problems in the 3000-3500rpm range; according to the math I?m able to support 33lbm/min-39lbm/min of air. Air flow wise I?m running about 30-35lbm in that rage. So I?m right at the edge of the theoretical. What I?m sure the mass flow rate I found isn?t taking into consideration is fuel temperature and pump slip. With those to, I?m sure the air supported is down in the range I?m running. So that sucks.

Out of this I put a ticket into Eric and the guys for 2 things to be added to the scanner.
1. Injection timing (SOI and EOI)
2. Calculated fuel pump mass flow rate
With those 2 we will know exactly how much air mass the fuel pump is capable of supporting at any given rpm and we will also know where exactly we are at in the injection window. This will allow me to reduce the fuel pressure (reducing pump slip) and increase the injection window if needed to commentate. If I can get down to a pressure where the pump slip is a little lower I should be able to support the air flows I?m at, if not I?ll have to turn it down a little bit in that area which is no fun! Other options I see would be leaning it out a little bit. Even going from a .8 to a .85 lambda is worth about a 2lbm/min of air increase in supported air flow.


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[Bugasu]

I created a spreadsheet to calculate roughly where the limit is based on data.
It doesn't do any correction for the HPFP's VE, but it gives a rough idea.

https://docs.google.com/spreadsheets...it?usp=sharing

[zfgracing]

I created a spreadsheet to calculate roughly where the limit is based on data.
It doesn't do any correction for the HPFP's VE, but it gives a rough idea.

https://docs.google.com/spreadsheets...it?usp=sharing

That's the goal of having HPT add fuel pump mass flow rate. then we will know for sure. I'm actually working on modifying my sheet know to do the theoretical calcs based on VE. ( totally didn't realize pump slip IE pump ve was right in front of my face!) One big problem that is see with that is fuel temp does have significant effect on mass flow rate. That HTP asks for the specific heat of the fuel I'm guessing it has a temperature correction built in. Also I see you put yours in hp which is fine but people forget that HP is a relative term when you are estimating BSFC. I think air flow rate is really a good way to look at the information, because you tailor your boost profile to that exact mass air flow, but then again there is a lot of people that don't understand how boost relates to mass flow rate and how mass flow rate relates to torque.

[Bugasu]

That's the goal of having HPT add fuel pump mass flow rate. then we will know for sure. I'm actually working on modifying my sheet know to do the theoretical calcs based on VE. ( totally didn't realize pump slip IE pump ve was right in front of my face!) One big problem that is see with that is fuel temp does have significant effect on mass flow rate. That HTP asks for the specific heat of the fuel I'm guessing it has a temperature correction built in. Also I see you put yours in hp which is fine but people forget that HP is a relative term when you are estimating BSFC. I think air flow rate is really a good way to look at the information, because you tailor your boost profile to that exact mass air flow, but then again there is a lot of people that don't understand how boost relates to mass flow rate and how mass flow rate relates to torque.

It was to just give people a ball park idea on the HP.
There is a temperature correction, as well as a correction for the assumed compressibility of the fuel (bulk modulus). Fuel temperature is inferred on everything with an HPFP I've seen, so no clue on how accurate it is.

[reubone]

but then again there is a lot of people that don't understand how boost relates to mass flow rate and how mass flow rate relates to torque.

need to study this subject myself. think i have the basic concepts but id like to have the math in my head

[zfgracing]

It was to just give people a ball park idea on the HP.
There is a temperature correction, as well as a correction for the assumed compressibility of the fuel (bulk modulus). Fuel temperature is inferred on everything with an HPFP I've seen, so no clue on how accurate it is.

1.9x10^5 psi I'm not sure how much of an effect that's going to have at the pressure we're talking about with this. I'm writing an actual program for this just because so I'll be able to not only take an account the volumetric efficiency but I'll be able to run it for different fuels and at different temperatures. I should have the program done by tomorrow maybe if I get super fancy I'll write a visual Basics program with the same logic so people can use it.

[zfgracing]

Okay so here is the flow chart corrected for VE. Next week I'll be working on doing the same but adding in a temp correction so we can see how temp effects the supported air flow.

[zfgracing]

I've been getting a few question on how max air flow relates lambda. So I have updated the pdf to included 0.75 lambda, 0.80 lambda and 0.85 lambda. You can see how each lambda ratio effects the max air flow supported.