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Discussion Starter #1
cliff notes on the car. Stock cubes, kong 2650, 112mm tb, built bottom end, fuel system is aem drop in pumps and AUX pump. e85 car.

So I am getting weirdly inconsistent fuel pressure issues. My tuner (well regarded) who has never led me wrong seems to think its my AUX pump not coming on "fast enough". I am not sure I agree as the log its showing me good fuel pressure on the hit for a few hundred rpms, then the fuel pressure drops off to 50 (injector pressure is on the 20's and idc compensate) from there the pressure holds until about 5000 rpms where the fuel pressure then ramps up to 70psi (around 50psi injector pressure) and holds. If I make a multi gear pull it will sometimes hold through the other gears. I do have a couple pulls where it dipped again in the middle rpm range.

I have emailed DSX about the AUX controller seeing if that could be on its way out. I dont have the units with the test buttons so I am trying to figure out how to diagnose if this is a AUX controller issue, AEM drop in pump issue, or maybe a lack of fuel pressure (but I dont understand why it recovers later in the rpm band and instantaneously)

The other odd thing is the requested fuel pressure stays at 50psi until about 5000 rpms when it jumps to 70 psi. My tuner said this isnt something he controls because at first I thought the second pump wasn't activating.. When I log the second pump activity (on/off) it says off all the time, even once the fuel pressure recovers as well so im not sure that pid is accurate either.
 

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You've probably already seen this but I stumbled accross this today:


Not sure if it would help.
 

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Discussion Starter #3
You've probably already seen this but I stumbled accross this today:


Not sure if it would help.
I actually havent, I will have to read it a couple times to try to process it all but thank you!
 

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Discussion Starter #4 (Edited)
So I checked my Max Deisred pressure, it matches my high flow desired pressure so I should be good there.

I am now looking at my regulating pressure table and I am not sure if its been edited or not, I am going to dig into my files and see if I have a stock FSCM. The DSX post says to increase this table but I am unsure where and how much so I dont want to tinker without knowing.
 

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Discussion Starter #5
Found my stock FSCM and it does look untouched. now the question is, how much do these values change as the DSX blog says to increase these numbers, but I dont know how much to increase them by.
 

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What’s your voltage doing? Both pumps are on the Same wiring that splits just before the pumps. Can’t log Seperate pump channels really.

I was chasing a similar problem and had to redo my alternator pwm tables

Also, the commanded fuel pressure is totally tunable based on fuel usage rate. With scaled injectors, these all need work to behave like stock.
 

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Can you tell us which tuner you are using?

Sent from my SM-G965U using Tapatalk
 

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Reading more of your posts...lol

I was unaware of the regulation pressure table...interesting

You need to make sure your commanded pressure peaks as soon as you stomp it.

To do this, figure out the lowest rpm you want to be able to hit wot, and back calculate fuel usage from maf and lambda data.

Go to your fuel flow tables and see what needs adjusting to change switch points.

I’ve never read anywhere much discussion on the alternator table...it is idc max and voltage commanded based on fuel flow.

With a double half scaled tune, the car always thinks it’s flowing half the fuel it is. This will shift all those tables.

I changed my alternator to kick in 99% DC
Much sooner and now have steady voltage from low rpm stomps all the way up (where previously it would hit lean, then pull inline from like 5k up (after stock fuel flow limits are triggered)
 

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Discussion Starter #9
Reading more of your posts...lol

I was unaware of the regulation pressure table...interesting

You need to make sure your commanded pressure peaks as soon as you stomp it.

To do this, figure out the lowest rpm you want to be able to hit wot, and back calculate fuel usage from maf and lambda data.

Go to your fuel flow tables and see what needs adjusting to change switch points.

I’ve never read anywhere much discussion on the alternator table...it is idc max and voltage commanded based on fuel flow.

With a double half scaled tune, the car always thinks it’s flowing half the fuel it is. This will shift all those tables.

I changed my alternator to kick in 99% DC
Much sooner and now have steady voltage from low rpm stomps all the way up (where previously it would hit lean, then pull inline from like 5k up (after stock fuel flow limits are triggered)
You would think command pressue would be based on tps or something like that because you can go wot at idle from a dig.

I did some reading and apparently the CMD fuel pressure is based on fuel flow numbers. I am going to see if I can add that pid so I know what my fuel flow is doing while I am WOT and maybe I can adjust that table to cmd higher pressure
 

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If you have your maf data you can back calculate fuel usage from eq ratio.

Or setup a pid to do it for you. Still don’t need new logs. (You can create custom pods after the fact I believe)

Lots of stuff is fuel flow based because the flow rates change so dramatically with throttle. But i see your point it could be tps on a blower car...

...and did I not say commanded pressure is based off fuel flow? :)

Did you not just go to 1300s? That would explain this stuff possibly. Or am I mistaken?
 

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Discussion Starter #11
You are correct I have ID 1300s in the car. I have to run the fuel flow numbers, I had another little surprise today losing 2 bolts out of my diff and having fluid come out. I assume this is because I put a 1 piece drive shaft in the car and it had a vibration and I drove it for about a week. So I guess it backed out those bolts. Back on the stock DS and the bolts are back in and all the rest checked and I think I dodged a big on there. Now back to this fuel flue stuff.
 
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