SCT Prp help

01blckcobra

Active Member
Established Member
Joined
Sep 5, 2009
Messages
314
Location
Wisconsin
03 cobra AMZ2 return style fuel system, unleaded. rc750, hpx 4"

Having issues with the A/f leaning out at WOT 4k and above. I replaced the regulator but forgot what the base pressure was at. A/f looks like the Rocky Mountain Range, from start wot (.775) to as high as 1.15 a/f. Commanding .773
Looking through the tune on SCT Prp, Under Fuel injectors - Pressure drop across Injectors is set at 37psi. Now under Returnless fuel pump - Desired Pressure Drop Across Injectors is 49psi.

Had base pressure set to 49psi. Car still leans as much as 1.15 at Wot. Tried base of 52psi same results.

New to tuning so have no Idea what any of this means or if any of this matters with a return style fuel system.

Or do I need to play around with the base pressure to find the sweet spot again?

The car still has the FRPS intact. Guessing the tune is based on what the FRPS sees, but not sure.
 

decipha

Well-Known Member
Established Member
Joined
Jul 12, 2008
Messages
1,019
Location
New Orleans, LA
if its leaning our first verify its not loosing fuel pressure and that the pump duty cycle isnt maxed out at .50 == 100%

if all checks out then just go kick up the maf 35% or so up top and dial it in
 

01blckcobra

Active Member
Established Member
Joined
Sep 5, 2009
Messages
314
Location
Wisconsin
Magnafuel protuner 750 pump. an 10 feed and return. Fuel pressure on FRPS maintains 50psi through WOT pull. Had a fueling issue before due to faulty regulator, why it was changed. Regulator is confirmed 1:1 fuel pressure through separate gauge
Injector duty cycle is .46-.55 through lean spots.

Will try increasing maf 35%. Kinda thinking about it but wasn't sure if it was due to base fuel being off with tune.

So really doesn't matter on a return style setup what base pressure is? just set base pressure to w/e and adjust maf to dial in fuel? Sorry I'm a newbie :)

Edit: Basically wondering if I have to do anything (adjust) fuel pressure in the tune itself. Under the "parameters?" Say the "Pressure Drop Across Injectors"
 
Last edited:

decipha

Well-Known Member
Established Member
Joined
Jul 12, 2008
Messages
1,019
Location
New Orleans, LA
as long as you have the correct injector data in your tune and preasure compensation enabled then you can change the base fuel pressure all you want and the ecu will adjust the injector data for it using the deltaP functions

if you do not have the deltaP compensation enabled then you will have to manually recalculate the injector data anytime you change fuel pressure and plug those new values in your tune.

i see your return style, pump dc doesnt matter

you should leave all the fuel deltap modifiers intact so the ecu will compensate for any pressure loss or base fuel pressure changes, be sure to disable the adaptive fuel pump voltagw corrections

do not mess with the pressure drop across injectors since the fuel pump isnt controlled by the ecu it wont change anything

make sure your frps still has a mainfold reference so it reads deltaP and not actual rail pressure

sounds like you just need to kick up the maf
 

Mike Dj

Member
Established Member
Joined
Feb 12, 2008
Messages
242
Location
Delaware
Look at your Base fuel table under fuel and make sure it is letting the fuel curve enrichen at the given spot you are having the problem.
 

01blckcobra

Active Member
Established Member
Joined
Sep 5, 2009
Messages
314
Location
Wisconsin
Decipha was right, MAF functions needed adjustment. As much as 45% so far.

Addition information - might be helpful to someone later on.

Previous tune was for bone stock engine. Cars best run was 9.5 at 143.5 mph

It melted a piston on the street with 14psi

So after the rebuild, the car would always fluctuate A/F at above 4K pretty rapidly. Figured the tune was off. Tried to tune it but no change. Tried different injectors with good known data. No change.

Ended up going through the whole fuel system, vac line, lol you name it. everything pretty much had been replaced with new.

Well long story short the MagnaFuel 9950-B goes bad pretty quick. They will "bench test" okay but in real world it didn't work. The brass plunger wears very quickly against the stainless seat. I mean 4-6 good hits and the plunger is shot. Will not regulate fuel properly. "hold pressure" Would have a 3,5, 6, and whatever it felt like psi drop across.. Took 3 regulators to figure this out for me. lol new doesn't always mean good i guess.

Ended up going with FORE. Only experience a 2psi drop. Had no more issues and the car taking adjustments perfectly. Still not sure why the MAF is off so much but getting her dialed back in nicely now.
 

Users who are viewing this thread



Top