parallel fuel rail problem?? or fuel pump.

[kunchris]

hey guys

 

i am running a V2 STI ej20g in my legacy with aftermarket v5/v6 440cc injectors

a sard FPR set to 3.5bar base pressure, all in parallel fuel delivery,

vf22 turbo,

FMIC,

walbro gss341 fuel pump.

with an ESL ecu tuned at 1.3bar boost.

all this is running on a MAFless/ speed density setup.using a scaled v3/v4 MAP sensor.

 

(problem also occurs when i go back to using the MAF sensor)

 

occasionally and annoyingly, i get a small pop or bang while boosting especially on first gear and 2nd gear, this is accompanied by abit of a jerk in torque delivery.

the rest of the gears are fine.

 

i am running v7, coils and plugs are 6month old PFR6B gapped to 0.7.

 

while logging i'd pick up abit of knock counts when this happens.

 

this will happen occasionally after long traffic stops, slow driving or shutdown periods. id floor it and boost will kick in but there will be a small bucking with a pop. then the rest of the gears are smooth with constant torque and power.

 

sometimes it will boost just fine with no problems.

 

there is no CEL whatsoever.

 

i have an AEM wideband which shows a slight lean out during the pop, like a jump from 11.2 AFR to 11.9AFR then back to 11.2 then it stabilizes..

 

i have interpolated by fuel tables perfectly and my map works well in other cars, including rally cars with my ecu with no anomaly.

 

which got me thinking could my fuel pump be burping or not holding pressure correctly at high loads/low.?? why is it only on first and second gear??

 

the rest of the gears pull fine and hard with no problems. i have a slight lean out at the peak of my power-band... which also is not consistent. as most of the time its stable at 11.2 AFR.

 

i used T-Pieces while doing my parallel conversion. should i use Y-pieces?? could they be causing some constriction thus air bubbles??

 

i have been having this annoying problem for the better part of the year, but i have tried everything with no avail.

 

doesn't matter if i have a full tank of fuel or half a tank.

 

help and suggestions would be appreciated.

[Th3Franz]

440cc injectors are too small for a VF22 turbo running 18 1.3 BAR of boost.

I highly recommend at least STI pink injectors.

Also Y blocks are much better than T blocks for a parallel setup.

[kunchris]

440cc injectors are too small for a VF22 turbo running 18 1.3 BAR of boost.

I highly recommend at least STI pink injectors.

Also Y blocks are much better than T blocks for a parallel setup.

 

same thing happens even at wastegate pressure 0.5bar

 

the injectors have been fine at that boost level, so far.

 

will use Y-pieces hopefully this solves my issue.

[KCwagon]

I would maybe look at adding a fuel damper to the inlet side of the fuel system. You may be getting some unwanted pulses in the fuel delivery system, that are allowing flat spots when the injector opens. The issues of pulses only becomes more critical as fuel usage increases. The issue is more prominent on factory fuel rails/lines and factory FPR's. Some aftermarket FPR's (Aeromotive) utilize a diaphragm which act as a damper for the fuel lines, especially if the FPR is close to the rails.

 

Not sure how the SARD works though. What I do know, is that Subaru adds the damper to the fuel system for a reason. It might be worth a $40 try. If you already have dampers in your fuel system, I would look at their effectiveness, as these can go bad.

2 cents