So I checked my base fuel pressure...

[c-rad]

I've been having some richness issues with my car since...forever. My idle AFR is erratic jumping from a normal 14.5-14.7 down to the low 11s at times. Sometimes while cruising it's the same deal. Suspecting it to be my walbro overrunning my stock fpr, I ordered a fuel pressure gauge to put inline between the filter and rail. Well, with the vac line DISCONNECTED I get 42psi and with it CONNECTED, I get 34psi. According to the FSM and searches on both here and sxoc I've determined that the pressures should be 36 and 28 accordingly. So would being off just 6psi be enough to wreak havoc on my idle AFR and rich condition under WOT?

[oversteer180]

Possibly with the stock ecu. Seems kinda weird though.

[r34 gtr]

screw the stock fpr!!!

i would say mine does the same but i dont have a wideband

[biosehnsucht]

yeah thats WAY off. think of it this way.. thats like what, 16% too rich?

[float_6969]

Actually it's not. The pressure isn't directly related to the amount of fuel injected. IIRC, you have to quadruple the pressure to double the flow. At least that's what I heard...

[dattodude]

6 psi will make a difference.

Adjust it back to where it should be, and then tell us how the engine behaves.

I use a walbro and sard reg on mine. I have aftermarket ECU, and I run 45psi base pressure, and on the dyno I watched it rise to 65 psi under full boost 1.2bar. It makes me rethink about reusing EFI fuel clamps!? :-)

[float_6969]

I think a good number of people have noticed a difference for the better by turning the fuel pressure back down.

[sideways danny]

sounds like you have an intermitent O2 sensor fault to me

[float_6969]

Well look what I just found...http://www.csgnetwork.com/fiflowcalc.html

At 42psi your 550cc injector becomes a 594cc injector. That's about an 8% increase in fuel volume.

Consequently, if you quadruple the base fuel pressure from 36psi to 144psi, the fuel volume increase is 100%, which agrees with what I stated earlier.

[c-rad]

Well, I have 450cc injectors... and by using that calculator, my injectors go from 450cc at idle to acting like 500cc injectors. At 15psi, the fuel pressure SHOULD be at 51psi. In my case with the 6psi variance its at 57psi which is like having 475cc injectors. And that's only if the variance is linear which I doubt it is.

[float_6969]

I concure. I seriously doubt that it's off by 6psi across the entire load and rev range.