Fuel pressure drop question

[Rem0v3r]

Zl1 fuel pump with zl1 programmed fscm on boosted ss.
Car hit 9psi boost fuel pressure dropped to 40psi. I got knock on 2 different logs around the 5400rpm area.. (yes it was knock). wideband said afrs were low 11s high 10s in both cases.

Timing was 13 degrees on 93 pump gas only. Sea level. 80/90f iat. 1.9 cyl grams.
Ill preface by saying it overboosted and i usually run 6-8psi.. 9 psi was not on the menu.

Could the low fuel pressure have caused the knock even though the wideband showed it wasnt lean?

[Pro-tuned]

Resolve fuel pressure issue and log.

[Greenhornet2]

Fuel pressure dropping isn't good. I an steady at 58psi with ZL1 pump and FPCM from Jannetty maxing out at 11PSI. I am at around 600WHP and am told this setup will support up to 650WHP.

[stevieturbo]

Originally Posted by Rem0v3r

Zl1 fuel pump with zl1 programmed fscm on boosted ss.
Car hit 9psi boost fuel pressure dropped to 40psi. I got knock on 2 different logs around the 5400rpm area.. (yes it was knock). wideband said afrs were low 11s high 10s in both cases.

Timing was 13 degrees on 93 pump gas only. Sea level. 80/90f iat. 1.9 cyl grams.
Ill preface by saying it overboosted and i usually run 6-8psi.. 9 psi was not on the menu.

Could the low fuel pressure have caused the knock even though the wideband showed it wasnt lean?

How do you know it was knock ? Were you using a proper detection device aside from what the ecu was recording ? Or if it was audible by your ears...then it would have been fairly severe.

And of course there could be knock regardless of what the wideband says. Timing is far more critical than AFR's

And where are you monitoring AFR's ? a single wideband, a wideband per bank of 4 ? It's easy to see how a wideband whilst very important...can also be of limited use really when things start to go amiss. Especially a single wideband on a V8.

But....bare in mind here. You say fuel pressure dropped to 40psi, that along with 9psi boost, leaves you only 31psi of actual pressure to inject fuel. That is pretty low.
It will affect performance, it will affect what's happening in the chamber etc etc. If you were tuned for a normal fuel pressure of what 60psi or thereabouts ? Or are you lower and boost referenced ?
It's hard to see how such a huge drop in pressure did not cause mixtures to be bad somewhere unless you have some sort of fuel pressure monitoring and compensations applied.

Anyways, you dont seem to be saying there is anything wrong with the motor, or any harm has been done.

Fix the problems and move on. Both whatever causes your fuel pressure to get so low, whatever caused the overboost etc etc

[Rem0v3r]

Originally Posted by Greenhornet2

Fuel pressure dropping isn't good. I an steady at 58psi with ZL1 pump and FPCM from Jannetty maxing out at 11PSI. I am at around 600WHP and am told this setup will support up to 650WHP.

Dang, thats pretty good.
Ive turned the boost down for now. Will get an aux fuel system and switch to e85 soon then relog. Thanks guys.
I agree, i think the 31 psi effective fuel pressure is too low and probably causing my injectors to piss the fuel out instead of misting it and causing poor fuel burn.

[Greenhornet2]

Yea i'm not on E85. Wouldn't support that running E85.

[Rem0v3r]

Me either.. 93 pump gas only.. gunna get an aux pump and make the switch

[Greenhornet2]

Originally Posted by Rem0v3r

Me either.. 93 pump gas only.. gunna get an aux pump and make the switch

Good plan. I was looking at the dsx aux pump. Post what route you go and how it works out I'd like to see the results. I am almost wishing i just went with an aux pump and didn't buy the bap. I'm doing the cam this winter and am hoping to get around 700whp. I should be ok for this, but i'll out grow it if i forge the bottom end.