Stay with me on this it gets kinda crazy...

I had a 10.5:1 A/F, started at 9:1 at 3500 RPM and went to 10.5:1 at redline, with my 10:1 FMU

OK.. so I get an 8:1 FMU and put it in my FMU, changing FROM a 10:1 FMU.

So now I dyno and at 3500 RPM I am at 8:1 A/F and then climbing to 10:1 at red line THUS making LESS power


OK so I am now RICHER wiht the 8:1 FMU than with a 10:1 FMU

So I switch the fuel lines to the FMU, no help.

I switch BACK my 10:1 FMU and dyno again and now I am STILL at almost the EXACT same A/F as with the 8:1

SO, I switch the fuel lines BACK on the FMU, NO change.

Things that have changed since my last dyno....

1) My vaccum cannister for the MEVI was leaking, I fixed it no leak

2) The dyno shop has gone to new equipment/program for A/F, BUT he tuned 2 cars today with laptops on board and everything was good with them.

So I am so lost and confused.

Any help??????????????????????????


Thanks

BAGS

 

That is strange that you got the same AFR right after changing back to the 10:1. Is your fmu stuck at a particular fuel pressure? Do you have a fp gauge?

 

What fuel pump set up do you have.

Most pumps will fall off their ability to flow as the pressure gets
higher. For instance, the Walbro GSS342 will support...
@ 40psi-60gph~720bhp
@ 50psi-56gph~650bhp
@ 60psi-52gph~620bhp
@ 70psi-49gph~588bhp
@ 80psi-44gph~528bhp
@ 90psi-37gph~444bhp
@100psi-27gph~325bhp
@110psi-13gph~156bhp

As you can see after 90psi is falls off real hard. Remebmer this is BHP not WHP so subtract drive line loss and it get even worse. This may not be your problem, but it could be, this is also a best case 14.4 volt situation, err on the side of caution.

Even at a higer pressure with a 10-1 FMU disc you may not be able to flow enough fuel to support you needs, hence it was leaner with the 10:1. Try a 6:1?

 

Mardi the gss342 is the 255 hi-flow correct? That is what I have.


But with an 8:1 FMU and 7 PSI of boost... that puts me at 56 PSI and If I remember correctly WOT stock fuel pressure is 46 so I was at 102 PSI, if everything was correct. I do need a fuel pressure gauge.

And I now understand why it was leaner, it was runnig out of "breathe" so it was ACTUALLY pushing less fuel.

WOW, ok thanks.. I will try and locate a fuel pressure gague soon and do some testing

And NO on the 6:1 I only had a 8:1 from bosco and my 10:1.

This has brought a new question, so I guess I will post that.

 

Based on Mardi's post wouldn't be better to just ditch the FMU setup and just run some 370cc injectors? A device like the greddy emanage or maybe the SAFC could probably help.

 

See my other post..lol

That is what I am tyring ot fugure out, BUT you'll need a rising FPR to get the fuel pressure up. Then a SAFC to trim it out.

AND IIRC matt has a 3:1 FMU.. I could be wrong

 

yes 3:1
with emanage i will ditch it