How much is the operating fuel pressure on our cars?

MMamdouh · Post by **MMamdouh** » Thu Sep 29, 2005 12:58 pm

Hi guys... i know it was discussed before but i am a little confused

is it 34 psi or 43 psi?? i am talking about Lanos fuel system here on both the 1.5 and 1.5 engines.

also if it is any different, please sepacify how much fuel pressure the Nubira and Leganza uses?

MMamdouh

smo · Post by **smo** » Thu Sep 29, 2005 6:54 pm

On the 2001 Nubira, the factory service manaul specifies 41-47 psi, (or 284-235 kPa).

ubuyau · Post by **ubuyau** » Thu Sep 29, 2005 9:06 pm

I have the 1.5 SOHC with the newer looking fuel rail (not the big silver one) and the base idle fuel pressure was 34psi. I measured this before i put the RRFPR on...

I've bumped this to about 41psi though and i got low 14:1 a/f ratio at idle on the wideband.

--Tim

MMamdouh · Post by **MMamdouh** » Thu Sep 29, 2005 10:20 pm

IC... does the fuel pressure vary due to the fuel rail shape? i mean i have the same engine as yours but i got the old shape fuel rale so does it mean that my fuel pressure is different than what you have?

MMamdouh

ubuyau · Post by **ubuyau** » Thu Sep 29, 2005 10:45 pm

I dont know... i would assume not. arent the silver fuel rails bigger? so more volume = less pressure? but then again its such a small part of the system that it probably makes little if any difference anyways...

--Tim

MMamdouh · Post by **MMamdouh** » Thu Sep 29, 2005 10:59 pm

i think it is more about the fuel pressure regulator setting rather than rail size.

it would only need more work from the fuel pump to maintain the same fuel pressure in a bigger fuel rail but again how much bigger are we talking here? the way i see it is that the size difference is not that relevant.

BTW: how does the OEM fuel pressur regulator work?? i see it is hooked to the intake so i recon the intake vacuum affects the fuel pressure but i don't know how? does the more vacuum makes the fuel pressure increas or is it the other way round?

MMamdouh

ubuyau · Post by **ubuyau** » Thu Sep 29, 2005 11:15 pm

Yep, i agree with you about the sizing, its too small a difference to make any noticeable (if any) change in pressure...

The vacuum line to the regulator controls the pressure (there is a spring controlled diaphragm inside to my knowledge). It will increase the pressure with the more air the regulator sees. So as you open up the butterfly on the throttle body, the engine sees more air and it needs more fuel. So the regulator bumps up the pressure.

Now we dont want to start the whole battle between fuel pressure and flow here...

hehehe

--Tim