just did some searching (I'm addicted to the search feature of this site) but couldn't really find the answers to my questions. I just installed my air/fuel ratio gauge and my fuel pressure gauge and was woundering a couple of things.

1. what should the pressure be on idle and wot?
2. (stupid question, sorry) how do I read the a/f guage. I know what lean, rich and stoitch is but all it ever does is when I push the gas is read rich. when I'm cruzing of course it goes back and forth because thats what it is supposed to do but any pointers would be great
3. and last of all how can I tell what my a/f ratio is like when people say 15.1:???? I have an afc but just don't know exactly how to use it for this function. Any help would be great!!!! Thank you.

 

Fuel pressure at the pump should be 64-85.3 PSI with .35 gallons/minute

 

thanks! know any of the other stuff?

 

That 15:1 thing is the Fuel to air ratio. 10:1 is considered rich. 25:1 is considered lean. Those are the extremes.

14.7:1 is the perfect ratio for cruise. That is the ratio your ecu is trying to obtain for cruise. That is why the lights flicker and move all over the place when you cruise.

Search for wideband when you search. That is the type of sensor/display you should use to tune your afc unit. The display you have is connected to a narrow band sensor. Which is your stock sensor. The stock sensor is only used for cruise when your ecu is trying to make a 14.7:1 AFR

James

 

The FPR maintains fuel pressure at 36-38psi above manifold pressure at all times. So at idle (say -16inHg or -8psi) it'll be around 30psi and at 8psi boost it'll be around 45psi.

If you ever see fuel pressure stop rising even though manifold pressure is still climbing, get off the gas! You've reached the maz flow of the pump an need to upgrade it.

The figures Icemark quoted are the zero flow pressures (i.e. pump output block off) which you'll never actually see on the gauge. The gauge should be teed in after the fuel filter.
That's what it's supposed to read. Full-load mixtures are always rich.
You can't! The stock O2 sensor is only accurate right on stoichiometric (14.7:1) and can't give you precise values no matter what you use to read it. To get actual ratios you need a wide-band A/F meter as used on dynos.

 

ahhh thanks now I get it. Never knew how to get that ratio. I do have a question though. the sending unit for the fuel pressure was added before I got the car. I looked under the car last night and found that the sending unit for the gauge is actually put in right before the fuel filter. How bad is this?

 

There would be a little pressure drop after the fuel filter that your not seeing with the gauge placed before the filter.

 

ok so not TOO big of a deal. Thanks.

 

yep I quoted the figures for testing the pump. NZ has it all right.

 

Oops, complete mind blank. I meant to say tee into the fuel line after the fuel filter, so the gauge shows the actual pressure the injectors are seeing. Otherwise you don't account for the pressure drop that occurs through the fuel filter, as turbo dan correctly pointed out.

 

hey I've been looking at my fuel pressure and I get about 35psi at idle and when revving in nutral it doesn't go above 40psi is this bad? also if I hold my foot on the gas in nutral it will rise up to 40 and go down again while my foot is on the gas, is this normal? Thanks.

 

ps. you guys with turbo's if you rev in nutral can you get your turbo to spool? I mean can you guys get positive pressure on your boost gauge? I rev and it goes up to 0 then it falls back down to like 20 while I I'm still revving. Any thoughts?

 

anyone?

 

Boost takes time to be generated, because it takes time for the turbo to spool up. With no load on the neengine, you can't hold the throttle open long enough to start making boost without hitting redline. That's why you can't make much boost in neutral.

 

I can get 5psi at least in neutral with a half clogged stock catback.

 

Clog it more then, get mad boost at ilde yizzoo! hehe

 

Well I don't think its the clogged catback doing it. Probably my custom TID helping. I would think a better CB would help get more boost.

 

i've got 3" downpipe and a tid mid and still when I rev it goes to zero but when the peddle is still veving the car it falls back from zero to -20? is this normal for it to fall while you are still reving it?