Hey,

I have already written some time ago that after changing my whole exhaust system (including the header and removing the cat) my car started running rich (12:1 A/F). I currently have no possibilty to install an EMS and get a tune.
However, I do have a fuel pressure regulator, so I thought I could adjust my A/F with it for now. (It will be a temporary solution untill I get the money to finish the project entirely and tune it with an ems).
I searched and found out that stock pressure is around 42psi (its 98 base, but its a european engine H22A5 which is obd1). So I wanted to know if I lower the fuel pressure by 1 psi, how much will my A/F ratio change?

Thanks in advance.

 

nobody will be able to tell that....just get a wideband o2 sensor and try adjusting with that...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">nobody will be able to tell that....just get a wideband o2 sensor and try adjusting with that...</TD></TR></TABLE>

So there is no way to tell it even approximately?
Thanks for your help anyway

 

somebody on here may have some wives-tale rule of thumb to spit at you like x reduction in a/f ratio per every 1psi of pressure, but none of it is proven, the only accurate way to know is to use a wideband....

 

The ecu will try to tune out any fuel pressure change you make. The only way to have it "stick" is to disconnect the O2 sensor or change the fuel pressure enough that the ECU can't compensate. I've also seen people remove the ECU memory fuse so the ECU resets every time you turn the car off. If your car is mysteriously running rich, you could have a bad O2 sensor. An exhaust modification should not change your A/F very much.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flyrod &raquo;</TD></TR><TR><TD CLASS="quote">The ecu will try to tune out any fuel pressure change you make. The only way to have it "stick" is to disconnect the O2 sensor or change the fuel pressure enough that the ECU can't compensate. </TD></TR></TABLE>
Is it also applicable to OBD1 ECU's. Correct me if I'm wrong, but I thought only OBD2 ecu's would do that.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flyrod &raquo;</TD></TR><TR><TD CLASS="quote">you could have a bad O2 sensor. An exhaust modification should not change your A/F very much.</TD></TR></TABLE>
It was actually runnung good A/F before the exhaust change, maybe even a bit lean (found out by looking at my spark plugs). So I think O2 sensor should be ok.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PreludEst &raquo;</TD></TR><TR><TD CLASS="quote">Is it also applicable to OBD1 ECU's. Correct me if I'm wrong, but I thought only OBD2 ecu's would do that.</TD></TR></TABLE>

Google for something like: closed loop fuel injection, or closed loop oxygen sensor...

 

First off if you know your air fuel ration is 12.1 then whats the problem. For a naturally aspirated car the sweet spot is like 12.6

Second if you know your air fuel ration then why are you asking us.

 

^^ first off, its a <U>ratio</U>, not a serving of food....

secondly, what the hell does the fact that he knows the ratio have to do with the fact that he need help fixing it...

 

isnt 12.6 the sweet spot for turbo cars?? i belive 13.1 is a better tune for n/a

 

the leaner the more power....but 13.5 is about as lean as you want to go....

 

ur not gonna see a noticable difference with a +/- 1psi fuel pressure change

 

how much do you know about tuning n/a?? is 13.5 as lean as you want at WOT?? whats a good ration for partial throttle anything under 13.5??
wow totally thread-jacking sorry

 

if your A/F is 12:1 at 42 psi WOT then you can pull out 6-8 psi and stay under 13.5:1 at wot. 6-8 psi will put you right around 13:1 or maybe a puss hair less.

 

As it was predicted ....<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">somebody on here may have some wives-tale rule of thumb to spit at you like x reduction in a/f ratio per every 1psi of pressure, but none of it is proven, the only accurate way to know is to use a wideband....</TD></TR></TABLE>

I just had to chime in here and suggest that you NOT drop your fuel pressure 6-8 psi, that seems like a bit much to me, and IMO, your better off at 12:1 than potentially running lean and burning **** up. Beg/Borrow/Steal a wideband before you start changing fuel pressure.

My $.02

 

OK, thank you guys for your help.
I think I will try to find a wideband here, or maybe just go to the dyno and adjust it there.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 01 LudeDude &raquo;</TD></TR><TR><TD CLASS="quote">As it was predicted ....

I just had to chime in here and suggest that you NOT drop your fuel pressure 6-8 psi, that seems like a bit much to me, and IMO, your better off at 12:1 than potentially running lean and burning **** up. Beg/Borrow/Steal a wideband before you start changing fuel pressure.

My $.02</TD></TR></TABLE>

yes the wideband is definatly the way to go. but my info is no rule of tthumb or wives tale. i used to work on a dyno and this is exact for my 4th gen. Just remember i am not telling you to do it. You asked and i provided a definate answer.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by junbb1 &raquo;</TD></TR><TR><TD CLASS="quote">

yes the wideband is definatly the way to go. but my info is no rule of tthumb or wives tale. i used to work on a dyno and this is exact for my 4th gen. Just remember i am not telling you to do it. You asked and i provided a definate answer.</TD></TR></TABLE>

I appreciate your help and probably if I can't get a wideband I will adjust it half of what you said just to be on the safe side.