Fuel Pressure & A/F Ratio

Hock

Registered User
First, what should my fuel pressure be with 42lb injectors, 39.5 or 42?

Second, every since I adjusted the IAC screw on my throttle body my AFR goes to between 16:1 - 19:1after I start the car. Doesn't matter if its a cold or hot start, does it all the time. Once I get moving everything acts fine even the idle AFR is normal once I stopped. This just happens after start up. I know that isn't right, but why would that happen? The whole reason I adjusted it was to get the engine to idle close to where it should be and not climb to 1500 every time I push the clutch in.

So it seems like I traded one problem for another.
 
Maybe because the computer is in control....not you :)

Seriously, baseline everything involved w/the idle, correct any vacuum leaks and let the computer take it from there.

As you've found, it will simply sniff the O2 sensors and compensate accordingly if you try to do something creative that is normally part of it's domain.

And why not...that's it's job.
 
Is this a wide band o2 your getting the readings from, or one of those A/F ratio gauges that run off the stock sensors ?

David
 
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Innovate wideband. Once I start moving the ratios go to normal which for mine is between 13.6 - 14.9 and usually stays close to 14.3.
 
It isn't a question of what your fuel pressure should be. it's what your fuel pressure is. Unless you have an adjustable fuel pressure regulator, your fuel pressure will be around 39psi with the vac line disconnected.

what are you calling an IAC screw that you adjusted? There is a throttle stop, and some throttle bodies have an air bypass screw.

How long is ever since? It is likely the adpative memory of the EEC remembered fuel trims prior to you adjusting the "iac screw". It will take some time to relearn and that might show up as lean conditions at startup, or idle.

Though more likely, lean conditions at idle or startup can indicate un-metered air being pulled in through a leak in your exhaust system and contaminating the wide band sensor.
 
BBK regulator and gauge.

New exhaust with no hint of leaks and when the gauge shows lean the idle is also rough so it is a real lean condition.

I adjusted the bleed screw for the IAC because my idle was hanging when I pushed the clutch in. That was a few weeks ago and that's when the lean startup idle started.
 
I'm having the same problem, but once I start driving everything is fine...but my air bypass screw is all the way tight (which is how it is supposed to be I believe)...I was told to adjust idle through the chip.

Not sure why it is so lean at cold startup
 
Here is the latest from Fraser found in this thread:
http://www.sccoa.com/forums/showthread.php?t=113149&highlight=idle+bypass

The throttle stop screw should be setup so there is a 10 thou gap between the screw and the linkage stop, then turn it in 1-1/2 turns and lock it down. Then the bypass should be fully closed, then opened about 2 turns, then see if the car will idle at that point.

If it does, then unplug the iac, start the car and adjust the bypass until idle is about 150 below target idle rpm... don't use the throttle stop screw unless the bypass doesn't do anything for you, then the throttle stop needs to be backed off, but watch out for the butterfly binding inside.

Thats the proper way to setup a TB mechanically, but on the other hand, did you by any chance forget to hook up the vacuum line that goes from the driver's side valve cover to the air inlet tube?
 
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