Air/Fuel gauge usefulness
 

Would you recommend an air/fuel gauge for an L-Jet daily driver? Previous threads refer to readings bouncing erratically while in closed loop. What will it tell a newbie?

Thanks...

useless, without a system to be able to adjust it, or boost to ensure it is rich under boost

Genereally speaking... not needed for a stock daily driver.

only good for racing, as to show when things go really wrong. not accurate enough for any type of real usefulness.
mk

Yup, only good to show if it's rich or lean, and mostly for cars with boost.

I've been thinking of adding one of these as well. I think it would be good info if nothing else for fuel economy. I was looking at one how are they hooked up? Are they spliced in to O2 sensor lead?

Narrowband Oxygen Sensors (like those on our non-OB 928s) are not accurate. they show low voltage when lean and high voltage when rich. The reason for the "bounce" is because it's bouncing between high and low voltage - this is the only way to know the stoichiometric point. In closed-loop mode, the engine just adds a touch more fuel if the O2 sensor reads lean, and a touch less with it reads rich. There is no accurate reading of the AFR because the sensor isn't accurate.

If you want an accurate AFR gauge, buy a Y-pipe for your '80 and mount a wideband oxygen sensor in the second EGO sensor hole (the two manuf's I've seen both have two sensor holes). WB sensors have come down in price dramatically in the last few years.

So your saying my OB would have a good sensor for it stock?

Might as well put on my devil's advocate hat, it is Friday :p

You can adjust the air / fuel on an L-jet. There is a screw on the AFM for this.

The screw doesnt effect anything but mixture at idle. :(

to change mixture of Ljet, you need to get in and change the AFM gauge itself internally. at the High output ranges, a rising rate fuel regulator works perfectly for WOT high power setting A/F changes.

again, the use of such a gauge is useless, except when things go wrong (like WOT switch not working) or to know when your cat is at temp. :)

mk

It's still a change :p

IIRC, the L-Jet AFM bypass screw will change the AFR almost a point at max rpm, on the dyno. You can't go very rich with it, though.

It's easy enough to change the WOT mixture by modifiying the TempII input, but it has to be switched in by the WOT switch.

It does NOTHING at WOT. all the the screw does, is open a very tiny false air (unmetered ) air hole. If you get a tiny change at WOT, it will be a BIG change during idle. Its used to adjust the AFM during emmissions testing.

I did an experiement with the AC inlet to the plennum,usingthe solinoid to open the hose to the plennum for more air. didnt do a thing, and it was much larger than the AFM bypass screw.

mk

It does do something at WOT. I have tested it on two cars on the same dyno, on the same day. Basically you can screw the bypass all the way in, or lean it out. (On my '81, it took 6 full turns out for emissions.)

It's not just the amount of unmetered air, it's that air going around the AFM vane in the AFM, changing it's potential. The same air leak elsewhere in the intake will have less of an effect.

The A/C solenoid has a small opening, it's only meant to increase the idle speed ~50 rpm.