Checking AFR's

[ben parrish]

I am a little confused by my AFR's.
A little background:
1986 3.2, 120k, Steve Wong chip, gutted cat, modified dual out exhaust
Recently replaced all intake gaskets and rebuilt injectors.

My exhaust smelled very strong of unburnt gas and the idle was a little rough. I also had a little bit of surging at low speed in each gear. I was sure that my AFR's were rich, causing my drivability problems.

I just installed a DynoJet wideband guage to see where my AFR's were.

I removed the O2 sensor in the gutted cat(pretty sure it was dead anyway) and replaced it with my wideband sensor. I discovered I was running very lean at idle.
I adjusted my DME fuel switch to position #2 (had put it on position 3 when I lived in Denver and first put in the chip) and the idle went to around 14.7
Full acceleration delivered 11.8,
Cruising at 70 was around 14.3
Partial throttle/accelerating gave me around 13.2
Off throttle at speed went to 18.

Is the off throtle normal?? I guess this is due to the fuel being cut all at once??
I know I am a little rich but is it too much?
What can I do to get the full throttle AFR's to lean out?
I suspect that I need to adjust the idle mixture at the AFM and play with the switch on the DME. Perhaps start at position "0"???

thanks,
Ben

[cgarr]

Where are you taking the reading from? The tail pipe? The off throttle will go way lean, you engine pretty much turns into a big air pump when the fuel shuts down, mine does too.

I ask about the pickup because if you have dual out exhaust and using the tail pipe probe you need to block off one tail pipe when taking the readings.

[ben parrish]

I removed the old 02 sensor and have the wideband sensor in the cat (gutted). I thought this would be the best/quickest place to get an idea of whats going on.

[Steve W]

You should not be in position 2. That makes the car run too rich. Put the switch and leave it in the factory default position of 0, and your full throttle AFRs will go back to between 12.6 and 13.0.

[ben parrish]

Will give that a try Steve. I thought about contacting you for input..now I don't have to.
I put it in position two to make it idle better...should have readjusted the AFM first.
Is it normal to go full lean on decel?

[ben parrish]

Also, will it hurt to continue running with the cars 02 sensor disconnected? Is there a better place for the wideband sensor?

[Steve W]

If your idle needs adjustment, you should be using the idle mixture screw under the air flow meter. If that can't get it to 14.2-14.4 at idle with the O2 disconnected, you may have a vacuum leak.

On decel, the idle switch closes, which turns off the fuel injectors, effectively making the engine just an air pump, so it will read lean.

You can run without the O2 connected. But connected or disconnected there's little difference in performance.

The factory O2 bung gives the most accurate AFR readings. But for a street car, the exhaust clamp from Innovate Motorsports works just as well.

[ben parrish]

Got the idle correct but the WOT is still arount 11.8. Cruising is around 14.5. What direction do I need to go to get the WOT to lean out?
thanks,
Ben

[Steve W]

did you put the fqs back on position 0?

[ben parrish]

yep. Idle is good and cruise is good. Just really rich at partial to WOT,

[ben parrish]

made headway today. Adjusted the afm screw to 2.5 turns out and set the fuel quality switch on the DME to position "0". The cruise 14.7 but the partial throttle is around 13.5 and the WOT reading is around 12.4...still too rich. Any more ideas?

[Eagledriver]

Those numbers are great IMO. Don't mess with it.

-Andy