dizwiz24

Common sense would say: 14.8:1

However, I notice mine fluctuates between about 15.2 to 16.0:1 when in closed loop. This at idle and during normal driving.

Im only monitoring the left side exhaust (Drivers side) and am using my stock computer/heated O2's to control part throttle fuel delivery.

No issues with the wideband sensor, as it reads 14.7:1 when you key 'on' but do not start the engine.

Im also aware with some GM tunes, there is a highway economizer mode which keeps AFR's lean for better MPG's. This makes me think this may be normal.

Finally, I am running the hotcam.

My tune theoretically shouldnt matter because Im in closed loop.

0Paul Ruggeri

It seems on the lean side to me. I have one and mine runs 14.5-14.9 at a cruise.

dizwiz24

I wonder if it has something to do with my hotcam (218/228 duration @ .050, .525/.525 lift).


it does seem lean - which at part throttle is good.

Lean = better mpg.

However, my gas mileage isnt anything exciting.

Also, its supercharged as well. Who knows if that has any effect on it.

WOT is where its supposed to be (I tuned it on a dyno). 12.0:1

JackDidley

Its a little lean. Light loads it may not hurt. Can you bump up the FP a couple #s and see what it does ?

5abivt

That's normal. Are you on a stock tune? Lean at part throttle and cruising is better for emissions as well. Lets not forget that emissions was a huge factor in these tunes in the 90s.

Why the heck would you want more fuel at part throttle and cruising anyways. you'll be at the pumps alot more and who the heck needs 2 more hp while driving at part throttle ?

Aurora40

I'm not sure that's normal at all. Mine reads ~22:1 when the engine is not running, because there is lots of oxygen in the air. 14.7:1 would suggest all of the oxygen has been consumed.

dizwiz24

My bad, i didnt do a good job explaining this.

When you first key on, it self-tests and displays 14.7:1 for a few seconds. It then goes lean beyond its readable range - due to atmospheric oxygen.

So I believe its good.

0Paul Ruggeri

I think the bottom line is, if its not pinging you're OK.

383vett

Mine reads 20.9 with the motor off. That is the 02 content of outside air. I'm not sure why your meter can't read fresh air. Are you sure you have a wideband?

383vett

Paul, it's possible to melt a piston or break a ring land without hearing detonation. Willie

mike100

under (very) light load, leaner than stoich has been known to be the best economy..the trick is to just be as lean as possible for the load to not cause higher combustion temps. the old honda cvcc and the later GM vortec combustion chambers capitalize on the resistance to detonation through superior swirl characteristics and allow more power with less timing/leaner mixes.

btw, max power on a normally aspirated engine is usually about 12.5:1 a/f ratio.

Rohn

If set to 14.7/1 as stoich then 14.7/1 is the desired reading CL. For instance if you run E10 then stoich is around 14.3/1. If set to 14.7/1 as stoich then 14.7 is where you want to be for E10. If you set to lambda then 1.00 is stoich regardless of fuel used(E85,E10, reg gas). My WB is currently set to stoich. Originally I believed my E10 should show 14.3 on WB. Not so as I had WB set to 14.7/1 as stoich. Confusing??

JAKE

My experience, Yes. Many years ago I burned a nickle size hole in the #7 forged piston on a 468 BB while racing a turbo Porsche and never heard a thing until the engine went south.

Power Valve vacuum problem. Sh** Happens, LOL.

Jake

JackDidley

100% correct.

0Paul Ruggeri

You're right Willie. What I should have said was that if you do hear any pinging you need to change something.

MK 82

Why would you say the tune doesn't matter in closed loop?

dizwiz24

Its my understanding, that on a 93 speed density PCM, fueling is controlled entirely as a function of oxygen sensor readings - which are the stock narrowband O2 sensor readings.

Solely a feedback loop relying upon narrowband O2 sensor readings. No other sensors.

The VE tables are there for fueling when in open-loop mode.

Right?

I didnt think stuff like IAT (inlet air temp) influences closed loop, non power enrichment fueling...

Maybe I am mistaken...someone set me straight.

Orr89rocz

15 is ok for cruise light loads... what do the plugs look like? Take it for a cruise then shut it off, let it cool abit and take a plug out. If its pretty white then you know your pretty lean

anything else that loads the motor up more, be closer to mid 14's and as boost comes on with the blower, quickly ramp that down to 12's where your at.

dizwiz24

This is light load, idle, highway cruise, downhill, etc. Putting my foot on the gas (but not enough to engage WOT) causes the AFR to momentarily jump rich (to about 12:1 or 13:1) and then it settles back in varying between 15.0 and 16.0:1.

plugs look fine. clean, tan electrodes. no deposits, no cracked insulation - which is good.

WOT is not in question. I successfully tuned that by manipulating the power enrichment vs. coolant temp and power enrichment vs. rpm tables.

mseven

The feedback from the O2 sensor (sensor voltage) is used by the ECM to aim at the target AFR. In closed loop, stoich can be changed/altered from the cross over/switch points (both 02 lower and upper threshold). The fueling will then be changed (via INT/BLM, including flow gain and prop term etc.) to move the PW to the targeted O2 switch point (the window).
Once in closed loop the ecm (if SD ) will use the input of both the upper and lower ve, and a myriad of other lookup and add-on tables to control fueling.
Open loop operation should have available look-up target afr tables v.s. coolant and v.s. map values (some v.s. rpm). IAT and or MAT (depending on ecm) may have add-on fueling v.s. temp. tables used in closed loop operation. Highway mode will be engaged through look-up tables based on vehicle speed, timer, map, and temp. inputs . Unless cruising (in c.l.) at one steady speed, for X length (timer input) of time, which based on your first post would not be the reason of your afr being higher at idle/off idle operation.