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Need Help Interpreting O2 Gauge On My Tii


Cris.MTL
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Hey guys, so in need some help in understanding my AFR numbers that I'm getting, and yes I have searched until I was blue in the face and still confused.

I have a 74tii with a stock motor.

 

First I set the Kfish according to the manual.

 

On idle the motor is at approx 12.5 (which seems rich but any leaner and it starts to hunt)

 

At WOT it holds steady at 13.5 up until 4000 rpm, and that point it starts to lean out. I can't tell you by how much because I run out out of road in my suburban neighborhood.

 

Now here is the weird part, at partial throttle, from anywhere from just a touch of throttle to just before WOT, I'm running super lean. Approx 16.0's

 

I know that the verboten screw has been played with in the past but i have a decent understanding of how that works.

I gone out for test runs after doing a few tweaks and tunes and have kept my test runs as consistent as possible.

 

If any one could shed some light and what might be going on or what I should look for, I'd really appreciate it.

 

 

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If you've searched, you've probably hit on my posts regarding my adventures in similar Kugelfischer-induced pain.

 

Keep in mind that today's fuel is oxygenated, making your car run leaner than it would with non-oxygenated fuel would, and affecting the AFM readings accordingly.

 

I'm no expert, but 13.5 at WOT is about where you want it to be. If you're 13.5 at WOT but 16 (too lean) at partial throttle opening, you can try enriching the mixture by pinning the kfish pump and setting the cam in the tuna can not at the edge of the hole but partially across it. Jim Gerock had a good long post about this, among many others.

 

--Rob

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Hey Rob.

I did indeed come across your posts and some of them left me scratching my head more then when I started, but they have helped me get this far and for that I am thankful.

 

I did not know about today's oxygenated fuel, I'm going to need to read up on that when I can.

 

Ok so I'm going to try that adjustment you mentioned and let you know how it works out.

Thanks for chiming in.

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Ok so I adjusted the throttle as per Robs instruction and I'm seeing good improvements to my AFR at partial throttle. It still needs some fine tuning but atleast now I feel comfortable driving it around town.

 

I still have the issue with the AFR going lean at WOT after 4000/4500 RPM. It will get up to the 15.0's. Anything below this RPM and its a steady 13.5.

 

Now I know that tii's with hotter cams tend to run like this but as far as I know, I have a completely stock motor. Just mostly out of curiousity, is there a way of indentifying what cam you have by pulling the valve cover and visually checking?

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Ok so I adjusted the throttle as per Robs instruction and I'm seeing good improvements to my AFR at partial throttle. It still needs some fine tuning but atleast now I feel comfortable driving it around town.

 

I still have the issue with the AFR going lean at WOT after 4000/4500 RPM. It will get up to the 15.0's. Anything below this RPM and its a steady 13.5.

 

Now I know that tii's with hotter cams tend to run like this but as far as I know, I have a completely stock motor. Just mostly out of curiousity, is there a way of indentifying what cam you have by pulling the valve cover and visually checking?

 

An ignition misfire will show lean because of the add'l air from the non-firing cylinder.

 

But I'd check for vaccuum leaks first.

 

Shall we assume all ignition components are in good order? Copper plugs, not Pt. Valves adjusted? No wear in the throttle body?

 

13.5 at WOT is lean in my opinion. 13 is much safer. Attached are target afr's for S14s. I don't see why there should be a significant difference vs an M10.

 

GL,

post-9251-0-68199100-1371279137_thumb.jp

Edited by ray_koke
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Ray,

Comments: Since you are tps loaded, you might examine the cylinder loading a low-medium rpm at various throttle %Open values.  If the PWs for various throttle %Open/RPM are normalized to a single AFR and plotted, the cylinder loading (relative to maximum for that RPM) is very high at relatively small throttle %Open values.

 

For instance, my data shows @2k RPM 20%Open throttle, cylinder loading is around 65% of max (for 2krpm); 30% Open throttle, loading is around 75% of max.; @3k RPM 15% Open throttle, 60% of max, @3.5k 30% Open, 70% of max.  (These values will vary a bit between installations due to differences in sensors used, etc. so my values are not absolute)

 

So my comment is I would lower the AFR in your map for low rpm columns a much lower %open throttle values.

 

On another note, if the S14 factory used a narrow band O2 sensor, then it ran at or near lambda at all loads except idle and WOT (idle having it's own map and same at WOT). Then performance aside, there shouldn't be much detriment to the engine life by running at mostly lambda.

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Ray,

Comments: Since you are tps loaded, you might examine the cylinder loading a low-medium rpm at various throttle %Open values.  If the PWs for various throttle %Open/RPM are normalized to a single AFR and plotted, the cylinder loading (relative to maximum for that RPM) is very high at relatively small throttle %Open values.

 

For instance, my data shows @2k RPM 20%Open throttle, cylinder loading is around 65% of max (for 2krpm); 30% Open throttle, loading is around 75% of max.; @3k RPM 15% Open throttle, 60% of max, @3.5k 30% Open, 70% of max.  (These values will vary a bit between installations due to differences in sensors used, etc. so my values are not absolute)

 

So my comment is I would lower the AFR in your map for low rpm columns a much lower %open throttle values.

 

On another note, if the S14 factory used a narrow band O2 sensor, then it ran at or near lambda at all loads except idle and WOT (idle having it's own map and same at WOT). Then performance aside, there shouldn't be much detriment to the engine life by running at mostly lambda.

Hi Jim,

 

I agree. Actually my map is at lambda throughout the useable rpm range at 60% throttle. I pulled the above illustration from s14.power and those values I wager have a bit of safety margin thrown in (I believe it's an open loop based map and I'm now running closed loop, which I expect you may be). For the OP running open loop (that is, no real-time afr fuel management adjustment based on actual afr's) the above illustration is likely safer IMO.

 

Cheers,

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Hey guys, so in need some help in understanding my AFR numbers that I'm getting, and yes I have searched until I was blue in the face and still confused.

I have a 74tii with a stock motor.

 

First I set the Kfish according to the manual.

 

On idle the motor is at approx 12.5 (which seems rich but any leaner and it starts to hunt)

 

At WOT it holds steady at 13.5 up until 4000 rpm, and that point it starts to lean out. I can't tell you by how much because I run out out of road in my suburban neighborhood.

 

Now here is the weird part, at partial throttle, from anywhere from just a touch of throttle to just before WOT, I'm running super lean. Approx 16.0's

 

I know that the verboten screw has been played with in the past but i have a decent understanding of how that works.

I gone out for test runs after doing a few tweaks and tunes and have kept my test runs as consistent as possible.

 

If any one could shed some light and what might be going on or what I should look for, I'd really appreciate it.

 

At partial throttle it should be lean.  

 

Look at the 5000rpm curve on this graph.  At idle (no load) it is rich, and gets rich again at WOT, but leans out at partial throttle.

 

afrtoairflow.jpg

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