Air Fuel Ratios

Gary57 · Post by **Gary57** » Mon Jun 25, 2007 9:25 am

Ok so I installed my new Zeitronix wideband, its super cool and so easy to install. Now I have found that my AFR's are SOOOOO far out that its not even funny.

On light throttle freeway cruising its about 18:1 which is a bit on the lean side but the car is not jerking or anything so thats not to bad but EGT is about 670degrees which is good.

When I accelerate slowly and boost is about 0Kpa (no vacuum no boost) its about 15.5:1 which is too lean, good for fuel consuption but not for torque.

If I floor it AFR would drop to about about 12.2-13.0 which is again to lean, althought that was with the water/meth on. I noticed sometimes that its even as low as 10:1 at about 0.6Bar boost but then leans out as boost goes up, it just makes no sence. EGT reaches about 850-880degrees on a 10 or so second run.

Also when cruising, straight after I tap off it richens up to about 11:1 and then leans out. Why does it richen up straight after I tap off when I have set the fuel cut active??

I did all of this using the datalogger which is a real cool function but shows your everything little problem in the map

. All of these results were done with all compensations off, air and engine temps, (I wanted to see the problems in the main fuel map).

Now I have found the problems what should I do?? Should I go to the map and adjust it accordingly or do a few more runs and see if there is a pattern and then adjust it??

Also this datalogger is very very sensitive should I concider ever little blipper in it or just the big ones?? It is reading at something like 75 samples/second

.

Gary57 · Post by **Gary57** » Mon Jun 25, 2007 2:54 pm

SO let me guess, no one here besides Duane knows anything about AFR's?? Damn just my luck.

Oh while on my way to site I floored it in 3rd and the max AFR was 13.3:1-13.7:1, which means its too lean.

veecee · Post by **veecee** » Mon Jun 25, 2007 2:57 pm

so turn down the boost dude!

Gary57 · Post by **Gary57** » Mon Jun 25, 2007 3:01 pm

Its boost at 0.6bar at 3000rpm

. I am going to take it back to the guy that tuned it.

The thing is even at those AFR the motor is not pinging.

ChemCool · Post by **ChemCool** » Mon Jun 25, 2007 3:33 pm

Gary, I just feel you miss something about water/meth and AFR. From normal 12.5:1 it should only drop a point to 11.5;1. Then add boost, up the timing, add boost up the timing and keep on going until dead sure no detenation of course. I think I did inform you in the past about this one?

Gary57 · Post by **Gary57** » Mon Jun 25, 2007 3:38 pm

Yeah Freddie you did mention that to me. But right now I am now really worried about the max power torque it is making but rather the part throttle and lower rpm power and torque.

I mean the car goes great, but it can go better.

Doesnt water/meth move the AFR towards stoich, so you should set the AFR to 11.5:-12:1 and the add the water/meth which should "lean" it out to 12:1-12.5:1.

ChemCool · Post by **ChemCool** » Mon Jun 25, 2007 3:43 pm

You tune the car without w/m = 12.5:1. Like normal. Then add w/m. You should notice the AFR drops one point to 11.5:1. Then add boost, timing etc. And that is it. Nothing like bottom, middle top etc. Tune once and off you go.

ChemCool · Post by **ChemCool** » Mon Jun 25, 2007 3:45 pm

Then like my unichip will take away and add timing during the feul map as is needed. Nothing more to it. This is how it is done with mine.

Gary57 · Post by **Gary57** » Mon Jun 25, 2007 4:04 pm

I would hate to be cruising the freeway at slight throttle and vacuum and have a AFR of 12.5:1.

The car idles smooth at around 14.7:1 give and take 0.3:1 depending on the conditions. So I would say the motor should richen up almost linear to 11.5:1 at WOT when the boost is more than 0.5Bar. On the cruise and light throttle, it should be around 16.6:1 - 17.0:1.

Now how would I go about tuning these AFR via datalogging and road driving. I would say the best way would be live tuning, me in the passenger seat tuning while someone else drives?!

Phinx · Post by **Phinx** » Tue Jun 26, 2007 10:30 am

Gary what fuel pump and FPR are you using if i may ask

Gary57 · Post by **Gary57** » Tue Jun 26, 2007 10:41 am

Walbro 255lt/h and stock fuel pressure. At 1 bar boost the fuel pressure is 3.8Bar.

Gary57 · Post by **Gary57** » Tue Jun 26, 2007 11:03 am

Ok well this morning I found the problem of running so lean. I had loaded an older map on the weekend while stuffing around and by mistake loaded the wrong one, anyway the AFR is now about 12.7:1 - 13.0:1 at WOT and max boost. Now the car pulls like it should, I thought the power was down but just thought I was getting used to it. Oh well now all my datalogging on the weekend was a waste.