I've been tuning like I've read. Compare my BLM number for a given load and RPM. Then do the correct math needed to get a good idea of what it should be. Ex. BLM is at 120 @ 2000 RPM @ a 50 KPA. SO I've been doing this 120/128x?= Thus giving me a close number to work with. I decided to start looking at my O2 volts. This is where I get confused. I understand that the lower the number the leaner? So why am I getting BLMs of 111 and O2 volts arounf the 164. I even show O2 volts around 93??? Here is a copy of my excel lay out from Datamaster. This is a SD setup.
What the freak is going on.

Speed BLM KPA RPM O2 Volts
56 111 39.5 2125 155
56 111 41.4 2150 142
56 111 42.1 2100 128
56 111 43.2 2175 115
56 111 43.6 2200 106
56 111 43.9 2175 102
56 111 43.9 2225 93
56 111 43.9 2225 89
56 111 43.9 2225 80
56 111 43.9 2250 80
56 111 43.6 2250 71
56 111 43.2 2275 71
56 111 43.2 2275 66
56 111 43.6 2250 66
56 124 43.2 2250 62

 

Making a real long story short.

Stoich is 14.7:, at that Air Fuel Ratio, the reactions that occur in the chamber pretty well balance out, meaning it's neither rich or lean.

The catalytic converter can't work it's best at 14.7, it must cycle rich and lean of Stoich to work.

So the ecm toggles the AFR across 14.7:1 to keep the cat happy.

Unless you program your brain with the same programs as the ecm, the swings in O2 voltages are meaningless in closed loop, other then they indicate things seem well.

While changing fuel usually has the most dramatic effect on the O2, and BL numbers, timing also to a limited degree comes into play.

Just as a random, example.
None EGR application.
And your trying to run 42d timing, and you know lean mixtures like alot of timing.
But, you get to where changing the fuel doesn't do much.
What's happened is that you have the actual chamber temp so hot, that fuel is being used to cool the chamber, and not really effect the combustion process.

Tuning means getting the timing and fuel optimised, and as you change one you effect the other. If your to where things aren't responding, as you would expect, I'd suggest you take some timing out of that region, and try again. The fatal common error is the more timing the better, and that's not universally true.

 

Thanks grumpy.

That helps me out a lot:hail:

 

AAAAHHHHHHH, my problem is the same:

BLM: 156
Adv: 44d
O2: 60
Change into VE table doesn't produces effect.

+ bad power + detonation.

(good vacuum, good fuel presure, good all = I can't understand).

Denis V.

 

Your problem is a little different. The BLM of 156 is adding fuel, a lot (156/128 = +22%). 44d of SA may also be a bit too much.

If this is a tuning issue I'd be adding at least 20% to the VE table at that location.

RBob.

 

Yes RBob, I know, but I've a big headache now with this issue, because when I change 22% the VE table, the lean condition remains very similar with too little variations, then....what is?, bad vacuum?, fuel presure?, fuel volume? 1 clogged injector? 1 spark plug without spark? 1 valve open?. I'll recheck all this weekend (I've holidays today afternoon, 18,19,20 & 21).


Thanks,

Denis V.

 

is this why my A/F gauge flashes a range of stoich? in other words the bars in that stoich area are maybe 20 but only 5 light up toward the middle or right or left . all within the stoich. is it changing the a/f back and forth right at that 14.7 like from 14.4 to 15/1 averaging 14.7? also the gauge seems to go on/off constanty is that reflecting the 02 is also sending that same signal on/off? when gauge installed instructions allerted me to this as normal but did not give a complete answer.

 

Yes, this is why it goes back and forth. Why it drops off could be a couple things, you really only want to use AC Delco parts on a GM, this includes the 02 sensor. A friend of mine was getting flat lines from the 02 sensor with the bosch replacement, it was a piece of crap.

Also, you might want to make sure that the gauges is getting 100% of the power it needs, if you have it running through the fuse box, you might have a slight power withdrawl with anything cylcing in and out. My stereo make a difference to my gauges also.

 

are you saying the bars should be lit constantly while in closed loop? it does cycle back/forth from red to bars in stoich which is what the instructions said. the only time it is "off" is when car is started cold and warming up. once closed loop hits per winaldl the cells populate and the gauge begins to function. i dont think it is every missing a beat so to speak when in closed.

 

The only time mine is off is when the car is off. The computer is not able to hold a cell lit, if you were to hook a voltmeter to the 02 sensor you will see the voltage fluxuate, just like the gauge is seeing.

Does that answer the question?

It will always move back and forth, that is the computer trying to get the best mileage and trying to get 14.7 out of the car.