Pandin: good stuff! My LSA is 114 so the reversion is there but i believe it is at idle only.

Quote: If the exhaust gases are burning between the motor and the O2, the oxygen content will be less (at O2), the farther away from the motor you are.

How does one know if the ext gasses are combusting? Or are they unburned fuel with high 02 content? I think that is my case(good burn in engine) as I believe the combustion process is not escaping the enginer chamber at mid RPM's. Maybe there is burning in the long tube headers? I dont know? The headers do not glow so I believe all is OK. Maybe an EGT would tell the tale.

So as it stands for me I have mismatched distance to the ext valves. I could move the NB sensor back to equal the WB position.

On the dyno they read the A/F at talepipe but that I believe is for WOT A/F calibration.

I have no emmishions.

Is the fact that at moderate load moderate RPMs my WB shows same as NB an indicator that both 02 sensors are seeing stoich-lamba at 14.3? Might moderate load and RPMs reduce the reversion/scavenging effect?

 

I have a question. With ours cars that have smog equipment how does the air into the exhaust manifolds and the air into the 3 way catalytic converters effect the A/F ratio in the exhaust pipe?

It would seem the smog equipment is adding extra oxygen into the exhaust that the motor does not see. Would this not effect the readings of the O2 sensors?

Edit: The air into the cats would effect an O2 in the tailpipe as on a dyno.

 

thats funny my innovative dc-16 in dash wide band. said i was way rich. like a 10 at wot.
i kept adding fuel and the car kept going faster.
hmm.
now i tune at the track by what the plugs look like and how the truck responds.
the wideband was crap and i got my money back.
i took the 400 i wasted and wet to a nice resturant. and bought some plugs. and the other 300 i kept.

 

First one needs to understand when the ECM adds Oxygen, and then how it compensates for it.

The ECM shifts the O2 mv .1 mv when the air is on the manifold.

The placement of the O2 sensor (NB or WB) or a big cam (high overlap) will likely change the ECM's calibration of the engines actual AFR (like plug reading and/or track times).

The AFR in the cylinder is the only one that matters.

Any reading from anywhere else is going to have a calibration factor to correct for the error.

At very rich mixtures, the fuel will have a cooling effect on the cylinder temp. If raw fuel gets all the way into the exhaust, then vaporizes in the hot pipes AFR can be way off because of the extra burning.

 

Thanks Pandin that is a good answer. So to sum things up if one is using a seperate wideban O2 sensor maybe the smog air system should be temporarily disconnected or made inoperative to get a more accurate reading with the wideband O2. Would that be a fair statement?

Edit: Actually I see a possible problem with my thought. When the ECM commands the air and adusts the O2 in put signal it might add or subtract more fuel if the smog air was not there.

 

Great info, thanks

 

wow im so happy this thread was brought back.

Some of this info needs to make its way into the stickies or if its there be more obvious in the stickies.

What i dont understand is the idiot that did a rough in on my tune locked it in open loop (didnt understand thats why he set what he did until just now) ran it on the dyno but i still had a completly stock VE and SA table and it was running piiig rich.

Started tuning myself at the end of the summer and blms kept maxing out on the lean side, so i stopped.

Going to get a WB before i start tuning again this year and i dont run a cat so im not sure if i want to tune in open or closed loop.

In the past the car ran like a bag of *** until it went into closed loop then i could actually do something with it, just couldnt keep the blms on the rich side no matter how much ve i gave it above 3500 rpms.

As i understand it if i lock myself in open loop i can just tune with the ve table and use my WB values, but then theres so much in this post about the WB values being off because of overlap and such. My cam isnt that huge 224/230 .510 deal so i guess we'll see what sort of readings i get from my WB and go from there.

Also put in some LT1 injectors so hopefully thatll help with getting enough fuel in it.

Man i forgot how much fun it is to bang my head off the wall all night trying to wrap my brain around all this. Trying to get this damn car driveable is going to be itneresting

 

First the ECM has to get the engine to start, add fuel to cold engine till it fires. The ECM is looking for the range that fuel will burn, in the cylinder.

Air/Fuel Ratio Limits

Somewhere between 22:1 and 6:1 (in the cylinder) the engine will "catch/fire". This is after all the fuel, that has to be loaded to "wet the walls" (the total surface area from the injector to the combustion chamber). If carb/TBI read lots of surface area.

If the cylinder does not "catch/fire", then it will have to wait till the next pass/cycle, pushing all that mixture into the exhaust.

Hopefully if all goes well (engineer or you being the engineer/programmer, loaded correct values into ECM ) then the engine will start and run.

Immediately after firing something happens called heat. As things warm up, all the "wet the walls" fuel that was needed to start the engine is now being added to the mixture. This will require that the amount of fuel being added by the ECM to be decreased to maintain the burnable AFR in the cylinder.

At the same time all this, "must be done this way to start engine stuff" is happening, the exhaust and cat is catching and trying to burn all the excess.

When everything is nice and hot the engine reaches a steady state of operation. The ECM will add "X" amount of fuel to "Y" amount of air (see chart above) and down the road you go.

Now comes the EPA and the Hydrocarbon (unburnt fuel) emissions amount. This has to be dealt with, so they added a cat converter, to burn the extra fuel. A cat can not run at the same steady state like the engine, it needs to run at it's own correct AFR (low HC output). To solve this dilemma, the O2 monitors the gases between the engine and the cat, but it can not serve two masters.

What the converter needs, to maintain a steady burn (low HC output), has to be delivered through and after the engine, like making a meal from leftovers.

So the ECM plays with (adds/removes fuel) to the cylinder AFR to satisfy the converter AFR. If and when the engine needs more power (richer AFR), also adding more air to manifold/cat via the air pump.

The game the ECM/O2 play is a up and down (richer/leaner) game, all in the name of lower HC. A cold converter will not burn, so some fuel is deliberately wasted to keep the cat hot (at a self burn temp). Too much air/fuel volume and the converter will melt, too little and the fire goes out.

This why open loop tuning (no cat) is attractive, it is all "steady state tuning".

Closed loop is anything but steady. So when you are being the "engineer/programmer", the more you know about how things work and when, the easier and "more correct" your adjustments will be.

The O2 makes adjustments at a lot higher rate then the sampling rate of the ECM, so all you see is, the strobe light effect of the ECM reading, on the O2 output, not what the AFR is really doing.

Some WB's can see the lean/rich/lean of a single combustion pulse. Remember that 4 cycle engines are all about pulses, rich/lean per strokes, not a steady flame type of burn (furnace/stove/lighter).

Engine/cat AFR adjustments are made long after the fact (time lag), from when the actual burn took place, (down the pipe is way later, "headers").

Tail pipe WB readings are more "averaged" due to mixing of the gases in the cats and/or exhaust pipes, then the usual NB reading at the manifold.

The new stuff has right side, left side, pre, and after cat O2's

 

When it comes to tuning the 'pilot folks' have it down. ROP vs LOP (rich of peak or Lean of peak) Load = throttle position

A tune of 16:1 at part throttle is cooler running than a tune of 14:1 or even 13:1. What you want to stay out of at throttle positions above part throttle conditions is 14 - 15 zone. That is the 'Deathzone under heavy - WOT throttle. But to tune at these AFR requires advance. No lean tune cruising with a centrifugal only distributor.

Good reading here: https://www.aviationsafetymagazine.c...n-of-peak-egt/

 

This thread is 15 years old!

 

Indeed but still very relevant info.