Neimad

Sensor 1 was originally ONLY there to tell it what to feed cat next, primary function. Has to go slightly rich then lean to keep cat working, that is why 02 is a voltage waveform, AF uses amperage waveform. Bottom line, it's not a big deal unless it's so confused trying to keep non-existant cats working that you get dangerous lean condition. Not likely because if would most likely richen things up because it thinks too much 02 is going through cats. O2/AF only see O2, if you have rich misfire, it will see the O2 and think its lean mistakenly.

I have all the relevant ASE's, I post this crap cause it keeps my brain working

djamps

iTrader: (1)

On a side note, rich misfire indeed causes a wideband sensor to read lean.

mgrotel

iTrader: (3)

is this for sure true?

if so, how can uprev sit there and tell me over the phone that my tune would adjust with elevation changes? tuning and 2000 feet and then driving to 4500 feet, if my wot map is not using o2 sensors, how does it know im at a higher elevation? my tune would be complete garbage at more than twice the elevation it was tuned at. if this is for sure true, i am very disappointed that uprev would sit there and tell me that on the phone.

Neimad

Ignores for fuel trim adjustment, but still looks at it to set codes. Elevation is not determined by O2 signal, gotta look that one up, probably by IAT, MAF and TPS.

mgrotel

iTrader: (3)

wouldnt it have to be the O2s? it wouldnt be the temp, the maf just reads a volume going in, not how dense the air is, tps would just be throttle input.

the density of the air would change the a/f ratio. more dense would require more fuel than less dense air. the only thing i can think of that would detect this are the O2 sensors.

Neimad

http://www.ase.com/getattachment/Tes...10817.pdf.aspx

Not quite same setup but there is a quote about the MAF reading at sea level, can't copy and paste off PDF.

It uses everything, density of air is different so MAF reading changes as you go up.

mgrotel

iTrader: (3)

that pdf is taking a while to download on my current slow connection, but what you say if very interesting to me. i always just thought the maf just measured the volume of air entering the engine.

Neimad

Mass is the key word. You know how it works? A wire has current passing through it, as the air passes the ECM tries to maintain constant amperage. It then uses what it had to do to maintain amperage to calculate useful MAF signal, IAT is combined in there too.

Neimad

P0171 (Lean Condition) on Toyota with MAF= dusty wire in MAF.

Some cars (Toyota!) used MAP to determine EGR functionality, my worst diagnosis ever, took years to realize to look at MAP. EGR was working, no NOX problems but when EGR came on MAP signal wasn't what was expected; open EGR + current throttle opening should cause MAP signal to approach specified reading for elevation.

djamps

iTrader: (1)

Correct, it can still throw codes but no fuel trims made off the readings at WOT.

To answer the other question (on a very high level) the MAF measures the amount of air coming in and then the ECU looks it up on the table in addition to air temp compensation. That method basically self-compensates for elevation and temp variations... lower elevation or lower temps = more air (denser) moving past the MAF = more fuel on the lookup table.

mgrotel

iTrader: (3)

ok, so as i go up in elevation, even though the same volume of air moves past the maf, it will still detect that is has less mass, therefore telling the ecu to use less fuel? and opposite going down in elevation?

djamps

iTrader: (1)

Right...even at the same volume (3.5L per x revolutions?? master tech help me out LOL), denser air has a greater cooling affect on the hot wire in the MAF, which in turn sends a higher voltage to the ECU causing the ECU to add more fuel..

Neimad

I'm getting tired, here's some great starter stuff to read if your into all this. I wanna make a "How to properly diagnose stuff" thread at some point.

http://smogsite.com/

mgrotel

iTrader: (3)

thanks, good reading

F2CMaDMaXX

iTrader: (2)

Certainly interested in this stuff, let us know if you ever get round to posting one

So, i think i missed it, but what exactly from sensor 1 tells the ECU that something isn't switching right on that sensor, and calls the secondary sensors (downstream) into play.

It's clear that the post cat sensors are not used until the primary sensors switch or have a problem.

As far as i can tell, they'd need to be faulty, or for something to change in the engine that stops them doing their normal thing. Changing the exhaust will not change the operation of the upstream sensors.

mgrotel

iTrader: (3)

i think the rear O2s are just used for stoich situations.

the O2 sensors have a pretty good paragraph on them on page 5 of the link in post #46

Neimad

You guys are close but not quite, its expecting a pretty steady reading from the rear O2, that is what good cat will put out, voltage hovers around the middle unlike the constant (amp) switching of the front AFs. Since clean emissions is the primary goal of the ECM, rear O2 is actually one of the most important sensors on today's vehicles, every OBDII car has to have one.

I had a Corolla that a shop changed everything on, cat, front O2, plugs etc. Ran hot, NOX sky high, no EGR, HC and CO made it look like defective cat, ended up being rear O2 failing just not bad enough to generate code.

I'm curiuous, how much power you guys make without cats? I've got 244whp/233tq with just a filter and dual exhaust. Ok I did some opening up of the intake plenum but I doubt it got me much. I can't risk my license with a modified car sitting outside the shop.

F2CMaDMaXX

iTrader: (2)

Yeah i read that section, all interesting info for sure.

Can someone give me the English version of stoich please? As far as i can tell, it's the 'perfect' mix/situation of air/fuel?

Based on that, although i'm certainly going to test this, djamps' problem with it switching to the secondary sensors doesn't seem to make sense. It's a fully normal circumstance, yet it's switching to the secondary sensors

Neimad

Perfect (impossible to achieve)emissions burn, HC and O2 consumed and only CO2 and N left. Slightly lean is best for emissions and slightly rich is best for power.

I had teacher pop three fuel and air filled balloons in class, rich=smokey pop, lean= loud pop, stoich=he was in big trouble next day, sounded like bomb.

Oxygen is actually the only thing that burns, the fuel is an accelerant, as it breaks down it produces heat which fires the 02 and expands the N to make power.

djamps

iTrader: (1)

Isn't the most power made in stoich? Problem is it burns too hot though, so slightly rich is best for making power.