Is 14.7:1 AFR alright for part-throttle boost?

[Leiden]

I managed to work around the Stumble Off Idle by adding extra fuel in the Emanage Ultimate using the Injector Correction.

I tested it by hooking up a Multimeter to the O2 Sensor and resetting the ECU after each adjustment, I got it to the point that right after a reset it will start and idle perfectly at 14.7:1 without any fuel trims being made. I ended up adding roughly 11.7% extra fuel over the entire fuel map to achieve this.

Car runs a whole lot better now, but I have a question...

When I'm cruising at part throttle the AFR is at 14.7:1 (about 0.5v on the multimeter) if I accelerate slightly I can get the boost up to about 5PSI before the O2 sensor output starts to rise from 0.5v. Is this OK for part throttle boost? The engine wouldn't be under alot of load as its just slightly accelerating. If I plant it the O2 output immediately shoots up to about 0.96v.

Safe? Or should I be adding extra fuel to tune this out?

[strx7]

Unless you had a brand new narrow band sensor, and a VERY good quality multimeter I personally wouldn't trust that method of tuning.

It should be around 13.0-13.5 in that 0-5psi range

[Leiden]

It was just to get things back to where they should be, I'm not going to tune the whole thing off the narrow band, I'd end up killing the motor agian

Normally I'd log the O2 data against RPM, Throttle Position, Boost, Injector Duty Cycle, Knock with the Emanage Ultimate, I've only just finished moving the ECU into the Engine Bay so I don't have the long wire runs.

I tried adding a little fuel and initially it was reading about 0.70v on the O2 as boost was building but then it slowly came back down to 0.50v, stupid fuel trims learning

[steve murch]

its surprising what you can get away with under boost but knock is very important and the tols you use to monitor,play safe and keep it slightly rich unless you have full faith in what your using

[Leiden]

I know you can get away with something crazy like 16.0:1 while highway cruising,

I'm talking about very light acceleration, I've only got a 7cm2 exhaust housing on a 2.0L so boost starts building very early on my vehicle, from about 1500rpm's onwards which is usually while the stock ECU is still in closed loop maintaining its 14.7:1 AFR. I add more fuel in those points and the stock ECU just tunes it out. Hell if its happy and not pulling timing then hopefully everythings OK!

At the moment I'm just making sure it stays above 14.7:1 by watching the logs and O2 data, if it drops a little below stoich then I'll add a little fuel and reset the ECU and log it some more. I might unplug it from the ECU and just log it, sometimes its hard to know if its lean or if its just the stock ECU cycling the O2. I'm just wondering because if I unplug it the ECU might go into scare mode and drop extra fuel.

[MAGN1T]

Have you had a look at the sparkplugs?. Sounds to me like your oxy sensor is toast.
You should never get a steady .5V reading at part throttle and .96 is way too rich, the plugs should be black.

Steve

[Leiden]

Its only a stock narrowband and as far as I know they only have a very limited feedback range, either rich of stoich or lean of stoich dont they?

The 0.5v reading does vary up and down a little while cruising (0.3v - 0.7v), but mainly I think the multimeter doesn't react fast enough

[KinLoud]

I think that you should STOP driving the car!

You WILL kill your engine again!

I have just read all your previous posts here on Toyspeed and I am of the opinion that you bent the rod on your first engine by getting detonation.

I think that you are/have probably run the car very lean with boost and high compression. It is likely you are detonating again.

You don't seem to realise that you will have to overhaul your engine again if you keep driving it without someone experienced and knowledgable (Not you!) sorting out all of your ecu/tuning problems using the correct tools.

DIY is not going to keep your engine alive.

Ken

[steve murch]

I know you can get away with something crazy like 16.0:1 while highway cruising,

I'm talking about very light acceleration, I've only got a 7cm2 exhaust housing on a 2.0L so boost starts building very early on my vehicle, from about 1500rpm's onwards which is usually while the stock ECU is still in closed loop maintaining its 14.7:1 AFR. I add more fuel in those points and the stock ECU just tunes it out. Hell if its happy and not pulling timing then hopefully everythings OK!

At the moment I'm just making sure it stays above 14.7:1 by watching the logs and O2 data, if it drops a little below stoich then I'll add a little fuel and reset the ECU and log it some more. I might unplug it from the ECU and just log it, sometimes its hard to know if its lean or if its just the stock ECU cycling the O2. I'm just wondering because if I unplug it the ECU might go into scare mode and drop extra fuel.

on Toyota's running stock ecu with any sort of piggyback disconnect the 02 when tuning then it doesn't fight you then reconnect and its happy and doesn't override what you've just done,sounds strange but it works.
my mate that builds the mapecu used this on his gen3 or maybe gen2 mr2,i did the tune( road only) and we got 175kw wheel at 12psi.
took it to the dyno and all trickytune could get was 4kw more over what i had done.
we also found it ran better with the 02 unplugged all the time,yes i know all about the default thing but the tune was better than closed loop so we didn't bother and as for the timing it never moved.
as for stoich dont get too hung up on it,we did a test between 14.75ar and 13.5ar and there was no change in economy but it drove so much nicer at 13.5 than stoich so we didnt bother.
when tuning any car you need to listen to what it wants not what the book says nor what your trying to make it do,listen to it you will learn alot and will be surprised what comes from it.

[Leiden]

Sounds like some good advice!

Does the stock ECU normally dump more fuel when it doesn't have any O2 feedback (some kind of safety thing) or is the base fuel table a tad rich from factory which then is leaned out to stoich with the O2 feedback... as you drive and it learns?

Also, just wondering if you could comment on the feedback range of the stock O2 sensor? Does it really just switch at 14.7 or does it actually have a small range to it? Say 13.0:1 - 16.0:1 or something?

[steve murch]

Sounds like some good advice!

Does the stock ECU normally dump more fuel when it doesn't have any O2 feedback (some kind of safety thing) or is the base fuel table a tad rich from factory which then is leaned out to stoich with the O2 feedback... as you drive and it learns?

Also, just wondering if you could comment on the feedback range of the stock O2 sensor? Does it really just switch at 14.7 or does it actually have a small range to it? Say 13.0:1 - 16.0:1 or something?

if you hunt the net for a narrow band output youll see its just that narrow and works its best around 14.75ar,so under load doesnt do alot.
when you disconect on early model cars it doesnt care too much as its manly used for cruze,yes it runs alittle richer but remember it only uses it for economy so when your legs hard up it not much is happing with it apart from taking up room in your exhaust

[Leiden]

Cool, will play around more with it tomorrow!

In your experience with Toyota ECU's do they just pull timing under knock or do they also add fuel, not long ago I was having a real bad bogging problem at around 2000rpm's (before I added the 11.7% extra fuel globally to achieve stoich).

When I looked at the narrowband output it read 0.92v which is pretty much the limit of richness I think it will read, it was definately above stoich so it wasn't a lean bog. I tried pulling some fuel and it seemed a little more reponsive but nowhere near what it used to be. I then looked at the timing and it was only 7 degrees before TDC.

I did an ECU reset and took it back out, put it in 5th and floored it up a hill from about 1500rpm's, the O2 read lean and I watched as the timing slowly decreased and the duty cycle increased. Eventually it was back to its 0.92v O2 readout and 7 degrees timing.

Would this indicate the ECU's defence mechanism against knock? Pull timing and add fuel? I also noticed it seemed to have more power accelerating up the hill with part throttle than full throttle.

Since adding the extra 11.7% fuel to get it back to stoich it seems to be happy.

[steve murch]

it only pulls about 6 degrees timing out at the time of knock,to be honest it sounds like you need to reset all settings and start from scatch.
sometimes ive even gotten carried away and hit reset,or there maybe other problems going on