Front wideband accuracy

[jamesm]

Originally Posted by s2d4

@jamesm looked into this when he did full close loop.
It's ridiculous how far off the previous forum golden childs had it so wrong.
A lot of the old dyno plots prior to 6-8 months ago had 13-14 AFR at WOT....

My full time closed loop setup uses a wideband imported into ecutek, not the stock sensor.

I've found that using ecutek's recommended expanded front o2 scaling, the thing isn't just off, it's inconsistent. Sometimes it'll read leaner than a proper wideband in the same car, sometimes richer, and never by a little bit. Suffice to say it's pretty useless for tuning anything. The most common case is the front o2 pegging rich while the wideband is reading something leaner, though it's not always that way.

I've always said if your tuner doesn't require a wideband for FI e-tunes they're doing it wrong. Nice to see someone else agrees..

[arghx7]

as @moto-mike is saying, in the end you have to do what's practical. How is the dyno and the knock reading responding to whatever AFR you are reading on your given sensor? The more instrumentation you can compare, the better.

While I'm thinking about it, here is another comment on the cam phasing and what is actually happening in the cylinder on a turbo DI engine:

For those of you who have tuned a boosted EJ and played around with cam timing, more boost, whatever, you expect to see a certain AFR. You have to remember that the port injected fuel gets thrown out the exhaust valve during overlap & open valve injection, but for DI it doesn't! That's raw unburned fuel that can affect readings.

Nobody has come up with a RAM value from the FA20 ECU or a calculated parameter to determine the end of injection timing for the FA20's PFI system. If the end of injection occurs during an open intake valve & overlap, you've got all that unburnt fuel possibly reacting in the exhaust manifold or otherwise skewing the wideband as I said.

This is why if you have an engine dyno you would look at your CO2%, CO, and O2%, and HC ppm. In full stoich part load, CO2% is very very close to wideband AFR, and can be a good indicator of in-cylinder AFR during scavenging too. O2% is related to scavenging pass-through, and can be associated with reactions occuring in the exhaust stream that change the mixture. CO is probably the simplest metric for enrichment. Before wideband o2 sensors existed, all you went by was the CO%. HC ppm can correlate with unburned fuel passing through the exhaust valve during PFI scavenging.

So that's the PFI skewing AFR thing. Meanwhile, the DI start of injection event is timed past the scavenging crank angle window. So that fuel isn't thrown into the exhaust and isn't skewing the reading--this is a major reason why DI turbo engines spool better than port injected engines. They are tuned from the factory for more scavenging because fuel pass-through isn't an issue.

And as a further side note, if the injection system is sophisticated enough there can be multiple injection events for knock relief. The FA20 doesn't seem to do this, but many other DI engines can. Here is among the most sophisticated on the market, the M133 2.0 engine by AMG/Daimler using Piezo A-cone injector:



So you've got different things going on actually inside the cylinder depending whether it's PFI, DI, or PFI + DI due to injection and valve timing.

[steve99]

very informative thread thankyou to all

[Circuit Motorsports]

Originally Posted by moto-mike

Well, lets just say this. We won't remote tune your FI FT86 unless it is equipped with a proper wideband or you're willing to eat the motor...

We require a proper wideband for FI tuning as well. I don't trust the stock sensor for anything richer than 12.2. Even then there are inconsistencies.

- Bob

[Xero-Limit]

You can calculate this. Take TDC as your starting point. Then add you IPW + latency and you can convert that to crank angle degrees with some math. Generally when factoring in latency (and the distance of the injector nozzle from the valve) I think we're safe in saying that overlap shouldn't play too much a role with PI on the FA20 with reasonable IPWs. With DI though it is a rougher calculation since you can specify start of injection much more precisely with the DI angle, and as a result have a much higher chance of hitting that overlap point. The variable here is that even with overlap, since the piston is moving down you may not necessarily have the fuel go out the exhaust valve. It may move down the combustion chamber instead. You'd need to do some flow analysis to really find this out, but this is exactly the kind of situation we can see on the dyno, and where the AFR in the cylinder vs pipe becomes important.

Originally Posted by arghx7

Nobody has come up with a RAM value from the FA20 ECU or a calculated parameter to determine the end of injection timing for the FA20's PFI system. If the end of injection occurs during an open intake valve & overlap, you've got all that unburnt fuel possibly reacting in the exhaust manifold or otherwise skewing the wideband as I said.

[cjsporl1996]

Originally Posted by Sportsguy83

AEM Failsafe if you are boosted is such a no brainer.

I don't think its necessary for a supercharged car. You don't have to worry about a boost spike.

[Sportsguy83]

Originally Posted by cjsporl1996

I don't think its necessary for a supercharged car. You don't have to worry about a boost spike.

Not absolutely necessary, yeah, true. Still good to have as it let's you know everything is working as intended and can let you troubleshoot a problem in the future.

For example, there is no way of telling if you are hitting target boost (only other way is upgraded Map sensor and OBD2 reading).



Whitefrs hates my phone signature

[Grip Ronin]

so while using the stock 02. a low 12, should be the best area to keep it?

[andrew20195]

Originally Posted by Grip Ronin

so while using the stock 02. a low 12, should be the best area to keep it?

If you're forced to use the stock a/f sensor, I would think the safe way to do it would be on a dyno, and increase fuel delivery until you start to lose power from too much fuel. Then dial it back a bit.

A decent wideband costs less than an engine, though.

[Grip Ronin]

Originally Posted by andrew20195

If you're forced to use the stock a/f sensor, I would think the safe way to do it would be on a dyno, and increase fuel delivery until you start to lose power from too much fuel. Then dial it back a bit.

A decent wideband costs less than an engine, though.

that would jus foul your plugs. you should study tuning a bit more before messing with it. ive edited my cl and ol differently

[andrew20195]

Originally Posted by Grip Ronin

that would jus foul your plugs. you should study tuning a bit more before measing with it. ive edited my cl and ol differently

Running the fuel delivery for maximum power would foul plugs? First I've ever heard of that. Running super rich would foul plugs for sure.

And to further respond to your previous post, in this very thread, posters have mentioned how the stock A/F sensor reads very inconsistently at lower a:f ratios.

[Grip Ronin]

Originally Posted by andrew20195

Running the fuel delivery for maximum power would foul plugs? First I've ever heard of that. Running super rich would foul plugs for sure.

And to further respond to your previous post, in this very thread, posters have mentioned how the stock A/F sensor reads very inconsistently at lower a:f ratios.

sry read your last post wrong, i was on a phone. i was getting my quotes confused because another andrew#### just tagged me in somthing lol but yes that would be better set o a dyno

[SirBrass]

Correct me if I'm wrong, but I think they're talking about front sensor unreliability for tuning in FI applications, not NA.

[Xero-Limit]

Spent a couple of hours wiring the AEM failsafe WBO2 and using our custom map to log the output (within .2 of what the gauge shows).

Note the huge discrepancy and the inconsistency. The AEM unit shows exactly what our dyno wideband was showing (but .4 points richer as it is pre-cat).

That huge spike that looks to be super lean at 15.8 but it is actually just 12.4...