A/F ratio not steady. Why??

[92eagleTSI]

I'm using the plx 300 and noticed my a/f ratio isn't very steady. Whether your just cruising or in it a little or wide open it will jump about .5-1.0 either direction like it's cycling. This isn't normal right? It should be pretty steady correct? It is like that even on the narrowband so its not the wideband. I think everything has been checked except resistor pack, can this where out? Also I had painted my ex. manifold before and noticed that after all the paint burnt off that there was still paint around the #1 & #2 runners at the head flange, it actually tappered off from 1 to 4 runners like 4 hotter than 3, 3 hotter than 2, and 2 hotter than 1. Also has anyone ever had their open wastegate trigger the knock sensor? Sorry for the lengthy post I figured i'd get it all out at once.

 

[donmagicjuan]

Your AFRs sound like they're cycling normally.

It is remotely possible for an external wastegate to trigger phantom knock, but I would still go through the normal procedures (higher octane, adding fuel) to confirm that the knock isn't real. Better to be safe than sorry when it comes to something as serious as that.

 

[92eagleTSI]

My boost controller is acting up so i can't open her up just yet for testing but when it ran up to around 25+ psi and i crapped myself i didn't have any knock. I may just route it back into the exhaust to be sure.

 

[92eagleTSI]

So even the wideband will cycle? What about when at wot shouldn't i be able to get it damn close to a particular ratio? Assuming everything with the car is right thats why i'm asking about the resistor pack.

 

[wishihadatalon]

So even the wideband will cycle? What about when at wot shouldn't i be able to get it damn close to a particular ratio? Assuming everything with the car is right thats why i'm asking about the resistor pack.

Yes that is what tuning is. Obviously there is more but on the afr side you will want to aim for xx.xx:1 afr and have it nice and steady. But you will not know how much you are off until you can actually get on it.

 

[donmagicjuan]

I have a PLX wideband, and when I do a WOT run the meter bounces around a little by a few tenths. When I look at the log of AFR, however, it looks like a relatively flat line. Digital meters are awful for analyzing trends. I'd say what you're seeing is pretty normal.

 

[CanadianTSi]

The car is supposed to cycle back and forth at Idle and cruise, this is how it works.

It sees that it's a little lean so it adds fuel then it see's its a little rich so it takes away fuel then it see's its a little lean...and so on.

 

[wishihadatalon]

The car is supposed to cycle back and forth at Idle and cruise, this is how it works.

It sees that it's a little lean so it adds fuel then it see's its a little rich so it takes away fuel then it see's its a little lean...and so on.

open loop operation always aiming for stoich right?

 

[oldman]

open loop operation always aiming for stoich right?

No, close loop.

92eagleTSI, fuel trim (close loop) is controlled by your narrow band O2 sensor so naturally a wideband (read only) will cycle along. However, like the narrow band, it should stop cycling during open loop operations.

 

[donmagicjuan]

Just to clarify, 92eagleTSI...
When you talk about the AFR cycling 0.5-1.0, your talking about points, not volts, right?

 

[oldman]

Just to clarify, 92eagleTSI...
When you talk about the AFR cycling 0.5-1.0, your talking about points, not volts, right?

I thought he meant .5-1.0 from 14.7.

 

[donmagicjuan]

That's what I thought as well. I think it's just normal fluctuation that he's seeing. The signal from the sensor can be pretty wacky without any smoothing applied. That's why I look at the meter readout to make sure I'm not grossly off-target, but I use the wideband plot from my logger exclusively to make adjustments.

EDIT: Except at WOT I assumed that his was oscillating around a lower AFR, of course.

 

[wishihadatalon]

No, close loop.

92eagleTSI, fuel trim (close loop) is controlled by your narrow band O2 sensor so naturally a wideband (read only) will cycle along. However, like the narrow band, it should stop cycling during open loop operations.

I always get them confused thats why I asked. I understand the fuctions of both but I can never put the right name on them.

 

[oldman]

I always get them confused thats why I asked. I understand the fuctions of both but I can never put the right name on them.

Just think of open loop as open throttle to avoid confusion.

 

[wishihadatalon]

Just think of open loop as open throttle to avoid confusion.

alright.

 

[92eagleTSI]

Just to clarify i am talking about points. Not .5 - 1.0 from 14.7 but when I get on it whether it's wide open or partial it fluctuates. I actually thought the ecu was just showing the idle afr cycling like that not that it was actually adjusting the fuel. I thought the ecu would be able to do a better job than that. Maybe i just need some more tuning time to get it to steady out.