Switchpoints Not Cooperating

[Atomic]

I have a 2004 5.3 silverado, and from what ive been told changing the switchpoints should have some effect since this is a gen3 5.3, but I cant seem to get mine to play nicely.

I have the switchpoints set to 300 but the average switching voltage is around 550mv which coincides with my wideband showing slightly rich.

Am I missing something obvious or what?

thanks

[Mep_q8]

why would you want to change your switch points? have u tried dialing in the VE first? Don't take short cuts, it'll bite you in the ass later on making you have to re-do the whole thing again.

[Atomic]

Ive done VE, MAF, everything and not taken shortcuts. I want to change the switchpoints so my wideband and o2s agree at stoich. From what I can tell, the o2s arent even switching where they should (450). My reason for caring anyway is I want to run closed loop MAF.

[eficalibrator]

Ive done VE, MAF, everything and not taken shortcuts. I want to change the switchpoints so my wideband and o2s agree at stoich. From what I can tell, the o2s arent even switching where they should (450). My reason for caring anyway is I want to run closed loop MAF.

If you didn't take any shortcuts, one of your first steps would have been to set the stoich point in your calibration to precisely match the fuel you're tuning with. If the calibration and physical fuel match for stoich points AND you have the proper injector characterization data, you'll end up with the right MAF and VE values that naturally have you switching close to the nominal 450mV point on the HEGOs... with almost zero fuel trims.

[Atomic]

Then perhaps my question is why are the trims not adjusting to the set switchpoint like they should be?

The injectors are stock and hence using the stock calibration which GM spent a lot of time making sure was accurate.

[69lt1bird]

You have the Stoich AFR table flat lined at 14.681, if you have any ethanol in the fuel in your area, this will need to be adjusted that to I believe 14.5 for the normal 10% ethanol.

The best part is, if you tuned everything correctly, when you change the stoich value, everything else should still be fine, you don't have to go back and retune if you run CL. The narrowbands will try to keep you at your new commanded stoich value. So, set the switch points back to stock and adjust the stoich table for the fuel you use.

[WS6FirebirdTA00]

Even if the stoich is right, the switch points may not be exact. I see this more so on cars with headers (and calibration to calibration). I see where you guys are going, maybe in WB tuning he is correcting to the wrong stoich. More times than not though, I see the switch points in need of tweaking, but not by much.

I know what you are trying to do. You tune everything, all is reading 14.7ish, then you put it in CL and the o2 sensors are trying to correct to a 14.4 or something. You need to post up a log and also verify the stoich of the fuel you are using. How are they switching? You may need to adjust proportional fueling as well to get them back in line and force them to have a better switching. It sounds to me like you may be having an issue with the oscillation of the sensors.

[Atomic]

Even if the stoich is right, the switch points may not be exact. I see this more so on cars with headers (and calibration to calibration). I see where you guys are going, maybe in WB tuning he is correcting to the wrong stoich. More times than not though, I see the switch points in need of tweaking, but not by much.

I know what you are trying to do. You tune everything, all is reading 14.7ish, then you put it in CL and the o2 sensors are trying to correct to a 14.4 or something. You need to post up a log and also verify the stoich of the fuel you are using. How are they switching? You may need to adjust proportional fueling as well to get them back in line and force them to have a better switching. It sounds to me like you may be having an issue with the oscillation of the sensors.

Yes exactly. I have long-tube headers as well. I will play with the stoich setting to see if I can get any results, any hints as to what it might be for a 10% ethanol blend? I also want to run it slightly leaner for gas mileage purposes.
Post a log of what exactly? I have one in the first post along with the tune and config file showing the o2s switching. What bugs me is they are switching around 550mv instead of even the default 450. I know the computer corrects to "Stoich" but doesnt it know what that really is from the switchpoints?

[69lt1bird]

The VE and MAF tables seem pretty aggressive for a 5.3L truck with just headers, your cruising speed timing is over 50*, it that correct? The O2's seem lazy, not switching very fast.
I just looked at one of my logs and the O2's look like the switch at least twice as fast, could just be the sample.

[murphinator]

I will play with the stoich setting to see if I can get any results, any hints as to what it might be for a 10% ethanol blend?

stoich for e10 is approx. 14.13 , I see a lot of people split the difference with non ethanol gas (14.7ish) and put a 14.4 value in stoich.

In my area all gasoline for several states is labeled as 10% ethanol so I went with the 14.13

the only way to be 100% sure all the time would be to test the fuel either manually with a test tube every fill up or install the flex fuel sensor with the zietronic ethanol tester but that would depend on how anal you wanted to get about it.

I guess if you set stoich for e10 and got some straight gasoline somehow while running that tune you could run slightly richer

[Atomic]

The VE and MAF tables seem pretty aggressive for a 5.3L truck with just headers, your cruising speed timing is over 50*, it that correct? The O2's seem lazy, not switching very fast.
I just looked at one of my logs and the O2's look like the switch at least twice as fast, could just be the sample.

I have a 207/220 571/578 118.5 cam as well. My spark advance during cruise is in the 35-45 range.

[Atomic]

I changed the stoich AFR to 14.42 and the switchpoints back to 450mv. There is clear difference in the wideband readings. If you look in the old log (OP) the wideband clearly bounces around below the commanded AFR, but in the new log there is a definate oscilation about the commanded which is what should be happening. For some reason the STFTs were not logging onto the histogram correctly in the new log, but just from the wideband this looks like it solved the issue.

Now to figure out why changing the switchpoints had no effect earlier...

thanks for the help

[69lt1bird]

Am I reading it wrong or are you commanding the 14.42 but the WB is about 12:1?

[Atomic]

I think you are reading it wrong. Use the scanner config file from my first post, and look at the second chart section.

So I think this proves the o2s are switching around 14.5....now how do I make them switch around 14.7...

[Atomic]

...So any idea why changing the switchpoints has no effect?

[WS6FirebirdTA00]

I havent been keeping up, but how much did you change the switch points?

[Atomic]

tried 200mv with no difference

[jimmyblue]

If your O2s are not switching fast and symmetrically,
the whole thing kind of breaks down. I have seen
a whole AFR point from moving 500mV to 350mV,
but things were well behaved.

VE, MAF are for open loop airflow. O2 switchpoints
are for aligning (or deliberately skewing) closed
loop operation relative to the open-loop.

[WS6FirebirdTA00]

Yeah, if the proportional fueling is also off and the switching is poor, you will see poor response to change.

[Atomic]

So you are saying the trims need to be very close for the change in switchpoints to have any effect?

WS6, could you elaborate on proportional fueling?