Question about low O2 #'s vs knock.

[my_gst95]

Not sure if this belongs in the noob section,

I'm not sure if my O2's are reading low because of a bad sensor or bad pump. My question is, if an O2 was going bad and reading lower numbers then it actually is coming from the engine...would the low numbers effect knock/timing readings? For example, if my O2's were atually .90V, but the sensor was reading .83V...would the false reading of .83V calculate into the ECU and pull timing and give a false sense of knock? The only reason I ask is because on my 90, I have 550's, 10k resistor mod, a walbro255 and a rewired pump and with my SAFC 0'd out, it reads REALLY lean at 15psi WOT(.80-.83V at 5000+ rpms) and has about 8 counts of knock. I have to richen it up to +10 on the HI settings for 0 knock and 21* timing.

If O2 readings don't really matter in the 0 knock/ 21* timing tuning area, then my next mods will be a new pump (190). If O2's do matter, then it will be a new senor and a afpr instead.

my_gst95

 

[Plague]

Stock o2 readings are inaccurate, tune for knock and timing.
I tune for 4-7 knock and 18-22 timing. Does me just fine.

 

[Kevin Jewer]

Originally posted by my_gst95
10k resistor mod

Not sure what you mean by this, but I have an idea. If you are using this shyte hack mod, you will need to compensate in your fuel settings. In other words, if you are leaning out with a resistor mod, you shouldnt be surprised if you are running lean Perhaps I am misunderstanding the situation, and more info is required.

 

[my_gst95]

I'm not sure if it's the same with my 2G, but I know in a 1G, you can put a 10k resistor or a 10k ohm potentimeter in series with the Intake Air Temp sensor at the MAS or on the ECU that will trick the ECU into thinking the Air is colder, giving you a richer condition. When I did this mod, my O2's went from .79 to .83-.85. So I can verify this helped a bit. I've heard people putting a 10k ohm resistor 'parallel' to the circuit and giving a leaner condition, but I didn't even bother with that. I just thought with all my fuel mods, the O2's would have drastically changed. Probably just overestimated. Thanks, that puts my mind at ease for the O2's.

my_gst95

 

[Enigma_Man]

Well, there's a few mistakes you're making first off.

The ECU doesn't read the O2 sensor's voltage at WOT. This is because a regular-style (like ours) O2 sensor is very inaccurate at telling A/F ratio from the voltage at WOT. All our cars do is read the O2 sensor at low throttle, when it's cycling low-to-high, which corresponds with "richer than 14.7:1" and "Leaner than 14.7:1" the car's in a constant battle to go richer/leaner/richer/leaner, right around 14.7:1 when at non-WOT.

That leads to my second point. O2 sensors voltage output varies day-to-day, hugely with temperature, and even sensor-to-sensor. If one guy says he has a .9V at WOT, and you have a .83V at WOT, and you both get no Knock, you may both actually have the same A/F ratio!! O2 sensors are not very good at doing what people use them for.

However, if you're at WOT, and your voltage drops below .80 or so, then you know something is probably wrong, because this means "less than 14.7:1" which is _very_ lean for WOT.

As long as you're not knocking, you're good. Wideband O2 sensors actually give you a reading of Actual Air/Fuel ratio, and they are a lot more expensive. This is why they are generally only aftermarket.

-Jesse

 

[my_gst95]

Great Information. But then that leads me to wonder, how will I know then if my knock is rich or if my knock is lean? I guess an EGT and fuel filter guage should be the next mod instead.

my_gst95

 

[Enigma_Man]

You'd smell it if you were rich enough for rich knock

-Jesse

 

[Kevin Jewer]

I run my car as rich as 9:1, and I havent seen rich knock. I did however see it on the dyno. But ever on the street or track no matter how rich I went. Still not sure what i think about that. Chances are if you are knocking its going to be lean (or other typical reasons to knock).

 

[bigjangin]

dont go by o2 voltage. It doesnt matter at WOT. As long as you are in the ballpark of .90v your o2 sensor should be working. For instance...with 550's and the safc at 0% I get about .94-.95. At -14% they will be about .93-.94. You cant tune with our stock o2's.

 

[btrux06]

ya tune to have 5 or less counts of knock, if your o2s come out to .82 then thats fine, i how ever have a my 02s, with no knock and car running real good, my o2s only get to .76 on average, bothers me alot but i cant figure it out, ive tryed new and differnt o2s and ecus. tune to the knock! but i feel that the low o2s in my case are hurting my tune, do u guys think that would be safe to say that the ecu reads the low o2s on spool up and wot and attempts to fix it by dumping in a lot of fuel caussing me to run rich with no knock and run slow? it feels like it

if any ones interested in my case, i have a thread on it titled o2 way lean, cant figure it out.