Due to the nice weather today, I was tuning my car again.

While working on getting the high RPM/WOT MAF sensor values tweaked (by disabling PE mode), I noticed something kind of odd.

At WOT the short term BLMs would fluctuate between about 123 and 132, with the O2s following.

Normally, with a single commanded AFR, you'd think they would stay around the same value, right?

Any ideas on why this would happen?

 

Anyone?

 

i would like to know how you diabled PE mode.

 

Disable PE mode? don't know why but its easy, go to your FUEL section in LT1 edit & for the WOT TPS values put down something over 100% say 110%, then you'll never hit PE mode.

 

Make the minimum MAP value for WOT over 100, like 125.

Bunker, any ideas on what I'm experiencing?

 

Not really, my friend is acctually talking about it, his buddy is experiensing the same thing, upload me your tune & I'll take a look at it:

bunker@telus.net

I'll help you out.

 

thank you

 

Just guessing, but if you are prohibiting it from entering PE mode, is it staying in closed loop, and still "learning"?

 

Yep, that's why I have it disabled. To get the MAF sensor as calibrated as possible in the WOT areas, so that when it's enabled, my commanded AFR for WOT will be accurate.

But, I am thinking that if I am at WOT, the engine is under load, and shooting for 14.7:1 AFR (PE disabled), that the engine should be producing a similar output... not going back and forth from rich to lean every other millisecond (123 then 134, etc.).

Does that better explain what I'm experiencing?

 

If its still in closed loop at WOT, why wouldn't it continue to function exactly like it does at part throttle. That's what closed loop is all about... the PCM looks at the O2's and reacts by adding or pulling fuel with the short terms (INT's). It tends to overshoot - a little too rich, a little too lean... back and forth.... and I think that might actually be intentional, since it provides small pulses of oxygen/no oxygen through the cats to allow the "homogenous" combined reduction/oxidation catalysts to do their work. The fact that its "averaging" about 128 for the INT's would appear to confirm that.

 

Yeah, I see your point.

If I accelerate at a steady pace at part-throttle, the BLMs tend to stay about the same... so I thought it was odd how they vary at WOT.

Also, with PE enabled, generally the O2 sensor values stay pretty much the same while at WOT, so I guess I expected the BLMs to behave similarly when PE is disabled.

Oh well, thanks for the input. It's probably somewhat normal like you say.