befuddled by O2's

[Warped]

32 years ago I got into Buicks. I stuck with them because I'm too stubborn to quit. Now I know that was just preparation for owning a turbo gn.

On my last trip to the track the O2's were tanking down to the 730's and 740's. This is with 33# injectors, new fuel filter, adj fpr set to 45 and a hot wired Walbro 307. With a car that will barely crack the 8's in the 1/8 I should have plenty of fuel and not have to be cranking the translator plus up 8% to a duty cycle of 130%.

Thinking the pump may be getting tired I replaced it with a new Red's XP+. Took it to the track last night. Nice and cold but crappy traction. Launching at 2" vacuum with translator set straight up on fuel the O2's start at 840 are at 800 at the top of 1st gear and down to 750 by the top of 2nd. This was with a duty cycle of 99.6.

Very next run they're at 780 at the top of 1st and 750 at the top of second. Didn't get any better after that.

Adding fuel with the translator+ helped the O2's a bit for a while but ultimately they continued to decline as the temp got colder. Duty cycle peaked at about 120% and the car just got slower.

Next item on the list is a new fpr but I've not heard much about the symptoms when they go bad.

Any ideas are appreciated.

 

[strikeeagle]

And do you have a FP gauge to establish that your FP is holding up?

 

[Warped]

I'll be taping the gauge to the windshield this weekend. Got too dark to read it last night.

 

[BoostKillsStres]

Were you seeing any knock in any of these runs? How did your changes effect your MPH?

 

[Warped]

Knock was not a problem. Adding 6% fuel slowed the car 1.5 mph.

 

[BoostKillsStres]

OK, I'm sure you know this already so don't get hateful. If your not seeing knock and add fuel and don't see a gain in MPH and your comparing runs are the same, aka only changed fuel and launched with the same boost and all, then the extra fuel isn't making you any more power no matter what the o2's are saying and you need to work your way back leaner to see if mph picks up.

As a quick example I have a GM o2 sensor, 10,000 miles, never seen race gas or alky, cross counts and BLM matrix are great and in my latest tuning on the street my wideband is reporting 11.3-11.5:1 actual A/F ratio and my stock o2 starts the run at 670 and drops to 620's. Only 1.0 knock on the 2-3 shift. So, I could care less what the stock o2 reads and if that was the only thing I was using I'd be pouring fuel at it too IF i had knock. So only add fuel if your seeing knock or think it might make more power and if you don't see more MPH go back the other way as your either too rich or possibly right where you need to be with fuel at that boost and conditions.

And, if your chip doesn't lock BLM cell 15 then your fuel between runs is most likely changing because that cell may be changing. Watch your INT numbers as your run starts and see if it locks to something other than your BLM cell 15 number, if it does then you have a lock patch in your chip and fueling should remain the same depending on what your maf is reading during the run.
HTH

 

[TurboDave]

I'd have to agree with BoostKills. Your O2 sensor could be mis representing what's actually happening. They shouldn't be relied on that heavilly anyway. Your expanation sounds as though you were going too rich for conditions/tune.

Then again, maybe not. There's no way of knowing unless you either turn the boost up in small incraments, or start leaning the mixture out, to the point of seeing 1-2° of knock retard (not counts), no more than that though if you're running big boost.

 

[ijames]

Also, how are you monitoring the O2 volts? DirectScan or TurboLink/other ALDL scan tool? With an ALDL scan tool you can't believe any readings from first gear and really can't trust a second gear reading either. The rpms just climb so fast compared to the 1.4 seconds/frame data rate that you have no idea where in the launch or first gear that number came from, and aren't really sure about where in second gear that number was recorded either (remember, the data bytes are spit out as the ecm can, in a fixed order, so the delay between two items in a single frame is approximately constant but can be up to 1.4 seconds if one item is the first data in the frame the other item is the last). Now, with DS at 18 frames/sec you can see and trust the lower gear data, but with an ALDL tool you really can only look at the third gear pull where the rpms climb slowly enough that you can believe what you see.

 

[MSDGN]

That's the exact reason I started using an EGT...relying on the 02 sensor readings at times it totally useless...I've had readings of 650mv at the end of the run...no knock...27-28 PSI boost...EGT looked fine so I just ignored the 02 number...

 

[Warped]

Good comments guys.

Boost during these runs was about 16. As far as a BLM lock it looks like it's locked on cell 11 which is set to 128. That may be correct for the extender chip. I'm not sure why you would lock the BLM's with the extender. That would seem to defeat the purpose. I also haven't changed the GNX O2 sensor in a couple of years. The O2 readings are from DS at the 18 fps rate. The puzzling part is making 3 runs back to back to back with no tuning changes and seeing the O2's drop like that.

I guess one of the misconceptions I'm operating under is, if you're shooting for O2's in the 790-800 ranged and you are seeing 740's instead, you're moving more air and you'll go faster by adding more fuel. As I've indicated in a separate post the DS shows WOT A/F ratio of 12.6 and I thought 11.6 was more common.

I have considered that maybe this turd is tuned correctly and it just won't run like a GN should. For what this car has in it, it should be faster than it is. I've been trying to get it straightened out for a long time.

 

[ijames]

You are also most likely starting the O2 sensor off at a different temperature every pass, especially comparing the first pass with a hot-lapped second pass, and that will shift the reading some and make the first part of first gear more variable.

 

[norbs]

Get a WB o2 sensor, I can't believe people are still counting mv's! . Spend the $300 and save your headgaskets and engine!