dyno results and A/F ratio

[Craig 94 TA GT]

The WOT csv runs are posted above.
So you don't have to go back:
http://s94938520.onlinehome.us/stock_tune_wot.csv
http://s94938520.onlinehome.us/stock_tune_wot2.csv

The partial throttle ones are here:
http://s94938520.onlinehome.us/stock_tune_test.csv
http://s94938520.onlinehome.us/stock_tune_test2.csv

But I don't see any problems with the PW at part throttle, with an exception to idle sometimes...I've seen 3-5 for some reason. Thanks bud.

[Craig 94 TA GT]

I hate to keep adding to my own thread, but I've been wanting to ask this question since the start.

I think it's pretty normal, but during the dynos, why is my car the only one to have "afterfire" when letting off the gas after the WOT run. It does it all 3 times, yet I cannot hear this from any of the other cars.

[Joe 1320]

I hate to keep adding to my own thread, but I've been wanting to ask this question since the start.

I think it's pretty normal, but during the dynos, why is my car the only one to have "afterfire" when letting off the gas after the WOT run. It does it all 3 times, yet I cannot hear this from any of the other cars.

Exhaust leak. The combustion gasses are still burning and expanding while exiting the head and heading down the exhaust pipe. Any additional air will accelerate the burn and you get the exhaust pop. All connections must be leak free, and sometimes it's next to impossible. I also think your whole tune is tied into this same thing. My bet is that your leaks are causing the tune to be off as well as the lifting pop out the back.

[fastTa]

Craig, here you go. I added some formulas to calculate fuel flow, air flow, and VE as well. Your duty cycle does not appear to be completely out of the ordinary, but they are approaching 90%. This shouldn't be a problem at that RPM range, but it's hard to predict when a injector will lose control or even go static over 90%.

Craig's VE and IPW Spreadsheet

[Craig 94 TA GT]

Exhaust leak. The combustion gasses are still burning and expanding while exiting the head and heading down the exhaust pipe. Any additional air will accelerate the burn and you get the exhaust pop. All connections must be leak free, and sometimes it's next to impossible. I also think your whole tune is tied into this same thing. My bet is that your leaks are causing the tune to be off as well as the lifting pop out the back.

Thanks for the explanation Joe. That now verifies the leak



Kev, I can't get the link to work. I've tried from home and work, but it says it can't be found?

[fastTa]

Thanks for the explanation Joe. That now verifies the leak



Kev, I can't get the link to work. I've tried from home and work, but it says it can't be found?

Did you try to right-click and save? Let me try another link.

[Craig 94 TA GT]

Yea, no matter what I do, it cannot find the link.

[fastTa]

Yea, no matter what I do, it cannot find the link.

Ok, weird. I was trying to use my Yahoo Briefcase but I guess I need to check the shared settings, PM me your email addy and I will send it to you that way.

[Kevin - Blown 95 TA]

I was able to clean the current white NGK plugs with a wire brush and a bit of seafoam. Does that still mean it's lean...if you can clean them off fairly well?

Watch that - cleaning a plug with a wire brush is considered a no-no. If you get any metal on the ceramic insulator, which you might if it touches the brush, it can then misfire like it is shorted to ground and foul a whole lot easier.

Well, I have been tuning my car with a wideband in the last week or so and learned a thing or two about AFR & Lambda. First, my car seems to be running at closer to 14.1 AFR in closed loop. This is because the fuel has up to 10% Ethanol in it, and it lowers the Stoich from 14.7. If you look at the Lambda is still 1.0 which is Stoich independent of the type of fuel used(Lambda is the % O2 lean or rich the engine is running before the reading is converted to AFR by a formula based on a Stoich of 14.7 [pure gasoline]) So the car was running perfectly in closed loop, but the AFR is off due to the fuel not being pure gasoline. Now as I get into boost at WOT, I am doing a progressive injection of 50/50 Methanol and Water which is adding fuel above and beyond what my PCM is demanding from the fuel enrichment tables. So, with my car running really rich at 11-11.5 AFR the injection of extra fuel starts to occur and what do you think happens? Shouldn't it richen up my mixture and result in a lower AFR? The answer is Yes & No. Imagine my shock when in boost, the spray comes in and the AFR jumps up from 11.xx to 12.8 and I have to get out of the throttle!!! Yes I am adding fuel and richening the mixture, but there is a lot of O2 in the Methanol which moves the Stoich value down and tricks the AFR into a higher number even though I'm really going richer. Now, taking the same data based on Lambda, which is going to be the same for all fuel, and I am actually at .74 which is richer than where I was with the .77 which is also too rich (need to be at .83-.84), so I actually need to take out more fuel all around. I didn't go leaner as the AFR gauge showed, actually richer - It was the Stoich point that changed with the fuel, which changed the AFR reading since the AFR was never correctly calibrated for the 10% Ethanol gas nor the the 50/50 Methanol Water injection. Now I am going to tune soley by Lambda like the rest of the world and not mess with AFR like they do in the US.

So my point of this doctoral thesis is that, yes, an AFR gauge can lie to you in certain circumstances.

[Kevin - Blown 95 TA]

Good article on reading plugs

[Craig 94 TA GT]

Wow Kevin, great info. I'm not sure what to say because I have no experience in that...but I guess the main thing to learn is that the wideband isn't all that accurate. Which makes me wonder...the more ethanol in the gas, the leaner the exhaust will appear to be, correct? And how long would it take for gas to break down/go bad? I'm running on the same tank since early July or late June. I just put in 3 gal of 91 before the dyno, but still had probably twice that in the tank.

Regarding the plug reading site, here's a description of mine (hard to see in pic), with the numbers referenced by the tutorial:
#1: Completely white on some, others part white or white spots, extending all the way down to where it meets the thread area.
#2: exactly as #1, completely white as the whole arm is the same color, or covered mostly with white spots.
#3: about 1-2 threads are black, and the rest are still with antiseize or near "same as new" color.
#4: completely white porcelain, just like new

Thanks for the tip on the plug cleaning too...I'll make sure to use only seafoam and a shop towel from now on.

Kevin (fastTA) sent me a spreadsheet that shows VE vs duty cycle vs RPM, and everything seemed to be within a somewhat normal range. So, if it's not the fuel, what about the timing chain? Is that a possiblity since the car has 110k, and it's probably never been changed? Or would a stretched, older one lose timing and act completely opposite?

[fastTa]

Craig, I sent you another spreadsheet reflecting your first run. Kept injector flow rate, AFR, and duty cycle calculations the same. You got mail!

[Kevin - Blown 95 TA]

Wow Kevin, great info. I'm not sure what to say because I have no experience in that...but I guess the main thing to learn is that the wideband isn't all that accurate.

Actually, the widebands can be very accurate - usually ±0.1 AFR - if they are well taken care of, calibrated, and placed in the proper place on the vehicle, but the reported AFR can be off if the lookup table for converting Lambda to AFR isn't adjusted for the fuel. Here is a page with the AFR of different fuels - as you can see - it changes with the fuel used...DIY Wideband Information

Which makes me wonder...the more ethanol in the gas, the leaner the exhaust will appear to be, correct? And how long would it take for gas to break down/go bad? I'm running on the same tank since early July or late June. I just put in 3 gal of 91 before the dyno, but still had probably twice that in the tank.

Right. Not sure about old gas what happens to the alcohol content. I know my bike won't start if it sits 3 weeks with the same gas (up to 10% corn liquor) in it, but I'm not sure exactly why.

[Kevin - Blown 95 TA]

Here's another good link from the Innovate web site. the guy running th show over there is real knowledgable.Tuning Tip: Ethanol Content

[Craig 94 TA GT]

The only thing is...with the dyno's wideband is that the tests on the LS1 cars seemed to be pretty accurate. We should be using the same type of gas, as it's a "California mix" isn't it? Unless, my gas went bad, or I filled up on bad gas as you've suggested. I'll try to fill up with fresh gas to dillute the current tank.

Kevin (fastTA) sent me a spreadsheet on my 1st WOT run and the pulse widths, at some RPM, are showing abnormally high for a bolt-on LT1. I'll try to get it posted when I get home. Thanks Kev for the spreadsheet.