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Hesitation/Power Loss on 100 Octane at WOT

kthor7031

kthor7031

Go Kart Champion
H132 said:
Yes, both 3rd and 4th gear logs. No throttle cut in 4th. Let me try to post...

3rd Gear:







4th Gear:



3rd Gear:



I have a couple of more 3rd Gear logs for Fuel Trims. Any help is appreciated!
Click to expand...

On the 2nd third gear log, you are short of requested boost quite a bit. Boost leak? Wastegate duty is pegged.

I have a similar issue atm, but only 200mbar off target.
 
H

H132

Ready to race!
kthor703 said:
On the 2nd third gear log, you are short of requested boost quite a bit. Boost leak? Wastegate duty is pegged.

I have a similar issue atm, but only 200mbar off target.
Click to expand...

I believe that's on account of the throttle cut immediately before. You can see that each time it cuts throttle, the ECU requests 500 mbar less boost, and so then my boost drops. But in the 4th gear log, and at all other times, boost never fluctuates. I did check though all my clamps and hoses. Don't think it's a leak.

Does anyone know if the DSG can cause the car to failsafe for any reason?
 
kthor7031

kthor7031

Go Kart Champion
H132 said:
I believe that's on account of the throttle cut immediately before. You can see that each time it cuts throttle, the ECU requests 500 mbar less boost, and so then my boost drops. But in the 4th gear log, and at all other times, boost never fluctuates. I did check though all my clamps and hoses. Don't think it's a leak.

Does anyone know if the DSG can cause the car to failsafe for any reason?
Click to expand...

The second to last column is specified boost right? If so, look again. At 6k, its asking for 2400mbar and you are hitting ~2000mbar.
 
H

H132

Ready to race!
kthor703 said:
The second to last column is specified boost right? If so, look again. At 6k, its asking for 2400mbar and you are hitting ~2000mbar.
Click to expand...

Yeah I see it....I'm down on boost that entire pull once the car failsafes. I don't think it's a boost leak, rather I just think the car never recovers from the power cut. You'll see in the other logs, it does mostly. If anything, perhaps it suggests a faulty n75 perhaps.
 
kthor7031

kthor7031

Go Kart Champion
Got it. If its asking for more boost, I would think it could recover. I don't see why it couldn't unless there was a leak or something preventing that, considering the watsgate duty being maxed. I agree though that the other logs suggest things are tight...weird.
 
H

H132

Ready to race!
Yep, APR calibrators looked at the logs and the best they could come up with was fuel sloshing in the tank. OR there's something going on between the data points in the logs they're not seeing. I honestly find both hard to believe. My tank was nearly full when it first started happening, so I doubt sloshing fuel was a problem. And although the data points are not real tight, the logs were able to record everything else at the point the hesitation occurred (throttle cut, low boost, dip in maf, etc) so why assume something more is happening and the logs are not recording it. My best guess at this point is DSG clutch slip, but does anyone know if the DSG can cause a failsafe in the car.
 
H

H132

Ready to race!
franco516 said:
if you ever figure it out dont forget to update the thread.
Click to expand...

I won't forget. My plan is to switch 100 octane fuels first and see if the hesitation still happens. Because one thing I noticed after re-logging the car on 91 octane gas is, as Hyde pointed out before, the amount of fuel the car was requesting was very low at about 4700 rpm -- about 139bar on the 100 octane logs. On 91, the car usually requests about 160+bar. So it's incredibly low. To me that suggests the car doesn't like the Sunoco 260GT Plus fuel. I've ran VP MS109 fuel without any issues, so I'm going to try that again. If it still happens, then I think the next step is a DSG tune. Thinking about going with HPA Stage 2.
 
clownish

clownish

just clowning around
I might be wrong but I have the impression that APR used Sunoco gtplus when they were calibrating the files.


Sent from my iPhone using Tapatalk
 
H

H132

Ready to race!
Clownish said:
I might be wrong but I have the impression that APR used Sunoco gtplus when they were calibrating the files.


Sent from my iPhone using Tapatalk
Click to expand...

Yea with regular Sunoco 260 GT I believe. The GT Plus has a different AFR value, gravity, and oxygenation. Jamie from APR once posted that more fuel would be required as a result to reach the targeted lambda value and the mass the car was tuned with. I'll post his comment below. What's odd though is I've used MS109, which in that case would also demand greater fuel mass, yet I didn't have any problems. So why now would the car's requested rail pressure be so low on GT Plus.



Jamie@APR said:
There are some significant differences between VP Racing MS109 and Sunoco 260GT and aren't really considered 'pump gas' equivelents.

Pump Gas
Stoichiometric Air/Fuel Ratio: 14.7
Specific Gravity: 0.740-0.770
Oxygenated: 0%

Sunoco 260GT
Octane ((R+M)/2: 100
Stoichiometric Air/Fuel Ratio: 14.1
Specific Gravity: 0.734
Oxygenated: 0%

VP Racing MS109
Octane ((R+M)/2: 105
Stoichiometric Air/Fuel Ratio: 13.41
Specific Gravity: 0.722
Oxygenated: 9% (just googled,not 100% confirmed exact %)

There are 3 major things to pay attention to with these fuels, stoich, specific gravity and oxygen content.

  • The lower the stoich value, the more the fuel system has to supply to achieve the target lambda value.
  • The lower the specific gravity, the more fuel needs to be sprayed to match the fuel mass the vehicle was tuned with.
  • The more oxygen in the fuel, the more fuel needs to be sprayed to compensate for the oxygen that makes its way into the combustion chamber via the fuel. Generally the percentage of extra fuel that needs to be supplied closely matches the percentage of oxygen in in the fuel. This can be helpful for power though, especially on a turbo that is flow limited like a K04.

As you can see, MS109 makes the fuel system have to supply more fuel than 260GT in all 3 categories. This is fine on a fuel system that is healthy and has the additional headroom to make up this difference with fuel trims. On a system that is close to being maxed out (fuel pump flow capability, fuel injector duty cycle, clogged fuel filter,etc...) you can max out the fuel trim and run the risk of running dangerously LEAN. If you run lean, the cylinder temps can get WAY hot. Enough to melt stuff, spark plug electrodes or exhaust valves, for instance.

If you are going to run this fuel or anything other than Sunoco 260GT I highly suggest logging your target/actual rail pressure, target/actual lambda values, instantaneous fuel trim and long term partial fuel trim to make sure the fuel system has enough headroom to safely supply the necessary fuel. Better safe than sorry.

Vag-Com Blocks
230-1 Target Rail Pressure
230-2 Actual Rail Pressure
031-1 Actual Lambda
031-2 Target Lambda
032-2 Long-Term Fuel Trim (partial)
033-1 Instantaneous Fuel Trim (Short-Term Fuel Trim)
Click to expand...
 
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