silverRS4

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Trying to diagnose a hesitation in my '08 RS4 with VAG-COM. No CEL's, but engine simply does not run smoothly. Its hard to describe, but its as if the AC kicking on/off quickly, or as if the throttle plate is wavering. The engine also seems to lack pick-up in 4,5,6 gear pulls (bogs). My experience would lead me to a timing issue,i.e., its not advancing enough. So I logged timing and retardation. Throttle angle is not shown because it was at 100% for the duration. I would think for 7000 rpm, timing would be at least 35 degrees. So to see it wavering on the log between 18-24 degrees, it just doesn't seem right. Are there knock sensors on each cylinder? I am using good gas, sometimes even 93 octane and it acts the same.

Any experience logging timing on a 4.2 FSI?

diagnosticator1

The ECU filters that data to extract knock signatures and assigns any detected knock activity to specific cylinders according to firing order and crank / cam position info.
The ECU filter must filter out road surface induced noise and other vibrations using a road roughness factor and other non combustion related noise from the raw knock sensor signals. If the knock sensor/s are loose, or if there is some unusual vibration noise effecting the signal, that can be mistaken by the ECU as combustion related noise. Logging the raw knock sensor signal voltages isn't accurate for knock detection, but the raw data logged may reveal some erratic signal noise that provokes inappropriate knock related timing corrections.
However, your log of the timing retard for knock correction does not seem involved, as the knock correction graph doesn't follow the variation of the ignition timing graph.

Try logging other parameters until something is found that shows variations with a pattern similar to the variations occurring with the ignition timing at the same time.

BTW, how do you know the throttle angle was 100% during the time interval logged? The DBW eGas throttle angle is varied by the ECU, and isn't necessarily only according to the accelerator pedal position.

silverRS4

to the timing variation. The throttle angle I recorded was the one that's available as a parmeter on the measuring block pop-up screen. It was at 99.6% for all the data points on my graph, so rather than graph a straight line, I just omitted it. If there is a parameter that includes pedal input adjusted by some factor, it would be interesting so see as well.

I am also going to graph an identical data set in a lower gear (2nd), when the engine seems to run just fine. It will be curious to see what the timing plot and retardation values like then. Thanks for your input.

diagnosticator1

the results will be interesting info for sure.

silverRS4

Is that on cold starts, cylinders 2,3,4 will each misfire a few times for a total of 10-15 misfires before the engine speed drops down to 760 rpm. Its apparently not enough to cause a code and no misfires are detected when I am doing my data log pulls at higher RPM and the engine is at normal temp.

I've done various logs with ESP on/off in 2nd and 3rd gear. The timing and retardation are similar in each case under load. The timing varies from 20-27 degrees and the retardation level from -3 to -9 degrees. Other parameters appear normal. I am tempted to dump in 5 gallons of 100 octane just to see if the retardation values change. Although I doubt the ECU would allow the change to be immediate. The timing just seems too retarded for a high performance, high RPM engine.

The only other thing that I notice (again regardless is ESP is on or off) is that the throttle angle does not always correlate to the position of your right foot. Maybe that is just the way it is, annoying or not.

silverRS4

Figured I'd try some Sunoco 100 octane to see if the ECU would stop retarding the timing so much. Waited until my tank was about empty and then dumped in 2 gallons. I suppose there was 2 gal of Shell 91 octane in the tank, so figure 95 octane mix. A 3rd gear full throttle data log showed a definite improvement. The timing wasn't as sporadic and the retardation dropped to 4-5 degrees. Its definitely just the normal feedback loop between the ECU and the knock sensors. The engine felt like is ran much smoother from 4500-7500 RPM as well. Conclusion - my engine is running just fine and good gas definitely makes a difference.

diagnosticator1

That's really good to learn, Thanks for the updates!