N75 duty cycle

VCDS block 011 reports N75 duty cycle of 96% and 4 %.Does the % mean the percenatge of time there is 12VDC power applied to the N75 solenoid, or percentage of time when it is not getting 12VDC power? Thanks!

I put my oscilloscope from the N75 "signal" lead to ground. Here are the results:

http://forums.tdiclub.com/showthread.php?t=268077&page=3

The ECU cycles a switch, allowing current to flow from 12V through the N75 solonoid, to ground.

The percentage in duty cycle is the percent at high voltage.

That's good info! What is the typical N75 duty cycle when coasting at 55 mph in 5th on level ground and when you floor it?

I am not sure I can give you a definitive answer. It depends upon the tune and type of car.

In my PD the more duty cycle the more vacuum you get from the N75. So the high voltage state ports vacuum to the controls which pulls the vanes to the max boost position.

so 95% DC gives 24" of hg, full boost.
5% DC gives less than 3" hg, minimum boost.

at 55 mph I am usually around 60 to 95% DC (hilly around here).
when I floor it, the DC goes to 95% (max boost) for a half second, then, as boost increases past the target value, the DC decreases to about 5% as it tries to prevent overboost.

When I start the car and it is idling, the DC is 95% and the vane position is max boost. This is because the requested MAP is more than the actual MAP in this condition.

I have an RC1+ tune on a PD, so your results may vary.

DanG144, thanks for the exc explanation. My engine is the 1Z with stock tune. I will take a log of block 011 MAP and post the duty cycle graph.

I used the graph function in VCDS to make this plot and did a screen capture. Excel does not make a discernible graph of the duty cycle because it's value is so small compared to RPM.

The light blue (or is that gray?) line is the duty cycle and is 93.4% at idle. red is rpm, green specified MAP. yellow actual MAP. The graph shows starting at idle 1st thru 3rd gear. There are excursions and pulsations (at approx. 1 hz/ sec) of the actual MAP at the higher rpm's. I can feel it as the car accelerates and I am trying to find the cause of it. Any ideas? I have checked the N75 solenoid valve with both pressure and vacuum and it checked OK, have also pressure and vacuum tested the lines to the ECU/ MAP sensor. I have not checked the lines to the turbo or the wastegater actuator yet.

What is your fueling and airflow doing at the time of the pulses?

Is this wastegate chatter? I have heard of it, but know very little about it.

Is MB 008 the one I should be looking at for fuel qty? Which cyl are the 3 columns of IQ? Anyway MB 008 col. 1 is at 37 mg/str, col 2 is 36 dropping down to 23 mg/str, col 37 dropping to 31 mg/str. This is while starting at 3000 rpm in 3rd and mashing the pedal.

Hello tdi brothers and sisters, i have similiar question about n75 duty cycle. In my 1997 audi a4 b5 1.9tdi 110hp turbo actuator doent pull leg as much as it should be i think. I think it have to be pulled at max till hits stopper bolt. It pulls like only 80%. Vcds at channel 011 shows 55% duty cycle at idle. Ive bought new n75, but still i have same issue. Actuator is tested and holds vacuum as it should be. I dont have any ideas. All vacuum lines are changed, vacuum pump is perfect and makes enough vacuum. Btw, my turbo always have sticky vanes, but used other new turbo i have for future project. Help me someone. Thank you, have a good day and sorry for my bad english

The ALH and PD motors have opposite N75% readings; if the ALH N75% is at say, 15% the ECU is giving the actuator as much vacuum as it can, if the N75% is at say, 90% the ECU is trying to bleed off the vacuum as fast as possible. With the PD motor the N75%'s work the exact opposite. The place you need to check the N75% is at full throttle in third gear. IIRC, my N75% at idle is around 14%. A reading of 65% @WOT in third gear is a generally good reading for a correctly tuned motor. Do not get caught up on having 3" of vacuum when the actuator starts to move and 18" when it hits the stop, not all turbos are going to work at their optimum with these settings. Those are the general settings for a factory replacement turbo, but if your turbo is modified in any way, those numbers are basically useless.