FINA4

Past few weeks I've had this weird problem with my car. On higher gears (especially 3rd and 4th) when building the boost (around 2500-4000 RPM), the car feels hesitating/jerking/surging. Also little extra noise is present in that RPM range (not a hizzzing or wooshing sound, maybe a sound of fully open wastegate or open DV). I've VAGed the car and here's what I've found out so far.

- No fault codes
- Channel 115: The requested boost is in align with actual boost, but the actual boost jumps up and down (you can feel it in the acceleration), sometimes even 150mbar. The requested boost is nice and linear.
- Channel 118: N75 duty cycle is crazy (jumping between 75-90-100-75-90%). When the actual boost is jumping, the duty cycle jumps ~20%
- Channel 32: Idle lambda correction is normal, but high RPM lambda correction is -15% (which tells that I'm running rich)
- Channel 2: MAF readings are OK (up to 200 on 3rd WOT)
- Channel 14,15,16: No cylinder misfires
- Channel 34: EGTs are in normal range

This is what I've tried so far:

- "Tennis ball" pressure test method (up to 15psi): No leaks audible/visible
- I checked DV twice (Forge 007P), everything looked fine and the piston movement was fine. I tried 2 different springs (green, yellow), no difference.
- I changed new spark plugs, no difference
- I bought a new MAF, no difference.
- Turbo inlet/outlet pipes are OK
- All hoses from TIP are tight

I'm running out of options, so I'm hoping you guys could help me out. Here are still a few question marks:

- Bad N75?
- Hose from N75 to wastegate leaking?
- Bad N249?
- Hose from N249 to DV vaccum line leaking?
- Wastegate broken from the KO4 itself?

I don't want to start blindly replacing the parts because that can get pretty expensive (N75 alone is 92 bucks!). I'm running Revo KO4 with FMIC and 386cc TT225 injectors. I have obly 7kmiles with the KO4 and 'til lately everything has been running really nice.

Here are my 115 and 118 logs:

115:
RPM LOAD R.Boost Act. Boost
1520 31.6 1120 1060
1760 69.2 1320 1030
1720 78.9 1600 1100
1720 82.7 1620 1130
1760 85 1630 1180
1800 88.7 1650 1220
1840 92.5 1680 1260
1880 95.5 1720 1300
1920 99.2 1760 1340
1960 103 1800 1390
2000 106 1870 1430
2040 110.5 1920 1480
2080 114.3 1980 1530
2160 118.8 2050 1590
2200 122.6 2110 1650
2240 127.1 2210 1720
2320 133.8 2260 1800
2360 141.4 2320 1880
2440 149.6 2370 2000
2480 157.1 2430 2100
2560 163.9 2450 2200
2640 174.4 2460 2330
2680 184.2 2460 2460
2760 188 2470 2510
2840 178.2 2480 2390
2920 185 2490 2390
3000 191.7 2500 2520
3040 182 2510 2410
3120 188 2510 2380
3200 191.7 2510 2520
3280 183.5 2510 2390
3360 191.7 2510 2480
3440 191.7 2510 2510
3480 188 2500 2420
3600 191.7 2500 2480
3680 191.7 2500 2500
3720 189.5 2500 2430
3800 191.7 2500 2440
3880 191.7 2510 2520
3960 191.7 2510 2470
4000 191.7 2510 2380
4080 191.7 2510 2470
4160 191.7 2500 2450
4200 191.7 2500 2380
4280 191.7 2500 2480
4360 191.7 2500 2400
4400 191.7 2500 2390
4480 191.7 2500 2440
4520 191.7 2490 2430
4600 191.7 2480 2360
4640 191.7 2480 2410
4720 191.7 2470 2390
4760 191.7 2440 2320
4840 191.7 2440 2300
4880 191.7 2430 2310
4920 186.5 2420 2320
4960 186.5 2420 2310
5000 187.2 2410 2240
5040 185 2390 2220
5080 181.2 2370 2280
5120 182 2350 2240
5160 182 2330 2180
5200 179.7 2310 2220
5240 178.9 2290 2180
5280 176.7 2270 2150
5320 175.9 2250 2140
5360 176.7 2220 2110
5400 174.4 2210 2100
5440 175.9 2200 2090
5480 172.9 2170 2080
5520 170.7 2170 2120
5520 169.9 2140 2060
5560 169.2 2140 2050
5600 168.4 2110 2030
5640 166.2 2110 2030
5680 166.2 2100 2020
5720 163.9 2090 2050
5760 163.2 2080 1990
5760 162.4 2070 1990
5800 163.2 2060 1980
5840 160.9 2050 1990
5880 160.9 2050 1960
5920 161.7 2030 1950
5960 159.4 2020 1960
5960 159.4 2010 1960
6000 144.4 980 2130
5920 16.5 980 1750
5720 12.8 980 1410
5520 13.5 980 1250
4680 59.4 980 1140
4480 43.6 980 1230
4440 41.4 980 1220
4400 28.6 980 1230
4360 18 980 1180
4240 13.5 980 1140
4040 13.5 980 1100

118:
RPM Temp Duty Actual Boost
2520 24 0 1170
2080 24 58.8 1070
2040 24 58.8 1130
2080 24 97.3 1150
2120 24 100 1170
2120 24 100 1240
2160 24 100 1320
2200 24 100 1380
2240 24 100 1460
2280 24 100 1550
2320 24 100 1640
2400 24 100 1760
2440 24 100 1870
2520 25 100 2000
2560 25 100 2140
2640 25 98.4 2290
2680 26 75.7 2430
2760 26 74.1 2480
2880 26 91.4 2320
2920 26 72.9 2410
2960 26 74.1 2470
3040 26 96.5 2310
3160 26 72.2 2430
3200 26 77.3 2480
3280 27 86.7 2350
3360 27 73.3 2400
3440 27 78 2440
3520 27 85.5 2300
3600 27 74.9 2520
3680 27 77.3 2450
3760 27 94.1 2310
3840 28 74.9 2400
3920 29 77.3 2470
3960 29 87.8 2330
4040 29 84.7 2350
4120 29 85.9 2410
4240 30 79.2 2420
4280 30 87.5 2350
4360 30 91.4 2340
4440 31 88.6 2400
4520 32 77.3 2410
4560 32 97.3 2380
4640 33 76.1 2350
4720 33 83.5 2340
4760 33 77.6 2380
4840 33 100 2340
4880 34 100 2320
4960 34 80.8 2270
5000 35 92.2 2240
5080 36 100 2240
5160 36 100 2240
5200 36 100 2190
5240 36 98 2140
5280 37 100 2130
5360 37 100 2120
5400 37 100 2120
5440 38 100 2050
5520 39 97.6 2040
5560 39 100 2040
5600 39 100 2080
5640 39 100 2040
5720 39 100 2020
5760 39 100 2020
5800 40 100 2000
5840 40 100 2000
5880 41 89.8 1980
5800 41 0 2140
5640 40 0 1570
5400 39 0 1330
5080 37 0 1220
4240 36 0 1160

Thanks guys!

twoquattros

<center><img src="http://pictureposter.audiworld.com/72954/l_hose_atw_pn.jpg"></center><p>This hose is often the cause of overboosting for many people. Check yours and make sure it's not riped. By the way, I have an extra N75 valve if you want to try it. Let me know
John.Rodrigues@Expressjet.com

FINA4

Thanks John. In older A4 models that L-hose was a problem indeed. I checked mine and it was OK. Where are you locate btw?

I did some more N75 investigation tonight. I disconnected (I f*cking hate those factory clamps!) and pinched the N75 feed line going from N75 to compressor housing and went for a test drive. I was taking log from actual boost and now N75 disconnected, there was no more jerking motion. The boost increases linearly and holds (althugh it jumps of the chart after 2540mbar when VAG-COM cannot read any higher numbers). But the question is that do I have a bad N75 (leaking) or am I just not getting the jerking motion since ECU cannot control the wastegate anymore (i.e. the problem is elsewhere and ECU is just trying to correct it via wastegate)?

Also, should the DV stay closed until I release the throttle or should it start opening the piston once I hit really high boost? I'm saying this, because in the high boost area I can hear this "air through metal pipe" type of sound and I cannot think of it anything else but the sound coming from DV.

We did the pressure test for the system (15psi) and we couldn't hear any leaking noises, but could it still be that I have a leak from N249 going to DV vaccum line hence DV doesn't stay closed when hitting high boost? But if the DV didn't stay closed, would I still see solid and linear boost increase on the actual boost?

My N75 seems to be 058 906 283 C. I've heard that the latest factory N75s are 058 906 283 F ones.