Boost Pressure VCD

[PCDoctor]

Hi All

I Have attached a graph with readingS for boost pressure which does not looks like the sample i have seen

I Sorted the data by rmp and was expexcting to see a nice steady graph rising but its all over the place..

I Do at the moment have suspicion of a faulty N75 .. MAKING NOISE's IT SHOULD NOT BE .. POSSIBLY

Any thoughts..

Boost Pressure.zip

[martin1810]

It's a mess because you need one continuos run in 3rd gear from 1000 - 4000rpm. Then take out any rpm values that occur more than once. Make sure you don't graph as a line graph.
That will smooth everything out, then you can diagnose.

[turpal]

Those boost spikes not looking good.

[PCDoctor]

Hi Martin

New file attached..

2 Samples taken and looks week to me boost wise.. but you have seen more of these than me.. all done with engine at 90 degrees and 3rd gear 100 to 3500 rpm (1.9TDI AWX)

Boost Pressure2.zip

[martin1810]

Engine Spec Actual
speed intake intake.
rpm press press
1386, 1128, 1104
1428, 996, 1116
1533, 1020, 1092
1659, 996, 1164
1764, 1872, 2220
2163, 996, 1140
2205, 1560, 1644
2247, 1056, 1092
2436, 1560, 1572
2646, 1512, 1656
2814, 1452, 1428
2940, 1440, 1416
3066, 1428, 1404
3171, 1440, 1404
3276, 1428, 1440
3381, 1416, 1392
3444, 1344, 1356
3486, 1344, 1332
3507, 1332, 1332


When interpreting these graphs you look at the overall shape and how the spec and actual figures compare. Apart from the odd bit highlighted below. Your spec vs actual figures are fine and the overall shape is fine. I've highlighted two engine speeds which don't make sense. From 2205 rpm the graph is fine but at 1659 and 2163 the results don't make sense. The spec and actual results are in sync so it is not a turbo fault.
Hopefully it is a read error. I suggest you run the test again. If this result was real you would have felt it when driving so hopefully it's a glitch.
The graph here gives agood idea of shape. VCDS AND PD TDI ENGINE HEALTH CHECK - PASSAT

[PCDoctor]

Hi Martin

Thanks for taking the time to look

These oddities where in yesterdays data also

If they were correct ie they are real errors what would you give it a guess to be....

Remember i still have that farting sound !!!

[smithy602179]

Hi Martin

Thanks for taking the time to look

These oddities where in yesterdays data also

If they were correct ie they are real errors what would you give it a guess to be....

Remember i still have that farting sound !!!

think you should leave missus at home when you go out lol

[martin1810]

Hi Martin

Thanks for taking the time to look

These oddities where in yesterdays data also

If they were correct ie they are real errors what would you give it a guess to be....

Remember i still have that farting sound !!!

I think I mentioned previously that the sound might be the N75 valve dumping vacuum through the air filter box. Those two odd (red) figures show the turbo boost effectively stop. At that point the N75 would be dumping vacuum and might make your 'farting' noise. This is not a turbo fault or an N75 fault because the ecu is telling it to do it. You can see this because the spec and actual figures match. Can you feel anything when you here the sound, does the engine hesitate or feel like it misfires. The most obviouse reason for what you are seeing is a missing sensor input. It might be worth logging MAF readings during the same wide open throttle run. If you get more data I'll have a look for you. This is quite complicated because if the fault is real it must be due to the ecu cutting boost because injection has been cut. So the fault must be related to injection quantity and the most obvious culprit is the MAF or it's wiring. BUT I would expect to see a MAF fault code logged if that was the case.

[PCDoctor]

Will do more testing

No fault codes thou

Did you take a look at the second sample in the attachment

Looks better i think

[martin1810]

Will do more testing

No fault codes thou

Did you take a look at the second sample in the attachment

Looks better i think

Sorry didn't see the second one. The second one is fine pattern and shape wise but the boost values on both are too low which is odd. You must do the run with wide open throttle. Perhaps you need formula 1 training. Try again 1000 - 4000rpm wide open throttle/pedal to the metal! We need to force the car to give one set of known readings from its turbo map and the only known point we have is flat out. That's why you do it that way.