Help revs fluctuation and p0299 underboost

[adil.zahir]

Hello

I have an audi a3 8P1 170HP with an engine code BMN.

The issue I am having is with the boost of the car which is appalling and revs fluctuation.

The car boosts but not in a consistent way. When the turbo kicks in the car will boost all the way up to 3500rpm-4000rpm max then cuts out, the engine is then capped to 3000rpm where the revs start fluctuating between 2800rpm-3200rpm. When this fluctuation happens you feel the car acelerate harshly and then decelerate harshly constantly which results in a jerky ride. When the car does boost all the way up to 4000rpm, the same harsh accelerations and decelerations are felt constantly, as at times the revs will fluctuate when accelerating. If you drive the car long enough less than a mile you eventually get the coil light flashing, where the engine will be limited to 3000rpm and will not go above it until car is restarted where the cycle repeats. At times when the engine is capped to 3000rpm alot of thin black smoke is released from the exhaust pipe

You do not have to drive the car to see revs fluctuate, when idling if I put my foot to the floor on accelerator. The revs will go all the way into the redline 5000+rpm constantly, but after a short while about 5-10 seconds, the revs gradually decrease to 3000rpm and then the revs fluctuate between 2800rpm-3200rpm occur, even though accelerator is fully depressed. Eventually the coil light will start flashing followed by thin black smoke coming out of exhaust pipe if I keep the accelerator depressed. Revs will be capped until I restart the engine where the process then repeats.

When checking for codes on VCDS. The Ecu throws a code for both situations are the same if I reset the codes and try revving on idling or driving the symptom repeat again.

VCDS code:

000665 - Boost Pressure Regulation

P0299 - 006 - Control Range Not Reached

Freeze Frame:

Fault Status: 11000001

Fault Priority: 5

Fault Frequency: 2

Reset counter: 40

Mileage: 123627 km

Time Indication: 0

Date: 2019.06.14

Time: 00:31:03



Freeze Frame:

RPM: 3040 /min

Torque: 296.0 Nm

Speed: 45.0 km/h

99.45 %

Voltage: 14.01 V

Specified Pressure: 2492.1 mbar

Actual Pressure: 1704.0 mbar



Based on the code I have tried the following.

I have checked for boost leaks and found none all turbo pipes are clean no holes no damages. I checked all vacuum lines to the turbo and other components which are fine no split no kinks or damages.

The next step I did was replaced the map sensor and the maf sensor from a donor car no change in symptoms but donor car still runs fine mine has not rectified.

I have put in a new n75 valve a new crankshaft sensor and a replaced the camshaft sensor from a donor car still problem persists.

I have checked all the wiring from ECU to the following sensor connectors:

The electronic turbo actuator sensor, N75 solenoid valve, Egr cooler solenoid valve ,swirl flap solenoid valve, crankshaft sensor, camshaft sensor, DPF pressure sensor, egr valve, throttle body valve (bit in front of egr valve),accelerator postiton sender 1 and 2, all of the injectors and glow plugs. All the wiring is spot on with no shorts and continuity of each wire is solid.



After trying all of this I then took the car in to Audi where they ran a diagnostic and the same code showed

P0299.turbos/super charger underboost

picture bellow is audi scan from main dealer

Audi has checked the vacuum lines and have said they are fine and have done a boost leak test

Where no leaks were detected, and have said the turbo is fine. they wanted to further investigate and spend another 6-7 hours at rate of £105ph which is too much to spend atm.



To further confirm the turbo is fine. I removed the turbo charger and took it to a turbo rebuild shop

Where they disassembled the turbo to check internal condition and they said nothing is wrong internally and all the vanes are clean with no carbon or soot build up. They also checked if the turbo is calibrated correctly and the electronic sensor and actuator are all working all which has passed and they provided a certificate for showing what flow rate it is producing.

Turbo is refitted and the problem of the is still there.



Could anyone out there please help me as I am hitting a brick wall and do not know what else to do with it



cheers in advance
​

 

[Kayobong]

Have you checked your EGR valve?

 

[NHN]

I wonder if it's getting any back pressure issues.

I would also do temp wire tests, as in, for a temp replacement of wires to the turbo, n75 etc as it may have damage not seen to the naked eye that also may still conduct & provide a circuit that at times breaks, it's hard to diagnose over the net.

 

[adil.zahir]

Kayobong I have checked the egr valve a while back. The wiring is fine however The valve itself isn't bad according to me. In the valve around the rod that moves up and down to allow the gasses to be recycled has slight carbon build up. But when I test the flap in vcds it move up and down freely. But it only moves up around an inch so the flap is in the middle of the hole not fully to the top hope I am making sense. Dont know what the normal movement is supposed to be. I'll tak a picture of the condition and movement that happens. I have tried blankig the egrvalve and egr cooler using blanking plates. Symptoms still the same, same error code and no error code for egr comes up as on would expect due to low flow through egr valve. The throttle body is clean aswell and rotates freely with no binding or sticking

 

[adil.zahir]

NHN how would I check for back pressure
issues.
Also if I understand correctly to do a temp wire test I would get brand new connectors for the relevant sensors and wire them all directly to the ecu, is the correct from my understanding or did you mean something else. As I have stated I did a continuity test of the sensors harnesses to ecu which checked out fine but no harm done in trying a tem wire test.

Before I do forget when inspecting the wire loom I found two brown wires around 1-1.5sqrmm connected to nothing this is located where the connector connect to the injector flow plug loom. Have no idea where it goes to will take a picture in the evening apart from those wires everything else check out according to the wiring diagrams.

 

[adil.zahir]

NHN I upload the image of the two brown wires.

 

[adil.zahir]

Kayobong I have attached images of the egr valve condition and movement when vcds actuates the rod. The rod actually only moves a little probs 0.5cm when actuated by vcds not an inch but moves freely. However when I stripped down the egr valve and got to the mechanism which moves the rod up and down. the rod can actually move a lot further which is about 1 cm and does so freely.
I have attached images of the swirl flap too.

 

[aqibi2000]

Did you buy any chance notice the boost fluctuations and issues trigger ok thr rare occasion it does when driving over a small hump or a bit of a bumpy road? I know it won’t do it on demand but when it did happen sometimes was this the case?It’s easy to miss

Additionally you most likely only performed continuity tests from the sensors. Best thing to do is a load drop test wire to wire. Because under load and vibration is where the high resistance it partly open circuit connections surface.
- Suggestion unplug all sensors and both pcm connectors and using a consistent current limited power supply test continuity end to end using something like 2a just momentarily for like 2 seconds.

a common area of this issue where this happens is at the boost pressure sensor wiring it breaks deep inside and difficult to isolate but common

Also block off the vacuum line coming to the intake manifold solendoid and swap the intake for a BKD alloy one (swirl flap delete).

finally to root cause your problem you can temporarily put EGR blanking plates on the Egr valve on both sides of the system. After 50 miles this will just trigger a emissions MIL.