Thread: P1247 Turbocharger boost pressure low

I had previously cleaned this sensor in the centre of pic with clc cleaner and was clean since my last wash but did flush clean again as requested.

to my next surprise - I pumped air into that top intercooler hose with the sensor left open and surprise no air came through. surely air travels and should come up through the hole of the sensor. I have had the Y section apart and partially cleaned so just dont understand where the blockage is or a tear somewhere in the system resulting in low boost. I need to follow the intercooler pipes and see where they lead to but no obvious holes in pipes from up top so suspecting lower part of engine or the rear crossover???

The two cooler pipes (3L) from the air intake go to the two turbos? then where?

Originally Posted by shamirj

I had previously cleaned this sensor in the centre of pic with clc cleaner and was clean since my last wash but did flush clean again as requested.

to my next surprise - I pumped air into that top intercooler hose with the sensor left open and surprise no air came through. surely air travels and should come up through the hole of the sensor. I have had the Y section apart and partially cleaned so just dont understand where the blockage is or a tear somewhere in the system resulting in low boost. I need to follow the intercooler pipes and see where they lead to but no obvious holes in pipes from up top so suspecting lower part of engine or the rear crossover???

The two cooler pipes (3L) from the air intake go to the two turbos? then where?

There is a throttle body before it that is close with the engine off that will be stopping the air from getting to the sensor is my summation of your test

1. removed the air box to inspect again and decided to clean out, very dusty inside but all good no tears for air to escape, washed and reinstalled

2. air filter filthy - so ordered off ebay a new air filter to rule that out, although i did start the car without the filter and seemed the same with no difference but a clean air filter cant hurt.

3. closer inspection again very filthy but also a tear along one of the edges so will need careful fitment on the new one to avoid any pinching or why it teared (incorrect fitment perhaps?)

Found this blurb from Disco3uk

there are many things to check with the p1247 fault code. had many issues with the CSOV(compressor shut off valve) which is bolted to the radiator pack on the drivers side. there is a vac pipe which runs all the way up the fan shroud and round to a vacuum solenoid valve on the front of the engine. if you remove this pipe let the engine idle for 3 mins it will start sucking a vacuum. lightly place the vac pipe back on and then remove you should hear a popping noise which is the valve slamming shut. if this does not happen or doesnt sound very convincing then the CSOV is sticking. also issues with secondary turbo solenoids and also vac pipe issues.

1. here is the pipe off at top of engine, no vacuum at all, smeared a little liquid soap on top of the hose no sucking at all

2. the pipe connects along the top of the radiator and down to the shut off valve (which maybe my problem so thought to test this theory out)

3. the solenoid on top of the motor hard to see but taken off the grey tubing connector thingy.

4. Found this bulletin very helpful but did not help me.

re tested on my other working D4 and no suction on that one either, did let the motor idle in the cold for 1-2mins but no suction. May re test with a warm motor instead of it being cold to see if any difference.

this was captured on live data while idling

I suspect the intercooler may have a leak either in the pipes or the actual intercooler itself as prev suggested.
Using this method I am unable to build up any pressure so getting a zero reading on my tyre gauge.
Soapy water applied on top bit hard to do solo below but with no pressure wont bubble either.
Suggestions for a better way to pressure test intercooler welcomed without removal

those live data were almost identical to my other working D4 except for the values for the turbo shut off valve, so guessing either the intercooler or the turbo shut off valve maybe the cause. Any way of testing both without removal would help please

The shut-off valve isn't hard to remove after removing the small cover behind the wheel. You should be able to get a hand in to operate the butterfly to determine if it's sticking but would need to remove it to clean it if the issue is a build-up of dirt on the butterfly shaft. When removing, expect oil in the hoses so don't be underneath them!

The throttle on my MY10 3.0 wasn't closed with the engine stopped.

The bypass valve shaft is spring-loaded and can be moved by hand by the vacuuum chamber - there aren't any gears.

The EGR valve rod operates the coolant bypass valve, not the exhaust valve which is internal to the valve asembly.

No pressure building in the inlet manifold with the engine not running can be due to a cylinder's inlet and exhaust valves not fully closed as occurs during exhaust/inlet overlap.

White diesel smoke is usually atomised unburnt fuel caused by excessive fuel for the oxygen content of the mixture.