Member Since: 24 Oct 2023
Location: Cornwall
Posts: 14
Engine won't rev above 2000rpm, underboost fault
Hello all, a quick summary of my issue: I have a power issue where the engine will not rev above around 2000rpm and it shows the fault code P0299-00 turbo underboost. I have checked the turbo actuator and it is moving freely, I have done a good visual inspection of all the accessible pipes and all looks okay, the EGR valves were blanked off about a year ago and I had no power issues after blanking, I have also installed a new MAP sensor, and used a MAF cleaning spray on the MAF sensor. The manifold pressure readings drop significantly when revving signifying quite a strong vacuum.
So I performed a smoke test straight into the main air intake (post MAF) to see if there were any leaks from less accessible or obvious pipes.
From what I can see there was only one leak point, and that is at the very bottom of the crankcase breather pipe, circled here in orange.
Click image to enlarge
I confirmed that it was this part leaking by using a borescope, which showed the smoke coming out of the circular joint at the bottom of the plastic oil separator / crankcase breather unit.
Click image to enlarge
So my question to you guys is can a leak in this part cause an underboost fault and lack of power? As far as I understand it the breather unit is plumbed back into the air intake system before the turbo, so in theory I was guessing this leak could cause the problem, but equally with my lack of experience and knowledge with this engine it could also be a massive red herring.
If you guys think this could be a problem, how difficult a job is it to replace this breather unit DIY?
Thanks in advance.
(2004 D3 TDV6 auto, 218,000 miles)
22nd Feb 2024 10:37 am
PROFSR G
Member Since: 06 Mar 2017
Location: Lost
Posts: 5043
A "red herring" is indeed very possible with this so I would put it on the "back burner" until you have eliminated every other possibility. The symptoms you describe does suggest one of the following.
EGR's, so have a look at the blanks and satisfy yourself there are blanked and sealed correctly. The other issue's here can be the turbo actuator rod sticking, a duff MAF sensor, exh crossover pipe leaking, leaking (under pressure) throttle body to manifold seals or the manifolds themselves! Or, leaking pipework to or from the turbo. You could also try disconnecting the MAF sensor plug, this will cause the PCM to use default data for MAF. If the problem goes away you know it's a dud MAF.
There is a scavenge pipe which runs from the breather over the back of the engine and down to the turbo. So this is not on the pressure side of the turbo, but recycles the crankcase fumes back into the the intake side via the turbo.
Check the joint on the right side of the radiator where the long plastic intake tube (the one on top of the rad) joins the intake side of the turbo. The seal here can fail, or is missing completely! Check also the air filter housing and the intake from the wing in case there is a blockage/restriction.
Check the long pipe on the left of the engine from the intercooler to the intake plenum. It could of course be an issue with the pipes down at the turbo itself, which can be seen by removing the heat shields from inside the passenger side wheel arch.
Since you have a borescope you could have a look at the exh crossover pipe for leaks. If it has failed it will prevent the turbo from spooling up sufficiently to provide enough boost.
The crankcase breather is a b@st@rd to get out. If you do remove it, you could try trim off a very small amount of the pipe where it enters the crankcase to get a better seal.yµ (idµ - eAµ) ψ=mψ
22nd Feb 2024 2:03 pm
Kernowek
Member Since: 24 Oct 2023
Location: Cornwall
Posts: 14
Thank you very much PROFSR G for your detailed reply.
I'm glad you have suggested that the crankcase breather probably is not the problem, as I had my doubts hence the red herring.
I believe I have already checked most of your suggestions but I will double check again, but what really caught my eye was your suggestion that it could be the exhaust crossover pipe. I have not considered this at all, so I will certainly use my camera scope to have a good look.
Is there a way to use my smoke tester to put smoke into the crossover pipe to physically see if it's leaking, by accessing a particular pipe or part of the system?
22nd Feb 2024 3:12 pm
PROFSR G
Member Since: 06 Mar 2017
Location: Lost
Posts: 5043
You could remove the d/s egr blank and try through there, or block one tail pipe and send the smoke up the other one?
Generally you can see it as the jacket wil usually be scorched or blackenedyµ (idµ - eAµ) ψ=mψ
22nd Feb 2024 3:18 pm
Kernowek
Member Since: 24 Oct 2023
Location: Cornwall
Posts: 14
I'll have a good look on the camera, and then send some smoke up the tail pipe while I'm there
22nd Feb 2024 3:22 pm
PROFSR G
Member Since: 06 Mar 2017
Location: Lost
Posts: 5043
It's a long way so be prepared for that, it would be quicker to go via the d/s egr valve.yµ (idµ - eAµ) ψ=mψ
22nd Feb 2024 4:39 pm
Kernowek
Member Since: 24 Oct 2023
Location: Cornwall
Posts: 14
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