Disco 2 Lack of Boost

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Si Click

Well-Known Member
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1,503
Location
Lincolnshire
The turbo on my 1999 D2 TD5 was showing signs of bearing wear (slight side to side movement and about a mm of fore and aft), so I have just fitted a new Turbo Rebuild CHRA cartridge. I followed the guidance (oil and filter changes beforehand, syringe inject of supplied oil into the turbo and turned it over for 30 secs before starting and confirmed good supply of clean oil). The installation itself seems absolutely fine and the rest of the turbo seems in good condition. However, sprightly performance has not resulted.

The Air Flow Fault Logged High fault I had beforehand suggests a new MAF is in order as well, although voltages are smooth upwards from 0 and do not exceed 5v. Before I go ahead and order another one, I have some queries for the experienced to ensure I'm not missing something obvous or have a bigger problem.
Live data gave a wastegate reading of only 6.92% going uphill with full throttle at 3000 rpm. Oddly it increased to 7.82% as I backed off at the top.
Manifold Air Pressure never exceeded 155 KPa.
Are these reasonable symptoms of a dead MAF or indicative of a wider problem?
I have cleaned the MAP and the AAP (correct 3 pin fitment), but I guess these are suspect too. How about the wastegate actuator?
 
If you suspect any sensor rule it out first, if you clear the air flow fault but it comes back you need a new sensor unless the low boost is caused by a boost leak between the turbo and inlet or through stuck open wastegate then the sucction through the MAF is increasing above limits cos the turbo is actually spinning hard but the boost doesnt reach the inlet

do you still have EGR?
 
Thank you. Happy there is not a leak between the turbo and inlet (new gasket and a good connection). The wastegate operated freely when not connected to the actuator arm and is in the shut position at idle.
EGR is blanked off, so no leakage there.
 
Swapped out the MAF for the spare, cleared the DTC and tried again.
Same wastegate figures, same manifold air pressure figure of 152 KPa max.
The Air Flow figures were 62 kg/hr at idle and just over 600 kg/hr at max which suggests the turbo is blowing OK, but that the boost is not getting to th engine.
On shutdown the 3030 Air Flow fault High Logged was back.
Could a faulty MAP give these symptoms?
I'll go over all of the hoses cm by cm tomorrow.
 
How are the AAP and IAT readings? at that 600 kg/hr sucction the MAP should be at least 230 but this contains the AAP and boost, that amount of air is absorbed and pushed toward the inlet by the compressor so it must be somewhere... the best would be to set up a boost gauge and check the real boost at the inlet then you can blame the MAP sensor for sure though if it's very old better replace it with new cos the piezo crystal in it gets ''tired'' in time
 
OK, progress. I was losing substantial pressure at the junction of the hose from the intercooler to the intake manifold. It looked OK, but the adapter supplied with the EGR blanking kit does not have much of a lip and the silicon hose was not holding securely. Some degreasing, a reposition of the hose to give better purchase to the Mikalor clamp and the problem was (very briefly) solved.
Great manifold pressure going up the hill, until half way there is a sudden sound of escaping air and a loss of boost. This time the hose had come adrift at the intercooler end. Then followed about 2 hours of trying to find a compromise position where both ends remained attached.
The problem seems to be that the silicon just compresses and slides out from under the clamp. Washing the hose in washing up liquid helped, but as the intercooler gets oily again the hose will become slippery again. A factor is that the aftermarket hose needs to be about 1cm longer. A fraction more length and I could push the intercooler end all the way on until it touches the wall of the intercooler. This is a problem because as the clamp is tightened it slides down the hose until it reaches the intercooler; if the hose not all the way on it just slides out from underneath the clamp. With the hose that far on the intercooler end it is difficult to get an overlap and a decent seal at the other end. As it is tightened the top clamp either slides off the end of the intake pipe or if mounted further up, the hose squeezes out from underneath. Is this common with silicon hoses? Would jubilee clips work better than Mikalor? To be clear this is not the clamp slipping when loose, it is the act of tightening that moves it. It is not possible to hold it where you want it and tighten it like a conventional jubilee clip and hose, like squeezing a wet bar of soap, the tighter you hold it the more it moves.
I have just about found a working compromise and pressure and performance are much better, with about 225 KPa the max manifold pressure I saw. However, this is not a long term solution and I need to replace the silicon hose with a proper rubber one.
 
Final update: The silicone hoses throughout the engine are made by Roose Motorsport and are really good quality. Fortunately they agreed to make me a matching custom pipe which I installed today. Finally I am getting the full benefit of the Alive Stage 3 map, the performance intercooler, the hybrid turbo I fitted a month or so ago and the genuine LR MAF I fitted a day or so ago. What a difference from when I bought it! With the Ashcroft V8 torque converter exploiting the power at lower revs and not just revving without delivering drive like the stock one did, she is now a real pleasure to drive.
The two photos are of the intercooler to EGR replacement intake pipe. The black tape is self amalgamating tape that I was using (with limited success) to enable the short hose to grip the intake without blowing off. The second is the longer pipe that has plenty of overlap for the clamp to grip.
 

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