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The 6805 Boost pressure riddle

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Old May 1st, 2021, 17:52   #1
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Last Online: May 6th, 2021 09:46
Join Date: Mar 2021
Location: Richmond
Default The 6805 Boost pressure riddle

There are more than a few threads already on this forum regarding this issue but we think we have exhausted those options....

My car is a 2005 XC90 D5 AWD with the D5244 engine - so no swirl flaps or resonator box under the engine. We think.

The last couple of months have been dogged by the dreaded Engine Service Required message coming on if, when cold, you accelerate up to approx 2800 revs. This can be temporarily cured by turning the car off, waiting 10 or so seconds and then start it again. You can now drive all day without issue.

What we have discovered is that if you let the engine cool, for example, park it up for 20 or so minutes, the Engine Service Required issue appears when accelerating over approx 2800 revs. If you park it up for less than 15 minutes or so, the issue does not appear when accelerating over 2800 revs.

Plugging it in to our diagnostic (Not Vida), we get the 6805 Boost Pressure Incorrect Flow error logged, which equates to the Volvo code 0244.

What we have done/replaced so far:

Both vacuum mounts replaced as the front one was leaking.
Tested the valve attached to the air filter box - switches around 1000 rpm as it should.
Replaced the control solenoid valve which sits under the crankcase/egr pipework.
Removed and cleaned the egr valve and pipework.
The turbo actuator arm moves freely under a vacuum as it should.
The car has had a new intercooler approx 2000 miles ago by the previous owner.
Replaced the MAP Sensor.
Cleaned the turbo vanes with Wynns Spray Turbo Cleaner.
Checked for collapsing pipes - All seem good.

What is puzzling, is that the issue is so consistent regarding the cooling times and switching off and then restarting. We are fairly confident its a sensor or switch somewhere...... but where?

When we did the Wynns turbo cleaner, the MAF sensor obviously came up as a fault as it was removed to carry out the spray cleaning. This is leading us to think that if it was a MAF issue, surely this would be logged respectively.

We have discounted an air/vacuum leak due to the fact that we can restart the car and its fine all day until it cools for 20 minutes. Surely the leak would be ever present. ??

If it was a turbo vane issue, the same would apply, it would be present all the time.

We have also considered the cat, but then this would also be present all the time.

We must surely be missing something really simple, or we have misunderstood the workshop manual, which I have to say, is rather a mishmash of every volvo model known to man... jeez that thing is confusing.

The other thing we are unsure about, (Because we cannot find any info on it anywhere), is where the hose connects to the turbo on the airbox side, there is a pipe which goes over the top of the engine (Presumably PCV/Evap?) with a sensor/switch inline quite close to the turbo. What is the sensor/switch? We cannot find anything about it. Can this be part of our issue?

Please can someone help two old timers out, that are seriously considering a volvo induced whisky problem
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