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The 6805 Boost pressure riddle

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Old May 1st, 2021, 17:52   #1
SushiNinja
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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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Old May 1st, 2021, 18:26   #2
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check the intercooler for splits pin holes and any bowing all can cause boost faults
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Old May 1st, 2021, 21:48   #3
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Check the intake pipe that goes onto the turbo,they have been known to go soft and split..when on boost the pipe can collapse. A smoke test would reveal any boost leaks.
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Old May 2nd, 2021, 11:22   #4
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Thank you for the replies Simmy and Camturbo.

What we dont understand is that if the intercooler had a pin hole etc, or the pipe that Camturbo suggests is soft/split, then surely a restart of the car would not solve those things and we would still get the limited performance. A restart of the car and you can drive without any restricted performance.

This solution although temporary is leading us to think it is a sensor or switch that is faulty.

Does anyone know what the sensor/switch is that is on the pipe going up from the turbo air intake pipe and over the top of the engine?
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Old May 2nd, 2021, 11:44   #5
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Not sure about the switch you are seeking so cant help you there,when was your fuel filter last changed as this can cause issues as well.
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Old May 2nd, 2021, 14:51   #6
Clan
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Quote:
Originally Posted by SushiNinja View Post
Thank you for the replies Simmy and Camturbo.

What we dont understand is that if the intercooler had a pin hole etc, or the pipe that Camturbo suggests is soft/split, then surely a restart of the car would not solve those things and we would still get the limited performance. A restart of the car and you can drive without any restricted performance.

This solution although temporary is leading us to think it is a sensor or switch that is faulty.

Does anyone know what the sensor/switch is that is on the pipe going up from the turbo air intake pipe and over the top of the engine?
the device on the breather pipe where it goes into the turbo air intake hose is a heater to heat the crankcase fumes and vapourise them so they don't condense in the turbocharger... Whats the highest vacuum your pump can produce ?
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Old May 2nd, 2021, 16:13   #7
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Quote:
Originally Posted by camturbo View Post
Not sure about the switch you are seeking so cant help you there,when was your fuel filter last changed as this can cause issues as well.
Camturbo, the fuel filter was changed around 200 miles ago along with the in tank fuel pump.
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Old May 2nd, 2021, 16:16   #8
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Quote:
Originally Posted by Clan View Post
the device on the breather pipe where it goes into the turbo air intake hose is a heater to heat the crankcase fumes and vapourise them so they don't condense in the turbocharger... Whats the highest vacuum your pump can produce ?
Hi Clan, the vacuum pump has a maximum of 760mmHg.

Thanks for the info on the device that is on that hose. It sounds like that would be a red herring considering the issue...
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Old May 2nd, 2021, 17:09   #9
Clan
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Originally Posted by SushiNinja View Post
Hi Clan, the vacuum pump has a maximum of 760mmHg.

Thanks for the info on the device that is on that hose. It sounds like that would be a red herring considering the issue...
mm/hg isnt an SI Unit

29.9 in/hg is an exceptional reading , I haven't seen one over 27 yet ....
so thats ok
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Old May 2nd, 2021, 19:26   #10
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Did you replace the boost control sensor with a brand new one,the one at front of engine below egr pipe? Just trying to find answers. What is your temp gauge reading when fully up to temp? Dont know if coolant temp sensor will effect boost as such but it might give ecu incorrect info so to speak
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