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:shocked:

check the intercooler for splits pin holes and any bowing all can cause boost faults

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.

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?

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.

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 ?

Camturbo, the fuel filter was changed around 200 miles ago along with the in tank fuel pump.

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 :teeth_smile:

29.9 in/hg is an exceptional reading , I haven't seen one over 27 yet ....
so thats ok

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

Yes, this was one of the first things we did. Its got a brand new Volvo one on. All the parts we have bought are genuine volvo ones, buy cheap, buy twice, so we always opt for the genuine parts.

The temp gauge reads normal (half way) when up to temperature. That is an interesting point though. We also have an iveco van we bought to convert to a camper and coolant along with fuel temps effect how the ECU manages the engine.

I will do a live data session on it today and see what the temp gauge is reading and post here what the results are.

Thank you Camturbo

We did some live data testing today and these are the results:

At Idle:
Coolant Temp - 49.6 degrees C
Inlet air temp - 11.2 degrees C
MAF - 52.10 kg/h
Boost Pressure - 991 hpa
Atmospheric - 967 hpa

Stationary at 1500 RPM
Coolant Temp - 53.4 degrees C
Inlet air temp - 10.3
MAF - 70.70 kg/h
Boost Pressure - 1039 hpa
Atmospheric - 967 hpa

Stationary at 2500 RPM
Coolant Temp - 54.1 degrees C
Inlet air temp - 10.3 degrees C
MAF - 212.30 kg/h
Boost Pressure - 1134 hpa
Atmospheric - 968 hpa

Driving at 60mph (2000 RPM)
Coolant Temp - 87.8 degrees C
Inlet air temp - 8.3 degrees C
MAF - 200.60 kg/h
Boost Pressure - 1487 hpa
Atmospheric - 980 hpa

Driving at 70mph (2500 RPM Slightly downhill though)
Coolant Temp - 87.1 degrees C
Inlet air temp - 8.4 degrees C
MAF - 191.40 kg/h
Boost Pressure - 1105 hpa
Atmospheric - 981 hpa

Another test was to accelerate up to 4000 RPM and the boost pressure read 2170 hpa.

After the drive we let it idle and these were the readings:
Coolant Temp - 86.7 degrees C
Inlet air temp - 8.4 degrees C
MAF - 48.70 kg/h
Boost Pressure - 1026 hpa
Atmospheric - 973 hpa

We did notice that the boost pressure did hang at its high value for 3 to 4 seconds before dropping off when easing off the accelerator pedal. Is this normal??

Hopefully this will help someone with far greater knowledge than us to figure out what our issue is...

What transmission is it? When you did the 70 mph run what gear were you in? Also when fully warm and at idle what is your rev counter reading? No idea about your live data but hopefully someone else does

what does your live data show when it drops into limp mode?

No this isn't normal and boost should ease instantaneously in line with engine speed and reduced throttle input.

It sounds as though the VNT is sticking slightly on its way back at cooler operating temperatures and frees itself to perform pretty normally on a hot engine.

The car is an Auto 5 gears and the revs at idle are around 600 to 700rpm

Hi Simmy, when we tried to get it into limp mode, my mate driving, lifted off the accelerator and quick booted it again... then it came out of limp mode... errrr!! I was hoping to see something obvious, but we never got the chance.

When it goes into limp mode, I slow down and just consciously limp it home. I have never tried just pushing it again.

Tomorrow, I am going to try the same and see if it acts the same or stays in limp mode.

Thank you chesired5... Does this mean the turbo itself is at fault? We did do a turbo clean with the Wynns Turbo spray...

Does sound as if it sticking if you throttled off then back on again and it disappeared. Like you say try again tomorrow and see if it happens again. Maybe its got some carbon build up on the turbo vanes. Cant help you with cleaning it,apart from giving it a good caning. Hopefully someone else will be able to help.

Well, the VNT mechanism (which is part of the boost regulation) sounds like it's not moving smoothly in both directions at all temperatures.
That's my best guess based on the behaviour you've described.

OK, well as much as I have tried over the last two days, I cannot get it to display the Engine service message...

I have spoken to the previous owner and he did admit it was stood for a few months before I got it.

So I think the sticky vanes was/is the issue, even though we did the Wynns Turbo Cleaner spray treatment, it probably needs another clean up. This weekend we are going to try the Mr Muscle method which is all over youtube.

Thank you everyone that has helped with your valued comments and I will post an update early next week to let you know how it went...