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The 6805 Boost pressure riddle

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Old May 3rd, 2021, 08:23   #11
SushiNinja
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Originally Posted by camturbo View Post
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
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Old May 3rd, 2021, 15:00   #12
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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...
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Old May 3rd, 2021, 18:53   #13
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Quote:
Originally Posted by SushiNinja View Post
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
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Old May 3rd, 2021, 18:55   #14
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what does your live data show when it drops into limp mode?
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Old May 3rd, 2021, 19:29   #15
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Quote:
Originally Posted by SushiNinja View Post
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??
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.
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Old May 3rd, 2021, 19:50   #16
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Originally Posted by camturbo View Post
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
The car is an Auto 5 gears and the revs at idle are around 600 to 700rpm
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Old May 3rd, 2021, 19:56   #17
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what does your live data show when it drops into limp mode?
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.
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Old May 3rd, 2021, 19:59   #18
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Originally Posted by cheshired5 View Post
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.
Thank you chesired5... Does this mean the turbo itself is at fault? We did do a turbo clean with the Wynns Turbo spray...
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Old May 3rd, 2021, 20:12   #19
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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.
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Old May 3rd, 2021, 22:27   #20
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Thank you chesired5... Does this mean the turbo itself is at fault?
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.
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