Low Speed Loss of Boost. Takes along time to buildup.
 

Hi all,

My car is a 2004 XC90 with 170k on the clock.

Over the last few weeks I've had a 'Engine Service Required' Message pop up. Sometimes it'll clear if we're travelling along (Dual Carriage way speeds), but if at low speeds it'll hang around requiring a stop, engine off and back on to clear it.

There is no black smoke emitted from the exhaust. MPG is its normal 29mpg.

The fault code is generic on a handheld reader, P0244 "Turbocharger".

The last state it failed in was:

• Load PCT - 74.5%
• ETC - 192(F)
• MAP - 41.2 InHg
• RPM - 2367/min
• Speed - 65mph
• DTCFRZ - C1600

A Genuine Volvo Fuel filter was fitted in 2020. Along with yearly oil changes and Genuine filter. The oil i used was Castrol Edge 5w-30, which now after digging away in the forums is probably incorrect and will be changed out for the 0w-30. The intercooler was replaced by myself in 2019 as it was cracked and leaking oil. The result of the crack has probably lined the intake system with gunk :angry_smile:

In the last few days the car now has zero boost from a standing start, pulling out of junctions requires some forward planning, the boost will slowly pick up and we're away. Driving along the road and increasing the speed doesn't produce the same effect, everything in the terms of boost is normal (which fairly slow as it's only 163bhp lol)

I've investigated the Vacuum system, I get that popping noise I hear a lot about, but no matter if I blank off the Brake Booster and Nipple at the pump to the rest of the system, it'll still pop away. The Needle on my reader will not bounce around at idle and pulling a vacuum shows the tiniest of leaks on the engine mounts. 5Hg over a minute.

The interesting bit is when I rev the engine up the needle will bounce everywhere, it's tee'd into the system straight after the pump, and this point I'm thinking how can things work if it can't pull a good vacuum.

On the second go a short while later, when I rev the engine its build up more vacuum and hold releasing when the waste gate releases, quickly builds up and holds. I recorded this one and linked it here: https://youtu.be/CL8nBxZC5rk

This leads me to think that something is effecting the vacuum intermittently, any ideas on what this could be?

Moving my thoughts away from that, the car does a lot of short runs for School, would it be possible the Turbo Vanes are full of build up that needs cleaning? I'm going to run some Turbo cleaner through the fuel system to see if that'll make any difference. Maybe the actuator on the turbo is sticking and causing a boost leak?

Cleaning of the MAP sensor would probably be beneficial. Can anyone recommend anything else I could try or clean before taking it to a specialist or dealer for diagnostics.

Many thanks in advance :shades_smile:

Morning , I had the same issue with my D5 , replacing the MAP sensor cured the problem , it was providing spurious values to the ECU . It is probably the cheapest item to replace . Hope this helps

In/Hg is a vacuum and is an incorrect value for the circumstances.

Check MAP (sometimes called intake manifold pressure) reading with engine off/ignition on, then at idle, then at 1k and 2k revs.
Do the same for MAF and IAT or intake air temperature and report back.

Engine Off

• Map (kPA) 100
• RPM (/min) Zero
• IAT (˚C) 19
• MAF (lb/min) 0.000

Engine Idle

• Map (kPA) 99
• RPM (/min) 746
• IAT (˚C) 17
• MAF (lb/min) 2.034 (0.92kg/min)

Engine 1000rpm

• Map (kPA) 101
• RPM (/min) 1091
• IAT (˚C) 17
• MAF (lb/min) 2.299 (1.04kg/min)

Engine 2000rpm

• Map (kPA) 114
• RPM (/min) 2069
• IAT (˚C) 17
• MAF (lb/min) 5.246 (2.38kg/min)

Looking at that my MAP sensor is going the wrong way meaning there's vacuum/flow issue or defective?

You're showing kPa (positive pressure) and In/Hg (vacuum) at the same time so I'm not following your figures at all.

The dashes you're typing are adding further to the confusion. I don't know whether the dash means minus or something else.
If a figure is a minus figure, type minus then the figure otherwise leave dashes out of your figures.

Some actual screenshots would probably help.

Also with MAF use kg/h or g/s as it saves converting to metric.

My OBD reader records in kPa for the Map sensor, I'll take out the other reading. :) Sorry my dash marks are just separators, habit of mine.

It does seem the pressure is increasing when at higher revs when it should be decreasing, which would mean I've got a restriction somewhere or a duff sensor?

I'm fine either kPa or psi for pressure.
lb/min for airflow on the other hand.....

A space is fine for separation.

I'll change it to KG

Kg/min means I still have to convert every figure to kg/h in line with Vida. No matter.

The IAT should be increasing as temperatures in the engine bay increase.
Out on a sustained speed run on a warm day like today, IAT should be within around 6°C of outside temperature.
When the car is warmed up and slowly driving or stationary, heat soak will raise the IAT to higher than ambient, maybe an additional 20°C when stationary.

At idle, your MAF should be around 25 kg/h (EGR open) then after around 2 minutes of idling MAF should increase to around 50kg/h so a noticeable step change in line with a correctly functioning EGR valve closing.

Underneath the car, you should also be able to physically see the VNT actuator moving when revving the engine as shown in this video.
The VNT actuator can be vacuum tested as shown in this video.

Until you can methodically check and confirm everything, you could have a combination of a general vacuum leak, malfunctioning VNT actuator, sticking VNT vanes, malfunctioning EGR, failing IAT sensor.

I think your problem will lie within these.

From your helpful info it seems like the MAF on mine is reading 55kg/h at idle, going up to 142kg/h at 2000rpm. So something is amiss there, I'm going to remove the inlet pipe that connects to the EGR and have a look, if that's clear I'll change the sensor, and if that makes no difference going to push on with cleaning the turbo, then onto the EGR. Thanks for the help.:regular_smile:

Excuse my poor typing and formatting, Dyslexia limits me a bit when typing, I read it back a few times and spot most of the mistakes.

Sirobbs channel has helped me out no end with bits and bobs. :teeth_smile:

I can see the VNT moving freely from the top of the engine, I got some engineering mineral oil on there the other day.