2010 XC90 Auto - loss of acceleration at higher speeds

[gmonag]

You normally get the Engine Service Required message when in Limp Mode. You should investigate the TPS more but resist the temptation to change parts before you know they are faulty

Greg

[cheshired5]

Originally Posted by NialStewart

Simon, after a lot of mucking about I have this working and have managed ot get the readings.

'MAF', is this manifold air temperature, I'd expected this to be air flow but I think the temperature was labelled as
MAF.

Readings taken with gearbox in park.

Speed.........MAP.......MAF
Engine off ...1002......41 Deg C
1K..............1018......44 Deg C
2K..............1127......41 Deg C
3K..............1221......38 Deg C

If the 4K reading would help I'll do it tomorrow, I didn't want to annoy the neighbours too much.

Thanks for any feedback,

Nial.

The MAF reading needs to be the flow reading which is in kg/hr on Vida.
The temperature isn't really of any use.
Yes all the way to 4k revs please.

As has been suggested, you have pretty sizeable overboost so go into Diagnostics >Vehicle Communication >ECM and look at the values in the parameters tab in comparison to what they should be (as described in details/description) then click activations and see if things work as they should when remotely activated.

It would be a huge help if you can actually see the actuator working travel whilst being activated.
My video here shows the travel on a vacuum actuated arm. You have a motor actuated turbo but the movement will be similar.

Your throttle value may or may not be correct but all the info is there for you to confirm either way.

[NialStewart]

Originally Posted by gmonag

You normally get the Engine Service Required message when in Limp Mode. You should investigate the TPS more but resist the temptation to change parts before you know they are faulty

Greg

Having looked at the price of the throttle body I won't be rushing to change it, but that last capture
shows it's goosed surely?

I'll check as many connectors as I can find and the associated wiring tomorrow.

Thanks,

Nial.

[NialStewart]

Originally Posted by cheshired5

The MAF reading needs to be the flow reading which is in kg/hr on Vida.
The temperature isn't really of any use.
Yes all the way to 4k revs please.

OK, I'll try to do this tomorrow.

Does this need to be under load or can it be when parked in the drive?

As has been suggested, you have pretty sizeable overboost so go into Diagnostics >Vehicle Communication >ECM and look at the values in the parameters tab in comparison to what they should be (as described in details/description) then click activations and see if things work as they should when remotely activated.

What things am I trying to activate, just the boost activator?

It would be a huge help if you can actually see the actuator working travel whilst being activated.
My video here shows the travel on a vacuum actuated arm. You have a motor actuated turbo but the movement will be similar.

OK, I'll get mywife to help here, again can I do this in the drive?

I have a cheap USB endoscope (£25 quid odd), worst case I can probably tie this in postition to see what's
happening and check it that way.

Thanks again,

Nial.

[cheshired5]

Engine doesn't have to be under load. Stationary is fine.

Activate everything and check their values.
It takes minutes so you may as well see that everything is working as intended whilst you're there.

[NialStewart]

Thinking about this in bed this morning I think I have a good explanation for what I'm seeing....

The throttle position sensor is goosed, as idle I mostly seee the sensor output at 93%.

So at idle (and many other times) the ECU is massively over-fuelling the engine, leading the much more carbon in the exhaust, leading to the turbo vanes getting fouled up.

I think looking at the lambda sensor might confirm this. At idle does this normally toggle on and off as in a petrol car?


Nial.

[NialStewart]

At last I've got the air mass/ Manifold pressure against engine speed Simon asked for "xc90_100904_reving_in_park.png".

I presume this shows the air flow sensors are OK?


Despite jumping to conclusions it looks like 93% for the Throttle position in idle _can_ be OK.

Having said that it looks like when we get the condition with no power this is stuck at ~93%.

When this happened I stopped for 5 minutes or so, started logging then started the car and drove off. For the first few seconds everything felt OK then I felt the flatspot kick in. From the trace it looks like this is when the throttle 'sticks' at ~90%. "xc90_160904_restart_after_pause.png".

So my thinking is that there's either something wrong with the throttle or something is causing the ECU to keep it at ~90%.

It would be good to try this on a car that isn't experiencing any problems to see what 'normal' is.

As always any thoughts are appreciated.

Nial.

[NialStewart]

Attachements attached this time.

[NialStewart]

Talking to myself a bit more....

I've just checked the fault codes the dealership gave my wife when she was in, one was...

TCM-0A31 - Control module communications. Signal missing from Engine Control Module (ECM).

I don't know why I didn't post this earlier.

Does this point to the ECM being faulty and not providing the signal, or the TCM being faulty?

Hopefully it's 'just' the TCM, though it looks like this is £Hundreds fitted.


Nial.

[gmonag]

You need to test, not speculate. You would probably be better off going to a diagnostic expert if you can't trace the faults easily. Stay clear of the dealers.

Greg