Engine: D52447: Real-time data logging: is my D5 healthy?

[ca2n]

2004 XC90 D5 163 Geartronic 184,000 miles

In the last week or so, I've had:

1. an "Engine System Service Urgent" warning,
2. an airlock in the fuel system after a fuel filter replacement (thinking No. 1 was due to a clogged filter), and
3. what appeared to be a slightly longer than usual cranking time.

On occasion, the "Engine Service Required" warning has also popped up when under load.

I don't have a DICE unit (yet) for diagnosis so decided to explore the capabilities of an ELM327 Bluetooth dongle and the Torque Pro app on my Android phone.

Knowing the engine pads were leaking, I blocked the outlet from the TCV(?) to them and went for a short drive to "exercise" the VNT. I didn't have the guts yet to got full-throttle for a long period, so below is a snippet of the data from the run.



From reading on here, especially from values quoted by @cheshired5, I think the MAP and fuel rail pressure values are reasonably "healthy", with MAP maxing out at around 31 psi and fuel rail pressure maxing out at around 20,000 psi during a couple of short bursts. I'm not too sure what the fuel flow rate values indicate, though, or whether they are healthy figures.

When I eventually feel brave enough, I'll take it for a longer, harder run and log the data.

Is my D5 healthy?

[Harley Dave]

I'm no expert but I have been driving/riding for more than 50 years

Lack of fuel (lower than necessary fuel flow) will give you a noticeable drop in performance.

If you didn't experience that, then I would tend to say your fuel flow is OK.

Cheers

Dave

[ca2n]

Before doing any hard runs, I thought it might be better to get some reference values at idle, just to avoid any surprises.

So, today I logged a cold start (if you can call it that; the ambient temperature was around 20 °C) and let it idle. I was rather surprised by what the data showed:



It seems that there is a sensor fault somewhere causing the fluctuations in the data at around 85 seconds into the logging. This faulty sensor appears to affect other engine operating parameters and readings. The question is, which sensor is the "governing" sensor? I'm guessing the MAF sensor?

Despite the erratic data, the engine seemed to idle perfectly.

It could may well be glitches with the data logging app and I'll be repeating the test. In the meantime, thoughts, anyone?

[SwissXC90]

Consider this:
As the engine warms up, the car changes from open loop to closed loop engine control. Maybe that's what you saw: an attempt at closed loop, and then a reversion back to open loop because the vehicle wasn't being driven, or had no load on it.
Your period of drop in fuel flow might be the engine trying to lean out the mixture as it warms up.
Or it could be the swirl flaps being put into use. Or the EGR opening.
Your MAP ps variance is very very small, only 0.15 psi change, and thus I would't necessarily think that would be a cause for concern.

You really need to read the technical descriptions in VIDA to fully understand the cold start procedure and the initial warm up phase. There's a lot going on.

And then the only way to know what is normal is to benchmark in VIDA.

I also have a D5, mine is a MY2009, so the newer generation engine, where the emissions systems are heavily revised compared to your car.

Your RPM looks rock solid steady, and the fuel rail pressure looks good as well.
It would be good to see engine coolant and oil temperature, and exhaust gases (O2, or exhaust temp, or mixture control...).


As you say, comparing to another car is key here.
But you also need to compare apples with apples, and make sure the other care has the same engine and the same recording software. VIDA is best.

[ca2n]

That is very insightful indeed, thanks. I had not been monitoring any other engine operations (e.g. EGR valve) and it could have very well had influenced what I saw.

VIDA does mention two ranges of the mass air flow at idle, in particular when the EGR control ceases (no exhaust gas recirculation?) the mass air flow is approximately 48 to 60 kg/h (13 to 16 g/s).

[gmonag]

The question is, which sensor is the "governing" sensor? I'm guessing the MAF sensor?

The MAP sensor. It is on the outlet of the intercooler.

[ca2n]

Originally Posted by gmonag

The MAP sensor. It is on the outlet of the intercooler.

Interesting. Would you say there is a reason to suspect a faulty MAP sensor from the erratic readings above?

[ca2n]

Just had another go.



The 70-second (approx.) dip in MAF is still there. Why it does that, I don't have a clue.

The MAP sensor readings, steady one minute and jumping the next is causing some concern. Perhaps the only way to rule out any issues with it is to replace it.

[SwissXC90]

I would not be concerned about the MAP sensor
Look at the scale of the graph: the variances are extremely small and you may simply be seeing data resolution, nothing more.

The MAP readings vary by +/- 0.1 psi, and the spikes up and down simply look like the minimum resolution of the data. Always interpret the data with respect to the scale size and data resolution.


The fact that the MAF change from 100s to 150s has occurred again at a very similar timeframe to the previous readings is a strong indicator that this is an intentional change.
The correlation of your new graph to the previous graph is far too strong to indicate a random event.
Random events occur at random times and with mostly random amounts.

[ca2n]

That's reassuring re: MAP, thanks. I suppose I can assume that it's reporting the appropriate values and the engine is not overboosting.

It would be interesting to know what goes on with the MAF dip as clearly it's not a random event. If anybody could point what it may be in VIDA that would be helpful as I have yet to find anything.