MAF sensor readings

[yoseff]

As well as MAF values, have a look at the MAP values. The MAP should be atmospheric pressure before starting the engine and once running using the accelerator pedal the values will change. If not then the MAP and/or its tapping point might be bunged up with carbon. Whilst not important, if you can, get the values in bar or mbar rather than psi.

Whilst not mentioned in the posts, I assume it is a C5 you are having problems with.

I've cleaned the MAP before, and will try to get its readings in mbar to see if they are near the expected ones. Will have a deeper look into that.

And yes - i've should specify what is the car - It is an 2011 C5 2.0 Hdi 163 , my personal one.
I currently "have" two - one is my personal one , and the other (not exactly mine , but from the company) , same engine but from 2010 , that is my working car.
The current problem is in my personal one. The working one have been with another set of issues described in another topic

I realized already that i use less throttle at lower speeds with mine that in the work one (1-4% vs 6-8% @ 20 ish km/h) , and that the roughness happens mainly in that initial area. Bad contacts in throttle pedal sensor? Unsure if it can be opened to clean...

Found a topic here that seems to be from someone with similar issues in the past and i'm seeing what i can learn from there. Clutch pedal position sensor and anti stall mode seems also a possibility , need to check that sensor in Diagbox.
viewtopic.php?t=65340

[yoseff]

To clean it you take it off the car and very carefully and liberally spray the sensor itself. Make sure you don't touch the hotwire with anything solid it will almost certainly snap if you do. Gentle is key

That's how i did with MAF sensor cleaner from Liqui Moly (https://www.liqui-moly.com/en/gb/air-fl ... 00537.html). Also sent a lot of cleaner inside the MAP sensor
In this engine it is so easy to take out that i dont mind cleaning it regularly.

[yoseff]

As a further, the MAF also controls the use of the EGR on a diesel engine so if you are unsure of the state of it, might be worth a look as they can & do suffer from a build up of carbon.

On that note, when I did my wife's 2007 C4 1.6hdi engine not that long ago, I was pleased to note the EGR was if not immaculate, then as close as you can get for a valve that spends it's life in the exhaust system.

I am pleased to announce I am certain this is due to the prolonged use of BP Ultimate (or it's equivalent) diesel. That and regular oil & filter changes.

MAF seems to be working relatively well , specially after cleaning it
I always use "premium" diesel in my car. Currently from Repsol (10e+)
Oil and filters changed every 15 - 20k km
EGR behavior currently under analysis , but apparently seems to be working properly (at least from the sensors point of view)

Been driving with FAP app and Torque Pro (constantly swapping between those 2 apps to see several parameters, as they cannot be working at the same time)

[darbuck]

Hopefully that's it sorted now

[yoseff]

Hopefully that's it sorted now

Regarding to MAF , it seems that the cleaning sorted it out. It's now near the expected values.
However, randomly i continue with my rough low speeds acceleration as mentioned here: viewtopic.php?t=80383
Something i've realized is that it coincides with the throttle body (or Air mixer , as appears in FAP app) not working randomly
In one trip is ok , then it stops working and car gets weird,
I'm driving most of the time with FAP app working & Logging , but no conclusion yet. Would it be a good idea to share some of my FAP Logs?

[yoseff]

Still the same - In some travels throttle body (it appears in FAP as air mixer) , works and car is smooth , but then randomly it will stop working and then the roughness starts once again...
Air mixer instruction seems to correlate with what is asked. The not working part seems to be that air mixer movement stop asking to work. EGR movements also look a bit suspicious sometimes . Could a bad / clogged EGR provoke that behavior?

[myglaren]

Topics merged.

[yoseff]

Adding a bit more info from the discovery journey, i realized that EGR is open (Around 50%) at Idle and from what i've read around it wasn't supposed to do that. It doesnt seem stuck , as the instruction fits close to what it is doing. Maybe the juddering i'm feeling randomly is EGR related afterall?
I'm tempted to blank it in order to test if it changes something , but probably that will throw out some error immediately... What would be the best way to test it without disassemble too much things?

[darbuck]

Try blanking it off it shouldn't throw a code for a while.

[yoseff]

Well, time goes by and i still looking to discover what may be doing that initial roughness. Not pleasant to drive in a slow way. However, some new light appeared to me today over this subject: As Turbo OCR goes around 70% plus in lower rpm the engine is smoother, Only when its at around 60% or less it is rough. What does control turboOCR?

Another interesting discovery is that sometimes when electronic handbrake is applied, ocr sits around 60% at idle and once i take it off, OCR goes to 70%, It changes also Voltage as seen by OBD from 12.5 (ish) to 14.6 (ish) with handbrake off or on... Battery could be signaling weakness?

[yoseff]

Need to solve that... It's driving me crazy and damaging the dual mass flywheel with the power surges.
It seems to be related to OCR being at a percentage that should not be.
Turbo is doing a bit more pressure than it should and hence the nervousness. I can see that pressure is bit higher than engine ask for. What can be doing that? One of the valves behind the engine?

At the moment vacuum reserve is bypassed, as there was a leak on it. I'm looking for a vacuum reserve box from another car to adapt, as in this engine it is in the intake manifold and don't want to change it. Could the lack of that reserve contribute to it?

Could be a perfect car. It's getting better in many ways. Front spheres were re gassed (the 3) to correct pressure, changed 2 central ones behind, one was blown , engine went out to change all those parts that could leak anti freeze from the engine, head gasket was done, lots of stuff done recently, but this detail is just taking the pleasure of riding the sofa on wheels...

Maf readings seem not correct either at idle. Got another Maf, but still bit on the high side. Will clean it well today to see if it goes from the 12g to something near 5-7g at idle. But on second thoughts, it can actually be the extra work of turbo that is pulling more air at idle, so not a Maf reading issue.

So, the big question is: What can affect turboOCR not going more towards 100 % at idle? Where should i look? One valve behind the engine was changed for a new original one. I think it was the first one near the smaller that controls EGR. But it was not me doing it, so not 200% sure if was that one. EGR provoking the issue is already ruled out.

Could someone please show me some light?

Thanks in advance