Odd pressure readings

[sweeper]

So I have just repaired my Viano, see previous post, engine light and limp mode, now my scanner wouldn't read the fault so I always think it best to take to Mercedes as they have the inside knowledge and should be able to sort things out quicker and usually cheaper, I couldn't get in for two weeks so I had a mobile guy come and check it, his diagnosis was to replace or clean the dpf, now i have some knowledge and experience with engine systems with factory training on diagnostics and I noticed the dpf pressure differential reading were off (reading 0 all the time) cut a long story short I bought a icarsoft MB V3 so i could do some testing myself, following a fault diagnosis chart from work, remove dpf sensor and check pipes are not split or blocked followed by replacing dpf sensor, this cured the problem and I ways able to initiate a dpf regen, everything is fine but i noticed exhaust pressure, boost pressure down stream and atmospheric pressures are all off (around -63b) now I assume the exhaust back pressure sensor is faulty and that the boost pressure downstream is a calculation using this minus the dpf sensor readings, but what about the atmospheric reading, does it have a sensor or is it a calculation taking the, we'll see once I change the exhaust pressure sensor i guess. once upon a time the atmospheric pressure was taken from a sensor in the ecu. I'm a little surprised no fault is showing with the reading being so far out, has anyone else had similar issues? how were they cured? I still have the vehicle booked in but i think i'll cancel it and wait until i've replaced the exhaust pressure sensor in the hope all readings correct themselves.

 

[M80]

I can't see mention of am atmospheric pressure sensor.
I haven't yet found the exhaust pressure sensor, aside from the dp sensor you're replacing.
I believe the boost pressure sensor is located on the inlet riser plastic pipe at the top elbow, pre inlet manifold. Part no A001 015 372 28

When I have the engine back in and connected to the ECU I'm hoping iCarsoft can confirm my conclusions by unplugging various sensors and the change of state being demonstrated.

 

[Doug1234]

Atmospheric /barometric pressure sensor usually on air box mounted above filter ,I only know that because it was not plugged in correctly on my 642 engined Jeep after oil cooler seal and turbo change . It just threw a code so I googled it to find I had not pushed its connector in properly.

 

[sweeper]

I can't see mention of am atmospheric pressure sensor.
I haven't yet found the exhaust pressure sensor, aside from the dp sensor you're replacing.
I believe the boost pressure sensor is located on the inlet riser plastic pipe at the top elbow, pre inlet manifold. Part no A001 015 372 28

When I have the engine back in and connected to the ECU I'm hoping iCarsoft can confirm my conclusions by unplugging various sensors and the change of state being demonstrated.

The exhaust pressure sensor is located on the pipe that goes to the egr valve, so if you follow it from the manifold around the back of the engine then up to the egr it is in the last bit of cast pipe pointing upwards, i think thye are a common fail part and some vehicles appear to ignore the signal whereas others don't and go into reduced power (as in my R class) but the Viano seems quite happy reading -63bar which of course it can't be, it will always be higher that the manifold pressure

 

[M80]

Thanks for that.
I'm presently trying to identify each sensor and the associated pin numbers in the ECU plug. So all input welcomed.
I haven't remounted the ERR (and cooler) to the engine yet, so I'll pick up that a little later.
If there is a resistance reading while static I'll have that too if it's of any use to you.

If my workshop manual would let me through to the drawings it would be a damn site faster. The pins and wire colours would identify the sensors far easier.

 

[sweeper]

I can't see mention of am atmospheric pressure sensor.
I haven't yet found the exhaust pressure sensor, aside from the dp sensor you're replacing.
I believe the boost pressure sensor is located on the inlet riser plastic pipe at the top elbow, pre inlet manifold. Part no A001 015 372 28

When I have the engine back in and connected to the ECU I'm hoping iCarsoft can confirm my conclusions by unplugging various sensors and the change of state being demonstrated.

Why is your engine out?

 

[M80]

Why is your engine out?

How long ya got?
Basically it failed on emissions, because MB applied a plate that requires stringent standards.

Trying to work in the confined engine space was near impossible. An engine that's over complicated, My being unfamiliar and not seeing how the masses of components would come out, I decided engine out.

That was January. I didn't have time so bought a 211, as a van, to get me by.
That grew on me v fast and it seems I landed on my feet.
Drives well, economical on a run, not bad around town, I'm enjoying it.

Still no time really but got around to removing the 651 lump. So I've learned a lot.
The 639 is multi purpose, the 211 less so.
I'm hopeful that I can remove the mysteries of all the gumph under the bonnet and not feel as though I'll be scratching my head in future. The hope is that the Viano will do us until diesels are under attack by Gov't drones.

So it goes back together, v slowly.
I'm trying to understand what and where each sensor + is. What expected readings can be taken, they being resistance, and running data of pressures etc.

But if I conclude that there is too much that can't be accessed with the engine in place I may well exchange for a petrol what ever.
Then of course it 'aint got the low torque. I'll be providing extra gasses to warm the planet, and the Gov't will see much more of my dosh.
And I will be really peed that I didn't just get it sorted in the quickest way.

An incomplete list of engine sensors, and such like.
Ambient air temp,
MAF, (likely includes intake temp),
PCV heater,
charge air temp,
throttle valve,
throttle actuator,
boost pressure,
vacuum switch (unknown function as yet),
inlet flaps actuator,
fuel filter sensor,
fuel pressure,
front of fuel rail,
rear of fuel rail,
switchover valve of secondary air injection,
cam ps,
crank ps,
EGR valve,
EGR coolant temp,
t'stat temp,
t'stat heater,
glow plug controller,
4x glow plug,
4x injectors,
2x knock sensors,
fuel pump pressure regulator valve,
fuel pump temp,
turbo temp,
turbo actuator,
exhaust pressure,
alternator,
AC compressor,
AC pressure,
vacuum pump,
HP fuel pump,
alternator,
starter,
steering pump sensor,
DPF temp,
DPF dp.

It was running well, but not so far w/o an MOT.

 

[sweeper]

I had similar issue with mot, took to Mercedes for diagnostics and no fault found, emissions perfect! Mot station wasn’t revving the engine hard enough, mb did it with diagnostics on which takes away the 3000rpm limit and Rev to the natural stop at about 4500rpm, clean as a whistle, mot station would just blip it, fail it and say it needs new dpf and the we’re going to report the MB dealer for having faulty equipment!