Diesel mechanics?

[gnipper 6,837]

Is there any diesel mechanics on here who know much about maf sensors and rough idling problems?  Basically my car idles rough when the weather is warm, fine when it's cold and everything points to a maf sensor problem, unplug the sensor and it goes normal. Tried a new sensor and it's worse. It's had the throttle body and egr and loads of other stuff inside cleaned by my mate. When it idles rough there's an exhaust smell in the car, decrease in fuel consumption and sometimes juddery to pull away.

 Any ideas? Cheers 

[Stavross 18,520]

That’s usually a fault with MAF sensor or the manifold pressure sensor, I’ve had it in the past where I’ve replaced the MAF with an aftermarket one and it’s just been the same, put a genuine one on and it works, also if there’s oil on the manifold pressure sensor it gives the same fault, when you unplug the MAF the ecu will change the fueling to compensate for not seeing the air flow it is expecting, also possibly a wiring fault to the MAF, this sometimes doesn’t put the EML on but will store a fault 

Edited June 16 by Stavross

[Stavross 18,520]

Just to add, these thing check for air flow and vacuum so if the air intake system has a leak after the MAF then this is the fault you will see and unplugged the MAF will take the sensor out the system so the ecu will compensate for it, normally by adding more fuel, this could be what you can smell in the car

A split in a vacuum pipe will also give this fault on some occasions 

Edited June 16 by Stavross

[gnipper 6,837]

1 hour ago, Stavross said:

Just to add, these thing check for air flow and vacuum so if the air intake system has a leak after the MAF then this is the fault you will see and unplugged the MAF will take the sensor out the system so the ecu will compensate for it, normally by adding more fuel, this could be what you can smell in the car

A split in a vacuum pipe will also give this fault on some occasions 

A split pipe could possibly be a thing? The pipe could be more pliable when it's warm allowing more of a leak?

[Stavross 18,520]

The reason it might only be doing it when it’s warm is possibly because the ecu doesn’t use the MAF sensor until it’s up to running temperature ( possibly? )another common one is if it’s got a plastic inlet manifold the have a tendency to crack and this will give you a vacuum/pressure fault 

[mC HULL 16,235]

3 hours ago, gnipper said:

Is there any diesel mechanics on here who know much about maf sensors and rough idling problems?  Basically my car idles rough when the weather is warm, fine when it's cold and everything points to a maf sensor problem, unplug the sensor and it goes normal. Tried a new sensor and it's worse. It's had the throttle body and egr and loads of other stuff inside cleaned by my mate. When it idles rough there's an exhaust smell in the car, decrease in fuel consumption and sometimes juddery to pull away.

 Any ideas? Cheers 

cat dpf blocked 

[Stavross 18,520]

That would throw up a Delta P fault and the EML would be on all the time and it would run like a sack of shit, hot or cold 

[mC HULL 16,235]

1 minute ago, Stavross said:

That would throw up a Delta P fault and the EML would be on all the time and it would run like a sack of shit, hot or cold 

depending on how old the motor is mate doesnt it 

like you say it runs until temp then starts adjusting fuel and air it could be like you say air getting in a bit of easy start sprayed about will soon let you know 

once you start getting that smell though moneys on dpf or  cat myself 

[Stavross 18,520]

I’ve had them where the inlet manifold is cracked and it does exactly this and the smell is an exhaust gas smell from running rich, not a blocked cat/dpf smell, easy starts is a good call, spray it around and if you can’t see it you will notice when the revs pick up if it’s drawn in through the manifold or a split pipe

[Lenmcharristar 10,330]

If its a chemical smell its most likely a blocked dpf, what kind of car is it?

[Stavross 18,520]

I don’t want to sound like a dick and I’m not saying the DPF isn’t blocked but I would expect that to show some different faults, from what you said is happening I’d firstly look at the air intake side, check the MAF sensor wiring, check the inlet pressure sensor because if this has failed it would put the EML on but if it’s got oil on it could give the fault you are getting, check the inlet/ vacuum side Mc’s way with the easy start is a good way, just spray a bit of it around vacuum pipes and the inlet manifold you might see it being drawn in if not the revs will increase if any gets into the engine ( just don’t spay it around the air filter) if the inlet side checks out then you can look at the exhaust side but to me that would show some different faults like going into limp mode or lack of power due to no being able to exhaust efficiently the fault would also be there all the time if the DPF was blocked and the EML would be on

[gunter 1,850]

What type of car you working with....THE NEW  MAF SENSOR WAS IT AN AFTERMARKET ONE YOU GOT OR IS THE GENIUNE PART SEE BUYING AFTERMARKET I DONT RECOMMEND AND WOULD BUY GENIUNE 

[gunter 1,850]

I'd recommend if you havnt putting a geniune maf sensor in that doesn't work check all your vacuum lines but go get a smoke leak test done you'd be suprised were it could be leaking or another thing to check with the fumes is a crack in manifold it can cause problems 

[downsouth 8,368]

22 hours ago, Stavross said:

I don’t want to sound like a dick and I’m not saying the DPF isn’t blocked but I would expect that to show some different faults, from what you said is happening I’d firstly look at the air intake side, check the MAF sensor wiring, check the inlet pressure sensor because if this has failed it would put the EML on but if it’s got oil on it could give the fault you are getting, check the inlet/ vacuum side Mc’s way with the easy start is a good way, just spray a bit of it around vacuum pipes and the inlet manifold you might see it being drawn in if not the revs will increase if any gets into the engine ( just don’t spay it around the air filter) if the inlet side checks out then you can look at the exhaust side but to me that would show some different faults like going into limp mode or lack of power due to no being able to exhaust efficiently the fault would also be there all the time if the DPF was blocked and the EML would be on

Listen McHull has said its the DPF so go and find yourself a different trade because you obviously don't know what you're going on about

[mC HULL 16,235]

1 hour ago, downsouth said:

Listen McHull has said its the DPF so go and find yourself a different trade because you obviously don't know what you're going on about

i cant fault what  stav is saying but an air leak is easy to diagnose with easy start or live data  checking fuel trims 

i’d say it more the cat 

we don’t know age and motor yet mate 

as  stav says a dpf on newer will flag with a light most of the time

id say stay knows exactly what he is on about