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Low intake air quantity

14K views 67 replies 12 participants last post by  Dorian Star 
#1 ·
Hi

I'm having problems with my Alfa 159 2.0 jtdm. The car has lost half of the power but there are no errors present when scanning with MES.

The engine is remapped and EGR off by software and blanking plate.

What I can see from MES is that the intake air quantity is too low (about 360mg/i) and I think it should be around 460mg/i at idle.

I checked(in the following order):
- air filter (replaced with new one)
- hose from air filter to MAF and from MAF to turbo (there aren't any splits)
- hoses that go in the intercooler and to the butterfly valve
- with the MAF disconnected the value is around 380mg/i and doesn't change much
- tested with new MAF and same readings

is the intake air quantity calculated only by the MAF or the MAP sensor on the intake has something to do with this too? (I thought the MAP only reads the boost value)

Please give some ideas because I'm kind of stuck...

Thank you!
 
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#2 ·
With MAF disconnected the car should be using default values, so guessing the numbers will come from somewhere, guessing the MAP will calculate it?! Often it gets gunked up, so try it disconnected (and give it s clean)


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#5 ·
I suspected that pipe too and to be sure I covered the connection with the main pipe with high temp black silicone.

the log values look a bit weird to me. becasue after 2500 rpm the Desired intake Q goes to 1499.5 and the actual air quantity is almost half that. Also I see that after this the ecu cuts the fuel.

I attached a log.
 

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#6 ·
2.8 bar requested boost pressure seems a little high. Is that what the 2.0jtdm run at? :O

It seems to be reaching the requested boost pressure okay but doesn't seem to have the flow rate that it is expecting to see.

Does this car have swirl valves in the intake? Possibly sticking shut slightly and causing boost to build in the intake (Where map sensor is) but not requiring as much air as car is expecting.
 
#7 ·
the engine is remapped but still isn't that the absolute pressure? From what I know the real pressure is the absolute pressure - atmospheric pressure. The strange thing is that it looks like it has underboost and overboost. Could this influence the intake air value or the boost values are determined by the low air intake? I'm asking because if this boost values determine low intake the problem might be sticking vnt ... but if it's the other way around then Idon't know what else to check :(
 
#8 ·
looks bad buy you are logging too many things at once ,data rate is probably too slow and data in same line may not be real.
your looking at maf and boost
i would stick to just logging maf and boost
i would expect a certain value of actual boost/maf
View attachment maf boost ratio excel.xls
heres one of mine
easier to see any abnormalities when graphed i think around ratio 2 normal for my car yours may be different but ratio should stay about same for your files / data
on remap i dont know but seems a lot of boost for not much fuel and very low maf
i run 2800mbar boost for 95mm3 of fuel and maf of 1300-1400mg/i
try less data lines next if i were you
 
#9 · (Edited)
just for example heres your data again
View attachment alfa maf boost log 1.xls
see how your ratio is way wider range ? boost and maf should stay somewhat constant if no egr operating.
as i said could just be delay in data skewing stuff you need a few data lines a second
no time in your data but looking how high boost has risen in one line i suspect way too slow to be of any use diagnosing stuff.
forget fuel bit as low maf is limiting fuel , low fuel causing low boost etc

i would be cleaning map sensor and checking again , cheapest things first
could be a map sensor over reading , what readings are key on engine off for map
eg at sea level 1000mbar approx depending on weather and temperature abient ?
then at idle id expect 485mg/i maf and 1000mbar boost
if you are very high altitude low boost and low maf expected urs looks too low boost or actual vacuum in reality at 700mbar if at sea level.
 
#11 · (Edited)
sample rate still looks too slow , not sure i could trust the data , where peak ratio is very high or very low do you think car has high airflow with low boost and also low airflow with high boost , or sample rate issue ?
also i dont know who did map or know much about 2.0jtdm but 1500 seems high for desired maf ? dont think the problem is your not achieving desired here , think that value is way above whats expected, maybe a function of the egr off part of map?
if you have oe intercooler i would not expect figures above 1200-1250mg/i with 2500mbar boost say
have put on your data expected maf using actual boost and overlayed it to actual maf in graph bellow yours
View attachment alfa maf boost log 1.xls
this is a more representative image of your issue in that what maf reading is low , back to looking for split or leakage unmetered air after the maf . check egr blank(cheap ones have been known to hole through, is it a full blank) , hoses breather hoses vapour tanks catch tanks etc.
and also test again driving and logging with the maf unplugged and see if you get back higher boost and higher fuel total when logging.
as someone said earlier with maf unplugged the car will use internal maps to guess maf using map sensor to measure boost and temperature and estimate intake air quantity which should be similar to what i put on second graph.
would just expect normal performance to return mostly , if so you still have maf , pipework or unmetered leak
edit not sure excel 2nd graph showing
here screen shot of your boost , your maf , and a perfect expected maf value.
your low but not as low as you think, low enough to cut fuel though.
https://ibb.co/cwoO0q
 
#13 ·
When I changed the MAP sensor it was pretty clean so I think the intake manifold should be ok. The swirl flaps I don't know... I tried testing using MES but nothing happened, no relay sound, no change in the engine rpm, nothing. Is there another way to test except MES?
I heard that to clean the intake on this engine is not an easy job and requires timing belt and high pressure pump removal, is it true?
 
#15 ·
You can take the pump off without removing the cambelt. There are two bolt holes through the pump drive sprocket to bolt it in place to the head whist the pump is removed. But to be honest unless you have a very recent cambelt and water pump you might as well do them at the same time.
 
#16 ·
Today I cleaned the turbo. It wasn't very dirty but now it's like new. The air problem still persists.

Taking the intake down isn't a easy job so I would like to be sure that the problem is from the swirl flaps before removing it. Is there any way to check the swirl flaps except MES?
 
#18 ·
the resonator box was checked and it seams ok.. I tried blowing air in it and it looks like there are 2 boxes with no communication between them. Is that correct?

On my list remain:
- the swirl flaps that need the intake to be taken off
- the oil separator (I don't know how to test it so I ordered a new one)
 
#21 ·
Today I tested the oil separator.

- I disconnected and blocked the hose that goes in the breather pipe.
- I connected another hose to the breather pipe; this hose goes in a coke bottle.

After 100 km, in the coke bottle had approx. 15-20 ml of oil in it !

I think the oil separator is definitely clogged and this explains the oil consumption.

The other conclusion is that the breather has nothing to do with the low air quantity because after blocking the small hose entering before the turbo, nothing changed.

I'll order a new oil separator but I think the existing one could be cleaned.

I'll come back with info after I change it.
 
#23 ·
the problem still persists. i didn't use the car for a while but now i'm back. I took down the intake manifold and cleaned it also removed swirlflaps and added blanks. I also replaced the oil separator with a brand new one.

The air intake is still low and the car seams slower and slower.

I don't know what else to check..
 
#24 ·
I'm back to checking air intake quantity.

Something weird is going on at idle:
- with MAF and MAP connected and no errors showing the air intake quantity is 360-380mg/i
- only MAF disconnected the value is the same
- only MAP disconnected the value is the same
- MAF & MAP disconnected the value is 490-495mg/i (witch is the correct value since I have EGR OFF and blanked with a solid plate)

Both MAF and MAP sensors are brand new, EGR off and blanked, intake cleaned new gaskets and swirl flaps off, and I checked hoses for leaks.

Could there be a leak inside the turbo?

Another strange thing is that after I turn the engine off, there is a hiss in the turbo area but I can't figure out from where it is coming. I thought it was from the vacuum hose so I unplugged it but the hissing did't stop. It goes away eventually and it sounds like air going out from a balloon but dimming the pressure very slowly in about 2 minutes.

Any Ideas?
 
#27 · (Edited)
I found a leak - it was the seal on the pipe that goes from intake to EGR. I fixed that so now the air value at idle is around 485mg/i.

now I have another problem :grumpy: - after I accelerate and release the pedal, the air pressure drops to 380mg/i and stays there. If I restart the engine after a few hours the idle pressure is ok again, so there is something happening when accelerating. Could it be the turbo actuator sticking?

Tks.
 

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