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Discussion Starter #1
The MAF (Air Mass Sensor) on my car is just after the filter and it basically measures the air flow into the car ... the MAP (Manifold Air Pressure) is after the turbo (somewhere) and measures the pressure of the air so that the ECU can determine the correct fuel/air mix ... so why do we need both? what does the ECU use the MAF for if it is using the MAP to determine the amount of fuel to use?
 

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I know a Petrol turbo can run happily with just a MAP sensor and a throttle position sensor plus intake air temperature sensor and ambient air temp sensor and ambient pressure sensors (the last two often built into the ECU itself).

A Diesel doesn't have a throttle valve, so maybe it needs the MAF to measure how much air is flowing in.

I am just guessing though!
 

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Discussion Starter #4
MAP is uded to determine boost, so for engine safety aswell as for regulating the turbo.
so are you saying that the ECU uses the MAF to determine the amount of fuel to inject? and the MAP is only used to determine if the Turbo is working correctly?
 

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N/A engines also have both MAF and MAP. I think that the former determines injection duration and the latter is used along with the lambda sensor readings to check the correct operation of the former plus the air-tightness of the whole intale tubing. An air leak after the MAF would fool the ECU into producing dangerously lean A/F ratios.

The MAP sensor is a valve right after the throttle that measures the pressure of the vacuum inside the intake manifold plenum.
 

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The N/A Alfas don't uses MAP sensors.

Obviously no Lambda sensors in the JTD
 

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Discussion Starter #7
I presume that the pressure measured by the MAP is a function of how fast the turbo is spinning and the pressure of the air on the input to the turbo ... I presume the ECU has a built in function that can determine how much the turbo should spin up at together with the air pressure reported by the MAF to result in the pressure it wants to generate at the MAP (i.e. the boost)... so it then follows that if the MAP reports a pressure that is outside of the range of the expected values that it reports an under/over boost ...



... or am I talking rubbish :confused:
 

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:lol: To the point answer if ever I saw one.
BTW, I thought MAP meant Manifold Absolute Pressure.
I've not personally seen/noticed n/a applications where a MAF and MAP is fitted. Generally where a MAP is fitted in n/a, only a throttle valve sensor is used. Both seems overkill to me.
 

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Discussion Starter #10
you're not.
... so then if follows on ... as there is no way of verifying the values produced by the MAF (the ECU can only tell if it's there or not which is why we get so many "may car is running rubbish but there aren't any error codes"), if the MAF was reporting slightly rubbish data (because it is dirty etc) then when the ECU comes to verify the MAP value with the "incorrect" MAF value might it report this is a boost error :confused:
 

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It's more likely the MAP sensor is giving the incorrect reading as it is downstream of the turbo bearings which will seep oil slightly and will then be covered in EGR gas and form sticky tar over the manifold innards which will clog the MAP sensor. Phew!
 

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Discussion Starter #12
Obviously these queries are loaded ... I get the odd MCSF when I start the car (although I hadn't had it come up for a couple of months until this week), it then clears itself after a bit of driving (usually by the end of my road) ... the error code is "boost error" ...

... when I had a rolling road done, there was obviously something wrong with my car, although you can't actually feel the problem when driving ..



Adie (AHM) thought it likely to be the MAF ... hence my MAF query ...
 

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Don't like to argue with such an exalted specialist. It could be, but as using brake cleaner and blowing out the boost sensor is far cheaper, I'd try that first.

Your power graph does drop out a bit though, so I think something is definitely amiss.
 

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Discussion Starter #14
Don't like to argue with such an exalted specialist. It could be, but as using brake cleaner and blowing out the boost sensor is far cheaper, I'd try that first.

How do you do that then? are you suggesting putting brake cleaner into the turbo whilst the engine is running ? (in a similar way to how powerboost works?)
 

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:eek: No no no.:eek: Cleaning the boost sensor. Take the boost sensor out of the manifold and clean it whilst removed.
 

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Discussion Starter #16
:eek: No no no.:eek: Cleaning the boost sensor. Take the boost sensor out of the manifold and clean it whilst removed.


Ah that sounds much better :thumbs: ... I was wondering whether you were going to suggest sandblasting it by adding some sand to the air intake next ;) ...
 

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Only if it's really dirty.:lol:
 

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The N/A Alfas don't uses MAP sensors.
BTW, I thought MAP meant Manifold Absolute Pressure.
I've not personally seen/noticed n/a applications where a MAF and MAP is fitted. Generally where a MAP is fitted in n/a, only a throttle valve sensor is used. Both seems overkill to me.
In the 1.6TS of the 147 there is a pressure valve embedded in the inlet plenum right behind the throttle plate. I've seen it with my own eyes. I am also positive that this valve was missing from earlier aluminium inlet manifolds of 145/6s and early 156s as I tried to fit one to my 147 believing it was better than the plastic ones -not the case- and I had to have a threaded insert for the pressure valve drilled in the plenum.

Also if you plug in the examiner and turn the engine on one of the readings you get is a "manifold pressure" indication in mmHG if my memory is correct.

Anyway, I'm off-topic so I stop here.
 

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Early 156 did not have the alloy intake.
Only the CF1 engines had that and the 156 started with CF2 engines.

If there were MAP sensors, you would be ably to buy replacement MAP sensors for them and I've never seen one.

Besides, a MAP sensor is not a valve. I think you may be looking at part of the crankcase breather.
 

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Ah that sounds much better :thumbs: ... I was wondering whether you were going to suggest sandblasting it by adding some sand to the air intake next ;) ...
Only if it's really dirty.:lol:


Could you stick my wheels behind your exhaust and sand blast them when it comes out the back? They need a good refurb :lol:
 
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