What does the MAF Control?

[JTaylor2005]

I know the MAF senses air flow, I have also heard it senses air temperature?

Ever since having this car I have had rattly injectors. Most of you lot on here probably know that by me asking questions about what I could do to sort it and what has been tried. However this is what recently happened.

I bought a new MAF about 2 months ago. I decided to do it as tbh MAF's wear out. They get dirty and slowly go out of tolerance over time. My MPG wasn't the best in the world (not low just not what a lot of people seem to get) So I thought stuff it I am going to have the car a while I will get one now.

Honest to god since then the noise of the injectors has pretty much disappeared. It was like an almost always there thing. Whenever I got in the car all I could hear when accelerating was the annoying rattle clickly noise of them. Was driving me mad. Since changing the MAF if I am unlucky I might get some rattle maybe once a week at worst now. Normally it is hardly noticeable. It wasn't even something I was trying to fix with the new MAF but I am sure it has had a significant impact on it but I have no idea how.

Just thought I would post my finding. I might have just gone totally deaf to it now but I can't hear it even listening for it on purpose. Is there any logic behind why that may have helped??

Jack

[toseland]

You have a HDi, the MAF measures the amount of air passing over it by measuring the amount a heated wire mesh is cooled down.. faster air flow, cooler wire, means more air is going into the engine.

it knows the surface area of the inlet hole (given area) and can then meter the amount of fuel being injected to match the air being sucked in, hence issues with bad performance if you have a faulty one (it thinks its getting more air than it is) or air leaks post MAF (it thinks its getting less air than it is)..


the rattle is pre-injection and i am betting as soon as you hit 3250rpm it completely dissapeared.. i know mine did,

with a new map the injectors are MUCH quieter, but its still there..

when i had the stage1 map they were noisy as hell and then shut up completely at 3250 as pre-injection turned off then.




As it happens, in the real world (ragging the absolute tits off of the car most places) i get 43-44 to the gallon.. if i drive it on a long run this will be nearer 50... if i drive it like an absolute saint on a long run, on a full tank of fuel i can get up to 55 (i have had that once in 15000 miles)..

people who claim that all HDis do 55+ mpg regardless are flying kites in their estimations.. if i drive mine only around town my MPG is shocking, 38-40, if i dont let it warm up in the morning before i pull off, my MPG is shocking... but as above, if its between 40 and 45mpg i would say you are on to a winner.. standard this should be nearer 50 in my estimation but thats an absolute max with a mix of driving styles and situations (stop start rush hour, around town, medium to long journeys etc)


bearing in mind this is stage3 with a bigger turbo and all that's associated it running 25psi... its running rich too

[Toms306]

Err all mine did 50-55mpg average every tank and I've had plenty to compare lol, if I'd ever got a tank average in the 40s I'd have been worrying about what had broken! I obviously don't drive like as much of an arse as you though.

[Redordead89]

307 SW 110 Hdi with fukt dpf and possible/ probable MAF issues ( pulls well when MAF unplugged ) over 5757 miles as of tonight I have 39.8 average, not driven granny stylee! not too good you would think for an Hdi but my average speed over the same mileage is 18 mph doing dominos deliveries so overall not too shabby for a 7 seater with issues! And thankfully it isn't a citreon or Renault egg!

[Poodle]

Toseland, you drive like a chronic twunt, i'm not surprised in the slightest that you can't get it past 50mpg. Seriously though, averaging over 50mpg isn't hard if the car is healthy, just takes a bit of steady throttle control and forward planning in traffic.

The maf does make an emormous difference to efficiency by nature, as without it the ecu can't achieve accurate fuel metering to match the air available, as you say. Very interesting theory, i might have to test this one out. I wonder if it's because without a reliable reference to air temperature it has to assume the worst and beef up the pre-iniection to ensure a complete burn of the main....

[JTaylor2005]

Since changing the MAF I achieved the highest MPG that I have ever had from the car as well which was 52mpg over a full tank. I am seeing what I get on this tank as well with steady driving but it does seem amazingly quiet rattle wise since the change.

[Ruan]

You probably want to get PP2k so you can start monitoring what the ECU is actually reading, then start looking into how the ECU uses this data to adjust what is going on with the engine. It will answer a lot of your questions

[pro_steve]

Basically it makes timing corrections and fuel quantity adjustments based on the intake temperature, so yes a bad MAF could make it run louder.

[JTaylor2005]

I am going to put the old MAF back in and see if the rattle comes back again on the next tank of fuel. See if that's definitly what is causing it all