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Old 11-19-2012, 04:27 AM   #1
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Mass air flow issue - need your knowledge

Hi all,

Firstly I should say that the workings of the combustion engine are a complete mystery to me. But I could really do with the benefit of your experience please.

About two weeks ago I had my focus (2006, Zetec Climate, petrol, 1600 with the VVT engine) serviced and MOTd, no problem. Then about a week after, with only about 40 miles of driving done the yellow engine warning light came on.

I got my mechanic to look at it and the fault report was 'Mass air flow'.

So the mechanic changed the Mass Air Flow sensor and away I went, 200 worse off and after another 40 or so miles of driving the yellow engine warning light has come back on.

I have spoken to the mechanic who says that he suspects the wiring or the ECU to be at fault, but it seems sensible to me that he should be looking at the air flow system as that is what the report is?

My worry is he will try to charge me for new wiring and god forbid a replacement ECU and still not have fixed the problem.

He's booked to take a look this coming Friday and I'd really appreciate your views on what the issue could be as I can't afford for him to go on a wild goose chase when it may be something simple.

I should add that the car now feels slightly gutless and that the fuel consumption seems to be worse than usual, but I could be imagining it.

Any input greatly appreciated.


Last edited by WYNIR0; 11-19-2012 at 04:32 AM. Reason: additional info
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Old 11-19-2012, 08:21 AM   #2
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It might be that he put the sensor in backwards , the sensor's on the US models are directional meaning they only work in 1 direction but can be put in backwards causing problems that sound similar to what your Focus is having.
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Old 11-20-2012, 05:31 AM   #3
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Thanks. I'll certainly take a look at that.
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Old 11-20-2012, 06:34 AM   #4
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Eh, that's possible, but on a stock vehicle it's not possible to reverse the MAF. Just because the MAF is showing a code doesn't mean that it's the cause of the problem. Wiring could be a problem, but you can trace that down yourself if you know where the MAF is. Wiring damage can be fairly easy to see visually on the harness if you make sure you rotate it around.

I'm doubtful that the ECU is damaged as that is very rare. It's not impossible, but when I hear someone say that I raise an eyebrow like Spock. If the ECU was damaged, the engine wouldn't run at all, and wouldn't give a code for anything.

I haven't personally worked on your car's engine, but here are a few things that cause the MAF code to pop up: the air filter is clogged tremendously. There is a leak in the air intake tube- or the air intake is loose. The oil breather (the hose that connects to the side of the air intake and goes to the cam cover) is disconnected or damaged.

Good luck!! If I were you, I'd spend some time learning basic engine controls and operation. It takes a while, but eventually you'll at least be able to tell when you're being ripped (not saying you are ATM), and maybe even be able to replace some parts yourself. The MAF for example, is about half what you were charged. IDK for sure since I'm on the other side of the pond, but it seems that for most parts our prices transfer over at a 1:1 exchange rate. I'm guessing if you called a dealer, you'd find that part for 100 (wth is my pounds symbol???), and then all you'd need was a star head screwdriver of the right size and 20 mins or so.
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