Is there a way of testing the Maf and what are the signs of a faulty one.

 

Anyone

 

hi chris it has been said that if you start the car up and disconnect the maf sensor it should stall straight away! if it continues to run the maf is knackered or on its way out...

JollyGreenMonster.co.uk

have a look at the link above too this explains how to read ur fault codes

hope this helps

 

that's not really a conclusive way of testing the maf, when i thought my maf was knackered i tested it as per the workshop manual, with a volt meter that was permanently wired in to check the voltages were in range, as and when they were meant to be, in my opinion this is the only way to check a maf properly, unless you have dealer level diagnostics.

 

When I unplug it the car seems to idle better but will rev very rough. When I plug it back in the car stalls straight away. I am going to see if a fault code comes up a also spray it with contact cleaner to see if it helps a bit. Its hard to explain what the car is doing if there was a way of posting a video of it doing it I guess that would help.

 

It's high time people stopped repeating that rubbish. It proves nothing one way or the other and can damage an otherwise good airflow meter, and, worse, can pass dangerously degraded ones as "good". Well meaning b*ll*cks like that does more harm than good.

Chris: The only way to conclusively prove whether a sensor is accurate throughout its working range is to bench test it on an airflow rig which you obviously don't have access to. You can do a little more if you have access to a voltmeter or the ECUs diagnostic stream, or with wideband AFR or knock monitoring kit.

The one thing you could try is to start the car *with the sensor disconnected* and see if idle stability noticeably improves - although it's a very bad idea to actually drive the car like this and it is not a conclusive test.

It sounds pretty much like you've already done that, so if I were in your shoes I'd probably order a new sensor. Often the most practical way of knowing whether an old one is broken is simply to replace it, reset the ECU and monitor what happens to the car's behaviour. If whatever's wrong clears up you know what caused it. If the problem remains after fitting the new one, you can take it out, put it on your shelf and carry looking.

 

Thanks Splitpin.

I do have access to a volt meter but that’s it. I tried plugging the two black connectors together under the dash but nothing happened. Maybe they were the wrong ones. They were the two pretty small connectors either that or someone has removed the engine check light as it doesn’t even light up for a few seconds when you first start the car.

If it was the Maf Would the car pop and bang a bit and when you try to get through the hesitation by accelerating a bit more. As this is what mine does and then tries to stall when you come to a stop so to stop it stalling I give it some revs but it starts popping and banging again. Almost like a misfire or unburnt fuel in the manifold igniting.

 

The check engine light being removed (or maybe blown) is quite likely if it doesn't come on prior to starting the engine. It'd be worth checking that out and replacing it if necessary as you may well find there are stored error codes which will clue you in quickly to the problem.

That does sound more like a misfire/ignition issue than something directly related to the airflow meter. More often than not if the MAF degrades it causes under- rather than overfuelling.

 

I will check the bulb in the morning cause not having one or a blown one is not good as i would never no if something goes wrong or if something has gone wrong.

I dont realy no the best thing to do. Get it to a garage i guess.

Im gutted as i blew the engine last summer thanks to a tuning company that that fitted a Power Fc for me and raising boost to 1.5bar with out telling me i needed forged pistons to take it. I should have done my home work before hand but i trusted some one like the guys who did it to know what they were doing. Since found out im not the only one the have done it to.
So i put another engine in and the standard ecu back so that i could sell it as i brought a new car but its not going as planed.

 

Just out of interst what are the signs of underfuelling

 

clap clap ur always a cert to follow on ur great knowledge but if u read the post again you will see what i did say it has been said! hence why i told him to read the fault codes via the jgm link... also ur telling him to do the same test only in a different order disconnect the maf then start it up the same damage can be caused either way!. simple advice is all chris is looking and simple methods has been given.
splitpin no harm but you really are a muppet

 

There was no engine check bulb in the dash which i thought was odd.
Looks like the last owner may have wanted to hide something.

First code was the idle control valve. Repaced that and have reset the ecu now its showing the Maf at fault.
Im guessing it can only show one fault at a time which means once the maf has be changed there could be another code pop up.

 

Any chance you could post that again in a manner that's legible?

No, you are incorrect. The way you suggested has the potential to cause damage via the sudden removal of power to the airflow meter while the engine is running (and air is passing the sensor). The method I suggested involves unplugging the sensor while the engine is off.

In addition, you repeated the old bollocks about how, if you unplug the sensor with the engine running "it should stall straight away! if it continues to run the maf is knackered or on its way out...". That is complete and total bullsh*t, no other word for it and anyone taking your comments at face value runs the risk of a degraded sensor being passed as "good".

You may be simple and no doubt meant well, but the old wives' tale you were repeating wasn't helpful. Whether you like it or not the only way to point that out is to say so. If you'd like to discuss in detail the manner in which the ECU responds to dropped sensor inputs while the engine's running, go ahead. Otherwise...

 

Unfortunately there usually aren't outward signs that you can detect without extra equipment. The consequences are a rise in cylinder temperatures and eventual detonation. You'll usually need something like a wideband AFR meter, and/or some knock monitoring kit to pick it up, unless it's really bad.

Hmmm, yeah, worrying, but it does happen. There was someone on here not long ago asking how to disconnect the light as it kept coming on!

Good stuff, at least now you're getting somewhere constructive.

It doesn't work like that. The ECU can theoretically display every single possible error state in one go if it needs to. In practice, the way the car is wired, if one item of equipment is malfunctioning, it can sometimes mask or otherwise prevent the ECU from detecting another. That's probably what's happened. Fingers crossed once the airflow meter is replaced you'll be error-free, although at least now you know you can rely on what you're seeing (or not) from the check engine light.

 

I feel a little more positive now i have a way of finding the fault.
Really hope its just the MAF that has gone.
I have read a few things on here that the water temp sensor, knock sensor, lambda sensor and even the crank case sensor can cause similar symptems to what im having. Is this true ??.
The car idles much better now with the new idle air control valve but is still hesitating when you accelerate and sounds rough while doing it.
Would you say this is the maf or still something else.

 

I too have similar problems that we are all desrcibing above (hesitation mainly), and suspect the MAF sensor from reading other peoples post and threads. So i'm thinking of investing in one these cables from here :http://www.gendan.co.uk/product_VAGUSB.html

This will enable me to read and record live readings from the ecu including the MAF sensor, what do you guys think?