Removing the MAF is not difficult. But…. Let me try to explain.
First remove the air tubes.
Next remove hose clamp on the pass.side bottom, pull off the hose, and remove the top of the air filter box (straps).
Take off the filter element. This is a good moment to remove any loose debris that you may find. Next is removing the two 10mm nuts and lift the lower air filter fox. You see the MAF very clearly now.
The MAF has a large hose clamp at the bottom that needs loosening. Normally you can use a long Phillips screwdriver from underneath the fuel rail on the pass.side to reach the screw and loosen it. If you don’t have one or cannot reach it, there is another trick. You take a blanket, put that over the engine and crawl onto the engine, lie on your belly. Yes, completely lie over the engine. That way you have a good view of what you are doing and can use a 7mm wrench or socket to undo the hose clamp. Be careful…. If you lose the wrench or the socket, it drops underneath the intake and you are in trouble. It is hard to get it out from underneath the intake body.
Ok, when the clamp is loose, you can twist the MAF a bit and feel it comes loose form the rubber seating.
Lift it up a few centimeters until you can unplug the cable connector. It is a short cable, don’t pull. Now, the MAF is out. It is good practice to cover the opening with a cloth or something just to make sure nothing accidentally enters the intake elbow and creates problems at the intake valve. You don’t to have it get stuck accidentally.
Be careful with the MAF. It is a sensitive instrument, and dislikes dropping on the floor.
As for the question of whether the car will start/run with a defective MAF, it should, and usually does. This "input" failure, as well as many other sensor failures, just puts the engine management system into: Emergency Running Mode. This will give it very fixed parameters, it would also be fair to call this the "limp home" mode. If you have other large problems (that were undiagnosed, like lots of vacuum leaks, etc) previous to this, it might be possible to exceed what the ER mode can do. Please keep us all informed of the progress! Kim
From what I was able to learn at the fantastic MAF tech session at this year's Frenzy 7, K&N seems to be a common culprit in accelerating the death of our MAF's.
Speaker Jon Holdsworth's explanation of the MAF is that the platinum wire sensor goes through a quick burn cycle at every engine shutdown. The thin MAF wire gets a high voltage kick to burn off any residue. Eventually the MAF wire will get so thin that resistance will fall outside the compensation range of the LH box. (the computer's responsible to do this ) A well lubed K&N filter will deposit K&N oil on the MAF sensor wire and cause more of the wire to burn off at each shutdown.
Someone mentioned that a carefully oiled K&N with oil application only on the top side of the filter may prevent this accelerated MAF deterioration.
Common consensus is to ditch the K&N and use the good ole paper filter.
Hope I got most of the salient facts straight.
Pretty well remembered I think you only got wrong (sort of) is the
"MAF wire will get so thin that resistance will fall outside the compensation range of the LH box"
yeah it gets thin and it's resistance increases - which causes it's output signal to be low. On a cat equipped car the LH brain can compensate by using the O2 sensor readings until the output becomes around 3.5-4% low at which point the LH cant correlate the two figures because the discrepancy is to high - and the cat equipped cars just wont run - like Marks car at the frenzy. On a non cat car like mine the car just runs weaker and weaker.
The mass airflow meter (often abbreviated to MAF), as fitted to 928s from
1984 onward, is mounted between the air filter and the throttle body, and as its
name suggests measures the amount of air being drawn in to the engine. At the
heart of the MAF is a very fine (0.07mmdiameter) platinum wire that’s heated to
100 degrees Celsius above ambient air temperature. As incoming air flows past it
the wire cools, and its resistance alters. Circuits within the MAF increase the
current through the wire to maintain the constant 100-degree differential. The
output voltage from the MAF varies with this current, and according to the flow
of air. This in turn provides information to the ECU that is used to ensure that
the correct amount of petrol is fed to the injectors to give the correct air/fuel
It sounds highly complicated, but the fact is that this all works remarkably well for as long as the MAF gives the correct output signals. But when it ceases to do so the ECU will inevitably be fooled into giving the wrong amount of fuel, and the air/fuel mixture will no less inevitably be either too lean or too rich.
In order for the MAF to give a correct reading the delicate platinum wire must be spotlessly clean. To ensure that this is the case, each and every time you switch off the engine after it has reached normal operating temperature, or has been run at more than 2000rpm, after four seconds the wire goes through what is known as a burn-off cycle – by heating up to 1000 degrees Celsius for about a second – to clean off any oil-vapor or other deposits.
This, too, works well, but over a long period of time the heating process takes its toll on the thin wire, and it erodes to the point that its resistance increases and the MAF output is no longer correctly calibrated. ‘To put this into perspective,’ says Speake, ‘an error of just two per cent at the MAF gives a ten per cent error in fuelling. And just a five per cent discrepancy on the output will make the car un-drivable.’
But even smaller errors will affect an engine’s performance....
There is a program routine in the LH ecu code, "limp mode", which allows you to drive the car home or to a workshop, even if the MAF fails. A MAF that is completely wrong can better be disconnected to force the LH into limp mode. Limp mode works with two pre-set fuel injector opening times- 3.5mS for speed below 2000rpm, and 6.3mS for speeds above 2000 rpm. This limp mode means you need to manage the fuel/air mixture with your gas pedal. In fact: add air so that the engine runs on it, not too much as the fuel mixture becomes very lean and the engine will stall, and not too little as the fuel mixture may be overly rich which makes the warm engine run very badly. Driving like this is possible with a little practice. Be gentle on the gas pedal !!