Maf
- Thread starter turbazz
- Start date
There is a diagnostic procedure for the MAF. - I think for the sake of the mixture control using the "mode II" closed loop with the lambda sensor. It's in the manual, but I can't find it at the moment. I've never bothered with it as I couldn't get at the adjustment screw anyway.
Most people just check that the element is giving the correct voltage, and clean (or replace) the MAF if it isn't.
According to Ed, re-earthing the MAF is a waste of time; it's just working around the problem that the wiring between the ECU and the MAF is poor. If you're going to do anything you should replace the wiring to the ECU rather than the body.
Most people just check that the element is giving the correct voltage, and clean (or replace) the MAF if it isn't.
According to Ed, re-earthing the MAF is a waste of time; it's just working around the problem that the wiring between the ECU and the MAF is poor. If you're going to do anything you should replace the wiring to the ECU rather than the body.
For a start, can you rev past 2400rpm? If so the ECU doesn't think there's a fault with the MAF or it would have gone into limp mode.
To get into diagnostic mode II you do the exact same thing as for mode I (once it's in mode I). - The check engine light will then operate like one of those cheap AFM's you can buy; it flashes on for lean and off for rich.
Stoichiometry is when the light flashes on and off five times in a ten second interval (i.e. changes between rich and lean once every second).
I think the theory is that there's a little trim pot inside the MAF that you can adjust to get the mixture back to stoichiometric at ~2000rpm with a warm engine... but it involves drilling the plug out and resealing it when you're finished. - I would imagine that most people would use a wideband probe in the exhaust to do this rather than relying on the ECU interpreting the narrowband sensor.
At idle the MAF should be reading 1.0-1.5V, and at 2000rpm it should be 1.3-1.8V according to the service manual.
To get into diagnostic mode II you do the exact same thing as for mode I (once it's in mode I). - The check engine light will then operate like one of those cheap AFM's you can buy; it flashes on for lean and off for rich.
Stoichiometry is when the light flashes on and off five times in a ten second interval (i.e. changes between rich and lean once every second).
I think the theory is that there's a little trim pot inside the MAF that you can adjust to get the mixture back to stoichiometric at ~2000rpm with a warm engine... but it involves drilling the plug out and resealing it when you're finished. - I would imagine that most people would use a wideband probe in the exhaust to do this rather than relying on the ECU interpreting the narrowband sensor.
At idle the MAF should be reading 1.0-1.5V, and at 2000rpm it should be 1.3-1.8V according to the service manual.
Fusion Ed
Active Member
Re-earthing is indeed pointless. I've still yet to see this be a problem, god knows where the myth came from, but I guess these things spread when people read advice and just follow it "cause some bloke on the net said so".
You can test the MAF voltage off with the ignition ON and engine OFF with a multimeter. From memory its about 0.5v, if you want to know exactly I can measure one and check on Tuesday.
As for MAF wires. There are three wires, Orange, Orange and white. White is ground. one orange is 5v and the other is signal out. So easy to work out which if the ignition is on.
As for lambda sensor, most are dead these days. I reckon I get about 60-70% of the cars I see with a dead O2 sensor.
You can test the MAF voltage off with the ignition ON and engine OFF with a multimeter. From memory its about 0.5v, if you want to know exactly I can measure one and check on Tuesday.
As for MAF wires. There are three wires, Orange, Orange and white. White is ground. one orange is 5v and the other is signal out. So easy to work out which if the ignition is on.
As for lambda sensor, most are dead these days. I reckon I get about 60-70% of the cars I see with a dead O2 sensor.
Yes thanks for the reply Ed.. Going to check it at the ECU end. Found a guide how to. Basically the wires run back to the ECU..if There was a abnormality in the voltage would this not trigger a fault code? Any point me checking?
http://www.mummachummas.co.uk/gtir/ECU_INSPECTION.PDF
is there anyway me checking the O2 sensor?
want to get a map by you want to make sure everything is spot-on though
http://www.mummachummas.co.uk/gtir/ECU_INSPECTION.PDF
is there anyway me checking the O2 sensor?
want to get a map by you want to make sure everything is spot-on though