Hiya, just wanted to fank you for your input on my MAF thread, didn't reply at the time cos I've only just noticed.

You've managed to completely remove my paranoia and made me feel a whole lot more comfortable about the whole deal. The main thing that was worrying me is the thought of the engine blowing whilst bombing along cos the MAF had failed at that point, but if the ECU sorts this kind of failure out then that's cool.

However, I have just 1 more very simple little question;

From what you say the problem with the MAF is them gradually under reading and the ECU working around this, thus giving a AFR that's gradually getting leaner? I've read that reseting the ECU stops this behaviour, and will throw up a CEL indicating MAF failure. Is this true?

And ref the knock link, there's one sat right next to me ready to be fitted to the RA. Just waiting for the car to fit it to now And I think for the sake of £80 I'm definately gonna change the MAF as a priority.

Cheers for your help, it is very appreciated.

 

Hiya Dude!

when she arrive?

Weava

 

Only a few days away now. Just waiting for the money to appear in the bank account.

I cannot wait big style, I've already had a phone call from Natwest's Fraud Prevention Dept cos they cant understand why i keep logging in every hour

 

No problem!

It is very rare for a MAF sensor to be fine one second and then literally fail, as in stop reading completely. However, if this situation does occur, the ECU will catch it, yes.

Yep. That seems to be by far the most common mode of failure.

No and yes. The point is that the ECU can't work completely around a failing MAF sensor. The sensor measures the amount of air going into the engine, and the ECU uses this information to calculate the amount of fuel it injects. If the MAF sensor is under-reading by, say 10%, the ECU will reduce the injector duty cycle by 10% to maintain the mixture where it thinks it should be. Thus, as the sensor under-read increases, it's actually running increasingly lean.

One of the problems with this is that the leaner mixture actually improves the car's performance, so far from feeling "off", it'll actually go better and better right up to the point that cylinder heating or det (or one leading to the other) kills it.

Erm, sometimes, maybe, but you can't rely on this happening, no. The sensor would have to be well on the way out for this to happen, and if it's that bad, chances are it's already bad enough to be causing serious leaning under boost, something you'd notice easily through looking at an AFR meter or KnockLink readout.

That's a good move. Probably goes without saying, but don't forget the separate sensor for the KnockLink if you don't already have one. Wiring into the existing knock sensor isn't an option.

[Edited by greasemonkey - 1/31/2004 5:14:59 PM]

 

Fanx again.

Yup the knocklink turned up without a sensor, I wasn't clear whether it came with 1 or not, so I ordered the sensor the day the link arrived.

Based on your input I think I'm gonna change the MAF on the Wagon before I sell her too then, I'd feel gutted if she blew up shortly after I've sold her on to someone else

 

A slight correction regarding fuelling with an under reading MAF; in closed loop operation the ECU compensates (assuming the lambda sensor is fine) to ensure mixture is still swung across an AFR of 14.7:1. The problem comes when you give full gas and ECU switches to open loop, using the values in the maps.

Under-reading MAF means a lower load scale value is used. Actually no huge problem for fuelling assuming a stock (pig rich) car....but load scale issue also means the timing will be more advanced than it should be. Not a nice combination

Richard