996 turbo sudden MAF failure
Discussion
Yesterday, was accelerating in 3rd (not particularly hard). At about 5k rpm, it suddenly felt like I hit a brick wall for a split second - was thrown forward in the seat briefly. A bit like the rev limiter effect x 10. About 2 seconds later, ABS / PSM lights came on. They stayed on with ignition off / on but acceleration seemed OK after that (didn't look at boost though).
Durametric says ABS is unreasonable signal (or something like that) and that could only be cleared once I cleared the MAF failure. As soon as I start the car, idle is a little uneven for a few seconds then the failures trigger again.
Since it happens immediately after starting the car, and not under boost I assume it is genuinely a MAF failure rather than a hose leaking.
Is there anything else I should check before I order a MAF? I know it's not uncommon for MAFs to fail but I've not heard of them failing quite so suddenly - with such noticeable effect - before.
Note : Car is mapped (about 18 months ago) but has a paper filter, not oiled foam.
Durametric says ABS is unreasonable signal (or something like that) and that could only be cleared once I cleared the MAF failure. As soon as I start the car, idle is a little uneven for a few seconds then the failures trigger again.
Since it happens immediately after starting the car, and not under boost I assume it is genuinely a MAF failure rather than a hose leaking.
Is there anything else I should check before I order a MAF? I know it's not uncommon for MAFs to fail but I've not heard of them failing quite so suddenly - with such noticeable effect - before.
Note : Car is mapped (about 18 months ago) but has a paper filter, not oiled foam.
monthefish said:
As I understand it, the car should run as normal with the MAF unplugged, and if yours does, then it points to the MAF failing.
Apart from when it suddenly seemed to fail, it did seem to run fairly normally after that (apart from the warning lights) which is why I didn't unplug it - I thought I'd get basically the same result.james964 said:
Had a similar problem recently and it turned out to be a hose had worked loose from the turbo. The ABS/PASM light came on immediately on start up like your symptoms. Car ran rough and I could here the turbos spooling up louder than normal.
OK, I didn't expect that - if it was a leak / hose I assumed it wouldn't happen at idle. A hose coming off might make more sense since it did seem to happen very suddenly. Could be coincidence, but it's also happened quite soon (mileage wise) after a major service - maybe something got disturbed.I'll delay getting the MAF and have a good check of all the hoses - see if I can find something that's popped off or split.
Vixpy1 said:
David, your welcome to pop up to my house sometime and swap MAF's with my car before you buy another one
Thanks - that would be a great help.I'll try to get a chance for a good look around the car one evening this week and see if I can find any problems with the hoses. If not, I'll PM you for a chance to swap MAFs.
Gave the car a good check over today - including underneath - and could not find any loose or split hoses. Also went out for a proper test drive - car is boosting normally to 0.9 / 1 (mapped car) although acceleration is not quite as good as usual.
It's noticeable that each time I start the car, idle hunts for about 2-3 secs, then the warning lights come on and idle smooths out. Seems the computer initially believes the MAF and then decides it's rubbish and ignores it.
I just used durametric to take readings - I didn't log, since durametric is playing up this evening for some reason and will only plot 1 or 2 values at a time - if I try more it freezes. However, with single plotting I checked the MAF readings. One of them is fine (think it was the HFM one) which varies with rpm. But the other one is simply "3" and doesn't change. The hot film MAF reading also seemed to be a fixed voltage with no variation.
So, it does seem to be the MAF because it's simply not giving some readings. I have previous logs of MAF readings from my car so I know that I should have readings for both.
Vixpy - thanks for the offer of checking yours but it's probably not necessary now. I think Durametric has proved it's the MAF.
It's noticeable that each time I start the car, idle hunts for about 2-3 secs, then the warning lights come on and idle smooths out. Seems the computer initially believes the MAF and then decides it's rubbish and ignores it.
I just used durametric to take readings - I didn't log, since durametric is playing up this evening for some reason and will only plot 1 or 2 values at a time - if I try more it freezes. However, with single plotting I checked the MAF readings. One of them is fine (think it was the HFM one) which varies with rpm. But the other one is simply "3" and doesn't change. The hot film MAF reading also seemed to be a fixed voltage with no variation.
So, it does seem to be the MAF because it's simply not giving some readings. I have previous logs of MAF readings from my car so I know that I should have readings for both.
Vixpy - thanks for the offer of checking yours but it's probably not necessary now. I think Durametric has proved it's the MAF.
Edited by davek_964 on Monday 17th September 19:14
Ring this guy before you spend £200. http://www.emissioncontrols.co.uk/page.php?domain_...
_gez_ said:
Ring this guy before you spend £200. http://www.emissioncontrols.co.uk/page.php?domain_...
Thanks - will give him a call in the morning.I downloaded a new version of Durametric, so have got logging working again. I was wrong earlier - it's actually the HFM reading which doesn't move - this time it was stuck at 2, sometimes flickered to 1. Clearly wrong.
The other MAF reading does vary, but the voltage sits at 1.03v and doesn't seem to change.
Seems odd that it died quite so suddenly, but it certainly does seem to be dead.
At idle warm the maf reading should be around 1.35 volts approx, + or - 0.5v
Should hold pretty steady at this with only a little variation of around 0.5v
Then when smoothly pressing throttle pedal you should see this voltage increase and respond to that action or rapidly increase if you were to press throttle quickly. Remember reset diagnostics after new maf has been installed
Should hold pretty steady at this with only a little variation of around 0.5v
Then when smoothly pressing throttle pedal you should see this voltage increase and respond to that action or rapidly increase if you were to press throttle quickly. Remember reset diagnostics after new maf has been installed
Appears must be at fault as should clearly see it increase in voltage with even the slightest bit of throttle, should respond immediately. Once you fit new one and collect some live data you will then see what I mean.
You will need tamper proof torx bits to remove so hopefully you have some at hand
You will need tamper proof torx bits to remove so hopefully you have some at hand
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