[Engine] 'Airflow higher than recommended'

[Pedronicus]

During this recent hot weather have had a couple of EML warnings pop up on the van which have thrown up the code P3008 'Airflow higher than recommended'  On checking with Lexia the Measured Airflow was 0467mg/stroke and the Reference Airflow is showing as 0405mg/stroke.

Anyone have any ideas what might be causing the increased airflow, please.

[cancunia]

It's possible that the MAF is giving false readings in hot weather, maybe also a hint that the MAF is faulty .

[Pedronicus]

It's possible that the MAF is giving false readings in hot weather, maybe also a hint that the MAF is faulty .

Or needs a clean perhaps?

[cancunia]

I've broken a couple of MAFs trying to clean them, other people have success. I think that mine were broken anyway, but they certainly were after I'd had a go.

[Pedronicus]

I've broken a couple of MAFs trying to clean them, other people have success. I think that mine were broken anyway, but they certainly were after I'd had a go.

[Sol]

I've cleaned them with a cotton bud and alcohol. Maybe you clean things like a bear cancunia....?

Must admit though, never made a difference. It's measuring the cooling effect of airflow over a hot film metal oxide resistor of a known value. They should be pretty robust.

What might actually be happening to you pedronicus, is your EGR is not flowing the amount it should be, and the measured air flow is higher than expected. Could be the doseur (EGR throttle), or EGR either way. When I blocked the EGR on my old m59 that's exactly the code that appears because of the issue I mentioned. It's expecting some EGR gas and some air. It's now getting more air than it calculated. It can measure air flow but not gas flow in most cases so it calculates what to expect when EGR is active.

[cancunia]

It's a good point, it could be an EGR problem. On the 1.6 16v, blanking the EGR does produce a fault code but no EML which is why, along with the hot weather, I thought it may be the MAF. I'm not sure how an 8v engine, or one with a DPF will react to an EGR blank.

Clean them like a bear? Just sprayed them with carb cleaner or brake cleaner, made no difference so assumed that they were either broken or on their way out anyway.

[Pedronicus]

Thanks for the feedback, guys. Interesting that the EGR is possibly involved but the vehicle has done over 76k.

Have just checked back through the vehicle’s log (yes, sad I know but stems from years of monitoring critical plant operation!) and it does appear that weather temperature could be playing a part in this as the other times this problem has arisen the external air temperature has been above 23 deg C. Now the ambient temperature has dropped the fault appears to have gone away (that’s tempting fate!!) Mmmmm.

@cancunia, I’m intrigued that you used carb cleaner or brake cleaner to clean the MAF as all the info I’ve gathered so far specifically states to only use MAF cleaner and nothing else and also DO NOT touch the inner wires/resistors. However not too sure of the different make-up of the various products.

I may just check the cable connections to the MAF unit to make sure they are sound.

[cancunia]

I did some reading about MAF cleaning a while ago. From what I remember I'd seen reports both ways about what to use and also looked at the safety sheets of various products to see what was in them.
I came to the conclusion that MAF cleaner was nothing special, but maybe I'm wrong so will be glad to hear about other experiences.
In my case, on 3 separate occasions with 3 different engines, cleaning the MAF made no difference but replacing the MAF was an instant fix.

On my 2.0 HDi Berlingo I had an EGR fault code so I replaced the EGR vacuum control solenoid to no effect, unplugging the MAF made an immediate improvement but also an EML so I had to replace the MAF before the MOT. No noticable difference in performance, but also no EML.

On my 1.6 HDi Berlingo, I bought the car with the EML on & a fault code that IIRC related to the MAF, but the car ran fine. Cleaning made no difference, but a used MAF from eBay fixed the problem.

On my 1.6HDi Volvo C30, I bought the car with what I thought was a turbo fault due to no boost and oil around the turbo vacuum control. There was no play on the turbo shaft, other reading suggested that it might be the turbo VNT solenoid so I replaced that. In the end it was the MAF, although the fault codes suggested the EGR. Replacing the MAF & clearing the fault codes made an instant difference.

[Sol]

Only winding you up CC as you said you broke every one you cleaned lol. To be honest I've never found cleaning to work either, and never actually found a MAF to actually be dirty. Unless the user had swapped the filter for a green cotton one and over oiled it. Then oil bakes into the hot film resistor.

So a factory setup with a good filter should never result in contamination of the MAF.

The resistor has a known resistance, it's in a bridge circuit where a fixed voltage is applied, and so a known current flows. When the resistor heats up, it's resistance falls. As the air flow over it cools it somewhat, the flow can be calculated from the cooling effect, since that raises it's resistance and lowers the current measured on the other legs of the bridge circuit. It's become a bit of an urban myth to clean them but I'd say on a stock setup, it's pointless. If it's broken it needs to be replaced.

Can also drift as it ages, so the reading is no longer accurate.