Unplugged maf's

[BigRuss]

I know there's a few Diesel owners out there who are running with the MAF disconnected saying there doesn't seem be any problem.

The figures below may prove interesting

The MAF measures airflow, the more airflow, the more fuel it injects.

With a fully working Bosch maf:
Airflow at idle fully warm 440 to 500 mg/stroke ideal figures 475-480
Airflow at 3000 revs 650 to 720 mg/stroke ideal ideal figures 680-690

With maf unplugged running on back up map in ECM:

Airflow at idle 560 mg/stroke
Airflow at 3000 revs 930mg/stroke

That's a 12% increase at idle
A whopping 37% increase at 3000 revs

It doesn't work out exactly that way in the the how it affects mpg as the ECM takes other factors into consideration when determining the amount of fuel injected per stroke but there will be increase in the amount of fuel used compared to having a fully working maf fitted.


Russ

[Frank Incensed]

I know I'm always complaining about my mpg, but when my MAF failed and was unplugged for a week last month (until I had time to find and fit my old one) I estimate my mpg went down by about about 1/3 - from the low 30's to the low 20's. It certainly spurred me into doing it.

[James.uk]

I think your car aught to be introduced to the T4 belonging to BigRuss Fwankie me boy...
...

[blacknwhite]

I had my MAF disconnected from the day I bought the thing (didn't know what a MAF was til I came on here). I have had a MAF fitted for the last 3 months now and I definitely do not have that difference in mpg. I was expecting to see a huge increase in my mpg, but I'm afraid it just did not happen. And yes it's been T4'd and PCV, EGR, Air Filter etc done.

[grivas]

Originally Posted by blacknwhite

I had my MAF disconnected from the day I bought the thing (didn't know what a MAF was til I came on here). I have had a MAF fitted for the last 3 months now and I definitely do not have that difference in mpg. I was expecting to see a huge increase in my mpg, but I'm afraid it just did not happen. And yes it's been T4'd and PCV, EGR, Air Filter etc done.

What engine temperature are you running at?

[Frank Incensed]

Originally Posted by James.uk

I think your car aught to be introduced to the T4 belonging to BigRuss Fwankie me boy...
...

Car's been connected to a T4 twice since I've had it, Bob. The second time, last month, they copied the programming of the ECU, then wiped the ECU clean and reprogrammed it again. I was told that sometimes an ECU can be getting good information from all the sensors but, because of a software corruption in the ECU itself, it doesn't do the right things with the information. Anyway, it's not made any difference.
When I've recovered from the recent bodywork and servicing/MOT expenses I'll start looking into remapping for economy. It's a lovely car, but at 30 mpg I might as well have got a V6. People with their MAFs disconnected should be in V8 fuel consumption territory.

[Mike Noc]

Originally Posted by BigRuss

The MAF measures airflow, the more airflow, the more fuel it injects.


Russ

Interesting Russ but as the diesels, unlike the petrol engines, don't throttle the intake air and always run on a full charge, isn't the MAF measuring the total amount of air that is available for combustion - i.e. the ECU won't necessarily inject more fuel just because it thinks the air is there with the MAF unplugged?

So if you drove gently with the MAF unplugged you may not see an increase in fuel consumption, but hit the loud pedal and from the figures it looks like you will end up running well rich.

Mike

[BigRuss]

Quite right, common rail diesels are effectively throttled by the potentiometers on the accelerator pedal

The maf measures the amount of air being drawn past it and into the engine, not what's available, the ecu decides on the amount of fuel to be injected based on the input of the pedal pots.

Other sensors that have an effect on controlling the fuelling include manifold pressure, fuel pressure, altitude, temperature and engine speed/load.

If you take your foot off the accelerator the ECM cuts the amount of fuel being injected ignoring the airflow, reducing it to an "idling" level.

I'm afraid driving gently wouldn't work, if you drove at a constant speed with a constant amount of accelerator input it would see the increased airflow caused by the disconnected maf and fuel accordingly.

Russ

[RPWC]

I currently have my maf unplugged,as at low revs in high gear,theengine was "hunting",eg chugging,as if I was pressing the throttle on and off repeatedly,since disconnecting,this has stopped,hoping to remove and clean it with IPA tomorrow ,if Brian brings his tools with him.