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Old 01-10-2013, 03:23 AM
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AFM does it need replacing?

Re 2002 Grand Cherokee 2.7 CRD

In desperation I am examining every sensor I can find, in an effort to put an end to the EVIC drop-out problem I am having. See my previous posts for details, Nov 11 thru Feb 12.

The Air Flow Monitor, in the air intake between the air filter and the turbo, is a Bosch "F00C 2G2 051". On the opposite face to the Part Number it has 2 metal tags that look as though something should be connected across them, but there is nothing there. One of the the tags has an "N" moulded in the casing adjacent to it.

Is there sensor wire or similar that should sit across these tags.

Just in case this little lot helps, the "on/off x3 + on" check yields (in this order): -

P1643: which is not listed in the fault codes
P0403: EGR Solenoid Cct.
P0100: Mass or Volume Air Flow Cct.

Comments from anyone who has experience of changing these parts would be much appreciated. My thoughts are that, as both the solenoids mentioned are vacuum operated it could be the vacuum system that is at fault. Are there any locations where vacuum pipes are most likely to split or perish? Is it the same vacuum circuit that operates the servo assistance on the brakes? I've not had any braking problems.

Thanks in advance.

Tony Norton
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Old 01-10-2013, 06:36 PM
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Re: AFM does it need replacing?

Yes, there should be a kind of a resistance in between there. I found this picture;
The sensing element is gone, so the sensor should be changed.
Donīt know what you mean with vacuum operated? The mass airflow sensor is just measuring the amount of air which is passing by, no vacuum system involved here.
Only the EGR solenoid is controlling a vacuum source
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Old 01-11-2013, 12:51 PM
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Re: AFM does it need replacing?

Thanks for that Frank,

if I'd looked carefully at the unit, or at the photo I attached, I would have seen the pictorial representation of an axial leaded component moulded into the body.

A bit of investigation revealed that it is not just a resistor though, it is an NTC Thermistor. NTC=Negative Temperature Coefficient - i.e. resistance reduces with increase of air temperature.

To test if that actually was the fault causing the system drop-out I fitted a 2K resistor between the tags. Lo and behold, as long as I'm on the move with air not much above 25 deg C (it's currently in the mid teens over here) going into the air box everything is rock-solid. When I stop, and keep the engine running the system eventually drops out. I guess that's the under bonnet temperature heating up the air in the air box and the resistor not dropping in value as it should.

Not to worry, the exercise has proved the point and, as I can't be sure of the exact specification of the thermistor, I guess the answer is a new sensor, as you said.

Once again, thanks for pointing me in the right direction. Much appreciated.

Tony N
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