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MG MGF Technical - Fuse no 6(engine mgt sys 30 amp) blows

Hi all,
Have just purchased a 2000 mgf vvc.On a couple of occasions the car has stopped whilst driving and the fuse no6 is blown. When I replace the fuse the car runs ok for a while then the same problem happens. Can anybody help?
Thanks Thierry
t clerc

According to RAVE circuit diagram, the only 30A fuses are F1 and F2 within the under bonnet fuse box. I'm guessing your reference to F6 a typo?

So... I've concentrated my thoughts on F1 and F2 (F1 feeds Engine Management Relay Module and F2 the Engine Management Relay Module / Alarm ECU). F1 is the top most fuse in the row of 7, when viewed with the 6 fusible links to the left.

F1 feeds the power delivery switches within the Starter and LambdaSensor Relays - i.e not the relay activation, but where the relays deliver power to when "on". I suspect the problem is the Lambda Sensor. It has sensory feed back to the ECU according to Oxygen content in the manifold and also a heated element as the sensor only works properly at high temperatures. This element is within the Lambda Sensor housing and has to cope with hot/cold/vibration and can fail/break. The broken live side of the element can ground to earth inside the sensor and when it does, will blow F1. With F1 blown the engine stops. However, the the ground to earth condition can be intermittent, and rectify itself as the manifold cools - whilst you're changing F1 and kicking the car in frustration!!

Replacing F1 may get you going again until vibration or heat allow the broken heater element to ground out once more. This intermittency is in line with your fault description.

The ECM cannot optimise fuel delivery if the Lambda is not at correct operating temperature. The heater element provides that temperature, especially for cold starts. A blown Lambda heater will not stop the car starting or running - you'll have less than optimal fueling and probably not pass an MOT emmissions test. If changing the Lambda is not feasible immediately, you could make a break in the Lambda feed wire as a temporary fix to blowing Fuse F1. The four wires to the Lambda are blue/red (power feed), grey and green (sensors to ECM) black is earth.

Hope this helps

Jeff
J Lennon

The one time I had a 30 amp fuse blow it turned out that the insulation on the lambda wire had been melted by the exhaust, it just needed to be spliced and then re-routed.

May be worth checking

Tim
Tim

Hello, i have a 2003 MG TF 1.8, today at morning, the car start ok but after 200 mts of land road the 30 amp fuse blow up, the second fuse, so i tried to change it and it works but after 50 mts it blow again, so anybody can tell me what could be, should i review the ground calvbes? or the inertia switch? thanks in advance and best regards
damy

This thread was discussed between 06/07/2009 and 29/07/2009

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