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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20361
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Ref Landrover Discovery 3 - Motor surging problem. I have tried

Customer Question

Ref Landrover Discovery 3 - Motor surging problem. I have tried to set out the background to problem including diverse advices from LandRover's technical advice service to an Independent LR specialist which has so far resulted in what is rapidly becoming an expensive suck and see approach to diagnosing what is causing the problem, with the latest advice - ie change the electric switch which I was advised is part of the pressure sensor control of high pressure fuel pump and if that does not work, change the HP fuel pump. Previous advices included changing the oil and filter in auto gbox, sending programme to LR who reprogrammed as original, which worked fine for 10 miloes before cutting out same as france, restarting and fine for 20miles then surging again.
Submitted: 2 years ago.
Category: Car
Expert:  Matt replied 2 years ago.

this might be simple thing to check but this could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

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