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Matt, Engineer
Category: Car
Satisfied Customers: 20396
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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1994 Range Rover started running rough after it would run

Customer Question

Hello all. I have a 1994 Range Rover County. A couple of weeks ago it started running rough after it would run for a time. The longer I drive it, the worse it gets until it dies, although sometimes it will go 20-30 miles before really starting to run rough. It won't start again until it sits for at least 20-30 minutes; the longer the better. I've taken it to my mechanic who has replaced the fuel pump assembly (including all of the tubing inside the tank, apparently). He's also replaced the fuel filter. He says it is acting like vapor lock and that he thinks there are vapors/air in the fuel system somewhere, but he can't figure out where the problem is. Getting ready to replace coil and ignition module (I think), but now he's just throwing parts at it. Any ideas what the problem could be?
Submitted: 6 years ago.
Category: Car
Expert:  Matt replied 6 years ago.

I'm assuming the engine is petrol so 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 and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometime 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.
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.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so they can be effected by the weather and engine temperature.

This leads them to be quite intermittent in the case of mild leaks

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