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We own a Nissan Caravan 3.2 non turbo diesel van. When on idle, there is often a "pop pop" type noise coming from the air intake vent, and air is blowing out rather than in!

Our local garage thought it was tight tappets, so has checked them, all ok.

The engine runs fine except it miss fires after a down hill run, and comes good under load.

No fumes out the rear. Seems to use excessive fuel compared to other Nissan Vans fitted with the same motor.

What do you think? I wondered about the diesel pump.

Pete

From the "Ask Jack" archives - 14 December 2009

While the diesel pump may need some reconditioning I don't think its the reason for the 'popping'.

Feedback from those who I have asked suggests the EGR (Exhaust Gas Recirculation) valve should be checked.

One easy way to do this is to simply remove the vacuum hose that operates the valve or block it off where it is bolted to the engine.

If the problem changes or is eliminated you know you are in the right area.

The popping noise sounds like backfiring in the inlet manifold and while your garage has checked for tight tappets, we have heard of wear in the valve gear causing a similar problem.

Rechecking the valve gear including the cam shaft may also be worth consideration.

Be careful with big ticket items like the diesel pump, you could spend an awful lot of money on components which are showing signs of wear but are not contributing to your current problem.

We do have AA approved diesel repairers on our books throughout the country, if you want to seek another opinion.