Holden Commodore Engine Problems

YOUR mechanic has covered the most common causes of a miss. The next things to check are vacuum leaks and fuel pressure. Start with the vacuum leaks, and look for leaking vacuum hoses or a leaking intake manifold. Next check the fuel pressure, which might show up a faulty fuel pressure regulator.

YOUR Commodore has a six-cylinder engine bought from Nissan, basically the same that was fitted to the Nissan Skyline here. The engine is a fine unit, but there was an installation problem when it was fitted to the Commodore, and it can give trouble when air pockets develop in the cooling system, causing the engine to overheat. It's important to use the correct coolant if you have to top up the cooling system -- don't use water, and be careful to bleed the cooling system properly if you have to service it for any reason. The auto is generally reliable, but it is expensive if you have to rebuild it. One thing to check is the service history. Older drivers often consider servicing too expensive, especially if they do few kays. Find out if the car has been well serviced, and if it hasn't think about getting it serviced.

THE flat spot sounds like fuel vaporisation. Fuel can vaporise in the fuel rail because of the heat generated while sitting idle, and it can cause a slight misfire when it's time to go. Get the fuel pump checked to see if it's delivering its full flow of fuel. Also check the fuel-pressure regulator to see if it's maintaining the correct fuel pressure.

We contacted Holden for their response, which is: ``While it is impossible to diagnose a car without sighting it, rough running on start-up and/or hard starting can be caused by many things, including leaking injectors, carbon build-up on the valves, etc. Injectors wear over time and are also subject to deposits from the fuel. Given the age of the vehicle, injector leakage is a possibility. This is not a generic V6 problem. If the injectors are in fact leaking, this is a maintenance item. Injector leakage can be tested by carrying out a pressure test and confirming pressure drop.'' I think this is good advice. Take the car to a fuel-injection specialist and have them check the injectors, and think about having them cleaned.

Your Falcon would have tested about 13 litres/ 100km when new. For comparison purposes, the Commodore V6 would return about 11.5 litres/100km, the 3.5-litre V6 Magna about 10.5 and the Camry closer to 13. Clearly, on that basis the Magna is the car for you.

The Commodore will need an upper cylinder lubricant added to the fuel if you run it on ULP. The Toyota should happily run on ULP without any additional lubrication.

IF THE noise is a light rattly one heard only when the engine is cold, then it's more than likely to be the hydraulic lifters, or tappets, as you've been told. You don't say if your car is a VL or VN, which was released in August 1988, but I'll assume it's a VL. The reason for the assumption is that the Nissan engine in the VL suffers camshaft wear and lifter rattle. The way to fix it is to replace the camshaft and lifters.