Holden Commodore Engine Problems

YOUR Commodore has a V6 with a timing chain, so no need to service or replace it.

YOUR car was developed to run on leaded fuel, so you should use premium unleaded with an additive such as Valvemaster or Flashlube to protect against valve recession. I recommend PULP because your engine has a relatively high compression ratio and will probably need the 95 RON of PULP.

THE V6 Commodore can have ignition problems, ranging from spark-plug leads to ignition coils to the crank angle sensor, but yours sounds more like a fuel problem. I'd have the fuel-injectors cleaned.

YOUR problem isn't unique. Start by making sure your ignition and fuel settings are correct. If they are, have a leakdown test done to determine if you have a leaking valve or valve guide. They are a common cause of backfiring. The air/fuel mix in the intake manifold is igniting and the pressure created is blowing your intake box apart.

I WOULD look at the oxygen sensor in the exhaust system or a temperature sensor. From what you describe I think your engine is running rich. Either the computer isn't getting the message that the engine is up to temperature and needs a normal mixture, or the oxygen sensor isn't working.

THE 253 was released in 1968 at the same time as the larger 308-cubic-inch Holden V8. Both were designed by engineers at Holden's Fishermans Bend plant. They had several innovations, including advanced use of thin-wall casting for cast-iron components; and extensive use of aluminium castings for components such as the water pump and inlet manifold. This saved weight and helped make it the lightest V8 in production at the time. The 253 was the economy V8 and was intended to compete with the 250-cubic-inch six-cylinder engine in the Falcon. Apart from its smaller capacity, achieved by a smaller bore, it had a two-barrel carburettor instead of the four-barrel carburettor that was fitted to the 308, the performance version of the V8. When the V8 was updated in the 1980 VC Commodore, the 253, then known as the 4.2, was fitted with a four-barrel carburettor among a raft of other changes. It was a sweet-running engine. I have no experience of the Fuelstar inline additive, so I can't offer any advice.

I WOULD lean towards the ignition system and have the leads, ignition coils and the coil mountings checked. You could also have someone run over the engine diagnostics for you.

GOOD luck. I hope Holden is as good as its word and that your problem is addressed and you're reimbursed for the money you spent on repairs.

MY INFORMATION is that this ute has a 3.46 diff ratio with the manual gearbox and a 3.08 with the auto. Going to a 3.73 would have made fuel consumption worse. I'm surprised you changed to this ratio. In any case, before you changed the ratio you should have had the car checked to determine why its fuel consumption was so poor. There is something wrong with it given the air-fuel ratio is so rich. By changing the ratio you have modified the vehicle, which I'm guessing is why Holden is refusing to cover it under warranty. Continue to talk to Holden to find a solution that is going to satisfy you. If you can't,, then think about resorting to legal action. But before you try the latter, have your car checked by an expert such as Mark Trounsen of Dynomotive to make sure it is as it should be.

THE 190kW version has continuously variable camshaft phasing on the inlet and exhaust camshafts. The 175kW engine has it only on the inlet cam. The 190kW engine also has a variable-length intake manifold.