Poor MPG after new engine and gearbox.

[Hayden]

Hi I have a 1990 Holden VN Commodore, I recently converted it to manual. I put the engine in with the manual gearbox. Just pulled the engine and gearbox out of the donor car and dropped straight into mine. The donor car is the exact same model. After converting it everything went fine. Started first kick.

The check engine light is on, it has a small exhaust leak on the exhaust manifold just in front of the catalytic converter. What do you think the problem is? The problem for the poor MPG and the engine light.

Also the car that the engine came out of was on LPG gas and unleaded petrol. Mine is only on unleaded petrol.

ALSO sometimes it takes a bit to start, it just cranks and cranks then eventually starts and coughs a bit until you rev it and it runs well (which is unusual for my type of car. They usually start easy)

I think that is all that i found wrong with it. It drives well just guzzles fuel.

Thanks Hayden.

Topic

[Bryan Carter]

First, an exhaust leak anywhere near your O2 sensor can throw off the sensor’s readings, negatively effecting fuel economy while tripping a check engine light. Secondly, many cars that were originally fitted with an automatic transmission have shorter (numerically higher) final drive ratios than manual cars. This would effect your fuel economy as well.

[Lorrin Barth]

The programmed shift pattern of automatics is designed to produce good gas mileage. With a manual the shifting is up to you.

[Author]

Replies