Tech Tips

AUTO TIPS AND TECH: Buying used car with GDI engine

In a GDI engine, the fuel injector is moved from the engine’s intake tract to a location directly inside of the cylinder, thereby delivering fuel directly into the combustion chamber. (HANDOUT)

Gasoline direct injection (GDI) engines have been flooding the marketplace for years as automakers work to deliver improved performance and mileage for their customers.

Though GDI engines are marketed under different names by different automakers, the premise behind them is universal.

In a GDI engine, the fuel injector is moved from the engine’s intake tract to a location directly inside of the cylinder, thereby delivering fuel directly into the combustion chamber.

Thing is, owners, technicians, and enthusiasts of numerous GDI-powered models have discovered a potential issue with the GDI engine as it ages.

That issue is the rapid formation of potentially-harmful valve gunk, which can build up unchecked on the engine’s intake valves in some situations.

All engines create the ingredients that form valve gunk, and all engine intake valves are exposed to it.

In a conventional engine, fuel is sprayed over the intake valves, cleaning them constantly.

In a GDI engine, with its directly-mounted fuel injectors, there’s no cleaning effect possible to keep the valves clean, since fuel never touches the intake valves.

So, in the increasingly-common GDI engine, the same gunk-causing ingredients constantly pass the intake valves, but there’s no cleaning effect to keep that gunk from building up to problematic levels.

Some GDI vehicles experience valve-gunk related problems as they age.

Others don’t.

Issues include poor performance, rough idle, poor fuel mileage, and even engine damage in extreme cases.

Below, we’ll look at a few considerations to bear in mind when shopping for a used vehicle powered by a GDI engine, and a few tips to avoid possible problems down the line during ownership.

Check all service records

If the GDI-powered model you’re after is still covered by power train warranty, be sure to inspect all service records and confirm that oil changes and other maintenance items have not been skipped by the seller.

Should a warranty repair be needed, owners typically need to prove that all such work is up to date.

If the vehicle you’re considering has missed an oil change or some maintenance, it’s power train warranty may be void.

Assume it needs new spark plugs

Here’s a top tip for keeping that GDI-powered engine from gunking up: Confirm that the seller or previous owners have never stretched their spark plug change intervals, checking service records against requirements outlined in the owner’s manual.

If the spark plugs haven’t yet been due for a change, find out what mileage they need to be replaced at, as per the “severe” use schedule.

Then, subtract 10,000 kilometres from that figure, and have the plugs changed not a moment later.

Clean and fresh spark plugs are absolutely vital to maintaining the clean combustion that’s required to keep GDI-powered engines clean, and even a slight prolonging of spark plug change intervals can cause a dramatic increase in valve gunk buildup.

Change the plugs early for maximum peace of mind.

Use good gas, not pour-in-tank cleaners

Don’t waste money on fuel injector cleaner, intake cleaner, or any other pour-in-tank cleaning additive for use in your GDI-powered vehicle.

Remember: In this type of engine, nothing poured into your fuel tank touches the top of the intake valves, where valve gunk builds up.

Instead, plan to always refuel using top-tier rated gasoline, which is available across all octane levels at major retailers.

Top-tier gasoline contains extra additives and cleaners designed to reduce GDI gunk buildup indirectly, by helping clean all other fuel system components, which contributes to cleaner combustion.

Research engine oils

Typically, you’ll want to change the oil in your GDI-powered car with the exact type and viscosity specified in your owner’s manual, and ensure that oil changes are completed not a moment after they’re requested by the vehicle’s oil life monitor.

Note that many smart owners change their oil far before being advised by the oil life monitor system, for extra peace of mind.

This is an excellent idea.

Do some homework, though. Tracy Lewis is the owner of Automotive Product Design and Engineering Group, and is an expert on GDI, who regularly tears down and inspects this type of engine.

“The only reason the owner’s manual calls for a 5w20 or similar extremely light engine oil is to achieve fuel economy targets, by reducing parasitic (friction) losses within the engine. It has nothing to do with what’s best for the engine,” said Lewis.

“In fact, these engines really need a premium full synthetic, such as Amsoil signature series or Mobil One for a lower-priced alternative. At the least, I’d recommend a 10W30-40.”

Check for misfire codes

Have the engine computer of the used vehicle you’re considering subjected to a diagnostic scan, regardless of whether or not you see a check engine light.

A GDI engine with excessive valve gunk buildup may reveal a misfire code when this scan is performed.

If that’s the case, further investigation by a professional is required.


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