Fuel Injector Cleaning

I participate in a kind of loosely formed round table of technicians and shop owners and we meet whenever three or more of us are at the same place at the same time. The last time we met we were reminiscing about the old days. The days when a customer would come in complaining about a rough idle, hesitation, no power and so forth and we were 90% sure a simple tune-up would take care of the problem. Those days are gone. Now when a customer comes in with these complaints it's almost automatic to suggest a fuel injector cleaning.

The Problem Is...

The main reason for a fuel injector cleaning is that deposits form at the tip of the injector and once it starts it gets progressively worse. Now the only time these deposits form is when the engine is first shut off and still very hot. This is the time technicians refer to as the "Heat Soak" period. When you shut the engine off the water pump stops circulating coolant and the engine temperature continues to rise for a while until it begins to cool off. The bit of fuel left at the tip of the injector bakes on, the lighter liquid portion evaporates away leaving the solid portion of the fuel. These deposits bake onto the injector forming a porous mass. This process is called "Coking". Keep in mind that coking only occurs during the heat soak period, not when the engine is running.

Not Only Injectors...

You fuel injectors are not the only thing affected by the coking process. The intake valves also fall prey to this problem. A great many technicians don't even realize this happens as well. It is a gradual process and by the time the driver notices any symptoms the deposits are well formed. What happens is the deposits reduce the amount of the valve opening but also acts like a sponge. The carbon deposits are porous and hold fuel like a sponge. So the larger the deposit the more fuel it will hold. The more fuel it holds the larger the deposits get. This also takes fuel the engine needs to run away from it.

This is most often felt when the engine is cold and needs that extra fuel to run properly until the engine goes into closed loop operation.

What Can Be Done To Prevent Deposits...?

For years automakers have been begging the oil companies to come up with and blend additives into fuel that will not only prevent carbon deposits but also prevent them to begin with. The oil companies have responded by coming up with additives that will help keep injectors clean but the down side is they tend to make the intake valve deposits worse.

The type of injector contributes to the problem as well. The pintle type of injector that has been used since fuel injection was first used is being phased out; replaced by a disc and ball and seat type design that are less prone to deposit formation. This is not to say that they never form deposits, just less likely to.

What To Do About It...?

The first thing to do is to stick with name brand fuels. You never know what you will get when you buy fuel at an Independent station.

There are many chemicals and cleaning systems available to clean port fuel injectors and some may even clean throttle body injectors; but there is no specified interval for performing injector cleanings. When I asked the technicians I meet with how often they feel injectors should be cleaned, they all have different opinions. Most off them only do an injector cleaning when a customer has a complaint that is consistent with injector deposit symptoms. A few of them are a bit more aggressive in that they perform injector cleanings for customers on a regular basis, every 30,000 miles for example. Some systems put a limit on how many times an injector may be cleaned. Since the some of the chemicals used not only clean the injector they also eat away at the injector itself. The most common limit with these cleaning systems is three times then the injectors will need to be replaced.

But what about intake valve deposits? Some cleaning systems claim to not only clean fuel injectors but clean intake valve and combustion chamber deposits as well. Drivability problems are often a combination of these problems so an injector cleaning may eliminate all of them at the same time. Do you really need to know which problem it cured? No, all you want is your vehicle to run the way it's supposed to.

When A Cleaning Is Not Enough...

In some cases the injectors are too far-gone for a cleaning and have to be replaced. This is fairly simple, relatively speaking. It's the buildup on the intake valves that can be more costly to eliminate. The accepted practice is to remove the cylinder heads, take the valves out and clean or replace them. However there is another option for valve cleaning available. It's called a Walnut Shell Blaster. It is a small sand blaster but instead of using sand or glass beads, it uses ground walnut shells. Why walnut shells? Good question! Walnut shells allow the valves to be cleaned without removing the cylinder head. All that needs to be done is to remove the intake manifold to gain access to the intake valves and they can then be cleaned. Unlike sand or glass bead, the walnut shell will not damage moving engine parts or clog catalytic converters. In fact several automakers sent their dealers walnut shell blasters as part of their required equipment packages.

I'm often asked about those additives you add to the fuel tank when you fill up. They may help slow down the buildup but they will in no way fix the problem. As a preventative maintenance measure they may have some value but they are not a replacement for a proper cleaning. So if you have an elusive drivability problem the fix may be as simple as a fuel injector cleaning.

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