Airflow maintenance can keep engines performing their best

Case in point: veteran technicians will recall the days of replacing the points and condenser in a distributor, then adjusting the dwell and the timing to finish the job. That was a time when 95 percent of gasoline engine failures were caused by the ignition system. With today's cars, a technician might have to replace the spark plugs at 100,000 miles but would not have to do any other required maintenance on the ignition system.

Less required maintenance leads us to reexamine what a tune-up consists of in newer vehicles. With the advent of computer controls, the internal combustion engine has evolved into a technological wonder. Now, virtually every subsystem on the engine is controlled by a computer module. However, this does not change the fact that an internal combustion engine is still (and always will be) an air pump. If we can move more air through the engine, we can burn more fuel and, in turn, generate more horsepower.

Poor engine performance is often experienced as a gradual decline as opposed to a sudden failure. It is possible to drive a vehicle for a long time and not be aware of its poor performance until we take a spin in a similar rig and realize that our car is, indeed, a dog. Yes, it is time for a tune-up, but what can a tech do to make a difference? Let's take a look at some tips for airflow maintenance that could help you put some snap back into your customer's power plant.

Air Filters

Here is a component that isn't going to get phased out anytime soon. Keeping the dirt out is the primary job of the air filter, but it also will lead to reduced airflow as the filter element fills up with particles. And increased airflow equals higher performance.

Remove the vehicle's air filter element during a tune-up, being careful not to drop dirt into the passage that leads to the engine's air intake. Inspect it carefully and replace it if it looks dirty. An old trick is to hold it up to a shop lamp and look for light shining through. If light can't be seen glowing through the element, replace it. Another old trick is to drop the filter on the floor. If loose dirt is seen laying on the floor after you pick the filter back up, it's time for a change. Resist the temptation to blow the old filter out with compressed air, as this could create small tears in the element. Before reinstalling it, be sure to clean out the housing and change the PCV filter (if it has one — older models only).

MAF Sensor

Technicians have attempted to clean a faulty MAF with alcohol and a cotton swab, or with brake cleaning solution if that was all that was available. The latter was especially risky, as the chemical could melt the sensor's plastic housing if the technician wasn't careful.

Aerosol products are now available that make it practical to clean the MAF periodically to help keep the sensing wire clear of debris. Simply remove the air intake ducting to provide access to the interior of the MAF and spray the cleaning solution directly onto the "hot wire" inside the housing. That's all there is to it. Take a careful look at the condition of the air intake ducting, looking for any evidence of broken or disconnected hoses or loose connections.

Throttle Bodies

The most thorough cleaning approach involves removing the unit from the air intake and setting it on the bench. However, it is more likely that a technician will wire the throttle open and go to work on it with a toothbrush and a can of throttle body cleaning solution.

It is in your best interests to wear protective gloves and make sure you have adequate ventilation when using these kinds of chemicals.

NOTE : There are throttle bodies that have a special coating designed to prevent debris from collecting on their inner passages. Look carefully for a tag or sticker saying "DO NOT CLEAN" or other similar warning. Use of a cleaner on these types of throttle bodies may damage this coating.

Decarbonizing

As we follow the intake air to the combustion chamber, the greater we see the need for periodic cleaning. Port-injected engines are designed so the fuel injectors spray directly onto the backs of the intake valves, so this is an area that sees lots of fuel fumes and accumulated residue. The stem side of an intake valve has a tendency to develop carbon-like deposits known as "cauliflower," which acts like a sponge during engine operation, causing it to run lean during periods that it is soaking up fuel and then rich when it gives up fuel to the intake air. This has an impact on not just the mixture but also the flow of air entering the combustion chamber. The combustion chamber itself can also harbor carbon deposits that hinder airflow.

To get rid of these deposits, purchase a good decarbonizing solution, which is available either as a liquid or an aerosol. If the vehicle you are working on has an MAF sensor, your best bet is to buy the liquid and meter it into the intake manifold with a fuel injector cleaning canister.

Speed-density systems (no MAF) will allow you to remove the air inlet ducting and spray the solution directly into the throttle body with the engine running.

Start by getting the engine up to operating temperature by taking it for a test drive, then shut it off and attach an exhaust hose to the tailpipe. Fill the canister with decarbonizing solution, then screw on the lid and attach its feed hose to a centrally located manifold vacuum port. Keep in mind that you will NOT be using shop air to put pressure on the solution – it will flow into the manifold due to vacuum only.

With the engine running around 1,500 RPM, meter the solution into the manifold at a rate just short of stalling the engine (do not increase the throttle opening to maintain the RPM). Once the solution is used up, shut off the engine and let it sit for 30 minutes. Next, take the car out for another test drive (15 miles minimum), making sure to do a number of WOT bursts. As the debris is purged from the engine, the smoke will gradually clear as you drive.

PCV System

Maintenance of the PCV system includes inspection and likely replacement of the PCV valve, and inspection of all related hoses.

Strangely enough, both a stuck-open or stuck-closed PCV valve can cause high oil consumption; one, because too much air is flowing through the crankcase and brings oil with it; and the other because pressure is building in the crankcase. How do you tell if the PCV valve is not right? You should hear it rattle if you shake it, but this doesn't tell the whole story. Regardless, a modern-day tune-up will still involve replacement of the PCV valve as a maintenance item.

A Final Word

There are many tune-up items that either do not exist anymore or the maintenance interval has been extended to the point where they are rarely serviced. However, engine airflow maintenance has not changed dramatically and should remain a focus of any shop's tune-up practices.Tony Martin is an associate professor of automotive technology at the University of Alaska Southeast in Juneau, Alaska. He holds Canadian Interprovincial status as a Journeyman Heavy Duty Equipment Mechanic. He also has 18 ASE certifications, including CMAT, CMTT, L1 and L2.