My car needs a tune up

Your car needs a tune up? Why?

When it comes to vehicle maintenance I can’t think of a more misused term than tune up. If I were to ask ten different people how they define an engine tune, I would probably get ten different answers.

For the sake of this topic I am going to assume most car owners think of a tune up as replacing the engine spark plugs as well as the air and fuel filters. Some may also believe this includes any adjustments that can be made to the engine to restore the performance and economy to optimum levels.

Unfortunately asking a repair shop for an engine tune is akin to asking them to have their way with your wallet. The definition of an engine tune differs from garage to garage much the same as it does from car owner to car owner.

Up until the mid 1980s and most cars still used moving parts to deliver spark and fuel to the engine. And, these parts did indeed wear and require periodic replacement or adjustment. At that time spark plugs were made of copper tips and lasted somewhere around 30,000 miles. The spark plugs could be removed, cleaned, and the gap adjusted if worn but it was often more cost effective to replace them. Filters also required frequent replacement which was also part of an engine tune at that time.

Newer cars use no moving parts to deliver spark and fuel to the engine. Thus, there are no adjustments to be made as part of routine maintenance. Spark plugs are now designed with platinum or iridium tips and will generally last for 100,000 miles. Air and fuel filters do not require replacement with the same frequency they did just 30 years ago.

In an earlier post I suggested digging your owner’s manual out of the glove box and becoming very familiar with it. Inside the owner’s manual is a list of maintenance recommendations that includes specific intervals for the air and fuel filters as well as the spark plugs. Most maintenance schedules are divided into two intervals; severe and normal driving conditions. For most car owners normal driving conditions apply. However I live in the hot southern California desert where hot and dusty weather make my conditions a little more severe.

If you don’t have the owner’s manual anymore I recommend going to the local auto parts store and buying a paper back copy of the repair manual for your specific vehicle which also includes the manufacturer’s service schedules. This is a good investment even if you have the owner’s manual. Not only does the repair manual include the service recommendations it also explains how to change the filters and spark plugs yourself.

So what do you do when the car seems to be a little under the weather? Throw a bunch of filters and spark plugs into the engine and hope for the best, and call it a tune up? It may or may not solve the problem. It may also be a terrible waste of money. Platinum tipped spark plugs are not cheap. Filters can also put a significant dent in your pocket depending on what you drive. However this is where you really need to look at the maintenance intervals listed for your particular car and decide whether or not it needs new filters and spark plugs. A simple fuel filter may solve the problem if it hasn’t been changed within the recommended interval. There would be no reason to install new spark plugs if the engine is well under the mileage recommendations. To put it another way the service schedule for my particular car lists a fuel filter replacement at 20,000 miles, and the spark plugs at 100,000 miles. If I follow the recommended schedule I would replace the fuel filter four times before replacing the spark plugs once.

There are additional considerations that I plan to cover in future posts. Fuel injector cleaning. Is that part of a scheduled service? Will it make the car run at peak performance? I plan to look into that and other snake oil recommendations.

In the mean time stick with what is recommended by the manufacturer for the best performance and reliability from your car.



Do you need a Diagnostic Scan Tool?

You are cruising along the open road. Traffic is light and you are making good time toward your destination. The stereo is blasting your favorite tune and the kids are behaving in the back seat. Then without warning that ugly amber colored warning light comes on: CHECK ENGINE. Or some variation such as Service engine soon.

Is it time to panic? If you have seen this light before you may be familiar with what to do next. If its the first time you have seen this light come on while driving you might become a little worried. The light may or may not accompany a change in engine performance. In other words, the car may continue to run fine as though nothing is wrong. In some cases engine power may be reduced while the light is on. In either case what do you do?

Most all other warning lights in the car such as BRAKE, TEMP, or OIL are red when they illuminate. This of course means to stop the vehicle immediately. The CHECK ENGINE light is amber in color meaning caution. There is no immediate danger to the vehicle however it needs to be serviced as soon as possible. But what exactly does this light mean?

All modern cars use an onboard computer to control engine functions such as fuel delivery and spark. Newer cars have several onboard computers however the one responsible for controlling the engine is known as the Powertrain Control Module, or simply known as the PCM. The PCM receives input signals from various electronic sensors on the engine and the exhaust system. These sensors measure such things as the temperature of the engine, the angle of the throttle (How much you have your foot buried into the gas pedal), the amount of fuel in the exhaust, and the speed of the car. There are as many as 15 or more input sensors on modern cars and all these sensors report their reading to the PCM. In return the PCM uses this information to determine output controls such as how much fuel the engine needs and when to fire the spark plugs. This allows the engine to perform with the best possible performance, fuel economy and lower emissions. In a future blog I plan to cover this a little more in depth.

The PCM has a strategy built into it. In other words the computer compares the signals it receives from all the sensors to the strategy programmed into it. If one or more of the signals sent to the PCM doesn’t jive with the strategy a code is logged for that failure and the check engine light is turned on.

Using a Diagnostic Scan Tool a mechanic is able to connect to the PCM and read what was logged in the form of a Diagnostic Trouble Code (DTC). This code identifies the sensor and circuit that is sending the funky reading that doesn’t match the strategy programmed into the PCM.

Can you as the car owner do the same thing? Most certainly. Diagnostic Scan Tools are available at almost all auto parts stores and have come down in price. A nice hand held scan tool capable of retrieving and clearing DTCs can be found for as little as $50 online and at some parts stores. This is compared to several hundred dollars just a few years ago. Some auto parts stores may even loan you a scan tool or offer to retrieve the DTC for you.

But what information does this provide you? There hundreds of Diagnostic Trouble Codes capable of being stored in most PCMs to cover just about any failure logged into its memory. Some of these are fairly straightforward, others a little more complicated. If you plug a scan tool into your PCM diagnostic connector the code or code you retrieve will only tell you the sensor or circuit responsible for turning on the CHECK ENGINE light. As an example you might retrieve information on the display such as: P0320 Ignition/Distributor Engine Speed Input Circuit. 

Where do you go from there? Once a trouble code is retrieved there is additional diagnostic information to trace down the cause of that failure. Is it a sensor? Is it the wiring to a sensor? Or something else?

There are many publications online as well as in books to help diagnose DTCs retrieved from a Powertrain Control Module. But this is only the beginning. The Diagnostic Scan Tools owned by professional repair shops are capable of retrieving the vast amount of information stored in the PCM to aid in diagnosis. These often show live data while the engine is running as well as the data that was stored when the fault occurred. The scan tools capable of providing this information start at about $2,000. A diagnostic flow chart and a scan tool capable of reading data are a must when diagnosing the cause of a CHECK ENGINE LIGHT.

But should you own a hand held scan tool capable of only retrieving Diagnostic Trouble Codes? In my opinion it is not a high priority as it is only good for information. Your money may be better spent on other tools. However it is handy to have to retrieve the Diagnostic Trouble Code before taking it to the shop. This may help you understand what the repair shop is dealing with. This may also give the shop a “heads up” that you are a car owner with some kind of knowledge of their car. If the Diagnostic Scan Tool has a feature to clear the code and turn off the light, do not and I repeat DO NOT clear the code after you retrieve it. This may also clear any data that was stored when the failure occurred. Doing so will make your mechanic dislike you very much and this may be reflected on your repair bill.