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Engine Tune-Up 2003

Is the tune-up dead? Do we still need to tune-up our cars and engines? The answer in a word is YES!
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You're cruising down the highway in the left lane at a pretty good clip. Traffic is heavy but moving steadily. All of a sudden you see your exit coming up and you have to get over quickly. There's a break in the traffic flow and you put your turn signal on.

You hit the gas and try to move into the right lane but you're too late. A 1972 Volkswagen Micro Bus trying to do the same thing beat your big V-8. It was right in back of you but was able to move into the hole faster than you could. So you swerve back into the left lane, drive 37 miles to the next exit to make a U turn.

After your wife gets done dealing with your five kids in the back seat asking "Are we there yet?" she suggests it may be time for a tune-up. But today's engines are computerized, have 100,000-mile spark plugs and don't need to be tuned up, right?

Well guess what, you're wrong. It is true we haven't had to replace ignition points and condensers for over 20 years. If it's a 2001 or newer vehicle, you may have a non-replaceable fuel filter under the hood. You have a maintenance free battery and the ignition timing is non-adjustable. However, while a lot has changed in the last seven or eight years, the idea of a tune-up is anything but gone.

The Federal Government has tightened emission laws but our air is still full of dirt and dust. Eventually your air filter will plug up and your engine will starve for air until you decide to replace it. They took the lead out of gasoline so your spark plugs don't get lead fouled anymore and the new high tech spark plugs last a lot longer then there earlier ancestors. However, they don't last forever and your engine will derive great benefit if replaced well before the manufacturers recommendations.

Under Hood Checks
The best way to start a tune-up on today's engines is to access any codes that may be stored in the Powertrain Control Module (PCM) with a code reader or scan tool. Just because the Malfunction Indicator Lamp (MIL), such as a Check Engine Light, Service Engine Soon or Power Loss light, is not on doesn't mean there are no malfunctions found or codes stored.

The MIL only comes on when a malfunction occurs that directly effects emissions and on the systems it was designed to check. Most Diagnostic Trouble Codes (DTC) will only show up with a code reader or scan tool. In addition, it is not uncommon for many "No Code" problems to arise.

If there is a DTC, you should check the whole circuit to locate the problem. If you get a DTC "P0185 Fuel Temperature Sensor B Circuit Malfunction" don't assume it means a bad Fuel Temperature Sensor. While eight times out of ten it is, there is a 20% chance it is a burnt wire or bad connector terminal. While it's not too bad to gamble with a $20.00 part, it is an entirely different matter when a $900.00 distributor is indicated.

Another thing to be careful of is mis-interpreting a DTC. A DTC of "P1130 Heated O2 Sensor (HO2S) 11 At Adaptive Limit" may sound like a bad HO2S, but what it's really saying is "Hey, I've corrected as much as I can. This problem's worse than I can compensate for." So you need to look for a problem in the fuel delivery system because the HO2S is doing its job correctly and replacing it is just throwing $100.00 out the window. It's like your wife telling you your car is on fire and you go out and get a new wife.

Okay, so you checked for DTCs and there were none. Now what do you do? The first tool to use is your eyes. Look under the hood for damaged or disconnected vacuum lines, loose or dirty connections, cracks in the large air intake hoses or a loose, burnt or disconnected ignition wire.

You can still do some basic checks of the engine controls and sensors. If you engine has timing marks, you can check the ignition timing with a timing light to see if it is within specifications. Always refer to the under hood emissions label for the proper procedure for checking ignition timing. If there are no timing marks, you can use a scan tool to check the ignition timing.

Set your scan tool to Timing Check and read the timing. Gradually open the throttle to about mid-range and look for a smooth, steady increase in ignition timing. If it is not smooth and steady, it may indicate a loose timing belt or timing chain.

If the timing is good, you can check the Throttle Position Sensor (TPS) and Mass Airflow Sensor (MAF). These, too, should show a smooth, steady increase as the throttle is increased. If there are any voltage spikes or dips, the sensor is bad. You can also tap the TPS and MAF to see if there are any voltage spikes shown on the scan tool or hiccups. If there are, then the sensor is bad.

Another common problem is the Coolant Temperature Sensor (CTS). With the engine cold use the scan tool to see what temperature it is reporting. It should be within four or five degrees of ambient air temperature. Now start the engine and watch the temperature reading. It should climb smoothly and steadily up to normal engine operating temperature, usually in the 190° to 230° range. The Manifold Absolute Pressure (MAP) sensor would be the next thing to look at. Disconnect the vacuum line from the MAP sensor and hook up a hand vacuum pump. Now slowly apply vacuum to the MAP sensor.

• When manifold pressure is low (high vacuum), sensor output voltage is low, under 1 volt.
• When manifold pressure is high (low vacuum), sensor output voltage is high, 4.5 volts.

Again, it should show a smooth, steady increase in the voltage readings.

Okay, now you've checked all these things and you still can't find a problem. The next thing to do is to locate and expose the PCM. In some vehicles it's located under the dashboard behind the glove compartment. In others it's under the hood. But most often it is located behind the right hand kick panel.

Once you have it out, and with someone slowly increasing engine rpm, tap the PCM and see if there is any effect on the engine. Also move the wires going into the PCM back and forth. If there is an effect on the engine, you have a bad wire and/or connection at the PCM.

» Part 1       » Part 2       » Part 3

Additional Information provided courtesy of and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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