All Info About Auto Repairs
Your One Stop Source For All The Information You Need For Your Vehicles.

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!
More...
» Part 1
» Part 2
» Part 3  

Replacing Spark Plugs
Not too long ago the spark plugs were out where you could see them, even if they weren't easy to get to, you could still see them. Now they are recessed into cylinder heads or under covers. In some cases you could trace the ignition wires to the spark plug but many cars have "Coil On Plug" COP ignition coils and are almost always under a cover.

Regardless of the design, it is important to remember to note wire connections and routing. If not you may cross a wire or connection and cause more problems than you solve. If your vehicle has ignition wires, check them for heat cracks or oil soaking. If it is, it needs to be replaced. If it is a COP, it will be fairly expensive.

Never pull an ignition wire off by grabbing the wire itself. Grab the boot and twist it back and forth while pulling it off. This will prevent damaging the carbon core of most ignition wires.

With the spark plugs out, look at the porcelain insulator around the center electrode. If they have a coating of black carbon on them, it is an indication the air/fuel mixture is too rich and you may have a problem with a HO2S that is just good enough not to set a DTC. You can use your scan tool to determine this.

If it is only one plug that has this carbon coating, it is a good indication you have a leaking fuel injector.

When you go to install your new spark plugs, a thin coat of anti-seize will make taking them out next time a whole lot easier. And don't forget to torque the spark plugs to specifications and no tighter. Otherwise you may wind up stripping an aluminum cylinder head.

Exhaust Gas Recirculation
Exhaust Gas Recirculation (EGR) valves can be the cause of many driveability problems. They can stick open, not close completely or operate in a jerky manner. If this happens the engine may stall. It will also run rough; your gas mileage will decrease and have an adverse affect on emissions. And the chances of passing mandatory emissions inspection will be pretty small.

What the EGR valve does is channel a measured amount of exhaust gas back into the combustion chamber to lower combustion temperatures. Like hosing down a fire. What this accomplishes is to lower Nitrogen Oxide (NOx) emissions and can often increase fuel mileage.

As the throttle is applied and the engine speeds up, ported vacuum is applied to a vacuum diaphragm in the EGR valve through a connecting tube. When the vacuum reaches approximately three inches, the diaphragm moves upward against spring tension and is in the full-up position at approximately seven to eight inches of vacuum.

This diaphragm is connected by a shaft to a valve that closes off the exhaust gas port. As the diaphragm moves up, it opens the valve in the exhaust gas port and allows exhaust gas to be pulled into the intake manifold and enter the cylinders. The exhaust gas port must be closed during idle, as the mixing of exhaust gases with the fuel air mixture at this point would cause rough running.

Engine Tune-Up 2003
Typical EGR Valve

Vehicles with an OBD-II diagnostic capable PCM can monitor the EGR valve for malfunctions and proper exhaust flow. When it detects a malfunction, it will turn the MIL on since it is directly related to an emission problem.

There are a couple of ways to quickly test an EGR valve. One is to simply unplug it, cap off the vacuum line and drive the vehicle. If the problem goes away, you have a problem with the EGR control system.

The other way is to connect a hand vacuum pump to the EGR valve and slowly apply vacuum to it. If the engine rpm slows down and stumble and probably stall when you get to full vacuum.

If there is no change in the engine rpm remove the EGR valve and perform the same test, this time watching the valve to open. If it does, then you have clogged EGR passages.

If the engine has been idling rough, look for heavy carbon deposits around the pin valve. If there are any clean them off with a wire brush. This will only work with an exposed pin EGR valve. If yours is a recessed pin EGR valve, it will have to be replaced.

Where To Get Service Information
When you perform any diagnostics it's not much good to get, say, a voltage reading if you don't know what the correct reading is supposed to be. And testing has become an exact science. Diagnostics have to be performed in a certain order or the test results you get could very well be meaningless. So you need to find the latest factory diagnoan 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.

More...
» Part 1       » Part 2       » Part 3

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

FREE Newsletter. Sign Up Now!

Help keep this site free.



Copyright (c)2006




Search All Info About


Related Articles