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Tuesday, July 20, 2010

IAT Sensor - Intake Air Temperature Sensor

The Intake Air Temperature (IAT) sensor determines the air temperature inside the intake manifold. Resistance changes in response to the ambient air temperature. The sensor has a negative temperature coefficient. As the temperature of the sensor rises the resistance across the sensor decreases. This provides a signal to the PCM indicating the temperature of the incoming air charge. This sensor helps the PCM to determine spark timing and air/fuel ratio. Information from this sensor is added to the pressure sensor information to calculate the air mass being sent to the cylinders. The IAT is a two wire sensor, a 5-volt reference signal is sent to the sensor and the signal return is based upon the change in the measured resistance due to temperature.

Fig. 1: The IAT sensor is located in the air cleaner outlet tube-2.2L engine and 2.4L engine.

By relocating your IAT (Intake Air Sensor), you can fool your car's computer into thinking that there is more cool air entering the engine than there actually is. This causes the engine to increase the amount of fuel that enters the cylinders, as well as altering the timing (advancing it 3 degrees), thus creating more power. This mod is especially beneficial when used with an aftermarket air intake system. Please note that there is a tradeoff with this mod: your car will loose fuel economy.


  1. Locate your IAT. It is a small sensor found in the S-Tube which leaves the front of the engine and into the airbox. Carefully remove this sensor by pulling it while wiggling slightly.
  2. Cover the hole you left in the S-Tube with some sort of tape (electrical tape would be a good choice, since it's black, as is the tube). Ensure that you completely block the hole, otherwise air will enter thru that hole unfiltered (which could cause engine damage later on).
  3. Relocate the IAT sensor to a suitable location in a grill near the front of your car. Be sure that you route the wires away from any possible sources of heat or where it could rub against another part, as this could cause the wire coating to wear off, thus causing a short circuit. Cavalier Z24 owners may wish to place the sensor behind the inserts near the fog lights, whereas Sunfire owners can place it anywhere in the hex grills. Remember, the idea here is to get as much cool air flowing over the sensor as possible. Don't place it behind your license plate or someplace where the air won't directly contact the sensor, as this defeats the purpose of the mod!

Oil Around Spark Plug Threads?

1998 Chevy Cavalier Z24 2.4L GM Quad 4 Oil Around Spark Plugs

I found oil around all 4 of my 1998 Chevy Cavalier Z24 2.4 Litre spark plug threads.Could this be the result of a previous compression test!?

It is unusual to find oil around the spark plug threads. What does this mean? Oil on your spark plug(s) may indicate worn piston rings. worn piston rings will allow for oil to "slip" past them. a cheap diagnostic test you can perform at home is called a "leak down", or vaccum test. most auto parts stores sell leak down testers at a reasonable price. most come with instructions on how to use them. the key to reading them is the behavior of the needle in the gauge. leak down tester will confirm several problems- worn piston rings, bad valves, among others. you may also consider a compression tester. another cheap easy diagnostic procedure you can do at home and save money

That means the valve cover oil seals are leaking, and if they leak bad enough, the oil can cause ignition misfires. So when it affects the engine performance, you'll have to have the valve cover removed and new oil seals installed. we used to call them '' rocker arm covers' but they are properly called valve covers. There is a gasket between them and the top of the engine . The gaskets are worn and leaking oil.

Don't try the quick fix of just simply tightening the small bolts that are around the rim cover. This could distort the metal cover and then it might always leak. Just go out and buy new gaskets and replace them.
While you have the metal covers off take a look at the oil drain holes on either ends of the cylinder heads and make sure they are not partially closed by sludge and if so then clean the holes up.

If it's your drain plug then this is perfectly normal. If there's oil on the threads of your spark plugs then there's a problem. First of all, check to see if there's any oil on the top of the cam cover (e.g. maybe weeping out from an ill-fitting or damaged oil filler cap) that could be running into the spark plug wells. If there isn't, then the oil must be coming from inside the cylinder. The most likely reasons for this would be worn piston rings and/or warn oil control rings, worn valve stem seals or a leaking head gasket.

A compression test will show if its either the rings or the head gasket. You can also check your coolant to see if there's any oil contamination in there as that's another sign of a leaking head gasket.

To test for worn valve stem seals, take your foot off the accelerator for several seconds when going downhill, then watch for smoke when you step on the accelerator again. If you see a puff of blue smoke, you probably have bad valve stem seals.

If you have a 4 cylinder motor you most likely have a problem with the spark plug tower seals.
To replace them you must remove the valve cover and replace the valve cover gasket AND the 4 spark plug tower seals. Some valve cover gaskets come with the tower seals and others don't, so make sure you buy them if not with the gasket.

Replace the plug wires if soaked in oil as they will short out and cause a misfire. If you've had a misfire for a while it would be a good idea to change the oil. Any gas not burnt because of the misfire will dilute the oil and cause bearing failure.

What Are The Signs Of Warn Piston Rings?

What are the signs of worn piston rings on a 1998 Chevy Cavalier Z24 2.4L LD9 engine?
Bad rings usually cause excessive blue smoke to emanate from tail pipe AT ALL SPEEDS.

  1. ruff idle,
  2. smoking exhaust,
  3. oil soaked plugs

Most modern 1998 Chevy Cavalier Z24 2.4L car engines are built to such high standards that piston rings nearly NEVER wear out, unless from improper maintenance, or using cheap oil and never changing it.

Most cars that use or burn oil do so because of worn valve oil control seals.

Sometimes, engine sludge traps itself on the piston ring set (there are usually 3 levels of rings on a piston). A good de-sludging chemical used properly will usually get this junk off and restore piston seal.

Bad rings usually cause excessive blue smoke to emanate from tail pipe AT ALL SPEEDS.

How to test for signs of worn piston rings in an LD9 2.4L engine.

A dry compression check and a wet compression check will tell you what mechanical condition the upper end pistons, rings, valves, head gaskets of your 1998 Chevy Cavalier Z24 2.4L engine is in. Dry and wet compression test, testing and checks will tell you what you want to know and need to know about the mechanical condition of the upper top part of your engine. Specifically, compression testing can tell you if the 1998 chevy cavalier z24 2.4L LD9 engine compression is down due to leakage caused by worn piston rings, defective valves and seats or a blown head gasket.

Bad rings usually cause excessive blue smoke to emanate from tail pipe AT ALL SPEEDS.

Start by removing all the spark plugs from the engine, next if your vehicle is fuel injected you'll need to remove the fuel pump relay switch located either in the fuse box in the engine compartment or mounted to the fire wall, and then remove your coil wire from the distributor, install the compression gauge in the number one spark plug hole, crank the engine over at least seven compression strokes and watch the gauge.

the compression should build up quickly in a healthy engine.

Low compression on the first stroke, followed by gradually increasing pressure on successive strokes, indicates worn piston rings,

a low compression reading on the first stroke which doesn't build up during successive strokes indicates leaking valves or a blown head gasket.

record the highest gauge reading obtained from all cylinder tests, your lowest-reading cylinder must be within 75-percent of the highest-reading cylinder,

add some engine oil (about 3 squirts from a plunger type oil can) to each cylinder, through the spark plug holes and repeat the test.

if the compression increases after the oil is added the piston rings are definitely worn.

smell of burning oil,blue smoke from the exhaust,excessive oil consumption,oil in the air bonnet that holds the air filter,low engine compression in the cylinders,hard starting,lack of powerand the list goes on and on the simplest way is to do a compression check on the motor their should be more than 5psi difference between any of the cylinders

biggest thing is smoky blue exhaust... could also be loss in power, due to lack of compression.