If you break it down, there are really only four elements an engine needs to run: fuel, air, spark and compression. Sounds simple, but if any one of these steps out of line, you can forget about your engine running, or at least running the way it should. These four things are simple, but the havoc they can create is diverse, complicated and usually expensive.
Turbo has a new project car in its garage: a 1990 Plymouth Laser RS Turbo. The car was practically given to us; after we picked it up we learned why. We found out this Diamond Star wasn't without its problems. So before having any fun with our Laser, we took the opportunity to diagnose its 4G63T powerplant from top to bottom - a good thing to do anytime you plan on picking up a used car, or before you start a buildup with your current ride.
First things first: The reason Project Laser was had so cheap was its broken timing belt. This concerned us right off the bat, since Mitsubishi employs an interference engine design here - meaning that if valve timing's significantly off, like from a snapped belt, there's a point in the cycle where the pistons will smack the valves. Naturally, this put a damper on our ability to run the engine, so our diagnosing procedures were quickly limited.
Being the practical thinkers that we are, we picked up the first tool that came to mind: a cell phone. Call this rule number one: if the car's a recent purchase, talk to the previous owner first. We found out more in just a few seconds than we would have using every diagnostic tool on the Snap-On truck. Besides the snapped belt, which didn't take a phone call to figure out, we learned that this Mitsu engine was a chronic smoker. We weren't able to establish the type of smoke produced since it wasn't running, but we knew the car had baggage. The last thing we want to do is put a new timing belt on, learn of some new problem, and take everything apart again.
Clearing The SmokeWhether it's coming from your kitchen or your tailpipe, smoke clouds rarely signal something good. And it really doesn't take more than your own two eyes to diagnose it. There are different types of clouds that can billow out of an exhaust port, each indicative of its own problem and color-coded for convenience. Most of the time, smoke goes hand in hand with a power loss; and even more often it'll cost you a citation or an early visit to the smog station. Since we don't know for certain what type of smoke Project Laser has been puffin', we'll run through each scenario.
Let's start with black smoke if for no other reason than it's fairly common in the high-performance world and relatively easy to diagnose. Black smoke signals an improper air/fuel ratio balance - specifically, a rich condition caused by excess fuel molecules wasting away in the combustion chamber. At the very least, this condition robs two things: horsepower, and your cash at the gas pump. It'll also sic the environmentalists on your back from the emissions nightmare it can pose. At worst, an overly rich condition can wash fuel past the piston rings into the crankcase. Mix enough fuel and oil together and you can say goodbye to important parts like rod bearings and rings.
There are lots of reasons a fuel-injected engine might run rich. The culprit could be mechanical - such as leaking fuel injectors, a clogged air filter or a damaged fuel pressure regulator, fuel pump or return line. Other times the problem might lie in the electrical realm with a faulty PCM, MAP or airflow sensor, or a misfiring ignition system. The best place to start is to check the system's fuel pressure and to follow the flowcharts in your vehicle's service manual. On turbocharged vehicles, be sure and check all intercooler pipe connections for leaks or clogs. Based on our visual inspection, we have a hunch Project Laser wasn't smoking from excess fuel, but we won't know for sure until it's brought to life.
Checking the fuel system is relatively simple. Use a fuel pressure tester to check the pressure of both the pump and regulator at the fuel rail. With the vehicle running, fuel pressure should increase when the regulator's vacuum source is disconnected and plugged. If fuel leaks out of the vacuum connection, this obviously signals a bad regulator. Fuel pressure should drop no more than roughly 20psi once the key is turned off. If it drops more, you'll need to check the pump, injectors and regulator. To determine what's causing the problem, block off the fuel supply line and look for a pressure drop. No drop? Replace the pump. If the pressure does drop, block off the return line and check it again. Pressure drop okay? Replace the regulator. Not okay? Look for a leaking injector. You can also use a stethoscope to ensure that the injectors are pulsing properly; they should all make the same sound under normal idling conditions. A noid light can also be hooked up to any injector's electrical connector to test whether or not it's receiving power, but that's a topic for next time.
When it comes to smoke, probably the last one you want to see streaming from your tailpipe is blue ... or gray as some may see it. Blue, gray, call it what you want; either way it means the same thing - oil's burning here and there's something wrong under that valve cover. Oil doesn't like to burn. That's why it stinks so much. Like the black smoke scenario, oil is escaping into the combustion chamber and smoldering along with the air/fuel mixture. This can't be good for performance. Mild cases result in little more than nausea from the oil stench, and the embarrassing smoke stream from the exhaust; while more extreme cases can foul out the spark resulting in misfiring. We're pretty sure this is where the Laser's smoke was coming from. After pulling the spark plugs, we noticed quite a bit of oil sitting on top of the pistons and coked onto the plugs. Again, no tricky diagnostic tools here. But we still don't know how the oil got there.
There's more than one place to look when trying to determine the source of burnt oil: piston rings, valve stem seals and valve guides are what you have to choose from. Sooner or later, they'll all wear out, causing oil to make its way into the combustion chamber. But you don't need to go yanking off that head just yet, blindly installing piston rings, stem seals and guides just to cover all your bases. If your car's running, there's much you can learn just by watching the smoke's habits for a few seconds.
Pay attention as to when the engine is producing its oil-burning smoke. At startup? When decelerating? In between shifts? They all point to different causes. Let's start with the common morning puff of smoke during initial startup. This often indicates worn valve stem seals or valve guides. After miles of abuse, wear and tear, their clearances increase. And while the engine rests for a significant period of time - overnight - oil drips down into the combustion chamber. The smoke usually lasts for a few seconds until the engine begins to reach its operating temperature and it burns off. Excessive smoke under engine acceleration or at idle is usually caused by poor piston ring sealing, if you're lucky though, it might be nothing more than thin or excessive oil. Do an oil change here with the proper viscosity and cross your fingers. Smoking under no-load deceleration is more than likely caused by worn valve stem seals or guides.
Oops. I take back what I said earlier. White smoke can be just as bad as blue smoke. And like black and blue smoke, the white stuff can be traced back to an unwelcome substance burning inside the combustion chamber, in this case, water or coolant. The white smoke you're seeing exit the tailpipe, though, is really just steam. Steam sounds harmless enough, but it points to a pretty serious problem. A point will be reached where there's too much coolant in the chamber to burn off, and the excess liquid will look for another escape - there's nothing to stop it from mixing with the oil down below now. Mix enough coolant with your oil and you can forget about proper lubrication. Water or coolant can enter the combustion chamber a few ways: cracked cylinders, a cracked head or a blown headgasket or intake manifold gasket are the most common. We didn't find any signs of coolant or water inside our Laser's combustion chamber. We're glad.
Wait. Don't panic. It's normal for a car to puff a small amount of white smoke in cold weather or in the morning. About a gallon of water is produced for every gallon of fuel burned - meaning the steam is not coming from the cooling system, but instead it's just a byproduct of good old-fashioned chemistry and the combustion process.
The best way to determine whether or not you're losing coolant is to perform a cooling system pressure test. Most pressure testers connect to the radiator cap location and can be done with the engine cold. Verify what your vehicle's pressure is supposed to be and monitor the pressure gauge with the vehicle running. Losing pressure? Look for a leak. Too much pressure? Chances are that cylinder pressure is escaping into the cooling system and coolant's getting inside the combustion chamber. You could use a scope to look for coolant specs on top of the pistons, but more than likely they'll be soaked. A combustion gas detection tester can also be used to check for escaped cylinder gases inside the cooling system, but isn't exactly the type of tool you'll find in the top drawer of your average toolbox.
The easiest way to determine whether or not you're losing coolant, though, is to pop the radiator cap. Stop! Not when the engine is that hot. Notice air bubbles here? Not good. Inspect the vehicle's oil cap for signs of coolant. If it's mixing, the oil will appear caramelized, foamy - you might even be able to detect a smell of coolant there. All signs point to a damaged headgasket or cracked cylinder in this case. A vacuum test is a good one to perform as well. A leaking headgasket will cause the vacuum gauge needle to vibrate erratically. Just hook the test hose up to any intake vacuum source and read away. A normal engine should produce around 18-21 inches Hg. We don't know what ours is.