Your Alfa smoking? Feeling not to peppy? Sluggish? I might suggest you need to take it to the doctor for an examination of its innard workings to see if it needs a compression test.
This is most likely one of those Alfa Romeo 101 Basics type of test that you think everyone should know, but they don’t. This test was taught to me by a very skilled and knowledgeable Alfa Romeo mechanic when I first started to wrench on Alfas.
Why a compression test? First if you are buying a car, it will give you an idea as to the condition of the motor and a bargaining position. If the owner gives you the compression then your that much further ahead. It is also a way to diagnose your own engine over time for issues that might come up.
Let me guide you through a simple but effective compression test so you know you are getting the right numbers.
Most Alfa’s have a compression ratio of 9.0:1 (nine to one) Compression can go up from there with higher compression ratio pistons and subsequently so does the gauge readings. What I have learned over the years is that most compression readings will be around 180 lbs per cylinder. The allowance is 10% between cylinders. If you get a large variance, then we have to dig deeper to understand what is exactly going on.
You are going to need a good quality compression guage that can give you repeatable results and last a long time. My recommendation is to get the a compression guage that has a screw in fixture to the spark plug hole. That way you can work by yourself and have two hands free to run the tests. You will also need a good device for squirting oil which I will explain later on. If you happen to have a leak down tester then you are even in better shape for diagnosing compression problems.
First you need a warm engine, so that the rings are properly sealed. Take some compressed air with a small nozzle and put a rag over the top of the spark plugs and blow out any loose dirt that has accumulated around the base of the plug. Why? Because dirt falls in to the hole. Want to guess the result of that? It falls on the face of the valve and creates a compression leak. The rag is to keep the debris from going everywhere.
Remove the wire from the + voltage side of the coil so you don’t get shocked or cause a fire when you turn the engine over. I just remove the center coil wire and drop it down to the frame so it sparks to ground.
Next take your spark plug wrench and give the plugs a 1/4 turn to loosen and then re-tighten. Do this for all 4 or 6 plugs depending upon your engine. Turn the engine for a few seconds. What you have done is to break loose any carbon inside the combustion chamber that has accumulated around the base of the spark plug. This breaks it loose and removes it out through the exhaust.
Next remove the plugs and lay them out in sequencial order (#1, #2 etc). Look at the color of the plugs and see if they are a greyish brown color. If they are you are running a good mixture. If they are dark it could be from being to rich to burning oil. If they are white, the mixture is to lean or the plug is to hot. Computer controlled injection will tend to be on the lean side and the plugs will be lighter than a carbureted car.
Next, put the compression guage in the #1 plug hole and secure tightly. Next, go inside the car, push the gas pedal to the floor to open the throats wide open and turn the engine over 10 revolutions. Hopefully you can remember to count. Here is why you open the throttles wide open. This allows the cylinder to load up with air as if it was driving down the road. If you should do it with the throttles closed you will get a significantly lower compression reading.
Note the compression and write it down. Do this for all 4 cylinders. If you have a healthy engine the compression should be within 10 lbs. of each other. Be sure you release the pressure in the gauge before moving it to the next cylinder. A normal Alfa with 9:1 compression will show about 180 psi on the gauge Higher compression pistons, a higher reading. If you should get a cylinder that is low, go back and rerun the test. It might change.
Here is what you do if you come across low compression readings. First have you rerun the compression test to verify it wasn’t a fluke or that carbon hasn’t fallen on the valve face? You might want to use a compressed air nozzle and blow out the cylinder to see if carbon is the culprit. If it still comes up the same, now you squirt oil into the cylinder. About 3 good squirts or a tablespoon of normal weight oil you use should suffice. The oil will seal the top rings to increase your compression. Re run the compression test and notice the results. If it stays the same, we try another test. If the compression goes up, you have weak or bad rings. A weak cylinder(s) will be low, usually under 130 psi.
Lets say the compression doesn’t go up, then chance are you have a burnt valve. If you think this is the case, bring the piston up to TDC with the valves closed and push in some compressed air. Listen through the intake and the tail pipe to hear leaking air to tell you which valve it might be.
A leak down tester is a comparative tool. It measures the incoming air from the source (50-100 psi) and what leaks out from the cylinder. It should be under 10%. If you have leakage, open the oil cap and listen to see if it hisses in the crankcase (rings). If you hear hissing air in the intake or out the tail pipe your valves are leaking.