A compression test can help you to nail down a hard to find misfire condition, since it's one of the most overlooked tests when diagnosing a rough idle or misfire condition.
The compression test will also let you know just how healthy (mechanically) the engine is on your Nissan 3.0L, 3.3L, 3.5L car, pick up, SUV or mini-van.
This article will walk you thru' the engine compression test and more importantly, I'll show you how to interpret the results of your compression test.
Contents of this tutorial:
Symptoms Of Low Or Zero Compression Problems
Engine compression issues will usually fall into one of two categories:
- Low compression in some but not all cylinders: This means that while some cylinders may have adequate compression, others may not, leading to an imbalance in engine performance.
- Zero PSI compression in some or all cylinders: This indicates a severe compression problem where one or more cylinders have completely lost compression, which can significantly impact engine operation.
These compression issues can manifest through various symptoms that affect the engine's performance, reliability, and drivability:
- Hard Starting or No Start: Compression is vital for the engine to start, so if there's insufficient compression, it may struggle to start or fail to start altogether.
- Poor Engine Performance: Compression provides the necessary pressure for fuel combustion. If compression is low or nonexistent, engine performance will suffer, leading to sluggish acceleration and overall poor performance.
- Misfiring: Inadequate compression can cause misfiring, where the air-fuel mixture doesn't ignite properly in the cylinders, resulting in uneven engine operation.
- Reduced Power and Performance: Without proper compression, the engine won't generate enough power, resulting in reduced performance and responsiveness.
- Excessive Oil Consumption: Compression issues can lead to oil leaking into the combustion chamber or poor sealing of the piston rings, causing increased oil consumption.
- Audible Engine Noise: Compression problems can result in abnormal engine noises such as knocking or rattling, indicating internal issues that affect engine operation.
Which Compression Tester Should I Buy?
There are lot of engine compression testers to choose from and many places to buy them. I'm gonna' make two recommendations to you:
1) Which one to buy: The engine compression tester that I have always used is the Actron CP7827 Compression Tester Kit. My only complaint about this engine compression tester is that it does not come with a case to store it in.
2) Where to buy: You can buy an engine compression tester just about anywhere, but you'll end up paying more for it (especially at your local auto parts store). The above links will help you comparison shop. I think you'll agree it's the better way to save money on the compression tester!
The ‘Dry’ Engine Compression Test
If your Nissan vehicle starts and runs, it's important to keep in mind that the engine compression test should be done with the engine slightly warmed up.
If your vehicle doesn't run, then don't worry about doing this test with the engine cold.
One last thing, this test is done with the engine cranking, so be careful and take all necessary safety precautions. Your safety is your responsibility.
NOTE: To get the most accurate test result, the engine should be slightly warmed up for this test, yet it can not be hot (technically: normal operating temperature). So, if the engine is completely cold, start her up and let it idle for no more than 15 minutes. If the engine has been running for a long period of time, let her cool down for about 1 hour.
OK, let's get started:
- 1
Disable the ignition system.
If your vehicle has a distributor, you can easily accomplish this by disconnecting all of the distributor's electrical connectors.
If your vehicle does not have a distributor (equipped with 6 Coil-On-Plug Ignition Coils), then you'll disable the ignition system when you remove then in the next step. - 2
Remove all of the six spark plugs.
Be careful and don't drop any of the spark plugs. Dropping them could cause their ceramic insulator to break and this will cause a misfire.
IMPORTANT: If necessary (on distributor equipped vehicles), tag each spark plug wire before you disconnect them from the spark plugs so that you'll know where they go when you re-install them. - 3
Hand-thread the engine compression gauge into the spark plug hole that you've chosen to test first. Do not use any type of tool to get it tight, hand tight is enough!
- 4
Once everything is set, have your helper crank the car or mini-van till the needle on the compression tester gauge stops climbing.
It normally takes no more than 10 seconds of engine cranking to get to this point. When the needle stops moving, you have reached the maximum compression pressure of that cylinder. - 5
Record the reading on a piece of paper along with the cylinder the reading belongs to.
The illustration in the image above will help you to identify what cylinders you're testing. - 6
Repeat steps 3 thru 5 on the remaining engine cylinders.
Let's take a look at what your test results mean:
CASE 1: No compression in 2 or more cylinders. This test result tells you that the engine has serious internal problems.
The most common issues would be: Broken timing chain. Or a blown head gasket. Or the engine threw a rod.
CASE 2: Low compression in one or more cylinders. To a certain point, it's normal for the compression to vary a little between cylinders (as the engine accumulates thousands of miles).
But if these values vary too much, then you're gonna' have a bonafide misfire on your hands.
The next step is to do some math to find out if this low compression value is within a normal parameter or not. Go to: Interpreting Your Compression Test Results.
