This tutorial will help you to do an engine compression test on your 1.8L Nissan Sentra in a step-by-step manner. More importantly, I'll show you how to interpret your test results to see if there's indeed a problem or not.
Contents of this tutorial:
Symptoms Of Low Or No Engine Compression
When the engine in your 1.8L Nissan Sentra has no compression in all 4 cylinders, it's not gonna start. On the other hand, when one cylinder has low/no compression, the engine is gonna' start but it's not gonna' idle smooth.
Let me go into more details about both conditions:
Engine Starts but Runs with a Misfire:
- Also known as an engine miss, rough idle condition.
- Usually caused by very low compression in one cylinder or...
- Uneven engine compression that varies more than 15% across all 4 cylinders.
- Check Engine Light on with misfire codes (if your vehicle is OBD II equipped):
- P0300 Random Cylinder Misfire.
- P0301 Cylinder #1 Misfire.
- P0302 Cylinder #2 Misfire.
- P0303 Cylinder #3 Misfire.
- P0304 Cylinder #4 Misfire.
- Bad gas mileage.
- This is caused by the simple fact that the engine is now running on 3 cylinders, which requires those 3 to work harder to move the vehicle.
- Engine pollutes more.
- This is also caused by the simple fact that the engine is now running on 3 cylinders, which now has to compensate for the ‘dead’.
Your Nissan won't start:
This usually is caused by having 2 or all 4 cylinders with no compression. When this happens, you'll see:
- The engine cranks very fast.
- This fast cranking speed is very noticeable.
- The Ignition System is sparking all 4 spark plugs.
- This tells you that the No Start Condition is not caused by a fault in the ignition system.
- The fuel injectors spray fuel.
- You can confirm this with a Noid Light test.
- Also, you can confirm this, although indirectly, by removing the spark plugs and checking to see if they are fuel soaked (fuel fouled).
- Fuel pump is working and providing pressure.
- The most common causes of no compression on 2 or all 4 cylinders are:
- Blown head gasket.
- Broken timing belt.
- Engine threw a rod.
OK, having covered the most common scenarios of low compression and no compression, let's get testing to see if this is the case on your 1.8L Nissan equipped vehicle.
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.
Engine Compression Gauge Testers
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!
TEST 1: ‘Dry’ Engine Compression Test
If you don't have an engine compression tester, you can buy one from your local auto parts store or, if you have an AutoZone or O'Reilly auto parts store nearby, you can rent one from them (they'll rent it for free, after you leave them a cash deposit for the tool, which you'll get back once you return it).
If you need help deciding where to buy one or which one to buy, take a look at my recommendations: Which Compression Tester Should I Buy?
IMPORTANT: You'll be working around a cranking engine, so you have to be careful and stay alert at all times. Think safety all of the time!
This is what you'll need to do:
Disconnect all of the fuel injectors. This will prevent fuel from being injected into the cylinders as you crank the engine.
Remove all four Coil-On-Plug (COP) ignition coils.
Remove all four spark plugs.
As you're taking them out, be careful and don't drop any of them on the floor, or you could cause the spark plugs ceramic insulator to break, and this will cause a misfire!
Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder (this is the spark plug hole closest to the drive belt).
Hand tighten the compression gauge only! Do not use any type of tool to get it tight.
When the tester is set up, ask your helper to crank the engine. Your job is to keep your eye on the compression tester's gauge.
Once the needle on the gauge stops climbing, have your helper stop cranking the engine.
Write down the compression value on a piece of paper. Include the number of the cylinder this reading belongs to.
Now repeat steps 4 thru' 7 on the other 3 cylinders.
Let's take a look at what your test results mean:
CASE 1: 0 PSI compression in 2 or all 4 cylinders. This test result indicates a serious internal problem.
The most common issues would be:
- Blown head gasket.
- To further test this, I recommend the following tutorial: How To Test For a Blown Head Gasket (Nissan 1.8L).
- Broken timing chain.
- Engine threw a rod.
CASE 2: Low compression in one or more cylinders. Depending on how low the compression value, it could be causing a problem or not.
We can easily find out, if the compression value is causing a problem or not, by doing some math. Go to: Interpreting Your Compression Test Results.
CASE 3: 0 PSI compression in one or more cylinders. The cylinder or cylinders with 0 PSI compression are considered 'dead' and are causing a misfire problem or a no-start problem.
The next step is to do a 'wet' compression test and find out if the problem is due to bad piston rings or bad cylinder head valves. Go to: TEST 2: ‘Wet’ Engine Compression Test.