The engine compression test is one of the best ways to find out the internal health condition of your 1.5L Honda Civic's engine. In this tutorial I'll explain how to do a dry and wet engine compression test.
The dry compression test let's us know what cylinders (if any) have compression issues. The wet compression test will pin-point the cylinder compression problem to either worn cylinder head valves or worn piston rings
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (1.5L Honda Civic) (at: autotecnico-online.com).
Symptoms Of Low Or No Engine Compression
Engine compression problems usually cause one of two things: a rough idle/misfire condition or a cranks but does not start condition.
Having low or no engine compression in one cylinder on your 1.5L Honda will cause your engine to miss at idle and you'll definitely feel there's something wrong when you accelerate the vehicle.
Having 0 compression on two ADJACENT engine cylinders or on all cylinders and your 1.5L Honda won't start. It'll crank but not start. This usually indicates that the head gasket has burned between the two cylinders.
When you have a situation where you have no compression on 2 or ALL 4 cylinders, you'll see:
- The engine cranks very fast and this fast cranking speed is very noticeable.
- The ignition system is sparking all 4 spark plugs... so you know it's not an ignition system problem/issue.
- 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 this scenario, are:
- Blown head gasket.
- Broken timing belt.
- Engine thru' 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 1.5L Honda.
The ‘Dry’ Engine Compression Test
In case you don't have a compression tester, you can run down to your local auto parts store (AutoZone, O'Reilly Auto Parts, etc.) and borrow one for a small cash deposit. Once you return the tool you'll get your money back. If you'd rather buy one, 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:
If your Civic starts and runs, crank it up and let it run for about 10 minutes. If your Civic doesn't start, then don't worry about it.
Disconnect the fuel injectors and the distributor from their electrical connectors. This will disable the fuel and ignition system.
Remove all four spark plugs. As your taking them out, be careful and don't drop any of them on the floor, or you could cause the spark plug's 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.
OK, when you're ready, have a helper crank up your Honda as you observe the needle on the compression tester's gauge. Once the needle on the gauge stops climbing, have him or her stop cranking the engine.
Record this compression reading on a piece of paper. Include the number of the cylinder this reading belongs to. Now repeat steps 3 and 4 on the other 4 cylinders.
Let's take a look at what your test results mean:
CASE 1: Low or no compression in 2 or ALL cylinders.. This tells you you've got serious engine mechanical problems. The most common issues would be:
- Blown head gasket. The following tutorial may help: How To Test For a Blown Head Gasket (1.5L Honda Civic).
- Broken timing belt. The following tutorial may help: How To Test For A Broken Timing Belt (1.5L Honda Civic).
- Engine threw a rod.
CASE 2: Low or no compression in one cylinder.. This indicates a ‘dead’ cylinder that's causing an issue. You now need to find out if this cylinder's low compression value is within specification. In other words, it should not be 15% less than the highest compression value you obtained from all 4 cylinders.
You can figure this out by:
- Multiplying the highest compression reading that you recorded by .15.
- So, let's say that cylinder #4 gave you the highest reading of 170 PSI. Well 170 X .15 gives you 26 (25.5 rounded off).
- Then subtract 26 from 170... which gives us 144 PSI.
- So then, 144 PSI is the lowest possible compression reading that any one of the rest of the engine cylinders can have. Any compression reading below this and that engine cylinder will misfire.
Here's a more specific example... let's say that I got these compression test results:
- Cylinder #1 175 PSI.
- Cylinder #2 160 PSI.
- Cylinder #3 20 PSI.
- Cylinder #4 155 PSI.
The next step is to do the math: 175 x .15= 26, 175-26= 149. So, now I know that cylinder #4 is the one causing the misfire!!
Now that you've found the cylinder with the low compression, the next step is to see if this low compression is caused by worn cylinder head valves or worn piston rings... for this test, go to ‘Wet’ Engine Compression Test.