Testing to see if low or no engine compression is the reason for a misfire condition, or a rough idle condition, or a no-start condition just doesn't really come to mind in a lot of situations. Well, in this article, I want to not only show you how to do one, but also interpret its results so that you can find out if low or no engine compression is at the root of your 2.4L Honda's problem.
So, in case you're not aware I want to tell you that internal engine components (mainly cylinder head valves and engine piston rings) that are worn can cause problems in idle quality or simply result in a no-start condition.
In your 2.4L equipped Honda, you can do the engine compression test yourself and avoid a trip to the shop. In this tutorial, I'll show you how to do both a Dry and Wet engine compression test and then interpret the results.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (2.4L Honda Accord) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.4L Honda Accord: 2003, 2004, 2005, 2006, 2007.
ENGINE CYLINDER MISFIRE DIAGNOSTICS:
ENGINE NO-START DIAGNOSTICS:
Symptoms Of Low Engine Compression
Every cylinder, in your Honda's 2.4L engine, needs 3 very specific things to output power and these are: air, fuel, and spark.
If any one of these bad boys are missing from the mix (or not in the correct quantities), your 2.4L Honda is gonna' misfire (or, in other words, the engine is going to run rough, idle rough, miss, etc.).
The air part is provided by the suction and compression created by the cylinder head valves and engine block pistons and if they are too worn, they will cause low engine compression.
This low engine compression results in less air entering and being compressed during the combustion cycle of the particular cylinder affected.
Low engine compression, in one or several engine cylinders, will have a direct impact on the way the engine idles and the way the engine accelerates. No compression on all cylinders and the engine won't start it'll crank but not start.
Although not an exhaustive list of thing your 2.4L Honda engine may experience, you'll definitely see/feel one or several of the following symptoms:
- Rough idle. Simply put: the engines shakes too much at idle.
- Check engine light (CEL) on with one or several of the following diagnostic trouble codes (DTCs):
- P0300, P0301, P0302, P0303, P0304.
- The spark plug (of the cylinder with low or no compression) will always get fuel fouled.
No compression in all of the cylinders will result in a cranks but does not start condition. The symptoms you'll see will be:
- No start.
- Everything else works, for example:
- The fuel pump will activate, so you'll see fuel pressure at specification (if testing with a fuel pressure gauge).
- All of the COP coils will spark.
- If the COP coils are sparking, then this indirectly proves that the crank sensor is OK too.
- The PCM will still activate all of the fuel injectors.
- The spark plugs (of the cylinders with no compression) will always get fuel fouled.
What Tools Do I Need To Test The Engine Compression?
It goes without saying but I'm gonna' say it anyway, that the most important tool that you're gonna' need is a compression tester. If you don't have one, don't worry if you're in driving distance from an AutoZone or O'Reilly Auto Parts, you can rent one from them (for a returnable deposit of $40+ US dollars).
If you're gonna' buy one and want/need to save some bucks, buy it online and below is where I recommend you buy it.
Since the COP ignition coils and the spark plugs need to be removed, you'll also need some of the following basic tools:
- Ratchet wrench.
- 5/8" spark plug socket.
- Extensions for the ratchet wrench.
- Motor oil (for the 'Wet' compression test part).
TEST 1: Dry Engine Compression Test
Although it isn't always possible (the engine may not start) you should do the compression test with a slightly warmed up engine.
In case you're wondering why it's because metal expands with heat and this expansion may have an effect on your compression tester readings.
Now, this isn't a super critical thing, so if your particular pickup or SUV doesn't start don't worry about this.
Before you start, take a look at the whole article and familiarize yourself with all of the steps. Please remember to always think safety first, since you'll be working around a cranking engine.
OK, to get this show on the road, I'll first explain the test steps. At the end of the test steps, you'll find two possible test results that will help you to interpret your specific test results. Let's get started:
- 1
Disable the fuel system. You can easily do this by simply by disconnecting the fuel injectors from their electrical connector.
This step is important because it will prevent fuel from being injected into the cylinder as you do the compression test, so don't skip it. - 2
Remove all of the 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!
NOTE: Make sure that you leave all 4 ignition coils disconnected from their electrical connector to avoid having spark discharged during the test. - 3
Install the compression tester. Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder. Hand tighten the compression gauge only! Do not use any type of tool to get it tight.
- 4
When ready, crank the engine as you observe the needle 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. Record this compression reading on a piece of paper. Include the number of the cylinder this reading belongs to. Now repeat steps 1 thru' 6 on the other cylinders.
Now that you're done with the test, let's take a look at what your results mean:
CASE 1: You got a reading of 100 PSI or less (less being 0 PSI) on all of the cylinders you tested. This test result indicates you've got serious engine mechanical problems.
It's absolutely rare for the engine to get to the point of 0 PSI compression on all cylinders, but if it were to, this would usually means a broken timing chain.
What is common, if you have a very high mileage engine, is low compression across the board. Low usually means anything under 120 PSI (although the service manual says 100 PSI is the minimum). If your engine has reached this point it's also smoking from the quart of oil it's burning every few days. The other symptoms you'll see is that the idle will be very rough.
CASE 2: One or two cylinders gave a low compression value. This might be normal, since each cylinder will not give the exact same compression value.
What is NOT normal is if the pressures vary by 15% or more. That's right, the individual cylinder compression readings of each engine cylinder can not vary more than 15%. To find out, go to: Interpreting The Engine Compression Test Results.
Interpreting The Engine Compression Test Results
Up to a certain point, it's normal for the compression of each cylinder to vary a bit.
But if the values vary drastically, then you're gonna' have a rough idle condition or a misfire on your hands.
Finding out if the low compression values are within normal operating parameters isn't hard to do. In this section, I'll explain the math behind it.
To find out you'll need to multiply the highest compression value by 15% (0.15). Then you'll subtract the number you got from the highest compression value you got. The end result of this is the lowest compression your 2.4L Honda Accord (or Honda Element) can before it starts to misfire.
To explain this a bit better, let's say that I got the following compression readings from my compression test:
- Cylinder #1 175 PSI.
- Cylinder #2 160 PSI.
- Cylinder #3 165 PSI.
- Cylinder #4 125 PSI.
My next step would be to:
- Multiply 175 by 0.15 (175 x 0.15). This would give me = 26.
- Then: 175-26= 149.
- So then, 149 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.
- This means that cylinder #4 is the one causing the misfire.
To further pinpoint the problem, the next step is to do a 'wet' compression test on the dead or low compression cylinder.
The wet compression test will let us (you mainly) if the problem is due to worn out cylinder head valves or worn out piston rings. Go to: TEST 2: Wet Compression Test.
TEST 2: Wet Compression Test
A 'wet' compression test will help you to find out if the low cylinder pressure or pressures you recorded in the 'dry' compression test are caused by worn piston rings or worn cylinder head valves.
It will also help you decide what you need to replace and how much it's gonna' cost you. To be a bit more specific, this test will tell you if you only need to have the cylinder head worked on (not recommended) or if you only need to have the block worked on. Both of these options are not the ideal since just repairing one and not the other is not a good idea. Why?
Because by repairing only one, but not the other, you're only delaying the inevitable by about six months, which is: you're gonna' have to replace or repair the entire engine anyway.
OK getting back to the test at hand, what you're gonna' do is add about 2 tablespoons of oil to the cylinder (that recorded no or low compression in the previous test) and then check its compression once again.
What will happen is that if the low compression values is due to worn piston rings, the compression value will go up from the previous one you got doing the Dry compression value.
If the compression value does not go up (from the previous one), then you'll know that the problem lies in the cylinder head valves.
OK, to get this pot of water boiling, this is what you need to do:
- 1
Add a small amount of engine oil to the cylinder that reported low compression or no compression in the 'dry' compression test.
The amount should be about 1 to 2 tablespoons of oil. - 2
Install the compression tester onto the cylinder.
NOTE: Do not use any type of tool to tightened the compression tester, hand tight is fine. - 3
When all is set up, have your helper crank the engine.
- 4
You'll get one of two results:
1) The compression value will go up (from the one you recorded before).
2) The compression value will stay the same.
Let's see what your result is telling us:
CASE 1: The compression value shot up. This tells you that the piston compression rings are worn out and thus the problem is in the bottom end.
The reason why the compression value shot up, with the engine oil added, is because the oil is aiding the piston rings to create a near perfect seal.
Since the oil is not letting the compression escape by the rings, this results in your compression gauge reading a higher value than with the 'dry' compression test.
CASE 2: The compression value stayed the same. This confirms that the problem is in the cylinder head valves.
The reason why the compression reading did not shoot up, is because the engine oil can not help the intake or exhaust valve seal the compressed air therefore, the compression value will stay the same.
More 2.4L Honda Accord Tutorials
You can find a complete list of tutorials for your 2.4L Honda Accord equipped car here:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The TPS With A Multimeter (2003-2006 2.4L Honda Accord).
- How To Test The Fuel Injectors (2003-2007 2.4L Honda Accord).
- How To Test The Ignition Coils (2003-2006 2.4L Honda Accord).
- How To Test The MAP Sensor (2003-2007 2.4L Honda Accord).
If this info saved the day, buy me a beer!
