Testing the engine compression, on your 5.2L or 5.9L V8 equipped Dodge Ram pickup or van, is not as hard as people think.
In this tutorial, I'll show you how to do it and more importantly I'll also show you how to interpret the results of the compression test.
Why do an engine compression test? Well, it may help you to find out if the engine is shot and if this is the reason why it won't start or the reason behind your pickup or SUV's hard to diagnose misfire condition.
NOTE: For the 3.9L V6 equipped Dodge pickup and van, see this tutorial: How To Test The Engine Compression (3.9L Dodge Ram Pickup And Van).
Contents of this tutorial:
Symptoms Of Engine Compression Problems
For the most part, engine compression problems cause one of two problems. Either the compression problem causes the engine to not start.
Or the engine compression problem causes a misfire condition. To be a bit more specific, the engine still starts and runs, but runs with a misfire.
If the engine is misfiring, due to a compression problem and your 5.2L or 5.9L Dodge vehicle is OBD II equipped, you'll see one or more of the following trouble codes:
- P0300: Random Cylinder Misfire.
- P0301: Cylinder #1 Misfire.
- P0302: Cylinder #2 Misfire.
- P0303: Cylinder #3 Misfire.
- P0304: Cylinder #4 Misfire.
- P0305: Cylinder #5 Misfire.
- P0306: Cylinder #6 Misfire.
- P0307: Cylinder #7 Misfire.
- P0308: Cylinder #8 Misfire.
You'll also see:
- Rough idle condition that does not set a misfire trouble code.
- Misfire felt only when accelerating the vehicle.
- Misfire felt when the engine is idling but goes away when engine is accelerated.
- Bad gas mileage.
- Heavy exhaust smell coming out of the tailpipe when the engine is running.
Important Tips And Suggestions
TIP 1: Let the engine cool down completely before removing the spark plugs.
Attempting to remove the spark plugs from a hot engine can damage the threads in the spark plug holes. This is a nightmare you want to avoid.
TIP 2: To disconnect the spark plug wires from the spark plugs, use a spark plug wire puller.
Using a spark plug puller will help you avoid damaging the spark plug wires when disconnecting them from the spark plugs.
To see an example of this tool, check out this article: How To Use A Spark Plug Wire Puller And Where To Buy One (at: easyautodiagnostics.com).
TEST 1: Dry Compression Test
To find out if an engine compression problem is behind a no-start or misfire problem, it's important to test all 8 cylinders.
If you don't have an engine compression tester, you can run down to your local auto parts store and buy or rent it there. If you'd like to save a few bucks on its purchase, check out my recommendations here: Which Compression Tester Should I Buy?.
Let's get testing:
Remove the spark plugs.
When removing the spark plugs, be careful not to drop any of them on the floor, or you run the risk of having the spark plugs porcelain insulator crack and then you'll have a misfire on your hands.
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.
Have your helper crank the engine till the needle on the compression gauge stops climbing.
Record the value at which the needle stopped and the number of the engine cylinder on a piece of paper.
Repeat steps 2-4 on the remaining cylinders.
Let's take a look at what your compression test results mean:
CASE 1: You got 0 PSI in the majority of the cylinders. This test result tells you that your 5.2L or 5.9L V8 engine has serious internal problems. This is usually due to:
- Busted timing chain.
- Engine threw a rod.
Any compression value below 100 PSI (even if it's not 0 PSI) means internal mechanical engine trouble.
CASE 2: All cylinders have compression but their values are not the same. It's normal for each cylinder's compression value to vary slightly from one another. But if they vary too much, you'll have a bona-fide misfire or rough idle condition on your hands.
To find out, the next step is to go to: Interpreting The Engine Compression Test Results.