In this tutorial, I'll explain how to test the engine compression on the 4.6L and 5.4L V8 engine in the Ford F150, F250, and F350 pickup.
I'm also gonna explain how to interpret your test results to see if any of the compression reading you got are causing an engine performance problem or an engine no-start problem.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 4.6L Ford F150: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
- 5.4L Ford F250 Light Duty: 1997, 1998, 1999, 2000.
- 5.4L Ford F250 Super Duty: 1997, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
- 5.4L Ford F350 Super Duty: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
E-SERIES VANS: The engine compression test tutorial for the V8 Ford E-Series vans can be found here:
- How To Test Engine Compression (1997-2007 4.6L, 5.4L V8 Ford E150, E250, E350) (at: troubleshootmyvehicle.com).
Important Tips And Suggestions
TIP 1: Don't remove the spark plugs with a hot engine. Removing the spark plugs from a hot engine can/will damage the spark plug hole threads in the aluminum cylinder head.
TIP 2: Perform the engine compression test with a cold engine. The two main benefits of doing this are:
- Preventing damage to the spark plug threads in the cylinder heads.
- Reducing the risk of burns from hot engine components.
TIP 3: Take all necessary safety precautions as you work around a cranking engine. Think safety all of the time.
Symptoms Of Low Or No Cylinder Compression
An engine compression issue will usually cause one of two problems:
- An Engine No-start Problem: This engine no-start problem is the result of more than three or more cylinders not producing any compression.
- A Cylinder Misfire Problem: This occurs when one or more cylinders produce a low compression pressure that's less than 15% of the highest compression value produced by the strongest cylinder.
Here are some other specific symptoms you may see with low cylinder compression:
- Blue smoke coming out of the tailpipe.
- Rough idle (engine misfires).
- Bad gas mileage.
- Engine 'misses' at idle but 'miss' disappears as you accelerate.
- Check engine light is illuminated with a MAP sensor trouble code (even tho' the MAP sensor is good).
- Misfire 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.
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 in any auto parts store in any neighborhood, in any city, but you'll be paying at least twice as much. Go to the above compression tester links, browse and compare, you'll see a big price difference!
TEST 1: Dry Compression Test
If your pickup is equipped with a 4.6L engine with ignition coil packs, I recommend two very important things:
- Label the spark plug wires with the cylinder number they belong to.
- Use a spark plug wire puller tool to unplug the spark plug wire from the spark plug.
Why use a spark plug wire puller? Cause pulling on the wire boot by hand can cause the wire's metal terminal to pull off and stay stuck on the spark plug. The following tutorial offers you more info: How To Use A Spark Plug Wire Puller And Where To Buy One.
OK, let's begin:
- 1
Disable the ignition system (4.6L V8 only) by disconnecting the ignition coil packs from their electrical connectors.
NOTE: This is a safety precaution that will prevent the ignition coil from sparking during the test. - 2
Disable the fuel system by disconnecting the fuel injectors.
NOTE: Disabling the fuel system will prevent fuel from being injected into each cylinder when the test is performed. - 3
Remove the spark plugs. Remember, the engine can not be hot!
NOTE: 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. - 4
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.
- 5
Have your helper crank the engine till the needle on the compression gauge stops climbing.
- 6
Record the value at which the needle stopped and the number of the engine cylinder on a piece of paper.
- 7
Release the pressure on the gauge and check the cylinder's compression one more time.
- 8
Repeat test steps 4 - 7 on the remaining cylinders.
Let's take a look at what your test results mean:
CASE 1: One or more cylinders had a much lower compression value than the others. Up to a certain range, this could be normal.
To further interpret these test results go to: Interpreting The Compression Test Results.
CASE 2: All six cylinders had almost no compression or 0 PSI compression. This low or zero compression on all cylinders will cause the engine to not start.
Having a compression value close to 0 PSI or 0 PSI is usually due one of the following problems:
- A busted timing chain.
- Blown head gasket.
- The engine threw a rod.
CASE 3: The compression value of all six cylinders was similar and above 120 PSI. This test result lets you know that an engine compression problem is not behind the misfire condition and/or engine no-start problem you're troubleshooting.
