Doing an engine compression test on the V8 engine in your Ford E-Series van is quite the challenge, mainly because removing the spark plugs is quite the job (been there, done that).
I'm not mentioning this to discourage you, though. An engine compression test is crucial for checking what's going on inside your engine.
In this tutorial, I'll show you how to perform the compression test and, importantly, how to read its results. This way, you'll determine if there are any cylinders causing trouble, like misfires or preventing the engine from starting.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 4.6L, 5.4L V8 Ford E150: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014.
- 4.6L V8 Ford E250: 1997, 1998, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014.
- 5.4L V8 Ford E250: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014.
- 5.4L V8 Ford E350: 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014.
F-Series Pickups: You can find the thermostat test for 4.6L and 5.4L V8 F-Series pickups here:
- How To Test Engine Compression (1997-2010 4.6L, 5.4L Ford F150, F250, F350) (at: easyautodiagnostics.com).
Crown Vic And Grand Marquis: You can find the thermostat test for 4.6L Crown Vic and Grand Marquis here:
NOTE: This tutorial applies to several other Ford, Mercury, and Lincoln vehicles equipped with a 4.6L or 5.4L V8 engine. You can see the application list in the 'Applies To' box on the left if you're using a desktop or at the bottom of this page if you're using a hand-held mobile device.
Symptoms Of Low Or No Engine Cylinder Compression
In my experience, problems with engine compression tend to lead to one of these headaches:
- Cylinder Misfire: The engine starts and runs, but it shakes a lot when it's idling. In tech terms, this is known as rough idle or a misfire condition.
- Engine No-Start: You'll hear the engine cranking, but it won't actually start.
When an engine compression problem is allowing the engine to start, you're going to see one or more of the following symptoms:
- Check Engine Light: The check engine light will be illuminated on your van's instrument panel.
- Misfire trouble codes: You many see one or more of the following:
- 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.
- Engine Performance Problems: You many see one or more of the following:
- Engine is not as peppy as it was once.
- Rough idle that goes away as soon as you accelerate the engine.
- Bad gas mileage: The engine has to work harder if one or more cylinders aren't functioning properly.
- Blue smoke: Having blue smoke coming out of the tailpipe is a classic sign of engine compression problems.
- A heavier exhaust smell: A heavier-than-normal exhaust smell coming out of the tailpipe is due to one or more cylinders not being able to properly compress and combust the air/fuel mixture within them.
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 three recommendations to you:
Disclosure: As an Amazon Associate, I earn from qualifying purchases. If my tutorials help you, using these links is an easy way to support the site at no extra cost to you. Thank you!
TEST 1: Finding The Dead Cylinders
To nail the most accurate result on your compression test, I strongly suggest checking all eight cylinders.
If you've already pinpointed a 'dead' cylinder and just wanna focus on that, no problem; no need to check them all. But you'll still need to compare it with one or two others to see if the 'dead' one's compression is more than 15% lower than the highest compression you get from the others.
After you get those numbers and if any cylinders are showing lower compression than the rest, we'll figure out (in the next part of this tutorial) whether they're really causing trouble or not.
If you don't have a compression tester, you can borrow one or buy one from your local auto part store. If you'd like to save a few bucks, check out my recommendations here: Which Compression Tester Should I Buy?.
IMPORTANT: If the engine has been running for any length of time, let it cool down completely before removing the spark plugs.
OK, these are the test steps:
- 1
Disable the ignition system by removing fuse #8 from the dash fuse panel.
This will prevent the ignition coils from sparking during the test. - 2
Remove the spark plugs. Remember, the engine can not be hot!
When removing the spark plugs, be careful not to drop any on the floor, or you run the risk of having the spark plug's porcelain insulator crack and then you'll have a misfire on your hands. - 3
Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder.
NOTE: Hand tighten the compression gauge only! Do not use any type of tool to get it tight. - 4
Have your helper crank the engine till the needle on the compression gauge stops climbing.
- 5
Record the value at which the needle stopped and the number of the engine cylinder on a piece of paper.
- 6
Release the pressure on the gauge and repeat step 4 and 5 one more time.
- 7
Repeat test steps 3 - 5 on the remaining cylinders.
Let's examine your test results:
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 eight 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 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.
Interpreting The Compression Test Results
It's not rare for some cylinders to show a lower compression value, especially if the engine has racked up a lot of miles.
Within a certain range, this variation between cylinders doesn't lead to engine performance issues. However, if the compression in any cylinder falls more than 15% below your top compression figure, that's when problems like rough idling or misfires pop up.
In this test section, I'll break down a simple way to check if these lower compression numbers are to blame for a rough idle problem or a cylinder misfire issue.
The basic principle here is that the lowest compression reading shouldn't be more than 15% less than your highest compression (recorded in TEST 1). If it is, you're looking at a misfiring cylinder, which will make your Ford van's engine idle roughly.
How do you figure this out? You can find out by using my online low compression calculator here: Online Low Engine Compression Calculator (at: easyautodiagnostics.com) or by calculating this 15% difference manually.
To understand how to figure out this 15% thing manually, I'll use the following compression test results:
- Cylinder #1 175 PSI.
- Cylinder #2 165 PSI.
- Cylinder #3 170 PSI.
- Cylinder #4 120 PSI.
- Cylinder #5 170 PSI.
- Cylinder #6 170 PSI.
- Cylinder #7 165 PSI.
- Cylinder #8 170 PSI.
The next step is to do the following math:
- Multiply .15 (15%) by the highest value: 175 x 0.15. This gives us 26.25, but we'll round it out to 26.
- Next, we subtract 26 from 175: 175 - 26 = 144.
- So now we know that the lowest possible compression value is: 144 PSI.
This means that cylinder #4, which has a compression value of 120 PSI, is the one causing the misfire because it's below the 144 PSI minimum.
Once we've found the 'dead' cylinder, the next step is to find out what's causing the low compression value. For this step, go to: TEST 2: Wet Engine Compression Test.
TEST 2: Wet Engine Compression Test
So, you've confirmed that one or more cylinders have low compression. This issue stems from either:
- Worn or damaged piston rings in the cylinder in question.
- Worn or damaged intake/exhaust valves in the same cylinder.
There's a bit of a silver lining, though. A wet compression test can clue us in on whether the problem is with the piston rings or the valves, and all this without needing to disassemble the engine.
All you have to do is add a couple of tablespoons of oil (two) to the cylinder showing low compression, then test its compression again.
If the compression goes up after the oil is added and tested again, then the culprit is worn piston rings. If the compression stays the same, then it's the intake/exhaust valves to blame.
These are the test steps:
- 1
Add 1 or 2 tablespoon of engine oil in the cylinder you need to retest. I suggest using a small and long funnel so that the oil will reach the inside of the cylinder.
- 2
Install the compression gauge on the cylinder you just added oil to.
- 3
Have your helper crank the engine till the needle stops climbing on the compression gauge.
- 4
You'll see one of two results:
1.) The needle will climb higher than the previous compression number you recorded for this specific cylinder.
2.) The needle will not move at all or stay at the same number you recorded earlier.
What ever value your compression tester reads, write it down again. - 5
Repeat steps 1 thru' 4 on any other cylinder you need to check.
Let's examine your test results:
CASE 1: The compression value of the cylinder you added oil to increased. This test result tells you that the low or near 0 PSI compression value is due to worn out piston rings of that specific cylinder.
CASE 2: The compression value of the cylinder you added oil to DID NOT increase. This test result confirms that the cylinder head valves of that cylinder are worn-out or damaged.
More 4.6L, 5.4L V8 Ford E150, E250 And E350 Tutorials
There are quite a few 4.6L and 5.4L Ford E-Series van 'how to' tutorials and wiring diagrams that you can check out here:
F-Series Pickups: You can find all of the available tutorials and wiring diagrams for the 4.6L And 5.4L V8 F-Series pickups in this index:
- 4.6L, 5.4L Ford F150, F250, And F350 Index of Articles (at: easyautodiagnostics.com.com).
Crown Vic And Grand Marquis: You can find all of the available tutorials and wiring diagrams for the 4.6L And 5.4L V8 F-Series pickups in this index:
If this info saved the day, buy me a beer!
