Testing the engine compression on the 4.2L V6 engine in your Ford E series van is a challenge, since removing the spark plugs is not the easiest thing in the world to do.
I'm not saying this to discourage you from performing the engine compression test; after all, it's the go-to test to find out the internal health of the engine.
In this tutorial, I'll explain how to do the compression test and more importantly, how to interpret its results.
You'll be able to find out if you have one or more engine cylinders that are causing a misfire or causing the engine to not start.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 4.2L V6 Ford E150: 1997, 1998, 1999, 2000, 2001, 2002, 2003.
- 4.2L V6 Ford E250: 1997, 1998, 1999, 2000, 2001, 2002, 2003.
Symptoms Of Low Or No Engine Cylinder Compression
It's been my experience, that an engine compression problem will typically cause one of two issues:
- Cylinder misfire: The engine start and runs, but it runs with a rough idle when the engine is idling.
- Engine no-start: The engine cranks but doesn't 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.
- 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 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.
TEST 1: Finding The Dead Cylinders
To get the most accurate test result from your compression test, I'm going to recommend that you test all six cylinders.
If you already know which cylinder is 'dead' and only want to test that one, no problem; you don't have to test them all. However, you'll still need to test one or two more to determine if the 'dead' cylinder's compression is less than 15% of the highest compression you obtain from the other two cylinders.
Once you've obtained the results of your test, we're going to interpret those results and if you have one or more cylinders with a low compression value compared to the others, well figure out if they are causing a problem or not in the next section of this tutorial.
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 disconnecting the ignition coil pack from its electrical connector.
This will prevent the ignition coil 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 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.
