In this tutorial I'll explain how to test the compression of the Ford front wheel drive (FWD) vehicles equipped with a 3.8L V6 engine.
These vehicles include: 1991-1995 3.8L Ford Taurus, 1991-1995 3.8L Mercury Sable, and 1995-2003 3.8L Ford Windstar minivan..
Also I'm going to explain how to find out if the compression of a certain cylinder with low compression is causing a cylinder misfire or rough idle.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (1991-2003 3.8L Ford FWD) (at: autotecnico-online.com).
Symptoms Of Low Or No Compression
When an engine experiences compression issues, it can manifest in two main ways:
- Low Compression in Some but Not All Cylinders: This means that the pressure within certain cylinders is lower than it should be, which can lead to various performance problems.
- Zero PSI Compression in Some or All Cylinders: This is a severe issue where there is no compression at all in certain cylinders, indicating potential damage or failure.
Regardless of whether the compression is low or zero, you'll notice several symptoms that indicate there's an issue with the engine's compression:
- Hard Starting or No Start: Difficulty starting the engine, or it may not start at all.
- Poor Engine Performance: The engine may run rough, feel sluggish, or lack power.
- Misfiring: This is when one or more cylinders fail to ignite their air/fuel mixture properly, causing jerking or shaking.
- Reduced Power and Performance: The vehicle may struggle to accelerate or maintain speed.
- Excessive Oil Consumption: Compression issues can lead to oil leaking into the cylinders, causing increased oil consumption.
- Audible Engine Noise: You may hear unusual noises like knocking or tapping, indicating internal engine mechanical problems.
On vehicles with OBD II diagnostics (1996+), specific codes may be triggered related to cylinder misfires:
- P0301: Random Cylinder Misfire.
- P0302: Cylinder Number 2 Misfire.
- P0303: Cylinder Number 3 Misfire.
- P0304: Cylinder Number 4 Misfire.
- P0305: Cylinder Number 5 Misfire.
- P0306: Cylinder Number 6 Misfire.
Important Tips And Suggestions
TIP 1: Don't remove the spark plugs if your 3.8L Ford vehicle's engine is hot.
You run the risk of stripping the threads, of the spark plug hole, if you remove the spark plugs with a hot engine. This is a nightmare I wouldn't wish on my worst enemy.
TIP 2: Be careful and take all necessary safety precautions as you perform the engine compression test (since the engine has to be cranked).
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 just about anywhere, but you'll end up paying more for it (especially at your local auto parts store). The above links will help you comparison shop. I think you'll agree it's the better way to save money on the compression tester!
TEST 1: Dry Compression Test
In this section we're gonna' check the compression of all 6 cylinders. Checking them all will help us to find out which cylinder or cylinders are dead (due to low engine compression).
Let me tell you that depending on the age and mileage of your Ford's engine, the compression of each cylinder probably will not be similar.
Up to a certain point, this is normal. Now if the values vary too much between themselves, then this could lead to an engine cylinder misfire or rough idle condition.
Don't worry, I'll explain how to interpret your test results to find out if those dissimilar values are within a normal range or not.
Alright, these are the test steps:
- 1
Disable the ignition system by disconnecting the ignition coil from its electrical connector. This will prevent the ignition coil from sparking during the test.
- 2
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. - 3
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
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.
Repeat this test step on the remaining steps 3-5 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 tells you that your Ford's engine has serious internal problems. You should check for a:
- Blown head gasket.
- Blown engine.
Any compression value below 100 PSI (even if it does 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 bonafide misfire or rough idle condition on your hands.
To find out, the next step is to go to: Calculating The Compression Values To See If They Are Within Range.
