Testing engine compression is becoming a standard test when diagnosing a hard-to-find misfire (rough idle) or no-start condition, especially when your 3.2L Isuzu Amigo (Rodeo, Trooper or Honda Passport) has clocked up a lot of miles.
In this tutorial, I'll walk you through the entire process step-by-step and help you interpret your compression test results to determine if one or more cylinders have low (or no) compression.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (3.2L Isuzu Amigo, Rodeo, Trooper) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 3.2L Isuzu Amigo: 1999, 2000.
- 3.2L Isuzu Rodeo: 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003.
- 3.2L Isuzu Trooper: 1992, 1993, 1994, 1995, 1996, 1997.
- 3.2L Honda Passport: 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002.
Tools You'll Need:
- Compression gauge tester.
- A helper
- Pen and paper
Symptoms Of Low Or No Engine Compression
When your 3.2L equipped Isuzu has an engine compression problem, it usually suffer one of two problems:
- Low or no compression in one or more of the engine's 6 cylinders.
- No compression in all 6 cylinders.
Low (or no) compression in one or more cylinders (but not all) is probably the most common problem I've seen.
This type of engine compression problem usually occurs on vehicles with a high mileage engine or an engine with a lot of wear and tear.
The main cause of low (or no) compression in one or more cylinders is usually worn cylinder head valves or worn piston rings (in the affected cylinder or cylinders).
Here are some more specific symptoms you'll see when one or more, but not all, cylinders have low compression:
- Misfire codes (if your Isuzu is OBD II equipped):
- 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 misses at idle (rough idle).
- Lack of power.
- Blue smoke coming out of the tailpipe at idle and/or when accelerating (this is engine oil burning in the cylinders).
If your 3.2L equipped Isuzu has 0 PSI compression on all cylinders, it won't start. The engine will crank but not start. This usually indicates that your Isuzu has a snapped timing belt, blown head gaskets or a blown engine.
The most common symptoms when there is no compression on all six cylinders are:
- The engine cranks very fast and this fast cranking speed is very noticeable.
- The ignition system is not creating spark (only occurs if timing belt is broken).
- Fuel pump is working and providing pressure.
Let's get testing to see what's happening to your 3.2L Isuzu Amigo (Rodeo, Trooper, Honda Passport).
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.
Engine Compression Gauge Testers
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!
The Dry Engine Compression Test
To perform an engine compression test, you need an engine compression tester.
You don't have to buy one, as you can rent one from your local auto parts store (like AutoZone or O'Reilly Auto Parts) for a cash deposit, which you get back when you return the tester.
If you need help deciding where to buy one or which one to buy, take a look at my recommendations: Which Compression Tester Should I Buy.
IMPORTANT: You'll be working around a cranking engine, so you have to be careful and stay alert at all times. Think safety all of the time!
This is what you'll need to do:
Disable the fuel system by removing the fuel pump fuse.
Disabling the fuel system prevents fuel from being injected into the cylinders when you crank the engine.
Disable the ignition system.
NOTE: This test step applies to the 3.2L SOHC engines with a 'coil pack' ignition system (1997 and older).
Disabling the ignition system prevents spark from being created and delivered to the cylinders when you crank the engine.
Remove all 6 spark plugs.
NOTE: When removing the spark plugs, be careful not to drop them on the floor (or ground), otherwise the spark plug's ceramic insulator may crack, resulting in a misfire!
IMPORTANT: Label each spark plug wire with its location before you remove the spark plugs so that you can reconnect them back to the correct spark plug once you're done with the compression test.
Thread the engine compression gauge into the spark plug hole for engine cylinder number 1.
Only tighten the compression gauge hand-tight! Don't use any tool to tighten it.
Have a helper crank the engine when the test is set up and watch the needle on the compression tester gauge.
Once the needle on the gauge stops climbing, have him or her stop cranking the engine.
Record the compression test result and the cylinder to which the test result pertains.
Repeat steps 4 thru 7 on the next 5 cylinders.
OK, let's interpret your compression test results.
CASE 1: Low or no compression in 2 side by side cylinders (of the same bank). This indicates a problem that's usually caused by:
- A Blown head gasket.
CASE 2: No compression in ALL cylinders. This isn't good and indicates that your 3.2L Isuzu has serious engine mechanical problems.
The most common issues would be:
- Broken timing belt.
- Engine threw a rod.
CASE 3: Low or no compression in one or two cylinders (that are NOT side by side on the same bank). With the compression values you have recorded, you now need to do a simple math calculation to find out if the low compression test result is within normal specs or not.