## Interpreting Your Compression Test Results

As I mentioned earlier, it's not unusual for compression values between cylinders to vary in high-mileage engines.

In most cases, if the variation in the compression values is slight, you're not going to see (or feel) any engine performance or drivability issues.

But suppose one or more compression values differ more than 15% from the highest compression value (that you obtained in TEST 1). In that case, you'll definitely have some engine performance or drivability issues.

To determine if a low compression value is causing a problem, we need to figure out if the low compression values are lower than 15% of the highest compression value you got.

You can do this (figuring out the 15%) in one of two ways: You can calculate this 15% difference with pen and paper, or you can use my low compression calculator found here: **Online Low Engine Compression Calculator** (at: **easyautodiagnostics.com**).

If you want to manually calculate the 15% difference, here's what you'll need to do:

**STEP 1:**Multiply the highest compression value by 0.15 (this is the decimal value of 15%).**STEP 2:**Round the result to the nearest one (for example: 25.6 would become 26).**STEP 3:**Subtract the result (the number that was rounded) from the highest compression value.**ANSWER:**The result of this subtraction is the lowest possible compression value any cylinder can have.

Now, let me give you a more specific example: Let's say that I got the following compression readings:

Cylinder | Pressure |
---|---|

#1 | 165 PSI |

#2 | 95 PSI |

#3 | 155 PSI |

#4 | 175 PSI |

My next step is to do the following calculation:

**STEP 1:**175 x 0.15 = 26.25.**STEP 2:**26.25 = 26 (rounded to nearest one).**STEP 3:**175 - 26 = 149.**ANSWER:**149 PSI. Any cylinder with this compression (or lower) value will misfire.

Since cylinder #2 is only producing 95 PSI, I can now conclude that it's 'dead' and causing a misfire.

To find out if the lowest compression value you got from your engine compression test is within a good range, you'll need to do the same calculation. Of course, you'll need to use the highest compression value you got and not the one in the example.

Once you'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 Compression Test

If you found a compression reading below 15% of the biggest value, the next step is to find out if that cylinder's head valves or piston rings are severely worn.

We can easily and quickly determine where the problem lies by doing a wet compression test. This test involves adding a bit of engine oil to the problem cylinder and rechecking its compression.

If the compression value goes up, you can conclude that the cylinder's low or 0 PSI compression value is due to severely worn piston compression rings.

If the compression value of the low or 0 PSI compression cylinder stays the same, the problem is due to worn cylinder head valves.

OK, this is what you'll need to do:

- 1
**Add a tablespoon of engine oil in the cylinder you need to retest**.

I suggest you use a small and long funnel so that the oil will reach the inside of the cylinder. - 2
**Once you've added the oil, install the compression gauge**.

As before just hand tighten the compression gauge in the cylinder's spark plug hole. - 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 with a low or 0 PSI compression value**.

Let's take a look at what your compression test results mean:

**CASE 1: Your compression tester registered a higher value**. This compression test result confirms that the low compression value reported in this cylinder in the dry test is due to worn piston rings.

**CASE 2: Your compression tester DID NOT register a higher value (than the previously recorded value)**. This result tells you that the low compression value reported in this cylinder in the dry test is due to worn/damaged cylinder head valves.

## More 1.5L Toyota Tutorials

There are several more tutorials that I've written that are 1.5L Toyota specific, that may be of further help. You can find the ones that are located here, at this site, by going to the Toyota 1.5L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

- How To Test The Ignitor -Step By Step (1995-1996 1.5L Toyota Tercel).
- How To Test The Throttle Position Sensor (1995-1996 1.5L Toyota Tercel).
- How To Test The Fuel Injectors (1995-1996 1.5L Toyota Tercel).
- How To Test For A Blown Head Gasket (1.5L Toyota Tercel).

If this info saved the day, buy me a beer!