TEST 3: Engine Compression Test
In some cases, one of the head gaskets will fail right between two side-by-side cylinders. The engine will start and run, but it'll have two cylinder misfires causing cylinder misfire diagnostic trouble codes (if OBD II equipped).
The cylinder misfires are caused by the compression pressure of one cylinder escaping into the other due to the head gasket failure, resulting in two 'dead' cylinders.
The only way to confirm this particular type of head gasket failure is by performing a compression test.
These are the test steps:
- 1
Disable the ignition system by disconnecting both ignition coils from their engine wiring harness connector.
- 2
Remove all of the spark plugs.
- 3
Install the compression tester by hand in the spark plug hole of cylinder #1.
Do not use any tools to tighten the compression tester. Hand tightening the compression tester is more than enough to get the proper results. - 4
Have your helper crank the engine.
The needle on the tester will climb as the engine cranks. Once the cylinder reaches its maximum compression the needle will stop climbing.
Once it stops climbing have your helper stop cranking the engine. - 5
Write down the reading and what cylinder it belongs to (you can use the illustration above to help you identify the cylinder).
- 6
Repeat steps 3 through 5 in the remaining cylinders.
Let's take a look at what your test results mean:
CASE 1: All cylinder compression readings were above 0 PSI. This is the correct and expected test result.
Your next step is to perform a block test with a block tester. For this test go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
CASE 2: Two side by side cylinders had 0 PSI compression. This engine compression test result confirms that the head gasket (of that bank of cylinders) is burned at the point between those two cylinders.
You'll need to replace both head gaskets.
TEST 4: Using A Chemical Block Tester (Combustion Leak Tester)
I've run into quite a few cases where the engine had a blown head gasket, yet it didn't exhibit any of the symptoms that the previous three tests are designed to confirm.
Usually, the engine would start, run and overheat within minutes for no apparent reason. In the majority of cases, the engine had previously overheated a few weeks or months before, and although the issue causing the overheating had been resolved, it was now overheating again.
In these cases, I've used a tool called a block tester (combustion leak detector) to determine if the overheating was caused by a head gasket failure.
In a nutshell, this is how a block tester works:
- A blue liquid chemical, which is blue in color, is placed in the tester (see photo above).
- The engine is started.
- The tester assembly is then placed on the open radiator neck (you may have to drain some of the coolant in the radiator since this tool needs to 'gulp' some of the air inside the radiator).
- The rubber bellow is then squeezed to suck in the air up through the two fluid-filled chambers. As the air bubbles up through the fluid, it will cause a chemical reaction.
- If the blue chemical turns yellow (for gasoline engines), then combustion gases are entering the radiator. This confirms a blown head gasket, a cracked block, or a cracked cylinder head issue.
- If the blue chemical doesn't change color, then you can conclude that you don't a blown head gasket, a cracked block, or a cracked cylinder head issue.
Where can you get the chemical and block tester? At your local auto parts store or here:
20%More 4.6L Crown Vic And Grand Marquis Tutorials
There are quite a few 4.6L Ford Crown Victoria (Mercury Grand Marquis) 'how to' tutorials and wiring diagrams that here:
E-Series Vans: You can find all of the available tutorials and wiring diagrams for the 4.6L and 5.4L V8 E-Series vans in this index:
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).
If this info saved the day, buy me a beer!
