TEST 5: Misfiring COP Coil Under Plenum
You've reached this test because you have a specific misfire code (P0301, P0302, or P0303) that accuses a cylinder underneath the plastic intake manifold plenum as misfiring.
In this section, you're gonna do two things (to find out the root cause of the misfire):
- Test the COP coil (that belongs to the misfiring cylinder) with a spark tester.
- Check that the COP coil's spark plug boot and the spark plug are not covered in engine oil (from a leaking valve cover gasket).
To get to the COP coil underneath the plenum, you're gonna' have to remove it. Once removed, and as a safety precaution, you're gonna' test the COP coil (that the misfire code accuses) by connecting it to a COP coil connector that belongs to the front bank of the engine (I'll explain the whole thing in detail in the test steps below).
IMPORTANT: Remove the fuel pump relay before you start testing for spark. This will prevent your Ford Escape (or Mazda Tribute) from starting. To see the location of the fuel pump relay on the Ford Escape/ Mazda Tribute, check out the photo here: Location Of The Fuel Pump Relay.
OK, this is what you'll need to do:
- 1
Remove the plastic intake manifold plenum.
IMPORTANT: Once the plenum is removed, stuff clean rags (shop towels) into the open intake manifold ports. This is a safety precaution to avoid having stuff fall down into those intake manifold ports (see photo number 2 of 5). - 2
Disconnect and remove the COP coil that the misfire code, you retrieved with your scan tool, indicates as the one that's misfiring.
- 3
Remove the rags that you placed in the open intake manifold ports and re-install the plenum back in place and bolt it down (its OK to reuse the gasket at this point).
I don't want to jump ahead too much, but what you're gonna' do in a few moments is crank the engine and re-installing the plenum is a safety precaution. - 4
Disconnect one of the COP coils (in the front engine bank) from its electrical connector.
Now, connect the COP coil (you just removed from the rear bank) to this electrical connector. - 5
Attach the spark tester to the COP coil.
Ground the spark tester using a jump start cable to the battery negative (-) terminal. - 6
Have your helper crank the engine while you observe the spark tester.
The spark tester should do one of two things: spark or Not spark.
Alright, there are 4 possible test results to choose from below, let's take a look at what your test results mean:
CASE 1: The COP coil DID NOT spark and was NOT covered in oil. This tells you that the COP coil is bad and needs to be replaced to solve the misfire condition.
CASE 2: The COP coil DID NOT spark and WAS covered in oil. This tells you that the COP coil is bad and needs to be replaced to solve the misfire condition and that you'll need to replace the valve cover gaskets.
There are some very specific recommendations to help you complete the repair head-ache free and you can find them here: Spark Plug And Boots Soaked In Oil.
CASE 3: The COP coil sparked and was NOT covered in oil. This tells you that the COP coils is OK and not the cause of the misfire.
Since you still have a misfire, I suggest testing the following:
- Fuel injectors.
- Engine compression.
Although it's beyond the scope of this article to test the above, you have at least eliminated the COP coil as the source of the misfire condition.
CASE 4: The COP coil sparked and WAS covered in oil. This tells you that the misfire condition could be caused by the oil.
Since the COP coil boot was soaked with engine oil this means the spark plugs are swimming in oil too. To effectively solve the misfire issue on your Ford vehicle, there are some important recommendations you should take a look at here: Spark Plug And Boots Soaked In Oil.
TEST 6: Misfiring COP Coil In Front Engine Bank
You've reached this test because you have a specific misfire code (P0304, P0305, or P0306) that accuses a cylinder located in the front engine bank.
Your mission, in this test section, is to find out if your 3.0L Ford Escape (or 3.0L Mazda Tribute) is misfiring due to:
- A bad COP coil that isn't sparking anymore.
- Or engine oil leaking on to the COP coil's spark plug boot and the spark plug (from a leaking valve cover gasket).
IMPORTANT: Remove the fuel pump relay before you start testing for spark. This will prevent your Ford Escape (or Mazda Tribute) from starting. To see the location of the fuel pump relay on the Ford Escape/ Mazda Tribute, check out the photo here: Location Of The Fuel Pump Relay.
OK, this is what you'll need to do:
- 1
Disconnect and remove the COP coil that the misfire code indicates as the one that's misfiring.
Check to see if the COP coil's spark plug boot and the spark plug are covered in engine oil (from a leaking valve cover gasket). - 2
Attach the spark tester to the COP coil.
Ground the spark tester using a jump start cable to the battery negative (-) terminal. - 3
Have your helper crank the engine while you observe the spark tester.
The spark tester should do one of two things: spark or Not spark.
Alright, choose the CASE that best fits your spark test results:
CASE 1: The COP coil DID NOT spark and was NOT covered in oil. This tells you that the COP coil is bad and needs to be replaced to solve the misfire condition.
There are some very specific recommendations to help you complete the repair head-ache free and you can find them here: Important Recommendations.
CASE 2: The COP coil DID NOT spark and WAS covered in oil. This tells you that the COP coil is bad and needs to be replaced to solve the misfire condition and that you'll need to replace the valve cover gaskets.
There are some very specific recommendations to help you complete the repair head-ache free and you can find them here: Spark Plug And Boots Soaked In Oil.
CASE 3: The COP coil sparked and was NOT covered in oil. This tells you that the COP coil is OK and not the cause of the misfire.
CASE 4: The COP coil sparked and WAS covered in oil. This tells you that the misfire condition could be caused by the oil.
Since the COP coil boot was soaked with engine oil this means the spark plugs are swimming in oil too. To effectively solve the misfire issue on your Ford vehicle, there are some important recommendations you should take a look at here: Spark Plug And Boots Soaked In Oil.
Important Recommendations
In TEST 5 or TEST 6 you found a bad coil-on-plug (COP coil) that feeds spark to one of the cylinders in the rear engine bank (and thus underneath the intake manifold plenum), in this section I want to offer you some specific recommendations so that you can finish the job and not have any comebacks.
They are:
- Remove and check the spark plugs for wear and tear.
- If you have never replaced the spark plugs and the engine has over 100,000 miles, replace them all. No 'ifs, ands, or buts' on this point.
- Use only the Motorcraft® brand of spark plugs. Motorcraft is the factory original spark plug that will work head-ache free in your Ford vehicle.
- Using any other 'high performance' spark plug is not only a waste of money, but may cause a rough idle or misfire condition.
- Replace the plenum gasket with a new one.
- Avoid the temptation to use RTV Silicone gasket sealer to aid the rubber plenum gaskets in their sealing ability.
- Using any type of sealant on the plenum rubber gaskets will only cause a come-back later, so install these bad boys dry.
- I recommend also replacing the intake manifold gaskets too (since you already have everything off).
- If your vehicle has over 100,000 miles, replace the intake manifold gaskets, because they will eventually (more sooner than later) start leaking engine vacuum.
- This will cause a misfire P0300 code, rough idle and a Lean air-fuel mixture condition.
- The intake manifold gaskets also need to be installed without any type of sealant.
- Replace all of the spark plug boots.
- The spark plug boots can become a source of a misfire since they don't last forever (being exposed to the enclosed heat of the spark plug tubes).
- Your local auto parts will have these in stock.
