What Tests Can I Perform To Find The Cause Of The Misfire Condition?
Now that you know that a misfire has its root cause in a cylinder's lack of fuel or spark or air, you might be wondering, ‘What do I start testing first?’.
Here are my suggestions on what to start testing first:
STEP 1: Identify the dead cylinder. This entails reading any trouble codes that are lighting up the check engine light (CEL). What you're looking for are misfire codes (P0301, P0302, P0303, P0304).
In many cases, the PCM does not give you any misfire codes, even though the engine is suffering a bonafide misfire. In these cases you'll need to do a manual cylinder balance.
This test simply involves unplugging one fuel injector at a time (from its electrical connector) to see which one has NO effect on the engine's idle.
A disconnected fuel injector that does not affect the engine's idle tells you that the specific cylinder it belongs to is ‘dead’.
STEP 2: Test the ignition system . After finding the ‘dead’ cylinder, I then recommend that you make sure that cylinder's COP ignition coil is sparking. I suggest you:
- Perform a spark test (using a dedicated spark tester) on the spark plug wire of the cylinder that the misfire code is accusing of being dead.
- Testing for spark with a spark tester is the most important first test since you'll know right away if the misfire is due to a lack of spark.
- Check to see if the spark plug boots and spark plugs are swimming in engine oil from a leaking valve cover gasket.
- If you got spark from your spark tester (from the cylinder the misfire code is accusing of misfiring), the next step is to remove the spark plug or spark plugs (of the affected cylinders) and check them for wear and tear, carbon tracks, anti-freeze, etc.
- The following tutorial will help you test the ignition coils:
STEP 3: Test the fuel injectors. If the ignition system is not the cause of the misfire, then the next step is to check the fuel injectors.
You'll need to:
- Resistance test each of the 4 fuel injectors.
- Do a Noid light test of each one to make sure the PCM is pulsing them (activating them).
- You can find the fuel injector tests here:
STEP 4: Test the compression of each engine cylinder. Testing the engine's compression is one of the most forgotten misfire diagnostic tests. You'd be surprised how many misfires are due to low engine compression in one or two cylinders (usually diagnosed after the Toyota's owner has spent a bundle on ignition parts).
Here are my suggestions:
- Perform an engine compression test.
- Check for vacuum leaks.
- You can find the engine compression test here: How To Test Engine Compression (Toyota 1.8L).
The above list of steps may seem/sound like troubleshooting a misfire is a complicated thing but it really isn't. Depending on your level of ‘wrenching’ experience, this is something that you can accomplish without taking it to the shop.
What Tools Do I Need To Test The Misfire Code(s)?
Finding the exact cause of the misfire codes or misfire condition is possible with the proper tools. Without them, you won't be able to diagnose/troubleshoot those issues on your 1.8L Toyota car.
Depending on what the root cause of the misfire is, you may need several tools. Most of these you can buy online, none of these will break the bank and I'll make some recommendations on them. Here's a guide to some of the basic tools that can be and are used:
- Ignition System Tests:
- A spark tester.
- A multimeter.
- A test light.
- Fuel System Tests:
- A Noid light.
- A fuel pressure gauge.
- A multimeter.
- Engine Mechanical Tests:
- A compression tester.
Now of course, you'll also need basic hand tools like: screw-drivers, ratchet wrenches, sockets, etc. You'll also need a generic scan tool to retrieve the diagnostic trouble codes (DTCs) from the computer's memory (if OBD II equipped).
Keep in mind that using the right tool for the job will save you time, frustration, and /or keep you from damaging the component that you're testing.
In Conclusion
Testing a misfire or a rough idle condition on your 1.8L Toyota equipped vehicle can seem hard but if you follow the above troubleshooting steps, you'll be able to avoid replacing parts that are good.
Take advantage of the other tutorials in the 1.8L Toyota section since I've written all of them from practical every day experience and tailored for the home mechanic. You can find them here: Toyota 1.8L Index Of Articles.
If this info helped, spread the word!
More 1.8L Toyota Diagnostic Tutorials
You can find a complete list of 1.8L Toyota tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The TP Sensor (1998-2002 1.8L Toyota).
- How To Test The Fuel Injectors (Toyota 1.8L).
- Diagnosing a Toyota Corolla Misfire Case Study (Toyota 1.8L).
- How To Test Engine Compression (Toyota 1.8L).
- How To Test For A Blown Head Gasket (Toyota 1.8L).
If this info saved the day, buy me a beer!
