P0303 Misfire

Hello TW, I'm new here so I thought I would introduce myself and see if you have any insight on my issue.

I just bought a 3.4L 1996 Tacoma with about 182,000 miles It has some serious bro lean!!! The PO removed a leaf from the rear leaf pack because it "rides nicer" (taking recommendations on a 2.5" rear lift!)


It came with a wonderful feature - a CEL with code P0303. The PO told me that the last time he changed the spark plugs was 14,000 miles ago. That didn't sound too bad to me, so I didn't immediately suspect the plugs to be the issue, but I decided to pull them and replace them anyway along with the coils and the cables. The tips on the old plugs were very eroded and they were not OEM. Almost every plug looked like this:


And the ignition coils:


When I was inspecting the valve cover while replacing the plugs I noticed that the rear passenger side has developed a small leak, leaving the valve cover pretty dirty on that side.

After replacing everything, I was pretty happy to see that the CEL was cleared. Unfortunately, as I drove to AutoZone to return the torque wrench I borrowed, the CEL came back on Same code. My next thought was that it could be a fuel injector issue, so I bought a bottle of Lucas fuel system cleaner and put a few miles on the truck. While I was going for a ride, I took the opportunity to photograph a very rare sight - snow in Joshua Tree!


Anyway, the CEL is still on (not sure if it will go off after the fuel system cleaner works its course). Does anyone have any other ideas on this one?? Thanks all!

 

So you replaced the spark plugs, plug cables and coil packs all with OEM parts?

Is it running different with the light on?

 

Yes! All OEM replacements

 

And it’s running the same or different with the cell light on? After the new parts were put in

 

Before and after the CEL - its been running the same. I know the code is a misfire, but to be honest it's running just fine, no rough idling and I can't actually hear it misfiring

 

Are you sure you cleared the code completely?

Maybe try and clear it again.

Typically when you replace the coils, plug wires and plugs this should fix this code

 

No, I did not use a tool to clear the code - I just applied the fix and was under the assumption that the code will be cleared when it's no longer detecting the problem. It did clear for a few miles, but came back on. I also don't have access to a scanner that can clear the code. Will unhooking the battery do it?

 

Ok, you need to clear the code.

You can stop by most auto shops, advance, pep boys and have them clear it for you

 

Thanks, I'll try tomorrow and see if it stays off!

 

A scanguage II is something you should look into for your truck.

You can get the cell codes, you can clear the codes, have the REAL engine temperature, fuel trims, Intake temps,
timing, open loop, close loop indicator info and a lot more for 125.00.
Super easy to install into the OBDII port and your good to go

 

Thanks man, this is exactly what I've been looking for since I plan on doing some of my own work on it

 

Read through my build thread, I’m sure it’s in there and some other ideas. We both have close to the same year and motors

 

I'll definitely give it a look. Nice truck

 

@1997tacomav6 bad news, I went to a shop and cleared the code with their scanner, but the light came back on after driving it around for a minute

 

So the plot thickens here.

2 other possibly are It could be your running lean.

MAF issues, 02 sensor,
Fuel filter under the cab is dirty

 

I'll clean the MAF (i'm sure it needs it) and take a look at the 02 sensor and fuel filter. Going to check the compression today or tomorrow as well

 

Do a general inspection of the vacuum hoses too and or exhaust leak before the 02 sensor.

There should have been a different code I think if there was a vacuum leak but a vacuum leaking hose is usually the number one reason for a lean code or messed up AFR

PCV valve check and the PCV hose while your there.

 

When I was doing the spark plugs, the hoses that I did have to disconnect were somewhat brittle on the ends, but it didn't look like any hoses were cracked. I'll take a closer look at those and the PCV tomorrow when I pull apart the MAF to clean it.

 

Remember to make sure the Ignition is off and that the MAF is normal air temperature, if it’s hot from driving the spray can can damage the bulb from the aerosol spray. Let it dry off before you start it too.
Use the spray cleaner to clean the bulb and there’s a top section too that gets missed that needs cleaning too

 

@1997tacomav6 update - I checked the compression in the engine, I was checking each cylinder twice and I managed to get through the passenger side before I killed the battery. The readings from the passenger side are: 1 - 195, 3 - 180, 5 - 195. Going to button it back up and drive it around to charge the battery.