Cylinder Misfire Troubleshooting... and other maintenance questions

Greetings, my 2006 Taco ran rough first thing this morning and I pulled P305 and P0137 (IIRC - it was the rear O2 sensor code). I swapped Cylinder #5's coil with Cylinder #3's and cleared the codes. After starting the engine, I got a flashing check engine light and code P303. Obviously the problem followed the coil, or at least that is my thinking. My plan, given the 180,000 miles on the vehicle, is to replace all the coils and spark plugs at this time.

Since I have an abundance of time on my hand, I was also considering pulling the fuel injectors to send out for overhaul. Thoughts on doing that? I think I was looking at witchunter's services for that. Before I get ahead of myself, I did notice oil on both coils - so I am thinking the valve cover gasket is leaking I did this job on my son's 1998 4Runner a few months back... to be honest I had to call in some help towards the end.

So my questions are: (1) Should I consider the misfire issue narrowed down to the coil? (2) Opinions on what brand of coil to use as replacements (3) Might it be a bit easier to change the valve cover gasket(s) on this motor vs. others (3rd Gen 4Runner), and (4) Thoughts on over hauling the injectors, since I will have all that stuff pulled off the engine anyhow.

Thanks!!

 

All good questions. Interested in the answers as well

 

Hi SNP

I would change both coils and plugs. The problem followed the coil so you know ones bad and rest may follow it's lead.
Changing valve cover gasket should be straight forward just don't rush yourself. And I'm sure there's a thread here for that repair.
If you need injectors I would replace with new. I'm not one for rebuilt parts only new but that's my opinion.
Check out reviews on parts and go with what you feel is right. Again search here lots for better info.

 

Cylinder 5 or 6 misfire on a ‘05 or ‘06 Taco is a possible indication of a head gasket failure. Many people with these trucks have a failure at about 173K miles. I know you mentioned that swapping the coil made the code follow, but you should still keep an eye on your coolant level.

 

That sounds scary.

 

It’s a big job to replace the head gaskets.

 

Hence my fear. I wouldn't try that one.

 

So far I've ordered the following:

Fel Pro Perma Dry Gasket Set #50634
1 x Denso OE Coil
6 x Denso Copper Spark Plugs K20HR-U11

$98.50 all from Advance Auto. I have Toyota gasket maker from the '98 4Runner job. Will sleep on the injector re-build, and will keep fingers crossed it doesn't end up being a head gasket issue. Perhaps a compression and/or leakdown check when I have the truck inspected in April??

Also, would anyone know what sections in the factory repair manual to reference? The copy I found only (thanks to this forum) does not have an index.

 

Some people have the opinion that their method of diagnosing head gasket leak is the only way to do it. Here are my preferred methods.

1. Disable the fuel or ignition system so it won’t start. Fill the radiator completely full. Have someone crank the engine while you watch the coolant level. If there is a head gasket leak, the water will rise every time that cylinder comes up on compression. A severe head gasket will cause the coolant to shoot up like a geyser.
2. Disable the fuel or ignition system. Remove the spark plug from the suspect cylinder. Pressurize the cooling system with a cooling system pressure tester for about 30 minutes. Hold a piece of white paper sort of over the spark plug hole. Have someone crank the engine. If you see coolant color on the paper, you have a head gasket leak.
3. Use a borescope in the spark plug holes to view the piston tops. A piston that looks cleaner than the rest is an indication of a leaking head gasket.

 

The new plugs are in, as well as the new ignition coil. Engine running smooth, no codes after ten minutes at idle.

 

Finger crossed. Let us know what it does when you fire it up tomorrow morning.

 

If you got a lot of spare time or can do the work over a couple days I don’t think it is that hard. I recommend you do proper diagnostic work before disassembling too much.

 

Take a bore scope down each cylinder. If you see a shiny pistons top chances are water is getting in and steam cleaning the piston.

 

So I've completed the valve cover gasket replacement. No CEL, engine running fine. I think it was a tad bit easier than on the 98 4Runner, although I was impressed at how similar the two engines are laid out.