Misfires in one bank of V6

[Biologist]

Hello,

I bought a 1999 4runner with ~250k miles and the 3.4L V6 yesterday and it has a very bad misfire problem. Codes I am getting are P0300, 302, 304, and 306. So the entire driver's side bank has misfires. The car idles horribly and gets bad gas mileage and has no power. I have changed the spark plugs which I thought might fix it but it didn't change anything. The condition of the spark plugs in that bank were different than the working bank. They were blacker and a little wet looking, especially for 2 and 6.

I have also changed the oil, used injector cleaner, seafoamed, cleaned throttle body and MAF etc. but those things haven't fixed the problem. Anybody got any ideas on what it could be that would make the hole bank of cylinders misfire? Maybe cam position sensor? Anyone ever had that go bad? I know there is a cam position sensor error code but I am not getting that one.

Thanks for any help!

 

[drdolittlerwc]

How about your wires...they could be cross firing or grounded.

You could also pull one and check for spark, sounds like you're not getting any spark at all.

 

[Biologist]

I bought an inline spark tester from harbor freight and tested all those cylinders and the spark is good, the light lights up and flashes and increases in frequency when I increase the rpms.

 

[jkoni426]

maybe that side's cam pulley isn't timed correctly, might wanna check compression also.

 

[Biologist]

I will buy a compression tester and check it out.

 

[jkoni426]

I will buy a compression tester and check it out.

pretty sure autozone has them in their loan-a-tool program fyi

 

[Firstborn10]

I would strongly recommend checking your coil packs and spark plug wires. My girlfriends '96 4runner had the same problem, and it ended up being a cracked spark plug wire that caused a bad coil pack. We ended up just replacing all the wires and just the one bad coil pack, and it fixed the problem.

 

[jgue467]

Yeah

I would strongly recommend checking your coil packs and spark plug wires...

swap coil packs, see where problem is then.

 

[TheDurk]

First is to carefully recheck your wiring against the below. If it checks out, then I'd open up the top timing cover enough to eyeball timing marks on the cams. Set pointer on crank pulley to "0" and you should be able to see if valve timing is right by checking the marks. Gotta be one of those two or something very bad in that valve train so step 3 is compression test.

Not gonna be cam position sensor 'cuz there is only one of those. Not gonna be coil packs 'cuz they are all firing on passenger side and it's a series circuit.

 

[drdolittlerwc]

I bought an inline spark tester from harbor freight and tested all those cylinders and the spark is good, the light lights up and flashes and increases in frequency when I increase the rpms.

Even though they are showing that spark is there, it could be grounding out somewhere and not reaching the plug.

Also, you can test the strength of the spark by pulling a wire and stick a screwdriver or some piece of metal in the plug end of the wire and hold the screwdriver up next to a ground then turn over or start and see what kind of spark you get. If it's pale, then it's weak. You want to see a fat blue spark.

 

[Biologist]

Thanks everyone for all the help. I am going to rent a compression tester tonight at Autozone and also get a mechanic's stethoscope at Harbor Freight and listen to the the injectors and make sure they are all working. I read of some other people having problems like mine that were caused by a faulty injector. I'm also going to double check the spark plug wiring.

I rechecked the codes last night and I also had a P0303 code, the first time I have seen a misfire from the other bank of cylinders. Not sure if that is just caused by the other bank or if it is indicative of a problem with all of the cylinders, not just one bank as I previously thought. The car is also backfiring now at idle.

 

[drdolittlerwc]

I rechecked the codes last night and I also had a P0303 code, the first time I have seen a misfire from the other bank of cylinders. Not sure if that is just caused by the other bank or if it is indicative of a problem with all of the cylinders, not just one bank as I previously thought. The car is also backfiring now at idle.

May also have jumped a tooth on the timing belt. A comp test should show something there too...

 

[Swimmerboy2112]

I had this exact same problem with the engine misfiring bad and showing all kind of misfire codes check to make sure that your charcoal canister is hooked up all the vacuum lines in place that was my problem one vacuum line was disconnected and it threw all those codes.

 

[Biologist]

The 4Runner is fixed!

Thank you to everyone for all of the suggestions. I checked the spark plug wiring with TheDurk's diagram and somehow someone in the 4Runner's previous life had switched the #4 and #6 spark plug firing. How anyone could do this and not realize they had done something horribly wrong is beyond me.

I really appreciate this guys, I am buying a new house and this car is currently my only car and I was going to be in a world of hurt if I couldn't get this fixed.

 

[Firstborn10]

Great to hear! Yeah when my girlfriend and I put back together her spark plug wires, we made the same mistake :doh: but we immediately fixed it after a quick google search! Glad to hear it's all good!

 

[TheDurk]

The 4Runner is fixed!

Thank you to everyone for all of the suggestions. I checked the spark plug wiring with TheDurk's diagram and somehow someone in the 4Runner's previous life had switched the #4 and #6 spark plug firing. How anyone could do this and not realize they had done something horribly wrong is beyond me.

I really appreciate this guys, I am buying a new house and this car is currently my only car and I was going to be in a world of hurt if I couldn't get this fixed.

Another save for the plug wire diagram!!! Seemed like a very good bet for your symptom set...

You are far from the first, and certainly not the last.