Hi all,

Great forum! Been reading & learning A LOT. Looking for some advice. Sorry for the long post.

So here's the scoop....While driving to Whistler last weekend, my 4Runner (93K miles) starting missing, particularly while climbing in overdrive. On the way back, the check engine light came on. Service shop (Goodyear) ran a diagnostic and said #3 cylinder was misfiring. They scared me away with a $740 bill to change the plugs & wires and wouldn't even tell me the code they got from the OBD II. I'm no mechanic, but I'm learning

So, I've done most of the work Goodyear recommended and what I've read here in the forum:
-Replaced old Denso plugs with Bosch twin tip platinum 4301. Old #3 plug was rusted and looked cracked. Thought for sure I found the problem. Could those have been original plugs?! Wow!!
-Replaced spark plug wires with OEM wires. Resistance of old wires were only slightly higher (ex 15.8 vs 15.0 KOhms)
-Replaced fuel filter.
-Replaced air filter.
-Checked PCV valve (sucks good, rattles nicely).

After that, it ran perfect for about 1 day. But now the misfire is back, but only occasionally. The check engine light hasn't come back.

Any thoughts?
Can an OBD II scan tool find the problem without the MIL on?
How do you tell if a coil has gone bad?
Are the Bosch plugs junk?

I will be sure to post/contribute my final solution.

-Jagin

 

Sounds like a bad coil pack to me.

 

Don't know much about the 4runner, but my latest misfire incident was in an Audi and was cured with new plugs and injector cleaning. Also, it seems most recommend the toyota supplied sparkplugs

 

How do you test a coil to see if it's gone bad?

 

Ah, just found the coil resistance test parameters in my Chilton manual. Gotta check that tomorrow.

 

You should change the plugs back to the OEM Densos, many have had problems with the Bosch Platinums.

They also make a very cheap OBD II reader for you to use in the future should a code come back:
http://www.harborfreight.com/cpi/cta...emnumber=46030

Other things to do include:
Clean the throttle body (carb cleaner)
Clean the IAC valve (carb cleaner)
Clean the MAF sensor (contact cleaner)
check the TPS for operation (resistance)
check the coil packs for operation (resistance)
You might consider just replacing the front O2 sensor

 

What did you gap those new plugs to?

 

I just had the exact same problem.

1996 4Runner TRD Supercharged with 133k miles.

I was getting bad hessitation, especially under load and a #3 misfire code AND a system running lean code.

Turns out I was still on the original plugs...I had replaced the wires a while back and thought my brother had done the plugs..he hadnt *LOL*...so I changed the plugs (thanks to Gadget and underdogracing)...new pcv just because its a cheap replacement and hadnt been done yet. I also cleaned the MAF (recommended by Gadget). I have a new O2 but havent put it on yet. Disconnected the battery to let everything reset. And it runs fine now. If I still had the problem, my next step was to check the coilpack...but it seems to be running fine now

 

I would get rid of the Bosch plug's, never had any luck with them, install Factory ND, find a shop with a SUN 500 Scope, have them do a Diagnosis on the ignition, top that off with a Motorvac Service, GOOD LUCk

 

I didn't gap them. The Bosch box and guy at Schucks indicated they were pregapped to .044. Besides, I wouldn't know how to gap these goofy twin tip plugs that seem to use a circumferential gap.

 

Folks, remember URD has a good selection of TRUE DENSO plugs in stock for the 3.4 V6.

Gadget

 

My final conclusion: The #3 coil pack was bad.

I pulled all the brand new Bosch plugs and found burn marks on the #3 plug again. I tested all the coil packs for resistance, but they all checked out fine. But the #3 coil boot looked discolored compared to the other two. So, I labeled the plugs and coils with their original position and reinstalled them in different cylinders. After 3 days of driving, the plug under the #3 coil showed burn marks again.

I replaced the #3 coil pack and installed 6 new Denso plugs from my local Toyota dealer ($115 total) and she's run great ever since.

Props to <96 Runner> for calling it out right away. Thanks everyone for your input.

 

Glad to know you got it solved and what the problem finally was.

 

Cool! Thanks for getting back to us about this, a follow-up is always a good thing.

 

I believe AutoZone will read your codes for free.