Hey folks,
anyone have specific issues regarding 303 (cyl 3 missfire)
And 300 (multiple missfires) on their v6 3.4 4 runner?
under a load.....stutters heavily, cold running nightmare and then flashing CEL . Thx !!

 

If you've check plugs wires and coils and coil boots, moved coils around and all looks good and missfire is staying in effected cylinder I would suspect since you have a 99' with updated injectors one of them is causing the missfire, I've delt with that for a friend and it acted very similar to your description. The 99 injectors seem to be failing, haven't seen many 2000-2002's doing this yet though and they have the same injectors so not sure what's up.
if you had any timing work done recently it could also be the crank sensor or crank rotor missing teeth, cam sensor, coolant temp sensor for ECU and even a knock sensor.

 

I’m another vote for bad injector. I spent the better part of a summer a couple years ago chasing down a heat soaked intermittent misfire.

As stated above, swap spark plug locations, clear codes, drive for 100 miles and see if the miss stays at 3 or moves to wherever #3 plug ended up.

Do the same for the coil pack, swap, clear, drive, and monitor.

Then do the same for the plug wire, swap, clear, drive, and monitor.

If the CEL code moves to a different cylinder as you move parts, then you know it is the part that got moved that is the problem. If the CEL stays at #3, then it’s either the injector or the signaling side that tells the computer when to fire that cylinder. If it stays at the same cylinder, I would lean more toward to tone ring on the crank versus the crank sensor because if it was the CPS it would malfunction for any and all cylinders not astronomically coincidental to always the same cylinder.

 

Great info here guys.....thx ...gonna do some switching tomorrow morning to determine whats up.
i'm hoping for a simple spark related issue.
crazy though.....it will run great for a while without a load....then run like junk no matter the rpm. Grrrr!!
The most frustrating thing with the 3 4 v6 is how a plug problem, maf sensor issue and fuel injector issue can all feel the same !!

 

That sounds a lot like heat soak. Basically an electrical component that works when it’s cold, but as it gets warm it starts to fail. From experience, I would suggest an injector, but the diagnostic flow chart will say to test the coil first. You can test it could with a multimeter and then put it in an oven set to 200*F and test it again.

 

Well.....i'm embarrased to admit that i got Snafu'd by a
BAD 6 month old NGK spark plug...... did a complete switch, cleared codes then switched only the plugs. Ugh!
But.......great for me....leave those pesky injectors right where they are....after 328,000 miles!
Thx guys....yotatech to the rescue!!

 

Did you get twin electrode plugs? The single electrode plugs cause trouble.

 

Yup....NGK Twin electrode 6 -8 month old. My runner ate up single electrode plugs.....2 of them cracked.
whats up with runners and plugs?

 

My guess is the waste spark system firing the plugs on every compression stroke. After doing a couple of factory original spark plug changes and finding Denso plugs on one side and NGK plugs on the other side I can say that the Toyota packaged Denso plugs held up noticeably better with a lot less wear, and came out way easier after 10-15 years and 150,000miles, I suspect the anti seize coating is also better. I was surprised to see this on a 2010 Taco 4.0L, Denso plugs came out pretty good with little wear, and I had to really work on the NGK plugs to get them out, even soaked them with ATF/acetone mix and they still squeaked all they way trying to get them out, I was sure one of the NGK's was going to snap off in the head:/, a different plug design with deep threads on the 4.0L but a huge difference in every way. And the 5vz-Fe Sumitomo plug wires with the mfg date on them fit a lot better than NGK wires, just changed my original 1999 sumitomo wires with 2020 sumitomo wires and it runs as good as it did with the 1999 wires which says a lot.