P0304 Code

Engine started skipping, P0304 code came up, cylinder 4 misfire. To check the coil I swapped numbers 4 and 6 coils to see if the code would follow to 6. I reset the code after the swap, fired it up with no code on #6. The truck idled fine, drove it roughly 10 miles with no issues.

I’m definitely not complaining but really don’t know if these coils can intermittently go in and out?? I’m assuming once they go they are dead or going dead?? Maybe the misfire will eventually go to #6.

Any input appreciated?

Regards,
Griff

 

Coils don't necessarily go in and out, but it could be a sign of pending failure. I'd run with it as-is for a few weeks and see if it returns on cyl4, or if it moves to cyl6.

A lot of guys on here replace them all at once, but a few have been fine just replacing the one that went out and not seen anything. If it were me, I'd wait for another misfire code. If it happens, because Denso coils are expensive, I'd buy two Denso coils from a trusted source (i.e. NOT scAmazon, fleaBay or WallyWorld), replace the misfiring coil, and keep the other as a backup for if/when the next one goes.

If the code stays on cyl4, even after the coil replacement, I'd be checking the spark plug for that cylinder. Or, if you know the spark plugs haven't been changed within the last 50k-60k miles, you may want to replace with some good quality NGK or Denso plugs to match what your owner's manual indicates is required, again buying from a trusted source (since fake plugs are rampant from some online vendors), and proactively replace them.

Don't buy off-brand coils. MSD is a hugely popular and trusted name in the ignition world, and we've seen some of the V8 guys (I know you're a V6) have issues with their coils on the 2UZ-FE.

 

Thanks for the advice and input, I’ll run it and see what happens and then go from there.

 

Another explanation could be the connector to the coil had a little corrosion and by unplugging and moving to another cyl and replugging it in could Havel improved the connection

 

OP, what's the mileage on your current coils? You could throw fresh springs and boots on them.

 

Truck started idling rough again so I figured the coil swap followed over to cyl6, didn’t check the CEL jus stopped and picked up Denso coil and put it on #6. It ran well for a couple days and now has an intermittent skip, CEL is showing P0171 on Bank one now….back to the drawing board!!! Suggestions are welcome at this point.

Also, the new Denso coil set me back $75 at Advance Auto…thought about just replacing all of them but wow at the price. After checking on the Internet I found them for less than $40 at Rock Auto. Now I have purchased stuff from RA in the past but that’s a huge difference in pricing??? Any comments on that?

 

RA is the go to source for Denso parts (also Summit Racing). Be sure to use the 5% discount code #235202980133346019

 

Thanks for the code, I’ve ordered Denso parts from Summit also, they are higher than RA.

 

Yes, they are...but sometimes the free shipping offsets that

 

I prefer Summit, and can pickup locally. RockAuto always has 5% off coupons. I usually go with whoever is cheaper, or whether I need it faster.

 

I just ordered a Denso Radiator from Summit for my Land Cruiser. RA didn't have it, and NAPA was TWICE AS MUCH!. I just found out that it's back ordered until October! That's probably OK since I'm buying it "just in case", but it irks me that they get to keep my money for 4 months! (The lead time when I ordered was 5 days). Had I known it would be 5 months I might not have done it.

 

So the misfire on 4 came back after putting the new Denso coil on 6, it’s odd though, I can start the truck up and it starts skipping, I can immediately turn it off and then restart it and the skip goes away and it runs fine. Anyone ever ran across this issue I’d appreciate input, just don’t want to start throwing parts on without having a plan. Thx, Griff

 

If it were me, I would not be making the assumption that it followed to # 6. Knowing any and all codes when it burps is beneficial.

This may fall into what they call 2-trip logic.



Has at anytime the MIL blinked or does it simply come on solid ?
I would stick with possible misfire on 4 as still a problem until a code gets set to lead you in another direction. For some reason there's not enough fuel at a moment in time(P0171-Lean)

 

I’m assuming that the MIL you called out is the same as the CEL…yes, it threw the cylinder #4 misfire p0304 code. I still don’t understand why turning it off and back on clears up the skip.

 

MIL = CEL = money light.

 

Yes, I tend to use the SAE terms Toyota uses as acronyms for items all thru out the FSM, sorry for confusion. In this case, CEL to you is what Toyota refers to as MIL(malfunction indicator light)

Unfortunately, intermittent problems, regardless of what one is working on, can be very frustrating.

Sometimes, unless one has a way to read live data, especially fuel trims, narrowing a problem down is difficult at best.
Take for instance your P0304....a number of items can be the cause, even as simple as an open/short wire at a moment in time, according to FSM diagnostic below. While frustrating and as you said, you just don’t want to start throwing parts on without having a plan.

 

You have the 3.4 V6, right? Does that have 6 independent coils or 3?

 

Damn now, why you trying to spoil my fun?

 

Twernt my objective but this 105 deg heat is doing a number on my G A S when it comes to working on truck

 

6 individual coils.

 

I hear you brother, heat index today down here in GA is over 100!!!

 

So I got started back on the misfire today…early am, before the heat took over. Pulled the plug on “4” cylinder, PO had installed Bosch plugs prior to my purchase of the truck. There was some discoloration on the plug but overall it looked to be good in shape with the gap set at appropriately 43. I went back with a NGK platinum with a 44 gap per NGK recommendation. I watched a video on Youtube on how to check a plug with a multimeter so I checked the Bosch accordingly. Had 4.5k ohm tip to tip which per the video should be good. But when I checked continuity tip to tip I had nothing which seemed odd??? So now it has a new plug and I’ve reset the code…will see what happens now.

 

Drove the truck 40 miles today after the plug swap pulling a trailer with lawn mower on it, no skipping and no CEL light…must have been a bad plug. Keeping the fingers crossed.

 

Yup, that was one of my initial suspects (bold below). I'd probably just proactively replace with NGK brand's part/model# listed in your Owner's manual, purchased from a legitimate local source. Bosch makes quality stuff, but you have absolutely zero way to know where the previous owner purchased from, and - to me, at least - it'd be suspicious for one plug to go bad so soon. At worst, you just reset your baseline on plugs and won't need to update again for 60k-100k miles, depending.

 

Replacing all the plugs is on my list of things to do. Gonna give a few days to see how things go. Appreciate all the input.