3.4L #3 and #6 misfire

I'm working on a friend's truck which has codes stating cyl 3 & 6 misfire. First things first I pulled the plugs, tested for spark, moved ignition coil pack to another cylinder and see if problem follows, did a compression check, looked for vacuum leaks, listened for clicking injector, checked wires and plug for igniter, all of these tests came back normal, everything is functioning but I still have a misfire on 3 and 6. I have a scanner and have cleared the codes several times and code comes back every time. We decided to replace 2 coil packs which were the original Toyota packs due to one of them being new and not on the misbehaving cylinders, all new plugs, and wires were replaced about 4 months ago.

Just for fun I decided to pull the fuel filter and blow through it to see what kinds of fun stuff comes out, nothing out of the ordinary, brownish blackish fuel. Reinstalled and the misfire went away for about 1min and came back! Wth? How could a clogged fuel filter cause a single cylinder on each bank to misfire which coincidentally are ignited by the same coil? The filter is pretty easy to blow air through and I feel like the fuel pump wouldn't have an issue pushing fuel through it with proper pressure. We ran out of time for the day so are going to replace fuel filter tomorrow but before I do, any ideas?

My next plan is to pull the intake manifold to rebuild the injectors and test fuel pressure, not necessarily in that order.

 

Wouldnt it be the actual wire that feeds the coil is bad if you played swaptronics with the coil and it still held the result on 3 and 6? Or the ecu? If indeed 3 is connected to 6 i dont remember which one it jumps to

 

You are absolutely right and thank you very much for the reply. I used a multimeter and a little LED bulb to verify that the coil is getting a signal and it indeed is. And yes, cylinders 3 and 6 or ran off of the same coil.

 

So you're getting DTC P0303 and P0306, and then swapping the coil pack that fires those cylinders with another coil pack and still getting the same P0303 and P0306 misfire codes? What did the plugs look like when you replaced them? Water getting into the cylinders can cause a misfire. Is the misfire felt as well the MIL is set off? Or does it feel normal still when the MIL turns on from the misfire detection?

 

Did you exchange the coil pack together with its wire, or just the coil pack itself? If you exchange just the coil pack, then the wire between cylinders 3 and 6 could be the problem. Just sayin'.

 

The plugs look great, a little black with slight white near the top of electrodes. Yes, p0303 and p0306. Moved the coil and wires and it did not follow, still 3&6. I don't think water is getting into the cylinder but I could be wrong.

Update: we replaced fuel filter and it ran right for about 2 minutes and then started misfiring again. While driving it, I noticed that there's spitting and popping coming from the intake after about 20% throttle, very low power, and now the misfires moved to 2&6.

New wires, plugs, coil packs, fuel filter, good compression on all cylinders, disconnected cat converter and it isn't clogged. I get the feeling that it's either the injectors or fuel pressure regulator isn't regulating causing too high pressure which the injectors cannot overcome. I dunno but it's driving me nuts! Please help!

Thanks so much for all your replies!

 

Wait, what are the odds this thing jumped timing? That would explain the spitting and popping but so does an injector that isn't atomizing fuel.

Or maybe crank position sensor?

 

Verifying the timing is on, like you mention, is a good thing to ensure. Shouldn't be too hard to check the cam sprocket marks and the crank pulley timing mark. When was last time timing belt was changed? It's not common to jump timing but has happened.
Kind of a pain to do, especially just for diagnosing, but might be able to swap the injectors from those cylinders with cyl 2 and 5 or whatever and see if anything changes

 

Wait, so new misfire codes for #2 and #6 after what?

 

After a fuel filter change, the misfires went from 3&6 to 2&6. Doesn't make any sense to me.

We have an injector rebuild kit on the way and a new valve cover gasket.

 

Mosdef the injectors could be plugged. They tend to get clogged up when opening and closing. Mine did that to me intermittently, thought i had new faulty spark plug wires. Changed out the injector and hadn't had a issue yet (knock on wood) lol. Truck was running good once i parked the truck. Started it up when i was ready to leave and misse fire! Was puzzled for couple days lol.

 

Ya ive never really lucked out on an injector misfire, i had an 06 wrx with a really bad single cyl misfire, changed the injector cause its really easy to do on an ej25, and it ended up being a badly corroded harness. I know its not relatable to 5vz but just puttin it out there. Personally hope your not just chasing ghosts other than a bad coil or a bad connection somewhere. Also seen those youtube vids here and there where tapping a stuck injector might help to free it up, but seems too much of a coinsidence that it was originally 3 and 6 on yours which would seem to point to a bad coil or wiring. Best of luck to ya.

 

Hi guys. I own a 2007 Toyota Tacoma SR5 PreRunner 2WD 4.0 L. I looked for this topic because this issue of chronic, alternating check engine light and blinking engine light had been a regular occurence for me since summer of 2019, plus the infamous DTC P0306 which is now a familiar fixture for me. Don't get me wrong it is still a bad ass on the road. But, coming out of nowhere, something triggers it, then these pestering DTC P0306 pop up, and if you are not used to it, could stall you, like it did me once, in from of my son's school 4 way stop sign.

Background of the problem: we were driving it in August last year here in Southern CA, as we were shopping for an apartment; we were apartment hopping practically everywhere looking for that ideal place. As we stopped in one of the guest parking spots, I ran the engine idle for about 5-8 minutes. That was when I saw the A/C button started to blink as we steadily lost cool air. Turned it off. Then back on. Never went away. When we took a break in our search to pick up our youngest in his school, the A/C system went back to normalcy.

However, as I approached the schools 4-way stop sign, the engine choked and stalled. Took me 10 seconds to fire it back. As we sped to our old house, I noticed that the thermostat started to rise to near overheat levels. Since we were only about a quarter of a mile from our house, I went on. That's what when I saw white smoke in front of the engine bay. I lifted the hood. and discovered that the large hose connector hooking it to the thermostat housing was disconnected, basically spilling coolant on the road.

Here was what I did: 1. Did a radiator flush, the small radiator under the dashboard included. The radiator flush would have been it, but I had lingering doubts: did I blow my gasket? 2. I removed the thermostat from the housing and had the truck ran on distilled water. Did a test run without coolant and it was ok, no overheat. 3. I put blue devil thinking still of my gasket. That was when the dreaded DTC P0306 started popping up. I have an OBD scanner, ignored it by clearing but it was a nightmare of alternating check engine and blinking check engine light. 4. Compression test was negative. I did remove the intake manifold and replaced the valve cover gasket. No good as the code persisted. I checked all the vacuum hoses and replaced the PCV valve and its hose connector. The problem persisted. 5. I replaced the spark plugs, checked the wires, switched the coils but it still persisted. I checked the cylinder for presence of oil or coolant but found nothing. 6. Finally, before the move to our new place, I replaced the belt and realigned the marks to TDC and checked the valve clearance which was still within specks since it was already opened.

The issue was never resolved. Today, the dreaded choking came back and kept popping up even though I cleared with it my OBD scanner but I am suspecting that the vacuum hoses are the suspects for the code this time. I have a hard time accelerating and I could feel the lack of pressure, and intake of air is wanting.

Please help. What did I miss? I maintain our 3 Toyotas but so far this was the most challenging. Thanks.

 

Have you checked the resistance of your injectors? Should be (on my 1998 at least) between 14 and 16 ohms between the two pins coming out of the injector.