Leebo
New member
I know there are several threads on this forum about misfires, ignition failures, etc... but I thought I'd chime in with another story that might help someone else. This is for a 1999 4Runner SR5 with about 155k miles. I'm the original owner.
It started out with a classic rhythmic stumble that I've experienced before that was the result of a failed plug wire. The CEL was on and the codes read P0300 and P0306. I through a new set of NGK plug wires on and the problem seemed to be gone, but then resurfaced the next day. I soon realized a pattern to the problem; with the engine cold, on start up it would run fine. If the engine were stopped then allowed to sit for at least 10 minutes, once restarted the misfire would surface again. If I shut off the engine and let it cool for several hours, once restarted it would be fine. It was as if heat were related, but only if warmed up on startup.
When the symptom would surface, it felt like an even, rhythmic stumble, not erratic... making me feel like it was isolated to one cylinder. Being that the codes were P0300 and P0306, I was convinced that it was an electrical/ignition issue and not fuel. At least that's what I had rationalized in my head at the time.
So, back to shotgunning parts... Since the plug wires were new, I made sure they were making a good connection. From there, I tried more and more things, checking to see if the problem went away after each attempt: new NGK plugs, new coil on cylinder 3 (since that feeds cyl 6 through a plug wire), new coils on cyl 1 and 5. No improvement other than when the engine would momentarily run right, it ran maybe a little stronger than before.
After poking around the forums some more, I read where others had similar misfire symptoms and it ended up being a fuel injector. I had already shotgunned parts and they weren't too horribly expensive, but new fuel injectors were a bit pricey even at the friendly local auto parts stores. I was running out of options short of yelling 'uncle' and taking the car to a shop for a pro to fix. So after looking around I found a reconditioned fuel injector on rock auto a lot cheaper than new ones and so I bought one. I took the intake manifold off and replaced the #6 fuel injector. After 3 weeks since the swap, the problem has not resurfaced so I consider it fixed now.
It still puzzles me how the engine can report a P0306 which is ignition related, yet the source of the problem had to do with a fuel injector. I guess my understanding of how the PCM determines a fault tied to a P0306 is wrong; wouldn't it just see an unexpected voltage level at the coil? i.e. not discharged as expected? I don't understand how the presence of fuel in the chamber, or lack thereof would have any affect on this. Clearly I'm wrong since changing the injector fixed it, but I still don't get why. Any thoughts on this?
It started out with a classic rhythmic stumble that I've experienced before that was the result of a failed plug wire. The CEL was on and the codes read P0300 and P0306. I through a new set of NGK plug wires on and the problem seemed to be gone, but then resurfaced the next day. I soon realized a pattern to the problem; with the engine cold, on start up it would run fine. If the engine were stopped then allowed to sit for at least 10 minutes, once restarted the misfire would surface again. If I shut off the engine and let it cool for several hours, once restarted it would be fine. It was as if heat were related, but only if warmed up on startup.
When the symptom would surface, it felt like an even, rhythmic stumble, not erratic... making me feel like it was isolated to one cylinder. Being that the codes were P0300 and P0306, I was convinced that it was an electrical/ignition issue and not fuel. At least that's what I had rationalized in my head at the time.
So, back to shotgunning parts... Since the plug wires were new, I made sure they were making a good connection. From there, I tried more and more things, checking to see if the problem went away after each attempt: new NGK plugs, new coil on cylinder 3 (since that feeds cyl 6 through a plug wire), new coils on cyl 1 and 5. No improvement other than when the engine would momentarily run right, it ran maybe a little stronger than before.
After poking around the forums some more, I read where others had similar misfire symptoms and it ended up being a fuel injector. I had already shotgunned parts and they weren't too horribly expensive, but new fuel injectors were a bit pricey even at the friendly local auto parts stores. I was running out of options short of yelling 'uncle' and taking the car to a shop for a pro to fix. So after looking around I found a reconditioned fuel injector on rock auto a lot cheaper than new ones and so I bought one. I took the intake manifold off and replaced the #6 fuel injector. After 3 weeks since the swap, the problem has not resurfaced so I consider it fixed now.
It still puzzles me how the engine can report a P0306 which is ignition related, yet the source of the problem had to do with a fuel injector. I guess my understanding of how the PCM determines a fault tied to a P0306 is wrong; wouldn't it just see an unexpected voltage level at the coil? i.e. not discharged as expected? I don't understand how the presence of fuel in the chamber, or lack thereof would have any affect on this. Clearly I'm wrong since changing the injector fixed it, but I still don't get why. Any thoughts on this?
