Chasing misfire

TW44LR

TW44LR

New member
I know I know, this topic has already been beaten to death. I have researched this a fair bit but just wanted some expert advice. I’ve been getting an intermittent misfire mostly on cylinder 5, code p0305. One time it gave codes p0300 0304 0305 0306 but most commonly p0305 or just p0300. I changed the spark plugs on Thursday so 3 days ago and it was fine until last night/today it started happening again. When I changed the spark plugs I also cleaned the MAF sensor, throttle body and changed out the PCV valve, I also switched the coil pack on cylinders 3 & 5 to see if it was maybe the coil packs. The code didn’t follow to cylinder 3 and I replaced the spark plug wires when I did the spark plugs last ~ 30k mi ago so I don’t believe it’s those. It seems to only occur after i drive it and then turn the engine off for less than 30 minutes when I start it up again it has a rough idle up to about 2k rpm’s. This along with everything else leads me to believe that it’s the fuel injectors, more specifically the one for cylinder 5. If I’m wrong or there’s anything else I could try to make sure, let me know. If not I’m wondering where the consensus on getting fuel injectors would be and if I should just replace all while I’m at it or just do the one and not worry about the others?


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Picture of old spark plugs. #5 doesn’t look overly bad to me but the electrodes seem to be a little more black than the others


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You probably know this, after doing all that maintenance, you performed learning value reset and idle learning I assume.
 
Just go back to basics:

Fuel +
Air +
Compression +
Spark +
All occuring at the proper time =
Normal running engine.

Sounds like you did spark-nope.
Air is unlikely an issue-nope.
Timing (both valve timing and spark timing) is probably not it since it’s one cylinder mostly and generally one major failure would affect more than one cylinder-nope.
So now you’re down to compression and fuel.

Compression testers are cheap, may even be rentable. I doubt it’s a compression issue since it’s intermittent and generally a compression issue is constant. But you could try.

That leaves fuel. This is further broken down into supply and delivery.
Unlikely a supply problem (pump, filter, bad gas, low pressure etc) since, again, it’s a single cylinder and generally an overall supply issue would affect more than one.

So now it’s down to delivery: injector, computer, wiring in between. You could install a little light bulb (special version is called a noid light) piggy-backed onto the wires of the suspected injector and look for a flashing bulb WHILE THE MISFIRE OCCURS. This would rule out the computer and harness. You want to see a flashing light (which is a command to fire the injector) WHILE MISFIRING. Means the injector is no good. Now, a non flashing light would lean towards a harness or computer issue.

It’s probably the injector. Had a similar issue back in 2020. Went through all the same steps since I already have all the tools. It’s about the same amount of time to do one injector vs all. All injectors are same age, same amount of cycles. So I’d say do them all if you settle on injectors.

I went through 5-0 motorsports. Small deposit to return old injectors. They’re reman’d OEM.
 
octanejunkie said:
I would swap coil packs and see if the problem moves with the coil

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When I changed spark plugs I swapped coil packs in cylinder 3 & 5 and the code didn’t follow to 3 but stayed on 5 so I believe coil packs are ruled out.


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Jakeepoo3 said:
You probably know this, after doing all that maintenance, you performed learning value reset and idle learning I assume.
Click to expand...


I pulled EFI fuse for ~15 mins if that’s what you mean and cleared codes with my ultragauge


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TW44LR said:
I pulled EFI fuse for ~15 mins if that’s what you mean and cleared codes with my ultragauge


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Here's part of what I meant. There's a couple more pages describing the procedures. Could be a possible cause of your high idle inconsistentcies..
 

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Most likely injector number 5. Have to take the plenum off to test number 5 but should be 13.8 ohms. at 68 degrees, ohms could be higher due to temp variations.
 
Jakeepoo3 said:
No learning involved with them period? I've relearned vehicles much older. Thanks for not griping me out this time! My bad
Click to expand...
The procedure itself doesn't exist for 3rd gens (or at least I have not been able to find it on techstream). The learned values reset after either disconnecting the battery or removing the ecu fuse and then will start relearning as you drive it.
 
spartacus said:
Most likely injector number 5. Have to take the plenum off to test number 5 but should be 13.8 ohms. at 68 degrees, ohms could be higher due to temp variations.
Click to expand...

I had an issue with intermittent misfires. Same codes and everything. It was an injector that would get stuck after the truck warmed up. Would run fine cold, but as soon as I shut it off it'd throw a code. It's not too bad of a job to do and a good used one is fairly cheap. I have 5 if you can't find one.
 
brillo_76 said:
You can verify the plugs wire with a mulitmeter.

https://www.toyota-4runner.org/3rd-g...on-5vz-fe.html

When was the last time the fuel filter was changed? Do you ever run some fuel injector cleaner with you gas tanks full.

Do you have good fuel pressure up to the injector rails?

Its possible to be spark or fuel at this point until you rule things out. :-)
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I’ll have to find my multimeter and check wires. Fuel filter was changed ~30k miles ago when I picked this rig up and changed a bunch of stuff up to get it up to snuff. I have been running some Lucas fuel injector cleaner since I changed the spark plugs last Thursday, so far no change but I haven’t ran a full tank of fuel through it yet. How would I go about checking fuel pressure?


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jhuerta22 said:
I had an issue with intermittent misfires. Same codes and everything. It was an injector that would get stuck after the truck warmed up. Would run fine cold, but as soon as I shut it off it'd throw a code. It's not too bad of a job to do and a good used one is fairly cheap. I have 5 if you can't find one.
Click to expand...


That’s what I’m thinking. Is it worth it to just do them all or just the one? Where did you get yours from?


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spartacus said:
Most likely injector number 5. Have to take the plenum off to test number 5 but should be 13.8 ohms. at 68 degrees, ohms could be higher due to temp variations.
Click to expand...


Gotcha I’ll try to test it this weekend. If it tests bad should I go ahead and replace them all or just the one? Any good sources on where to get them?


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Bad Luck said:
The procedure itself doesn't exist for 3rd gens (or at least I have not been able to find it on techstream). The learned values reset after either disconnecting the battery or removing the ecu fuse and then will start relearning as you drive it.
Click to expand...

There must be a procedure to manually reset it. Like my 94 xj it's a key and headlight off/on sequence. When you add higher performance goodies it's better to relearn from scratch and much quicker. I have awesome results doing this. I think I actually did this in my 2010 runner with a key and e brake sequence after servicing all PCM inputs now that I think back.. you can loan me your techstream though ��
 
TW44LR said:
Gotcha I’ll try to test it this weekend. If it tests bad should I go ahead and replace them all or just the one? Any good sources on where to get them?


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Ever used a non dismantle injector cleaner? Hooks directly to fuel rail service port and compressed air to blow those suckers out brand new. Only 60 bucks and priceless results. The dealership and bad luckers might get p1ssed if they see this. They conceal info such as. I use it on all my old rigs. Injectors good as new.
 
TW44LR said:
Gotcha I’ll try to test it this weekend. If it tests bad should I go ahead and replace them all or just the one? Any good sources on where to get them?


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Click to expand...

It's up to you. I have had a misfire and replaced injector 3 with oem and have added close to 100k miles without any issues.
 
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