Hey all,

I have a 1998 4runner 3.4L V6 4x4 Auto 222,220 KMS.

I get pending and faults, check engine light comes on. P0300, P0302, & P0305. Misfire in cylinders 2 & 5. These codes happen all the time and have for 3 - 4 weeks. Once and only once did I get a pending misfire in cylinder 1. The truck is running extremely lean. Toyota used a four gas analyzer to test it. An average reading would be 14.7-1, mine is at 28.38-1. I get no other codes. The codes come on at idle and under load. There is also a knock at the bottom front of engine.

Replaced with OEM Toyota parts
Spark plugs
Wires
Coil Packs
Injector #2 (had bad resistance)
Engine Coolant Temp Sensor (had bad resistance)
Alternator
Batteries
All Ground and Positive wires
Air filter
Fuel filter
Timing Belt (20,000 kms ago)
Waterpump (20,000 kms ago)

Tested and is okay
Mass Air Flow Sensor
Throttle Position Sensor
Grounded each spark plug
Spark Plug Wires
Swapped Spark Plugs
Crank Position Sensor
Cam Position Sensor
O2 Sensors
Injectors
Intake Leak
Vacuum Leak
Vacuum Lines
Coil packs swapped around
Crankshaft Timing Pulley Bolt
Injector cleaner through a full tank of gas
Cleaned MAF
Compression Test
1 – 170
2 – 155
3 – 160
4 – 155
5 – 160
6 – 165

Any help would be appreciated

Did you use the exact original equipment spark plugs?
I know on my Trooper if I use other then factory Nippon Denso's I get random mis-fires.

Of course it's misfiring! That's not an ign. problem, it's too lean for the engine to run. Didn't the dealer tell you that? If not they must be idiots or were trying to sell you a lot of parts you didn't need! If it's really running at 28.38-1 you shouldn't drive it anywhere like that until you find out why it's way too lean or you'll damage the engine. You are either getting much less fuel than you need or way too much air. If the injectors are OK and there aren't any huge leaks in the intake manifold I would suspect a clogged fuel filter or bad fuel pump. Have you checked the fuel pressure and the output volume to see if it's enough to run the engine properly? You don't have a pissed off EX who dumped sugar in the tank do you?

all parts replaced are OEM.

Fuel filter has been replaced.

It is going in today to test fuel pressure as I have no way to test that.

Injector #2 had bad resistance and was replaced. All others tested fine and looked great.

Yeah, that gas analysis changes everything. (I have been following an older thread on YT.) The weird thing is the MF on two cyls on the same coil. I'm going to speculate there is something in that circuit causing a weaker spark--say a high resistance leak to ground--, so those two fail first and worse in the lean environment. Only way I can explain this.

I just can't figure out where, since he has changed wires, plugs, and coil. Head scratcher.

Is this a trick question?
..my runner had p0300(random) and p0302/05. ended up being a crack in cyl#3 and was filling up with coolant. I did not have an AFR on it at the time, however; I don't think you'd have power at all if it really is running 28:1, let alone start.. 14.7 isn't just average: it's required. 14L of air to 1 liter of gas for complete combustion.
If i'm engine braking downhill my afr will peg at 22:1 but the ECU is still in control.
If that number is not an error, I would certainly not drive it.
Did the onset of the knock coincide with the misfire? Does it actually feel like it is misfiring or is it just throwing codes?
I agree you need to look at fuel. I've read a few threads that end with replaced injectors fixing misfires.
I'm keenly interested to find out what's going on with your truck..
What do you think is going on?

make sure you dont have any air leaks then check out your fuel system. you cant completely test your injectors with just a meter.

Right, there's a fairly easy way to test them off the vehicle by applying 6 volts to them while you squirt carb cleaner or something like that through them to see if it sprays out OK. There's also a test that applies fuel at full pressure to see if the spray coming out is correct in shape and amount but that's a lot harder to setup and perform.

fuel pressure was tested and is perfect, timing marks, timing advance, crankshaft keyway all fine.

When it misfires, I can barely feel it. The truck runs pretty good, I would say its only running 5% rough 95% perfect.

My non toyota mechanic used their snap-on stand up diagnostics on it and can only read one bank of data (ie: one side of info from engine, not both) They have never come across that on any other vehicle. Without being to see that data he can't help me fix it.

The knock is coming from the back side of the passenger side of the engine. Every single person who knows anything about Toyotas don't believe it is the ECM.

I am completely lost as to where to go from here. All injectors open and close fine, increase clicking with increase throttle, I had them all in my hands and they look good, as in new. One had bad resistance, there are no marks, signs of wear, grime, etc at all.

Is there smoke in your exhaust at startup or warmed up?
Could the issue be related to significant temp drops in your location?
Does the truck drive, accelerate, sound normal?
Is the misfire completely random? Can you pinpoint a correlation to anything?
Have you tried the old ECU reset?(pull the ECU fuse for 10sec)
If there is bad gas/water in your gas it will cause a lean condition/misfire.
My compression looked just like yours with a crack between intake and exhaust valve on cyl #3... is your coolant low?

If you or a friend has a smart phone: you can purchase an OBD2 scanner that plugs into your port and links with your phone via wifi or bluetooth from eBay or Amazon for about $15. they are cheap but they work. You can use the torque app for free to link to the scanner and it will give you a read-out of all the sensors real-time. you can also check and clear codes with it. It should give you a lambda readout from your o2 sensor which you can translate into an AFR ratio(close enough to see if your at 14.7 or 28:1).


No disrespect, I don't know your background; I have had my injectors in my hands too and they all looked great to me and were in spec, but one was bad. Every time I reinstalled my injectors; I got a misfire; until I replaced all of them.

Well as it turns out, Toyota didn't check the crank pulley bolt like I had asked and paid them to do. Long story short, pulley bolt had come loose causing all kinds of problems.

It has since been fixed. Thanks for all the help

loose crank pulley bolt!!! for crying outloud..
thanks for updating.

OK Here's the deal. Because of high gas prices Ive been stopping at a gas station thats usually .20 cents cheaper. Been filling up there at least 3 times. Hubby tells me that he doesnt stop there anymore since it causes a little bogging down. Was told to put hi test gas into it. So I filled it up with the good stuff. Ran fine for about 55 miles. Then all of a sudden it starts missing out/misfiring. I put gas cleaner and fuel injection cleaner in it. Still missing out. Maybe blew a plug? Made appt to get plugs and wires changed. Does this sound about right?

Here is the deal - if you have moisture in your tank it will act very similar to what you are saying. As the fuel gets lower the fuel pump will start to suck the moisture in.

Put some fuel dryer into the tank (follow the directions carefully) and ensure that is not whats going on.

Moisture getting into fuel does not happen to just lower grade gas. ;-)

Thanks so much Blitz...Will def do this!