Trouble with misfire

Having trouble pinning down an issue. My 04 tundra (3.4L 5-speed manual) started running a bit rough. Later that evening, problem gone. Next day or so, no issue. Then happened again randomly, but now CEL is blinking.

Codes are:
P0171 (nothing new as I’ve had this code a little while)
P0300 (Random misfire)
P0304 (cyl 4 misfire)
P0305 (cyl 5 misfire)

My question is.. what could this be? I was originally thinking spark plug/wires, but would that really cause 3/4/random misfires at once? Or could it be something different? Thanks in advance!

Also, problem seems to get worse with acceleration.

 

Well, first off, running with P0171 is not a wise choise, but I'll save you the lexture. Engines don't just throw codes for no reason. Stop fucking around, fix the issue, else you end up with other issues.

Of course, running lean you may've fucked up your plugs, which will lead to misfires. I assume you've checked your plugs already, and that you actually used the right plugs (a lot of people don't), and you got your plugs from a legit source (i.e. not on scAmazon or fleaBay, which is notorious for counterfeits)

I'll ask: Hear any hissing under the hood?

Misfires with "too lean" stinks of a blown intake manifold gasket. No big deal, just make sure you use an OEM gasket on replacement, or Fel-Pro. I can show you one member who's had to reinstall 3 times because most aftermarket gaskets are utter shit. This is NOT a job you want to do twice.

Why do I say this? Dumbing this down a lot but basically:

1. Your MAF tells the ECU how much air is coming in
2. ECU sprays enough fuel to mix properly with that air volume in order to achieve proper combustion
3. Combustion happens, and passes out of the manifold
4. Air/fuel sensor (aka "O2 sensor") sniffs the exhaust gasses coming out of the manifold before it hits the cat to check: Is it rich? Is it lean? Is it just right? It uses that info to know if it should adjust fuel trims or spark.

Rich = more fuel than air at ignition, so fuel is left over. Lean = more air than fuel, so all fuel is ignited.

So, what happens if the intake manifold gasket is leaking?

Well, natural suction in the engine (combustion engines are one big air pump) will allow extra air to get sucked into the cylinder. Suddenly, you have more air than fuel, and all the fuel gets burnt up, i.e. you're running lean. Because you have specific timing on the engine, misfires can happen when your air/fuel mixture is piss poor.

 

//clapping noises//

 

Thanks for the reply and skipping the lecture.. sort of? I only recently got this truck and the owner said it came on not long ago.

Anyhow, no, I don’t hear any hissing to my knowledge nor do I smell anything out of place. I will be replacing the plugs in a couple of days from Toyota, so hopefully that will give some more info. More than anything I guess I am just trying not to throw parts and money at it blindly. Thanks for your input

 

Promise, no more lectures

And new owner. Makes sense. Welcome to the forum! If you didn't already get there, community-generated "read this" thread to help with your new truck if you haven't already seen: https://www.tundras.com/threads/so-you-wanna-buy-just-bought-a-1st-gen-tundra-eh.115928/

I didn't mention this before, but blinking CEL = major issue. Solid CEL = minor issue. Misfire is a major issue.

I also didn't mention before ... But the P0171 is a great hint to what's probably happening when it's paired with misfires: Typitcally either (A) too much air or (B) too little fuel.

Given you're telling me "no hissing noise", and the misfires aren't on a single cylinder, it's potentially not air leak, so next likely culprit is a fuel delivery problem. If you didn't have the lean code, and this was just a misfire condition I'd be looking at your coil packs.

Why? "Too lean" and "misfire" with no noises under the hood could be a failure for the fuel pump to deliver fuel to the engine. In step #2 above, the ECU would be trying to get the injectors to spray, but lack of fuel pressure (due to blockage in the line or dying pump) would not allow enough fuel to be delivered for the amount of air volume entering, i.e. not enough fuel for the air, i.e. you ignite all the fuel and are burn lean due to excess oxygen.

I'm pretty sure the '04 still had an inline fuel filter. Now, it's absolutely not normal for the OEM fuel filters to clog up, but we've seen cases on here where someone replaced the fuel filter with aftermarket and that jammed up and was choking off fuel supply. It can also happen if vehicles sit too long, especially with high ethanol gas.

It's up to you to figure out which. If you can get a gauge to test fuel pressure, that would 100% tell you if your issue is fuel delivery. If pressure is higher than 35-40psi (should be ~40psi at idle, IIRC) then delivery may not actually be the issue.

Anyway, if we can help somehow, give a holler. If you can't test for fuel pressure, any competent shop probably can. I'd have them start there.

 

Response: Thank you! New here, second day on the site and already think I did right signing up. Have been 3 months dealing with miss fires and total shut down of engine even in middle of intersection. 2001 with 250K miles all tuned up about 2 years ago. Pulls a light weight 5th wheel Scamp trailer even older than the truck twice a month on 200 mile round trip. I over night in the camper so as not to have to drive at night to get home from music gig as I play fiddle ♪♫♪ but I refuse to get a new truck when I have a gen 1 Tundra. Two great clues here are the fuel filter with the ethanol gas as the fuel filter is 2 years old or more and could be aftermarket brand and Also I was burning only non-ethanol for years but with recent trips and using so much and burning it out I had gone back to ethanol HOWEVER the point about it sitting (which is why the other two vehicles in the heard use non-ethanol) was a good wake up call. Great post by "shifty" above. Fortunately I have always been able in the three of four occasions to always work through it and get home with some patience. Last full tank of ethanol will be burned out and then back to non-ethanol and that with new fuel filter to be installed before burning out this tank of gas. I will post here again to advise weather or not this is/was the solution or what ever is/was required to resolve the issue and what order was taken to get there. end. for now.