Hello,

I am pretty stumped on this so I hope someone has insight! 00 tacoma 3.4 truck runs great for about 30 minutes when started cold, then all at once it starts to run like crap and gets misfire codes for cyl 1, cyl 2, and random/multiple cylinder misfire. Coils, plugs, wires, MAF, O2 sensors, and fuel filter have all been replaced but the issue persists. When I changed the plugs none of the cylinders look washed and the fact that it is 1 cylinder on each head makes me think that head gasket issues are unlikely since the odds of both head gaskets failing simultaneously seems very unlikely. So I know it has spark, I really don't think it is lacking compression, that leaves fuel. Both injectors failing simultaneously also seems unlikely, I am kind of thinking maybe fuel pump since low fuel pressure could cause multiple cylinders to miss. I am more of a diesel guy but do the fuel rails dead head at the end or is there a return at the end? Also is there a test port somewhere to check fuel pressure?

 

If i was you i would start to check if the engine computer s sending the ground pulse on those two injectors you could used a digital test light or the adapter that u place across the fuel injector plug and u should see the blinking light and if you see that the computer is sending that ground pulse to the injector, if u do get tha signal u would have to check resistance of the injectors but pull them out and if resistance is good then i would swap them out to see if the misfire fallow the injector in question. Fuel pressure need to be between 33 to 38 psi and on the driver side you a going to see were the fuel line meets with the fuel rail and you have to have an adapter so you could screew on and check the fuel pressure. Fuel injector resistance is 13-14 ohms

 

What brand/type: plugs? Wires? Maf? o2 Sensor? If it could possibly be a fuel pump. They're a PITA to get a gauge on, but worth it. There is no test port. There's a banjo bolt at the end of the driver side fuel rail you have to put an adapter on. You can rent a fuel pressure test kit of part store that has the right fitting.

What are all of your exact codes?

 

Do you know if I can test the injector ground pulse with a digital multimeter? If so how would I do it? Thanks for the info!

 

Denso dual ground strap plugs, Denso wire, Denso coils, Denso MAF, Denso O2. So basically it's all the OE stuff. Okay, I will try that, it is on the end at the front of the motor or rear?

Codes are P0300, P0301,P0302 and they all come at the same time after the truck has been running for about 30 minutes. Can't think of too many things that would cause a simultaneous multi cylinder misfire especially since those two cylinders don't use the same coil.

Also when it starts happening you can feel it at idle but it doesn't actually set any codes until you romp on it then the check engine light will start to flash and set the codes which could also point to fuel pump not meeting demand at higher RPM once it heats up.

 

You might be on to something. That's exactly how a failing fuel pump can behave. Experienced that same scenario with a Sequoia one time. Good luck.

 

I will see if I can get a fuel pressure gauge on there that might shed more light on the situation because I don't want to just throw a pump at it blind. Do you know if I take the bed off if I will be able to get the pump out that way? I don't want to drop the tank very badly.

 

My money is on injectors dieing.

I had nearly the same symptoms. Would run great cold and for 30 minutes or so. If I ran it around the block, parked, and started it back up after a few minutes I was guaranteed to have the miss. The windings in the injector are failing after heat soak, or at least that was my issue.

https://www.yotatech.com/forums/f2/p...-p0171-295902/

 

For the record it was the injectors. Thanks for the help everyone!