15' TRD Pro P0300 / P0302 / P0306 (And sometimes all cyl. Misfire) Nightmare.

Truck: 2015 TRD pro Tacoma,

$151 4door QAA is Compatible with 2016-2020 Toyota Tacoma 6 Piece Stainless Body Molding Insert Trim Kit, 1.5" Width MI16172

4door 5ft bed. 150k. SAIS removed and Tuned through a guy on here who no longer writes tunes as he works for a company.

Background: For the past 4 months I have been chasing a misfire sometimes just p0300 and others P0302 and P0306. The lower I get in fuel the more cyl's log misfires. I'm going to keep it short because I could make this very long.

Symptoms: Truck will start and run fine, hot, cold, it doesn't matter. While driving ~ 60 MPH at 2-2.2k rpms I will (at random) get a CEL and the engine will idle rough as I pull off to the side of the road and read the codes and then clear them. I will turn the truck off and back on and then it runs fine until it happens again. Sometimes 2+ more times in an hour and other times nothing at all. Most of the times it's the P0300, P0302 and P0306 but like the title says sometimes I will get all of them. <<Only Recently have I started to attribute these to fuel level and I think I am correct in that assumption>>

I replaced (all OEM):
Plugs
Coils
Cam Sensors
Crank Sensor
Intake Plenum Gasket
Throttle Body Gasket
PCV and Hose

After I threw all those parts at it I took it to Toyota because I was lost. Toyota did not charge me to look at it for an hour because they couldn't figure out what my problem was it was then I bought all the injectors and replaced them. I thought I had it fixed when at a half tank, actually on my way to replace the oil pan gasket for a man I go to church with and the truck misfired again. P0300, P0302, P0306. I filled it up and continued to his house with no more codes there or the way back which is about an hours worth of driving.

So now I figured, maybe the fuel pump at half a tank is getting hot and so I bought a new fuel pump and I put it in today. I had to cut off the very rear vent hose the smaller one that's is molded to the nipple it's fit to on the tank because the QD fitting was shot on it and you have to buy a whole new fuel tank to get a new one and so I put fuel line/evap hose on it and used a screw clamp on each end to secure it.

I lifted the tank back up and poured in all of my siphoned fuel up to just above half a tank and now the truck will not start. I am thinking I damaged the fuel pump relay as I removed it to relieve pressure from the line but with my luck (read above) I don't think it's going to be that easy.

Fuel Pump is OEM
All other QD's went back on undamaged.
Truck cranks fine but will not turn over. I heard others have problems with SAIS shutting down fuel pump is it possible I have to re flash my tune even though I just unplugged the battery and installed a new pump?

Any help would be greatly appreciated, thank you very much.

 

I would get rid of that tune and try going back to stock tune. That sounds like the only thing you did to the truck

 

Hey Chueflee,

So for the tune, I have had it on the truck for a year now and never had problems. I can't go back to stock as the SAIS system is completely removed. My theory about all of this from the beginning is that I, not knowing that a fuel pump is cooled by the fuel in the tank, did an Italian tune up on the truck exactly the time this started happening with less than a quarter of a tank and after fill up got these codes about 2 minutes down the road thinking it was bad fuel. I treated it and treated it replaced all of the parts and still nothing which is why I attribute it now to an overheating fuel pump.

So I replaced that but can't test that as the truck will not start now.

 

Whats an italian tune up? Did you change your fuel pump?

 

It's an idiom for running the truck a little harder to burn off carbon deposits if it's been babied for a while (mine had).

I did, I changed my fuel pump yesterday and buttoned everything up and then it wouldn't start. I pulled the Fuel Pump Relay as the Haynes manual says to do in order to release pressure in the fuel system and it was very stubborn as I was pulling it out I had to use a plastic pry bar that I use for body panels. I have a new one on order from Toyota and am praying that I some how messed it up during extraction. But the truck sounds normal it's just not getting fuel (I think) I do not own the special T connection I need to test the fuel pressure in these 2nd gens. I did pull the fuel line under the hood and a little bit of fuel came out but that didn't tell me if it was pressurized enough.

Toyota will have the relay tomorrow so I will know for sure if I need to look somewhere else but again with my luck it's something way off in the distance that I can't see yet which is why I'm here asking you pros.