Fuel pump or relay or gremlin?

hey guys. 2007 4.0L pre runner, automatic, 2WD. 215,000 glorious miles.

i promise, I've done the appropriate 'search' on here for my problem and while many of the posts have pointed me in the right direction, i need higher experience at this point.

i've had a mystery problem with my truck running perfectly, then one day it turns over but won't crank. sounds like the old 'no ignition or no fuel' problem, but appears to be fuel, as the spark is good. it runs like a champ for 2-3 days, then when i park it one time it just won't crank. might come back in an hour and it cranks right up. might not crank for 2 days, but then it cranks right up. this has been going on for a month.

what i've thrown at it: new battery (was getting old anyway), a buddy has a fancy OBD2 code computer and i got a couple of random codes so i replaced MAF sensor, bank 2 upstream Ox sensor, then out of despair i dropped the tank, cleaned it and replace the fuel pump assy. while checking fuses and relays, the fuel pump relay would 'click' like it was supposed to, then suddenly wouldn't. thinking this was indeed the problem, i replaced the relay. still the same problem--won't crank. i put the voltage meter on it and i 'think' i might not be getting power to the fuel pump relay? rather than start yanking wires and ripping through harnesses, or the alternative of me building a small fire underneath it and casually walking away, i'm begging for some help here, if at all possible.

i am NOT a mechanic, but the things listed are within my capabilities. anything more complex really, will be out of my wheel house and i'm going to have to throw up the white flag and have it towed to a shop. i hate giving up.

cheers
drew

 

i ran across a thread on another forum that said if my crank position sensor was malfunctioning, then no power would be sent to the fuel pump.

to be absolutely certain, i removed the tank again and verified the fuel pump i installed is indeed a working unit. when pipped with 12v it hums.

i 'think' there is no power to the harness/tank connector. i put the voltage meter on the plugs on the connector. when someone turns the key over, my voltage meter doesn't even wiggle. ground on the frame, power to either connectors on the harness and no power. switch connectors, same outcome of no power. put neg of the meter on one pin, red on the other and still no wiggle. switch sides, same outcome. i think i'm satisfied the pump works, but no power is getting to the fuel pump.
i reinstalled the tank and lines, and put 10gallons of fuel in the tank. when i turn the key on, the gas needle moves a tiny but, but never really 'moves'. i assume this is also an indicator of no power to the fuel pump.

taking the advice of the CPK/CPS being bad, i drove to the next county and bought one. it was a pain to install--have to remove shroud/fan/hoses, then remove the generator to find the sensor behind that. the old one looked dirty and oily, but i have no idea what a bad one looks like. something about checking ohms and whatnot. that's out of my pay grade, so replacing it should do the trick.

at this point, with everything put back together it still will not crank. the fuel gage still sits below E. when i installed the new fuel pump relay switch, i 'thought' i felt it click, when the key was turned. now, i don't think it is clicking. it might not have been clicking before, and i just thought it was.
the EFI relay is clicking. i also switched it with the horn relay and verified the switch is indeed good. there is no relay similar to the fuel pump relay, so i can't just switch with another one.

i have checked all associated bayonet fuses in the fuse block under the hood and in the dash block, both visibly and with volt meter and every one seems to be moving power.

so what the heck is going on here? i 'think' something is refusing to tell my fuel pump relay switch to click 'on'. what else can i check?
i'm nervous about trying to jumper it to test, if there is something else going on.

cheers
drew

 

What about the ECM? might i just have a bad ECM? any advice on checking this?

 

If it has failed, this is one of those cases where it might be cheaper to tow it to a shop and let them diagnose as they can quickly detect why the fuel pump is being disabled. There are a LOT of parts that can cause this, and replacing even half of them will probably cost more than the shop diagnosis.