roarkace

when temp is below 32 degrees,cranks but will not start, Let it sit in the sun for a couple hrs and warm up the interior of the cab ,it will fire right up even if it's 10 degrees outside,i have replaced fuel filter and coolant temp sensor,cold star injector works ?

L5wolvesf

What testing did you do to determine the fuel filter and coolant temp sensor needed replacing?

coryc85

As long as the cab warms up, then it will start? Hmm, well, you can check the COR, which is a relay that is inside the truck, lots of info on here regarding it, but you can do a simple test. Jumper Fp to B+ in the diag connector under the hood, turn the key to ON and you should hear the fuel pump running. Try to start it this way, see if it starts under your trouble condition of below 32 degrees. There may be other tests in the FSM regarding the COR, I wouldn't just go blindly replace it without doing some of those checks, and leaving the jumper from Fp to B+ is not a permanent fix since the COR is a safety component and really should be there.

RAD4Runner

You can have the best sensors in there, but if the mounting threads are not cleaned to bare, shiny metal the temp sensors will do no good.

roarkace

first what is the COR ? I admit i have no idea how to do some of these checks . i did read in another post of a similar problem and he put a heater in the cab ,I thought i'd try it . Put small ceramic heater in pass compartment ,took off kick panel ,i guess that's the ECU in there and a couple other relays. waited an hour ,and it fired right up. It's 10 degrees out here.So help what's in there that needs heat to fire the engine ???

L5wolvesf

My questions still apply as neither are in the cab.

Far as in the cab goes, are there any water leaks into the area where the ECU etc are?

Co_94_PU

iTrader: (-1)

Preform the testing as Cory stated above. This will tell you if it is an ECU issue or faulty circuit opening relay (COR) issue.

You may have a water/condensation problem, maybe a bad connection, maybe a gunked up or damaged relay.

RAD4Runner

Seek and you shall find...

C.O.R. is where windshield leak or splashes through poorly-sealed grommets from wheel-well could easily get to.

coryc85

roarkace - under the hood, on the passenger side, kindof near the battery (I think) is a black connector labelled DIAG CONN. Open the plastic covering and you can see it is a bunch of connections to various things. The pinout is listed inside the lid, so you should be able to find the Fp and B+ pins. Bend a paperclip into a U shape and stick one end down into Fp and one end into B+. This bypasses the COR relay and sends B+ (battery +) to the fuel pump when the ignition switch is on the ON position. Then get inside the truck, turn the key to on, but don't try to start it, you should hear the fuel pump running. That is your sign that you have connected things properly. Then try to start the truck under the conditions you mentioned, when sitting below 32 degrees. If the truck starts I would strongly suspect the COR is an issue, but like I said in the previous post, I would find out if the Factory Service Manual has any further tests for the COR, such as any pin to pin resistance checks. If you have trouble finding the DIAG CONN, take a pic and post it, somebody will be happy to circle the connector in your picture.

And you asked what is the COR. Sorry for acronyms, if you hang out long enough on Yotatech you'll start to get used to these things. COR is short for Circuit Opening Relay. It is a relay that shuts off the fuel pump if the engine dies. And conversely, can prevent the fuel pump from running if things are not working properly. I believe the signal for allowing the COR to close comes from the Vane Air Flow Meter, essentially the air box. If the engine is not sucking any air, then then vane is closed and this opens up the COR. So in an accident, if the impact kills the motor, the fuel pump will stop. The pins in the DIAG CONN allow you to temporarily bypass the COR to force the pump pump to be on.

One more edit, Ray, our resident Toyota electrical expert, has a nice writeup on the COR here: https://www.yotatech.com/forums/f116.../#post52387681