My truck wont start and the 24 fuse in the power distribution block blow as soon as I turn the key on..where does it run to? or has anyone had this problem

 

on a 99' it would go to Heated oxygen sensor #12 and #22. Also to 4R70W transmission Internal Solenoids. It just supplies 12V to these. I would guess the heater in sensor's is shorted or an internal trans solenoid is shorted. I would guess the oxy sensor. You might try unplugging the sensor's. To say more we would need engine and truck year.

 

its a 97 f150 5.4 liter..I will try unpluging the sensor and see if it keeps it from blowing

 

ok I dont know which ones are 12 and 22 so I diconnected them all and now the truck starts..Now for my next question can I drive the truck with them being disconnected for a day or so or will i screw things up more

 

After you start your truck, does the Check Engine Light stay on?

 

i didnt leave it run long enough for it to come on

 

With both 12 & 22 disco, you can get a CEL.
11 & 21 are the front ones, 12 & 22 are the 2nd set, which just check that 11 & 21 are doing their job. 11 & 21 are the ones that are used for close loop flow control, if my memory is working correctly ( which is might not be after deling with the amatures at airport today ).

I will try to find the closed loop flow control write up, and post it back here.

 

what is a cel?

 

Check Engine Light, AKA SES (Service Engine Soon) light on your instrument cluster.

O2 sensors harnesses have a nasty habit of getting onto exhaust components, melting the insulation, and shorting important stuff to ground. Oh, on these trucks, it can blow BJB F24 which kills the power to the PCM. Nice going Ford! At least it doesn't burn the truck to the ground....

The upstream O2 sensors (11 & 21) are for fuel trim control, the downstream O2 sensors (12 & 22) are there to monitor catalytic converter performance only.

Inspect each sensor harness for melting. If no visible evidence is found, plug one sensor back in at a time until you find the one that blows the fuse. Replace that sensor and the fuse.

Your engine will run with no O2 sensors connected. However, it will be running pig-rich with the upstreams disconnected which will kill your fuel economy and risks damage to the cats from fuel loading if left that way for very long. If you disconnect the downstreams only, the engine will run correctly but that light on your dash will be on.

Steve