[FIXED] 2005 Ford f150 5.4 vin 1ftpw14585ke76615

Truck came in after another shop installed a remanufactured Ford motor it will run for about 1 hour then shut off .........after it stalls it will not start up it will spin for a couple full engine rotations then the starter will disengage if you hold the key in the start position the starter will re-engage and begin to crank the motor again I have a capture of this I will share also sometimes it spins like a starter dragging or timing out other times spins normally but always with the engage disengage of the starter after the stall........when the engine stalls and when the engine will not start it appears the crank sensor signal is failing I also have a capture of that I will share.

In the first pic the green. Trace is the crank sensor? You could if you wanted put it in clear flood mode or unplug fuel pump fuse or relay then scope the cam and crank sensor check amplitude when it’s cold because you know it’s a good signal. Then compare when it stalls . Any codes?

In the first pic, the (green trace) crank sensor's riding on 2.5v bias then later on it flatlines to 0v for a brief moment. I'm asking myself what happened to the bias? Did it short? Did the computer hiccup? Do you still have 5v ref and communications? Perhaps recapture with a lead on a 5v ref somewhere.

Then in your capture you labelled as "wtf.vsm" the green trace doesn't appear shorted to ground as there's noise on there. So maybe its been disconnected from the PCM. If there's an open to the computer, where's the crank signal then, lol ?
The second pic has a flat green line, so maybe it's shorted then, I dunno.

Wait. Try taking the computer out of the picture. Disconnect computer, probe the CKP + and - and touch starter s pin with power. Does the crank signal look okay now?

In the last two pictures is after a stall and cranking the engine as I said hold the key and the starter engages then disengages it did that three times the last time is zoomed to show a drop in the cam crank and cam leads I am not sure why but this is when it cranks with a drag or timing off..........I hope that makes since.

Yes it is the crank sensor , there are no codes

This is a cold crank with the crank shaft sensor unplugged is it me or does the notch look weird? Also notice the volts this is in ac volts on a 200 mv scale.

This is after it stalled and would not start up with the crank sensor unplugged and testing at sensor, notice notch and when I set it at 200 mv it was off the screen so I had to retest at 500 mv.

That sync notch does look weird. In the second picture, the sync notch is clean again. I'm suspecting the crank sensor's not tightened down enough and there's some movement of the sensor.

Are you probed into the CKP negative? I'm used to seeing the CKP notch rising, not falling.

Are you getting an rpm reading on the scanner when it becomes a crank no start? Also have you ohmed out crank sensor when it malfunctions?

I’d scope one fuel injector control circuit see if your missing injection pulse when it acts up. What does the fuel pressure pid read?

Okay so two things ...........this truck has had a cranksensor replaced before it came to us also a ecm the cranksensor is a Ford sensor ........we tried replacing it before we really did any testing so I don't believe the problem is in the sensor both did the same thing..........not sure if I am on the positive or negative I could check in the morning but not sure it is that important for diagnostic right?

tim.smith1 wrote: not sure if I am on the positive or negative I could check in the morning but not sure it is that important for diagnostic right?

Nope just curious, lol. Hmmm. Let's try another direction. You said the starter will disengage if you hold the key in the start position, I wonder if the PCM stops providing a ground to the control side of the relay (pin 85 on relay). You describe it "spins like a starter dragging or timing out." If you jump the load side with the relay removed does it still drag or timeout? Swap the starter relay with another one right next to it? If the PCM is ALWAYS providing a ground with key in start position, I would voltage drop test the power feed, the S post and the ground at the starter itself.

Chasing the starter maybe the wrong path, that's always in the back of my mind. Perhaps you can check to see if the bias voltage is present from the computer during crank, with the CKP sensor unplugged. Perhaps system voltage at the PCM relay is insufficient.

not sure i worded this correctly but if the crank sensor is unplugged then the starter turns over normally i am concerned about the crank sensor because just not sure if i should focus on an internal issue or something maybe shorting the wires out...............or does that seem like the wrong direction and if so what am i missing that would point away from the crank signal issue.................i am almost certain the computer is not liking what it is seeing and that is why the starter is acting up.

Okay so I got back to working on this thing today and could not believe it was anything but a shorted wire I proved that by taking a scope pattern off both wires of the cranksensor on an ice cold engine with it not plugged in..........after that I plugged it back in and disabled the fuel pump and scoped at the PCM same signal as the one above...........I then decided to run the engine until it stalled and repeated both of those test with the scope the first test with the sensor unplugged was a good pattern the second test with the sensor plugged in resulted in a bad signal and the starter was acting up.................lastly I cut the gray wire that is the cranksensor negative at the PCM and the sensor and used my aes wave scope lead and back probed the connectors to use as a jumper the engine then came back to life and purred like a kitten..............lastly to answer the question if I was scoping the positive or negative it was the negative and explains the notch falling rather then rising.................thanks very much guys and gals for the help as always I will never leave a post with out a closing as I feel that does not help our awesome community here.

Can someone update this to fixed please........thanks in advance.