So I was driving around yesterday and the truck sputtered a bit, died and wouldnt start again. Towed it home. I did get 2 codes, but didnt write it down (kicking myself), thought it was tps related. I have replaced that within the last year, in fact the whole throttle body for another issue. Anyway I reset the computer on the side of the road hoping to get it to start with no luck. Today I got into it. I still had my old tb (which never had starting problems) so I swapped that back on and reset the comp, still didnt start. Got a new program on my phone (car scanner from play store) which seems way better than torque lite. Checked and I am getting fuel pressure within spec, so that doesnt seem to be the issue and it shows my peddle moving the tps . While cranking most of the time it doesnt sound like it wants to start at all. I noticed I wasnt getting any kind of rpm signal thru the obd gauges while cranking. Does that come from the crank sensor? Then suddenly while I was testing it after screwing around for hours, i got an rpm signal and it started rough, then cleared up and ran fine for 5 mins. I shut it down and started it again, not easily, but not horrible (sputtered a bit) and it ran good again. Shut it off one more time and now its back to cranking and not even acting like it wants to start. My guess is the crank sensor, but looking at that it seems to be a pain to get to. Anyone else had this issue before? It looks like I have to remove a bunch of stuff on my back to get to that sensor, so want to be a bit more sure before I jump in. Thanks in advance for any help you can give. Oh ya 2005 f150, 5.4l engine with a/c

 

Check the FPDM for corrosion. You may also have leaky injectors, that was an issue with 2005's. If it's the injectors, it should start if you floor the pedal while cranking.

 

Based on what you described, I would guess the crank sensor in my non-mechanic mind. But, these sensors don't often fail on these trucks do they?

 

The lack of a crank sensor signal in the PCM means it won't fire. You should be able to observe either the tach while cranking, if equipped, or the MIL which should go out during cranking if the crank sensor signal is being sensed by the PCM. If it stays on solid during cranking, that's a good indication also that there's no crank position signal getting into the PCM.

Since it fired when the crank signal re-appeared, that's pretty strong evidence that the problem is the crank sensor circuit. Keep in mind that the circuit includes the sensor, wiring and PCM.

 

Thanks for the response, could you tell me what MIL is short for? Also could anyone point me in the direction of where I could find a wiring diagram for the crank sensor circuit, I have a feeling its could be a bad wire and not the sensor on this truck

 

MIL = Malfunction Indicator Lamp aka "Check Engine"

I've got the diagrams but they're on a different computer that I don't have access to at the moment. If no one else posts them, I'll upload it when I can.

 

Well I got it going again, just needed to remove the crank sensor plug, hit it with some brake clean, then fill it up with some dielectric grease and put it back together. Seems to be working fine now. What a joke of an engineering masterpiece that thing is, hidden behind the ac condenser frame rail and steering rack. Just getting the plug off took a gumby arm and some needle nose pliers. Still if ya get a chance could you put up those wiring diagrams incase an issue pops back up. Its so tight in there I cant tell where that harness is going and if it screws up again Id like to just replace it..

 

 

I had a cramk no start on my 2002 f150 after doing some work on rhe intake and fan clutch assy. I purchased a ckp sensor which didn't help. After weeks of troubleshooting electrical system possibilities, I ran across an article that described my symptoms exactly. Was getting good fuel pressure in the rail but injectors would briefly show a response on noid light and then have no response. Had no spark. Rpms registered once briefly and went unresponsive much like the injectors. Problem turned out to be te 2 wires at ckp connection. Brand new ckp sensor had reversed polarity from the one I took off. I really didn't think that would fix my crank no start condition as, well, who would think that could be an issue with a brand new sensor, same manufacturer as the one removed. 🤔
Decided after scratching my head for several days not sure how to proceed next, to go ahead and switch the wires in the ckp connector as it literally only takes 5 minutes. Much to my surprise, it fired right up. I almost fell out of the drivers seat. Here is link to article

https://www.underhoodservice.com/tec...p-replacement/