Intermittent starting problems
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Intermittent starting problems
I have a 2008 F150 XLT and for the past few weeks I’ve been turning the key and hearing a click, sometimes it starts in neutral, sometimes in park, it’s completely random and unpredictable. At first I thought it was the neutral safety switch but it was replaced and was not the problem. Just wondering if anyone has any ideas.
Last edited by Fakeraptor; May 23, 2021 at 07:42 PM.
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Use your test light to see where you are losing start signal . Start relay should be in main fuse panel passenger side kick area. look at your book for start relay location . Contacts may have started to go bad , any big box auto will have a generic one .
Keep your eye on pats security light if it satrs flashing fast then you may have intermittent pats system problem . While you are in fuse box area clean all those metal grounds that start to rust out or relocate to better metal .That can also be a problem .
But keep in mind the key system gives the positive to the start relay but the pcm only supplies the ground to the start relay if its happy with the pats system .
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Use your test light to see where you are losing start signal . Start relay should be in main fuse panel passenger side kick area. look at your book for start relay location . Contacts may have started to go bad , any big box auto will have a generic one .
Keep your eye on pats security light if it satrs flashing fast then you may have intermittent pats system problem . While you are in fuse box area clean all those metal grounds that start to rust out or relocate to better metal .That can also be a problem .
But keep in mind the key system gives the positive to the start relay but the pcm only supplies the ground to the start relay if its happy with the pats system .
1) Because it intermittently started in neutral/park, we started by replacing existing neutral safety switch with a known good one. Issue remained.
2) We checked fuses 101 and 102 in the fuse panel. Both were good.
3) We tested the starter relay with a multimeter, which shows it to be functioning. We also swapped with other nearby relays. Issue remained.
4) We jumped pin #30 to pin #87 and the starter cranked each and every time - which eliminates anything being wrong with starter connection.
5) Used test light on pin #86, which illuminated every time the ignition key was turned to start position. That, in theory, should eliminate the possibility of a bad ignition switch and/or Transmission Range Sensor (Neutral Safety Switch).
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Further investigation...
I now believe it to be theft system related, does anyone know how to reset the theft system or bypass it?
I now believe it to be theft system related, does anyone know how to reset the theft system or bypass it?
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Since you had indicated that it would start intermittently, that sounds like a marginal connection could be the cause.
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How about pin 85? Check it’s circuit back to the PCM connector for an open. The PCM provides the ground to that relay if everything is good, which will power up the relay.
Since you had indicated that it would start intermittently, that sounds like a marginal connection could be the cause.
Since you had indicated that it would start intermittently, that sounds like a marginal connection could be the cause.
Did the test to pin #85 this morning. Connected test light to hot, then tested pin #85 (ground from PCM module) repeatedly while turning ignition switch on and off. Did it about 15-times, and the test light illuminated each and every time, indicating the ground being provided and proper circuit operation. Replaced relay, turned the key, and the truck started right up. Started the truck and turned off 8-times in a row. Noticed security light lit solid while starting. Took the truck on a short drive, returned and turned it off. Gave it about 10-minutes and tried again -- truck would not start, and security light flashed rapidly again.
Battery tests out good (has 3/21 sticker on it). I don't know what more I can do at this point; I've looked at everything in the chain.
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I just went out again, and the truck did not start after several attempts. I pulled the relay, and once again put the test light (from hot) to pin #85 and turned the ignition key several times with no illumination of the test light. So no ground from the PCM this time. To answer your other question, there is no corrosion in the relay area. FYI, I've also tested and swapped the PCM relay as well.
Would you say at this point, this would be an intermittent failure of the PATS transceiver at the key tumbler? I only have one key, so obviously, I cant try this with others. Is there anything else this could be? I'm out of ideas at this point.
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The pcm supplies the ground so pcm needs the grounds on it checked there are about three . . I doubt if that's your problem if pats light rapidly flashing then something causing a pats failure . There are things that can cause this externally, stuff on your key ring etc . Try the other key .
I don't know which signals the flashing light . But realistically its either a bad key ,key reader or pats module . I hear the pats module is under the dash and it sends a code to pcm if happy . My guess is the pcm controls the flashing light .
There is no bypass , I have looked in case I have an emergency . Yes we can bypass the crank signal but not the signals to the cops-injectors in time with the crank signal . The pcm controls all that, no way to fake it .
To deal with pats you have to have the elaborate scanners with controls and a lot of instructions even if you have new stuff to replace . Way over my head -most shops call for an experienced guy to sync them up .
You need a ford tech malukoco or eric of south main auto in new york .
Maybe we can learn something here. i have heard that its possible to get a pcm with pats disabled . That's what i would want on my old 05 if i had trouble .
I don't know which signals the flashing light . But realistically its either a bad key ,key reader or pats module . I hear the pats module is under the dash and it sends a code to pcm if happy . My guess is the pcm controls the flashing light .
There is no bypass , I have looked in case I have an emergency . Yes we can bypass the crank signal but not the signals to the cops-injectors in time with the crank signal . The pcm controls all that, no way to fake it .
To deal with pats you have to have the elaborate scanners with controls and a lot of instructions even if you have new stuff to replace . Way over my head -most shops call for an experienced guy to sync them up .
You need a ford tech malukoco or eric of south main auto in new york .
Maybe we can learn something here. i have heard that its possible to get a pcm with pats disabled . That's what i would want on my old 05 if i had trouble .
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Thanks for the reply...
I just went out again, and the truck did not start after several attempts. I pulled the relay, and once again put the test light (from hot) to pin #85 and turned the ignition key several times with no illumination of the test light. So no ground from the PCM this time. . .
I just went out again, and the truck did not start after several attempts. I pulled the relay, and once again put the test light (from hot) to pin #85 and turned the ignition key several times with no illumination of the test light. So no ground from the PCM this time. . .
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So, just to prove out the final leg of the pin 85 circuit back to the PCM, unplug the PCM and ohm out the circuit from pin 85 back to the PCM plug. If it reads open, or high resistance, that could be why the PCM isn’t providing the ground. If it shows good continuity, then we need to figure out why the PCM isn’t providing a ground.