Issue: Management of Hot At All Times (HAAT) FPPDB

[Bob Brandle]

ISSUE: (HAAT) Hot At All Times instruction for FPPDB of Ford 5.0 Coyote (Gen2) electrical system per Control Pack Instruction Sheet.

How does one effectively abide by the Ford Performance 5.0 Coyote Instruction Sheet’s “HAAT of the FPPDB instruction”, yet still have a usable Main Power Shut Off-On Switch for the car? Is there a good design work-a-round?
Obviously such a Main Power Off Switch can and should still be in place and used for an all power shut off during absolute emergencies, such as a run-away engine or car crash, etc., but what about just wanting to cut power to the whole car during serious maintenance or car work, especially involving the electrics?

Per the 5.0 Coyote (Gen2) Instruction sheet, such a power cut to the FPPDB will “result in loss of diagnostic trouble codes, adaptive fuel parameters, and other information stored in KAM by the PCM.”

How about a separate Power Off-On Switch for just the Chassis Harness, which would cut power to everything except for the Coyote Harness & it’s FPPDB?
Thus electrical work could still be done CAREFULLY on a majority of the usual trouble and maintenance areas but keep the engine’s electrical and HPPDB hot.

There would still exist the Main Power Off-On Switch for overall total car Main Power Off-On for The Absolute Emergencies and when engine electrics really need to be powered down. This Main Switch would be more visible and properly labeled than the chassis harness only Off-On Switch that would be located “tucked away” somewhere.

Any comments or solutions?

https://thefactoryfiveforum.com/attachment.php?attachmentid=122411&d=1581445863

Bob

[Railroad]

My Gen 1 has the same instructions. I fed off the hot lug of the master disconnect to a second disconnect for the ECU.
I can kill all the feeds except the ECU with the master disconnect and leave the HAAT fed. If for some reason I need, I can kill the power to the ECU also or independently.
Hope this helps.

[edwardb]

I also wired the Coyote PDB to the hot side of my master disconnect. So the Coyote system is live all the time. That meets the Ford Performance requirement. In an emergency, switching the master disconnect off with the engine running would in theory also shut off the Coyote and as a result the fuel pump. I say in theory because I haven't tried it and don't plan to unless it's really an emergency. But with no power to the RF panel, the Ignition Relay Trigger wire (light green) in the Coyote pigtail which is normally tied to an ignition circuit on the RF side, like the Orange EFI/Coil wire, would no longer get power and the engine would stop. I figure if need to shut everything off including the Coyote system for maintenance, I'll remove a cable from the battery. Not something I've had to do in three years running the Roadster with the Gen 2 Coyote.

Another solution some use is to put a jumper across the terminals with a low amperage fuse, e.g. 10 amps. That allows current to remain flowing for the EFI or PCM even with the switch off. Trying to start the car with the switch off blows the fuse. All due respect, I don't quite get this solution. Maybe I'm missing something. Much prefer what I described above.

[Bob Brandle]

Railroad and Edwardb,
Thanks so much for your quick responses. Paul, I understand your setup, the logic and will follow your lead on this. THANKS!
Bob