Won't start Fuel relay? (HELP)
10-28-2018, 01:33 PM
#16
Rennlist Member
Thread Starter
With a little help from GB on the phone we managed to resolve the issue and it runs perfectly again. We ran a wire from #85 on the FP relay to the #21 fuse block ( the brown and white ) wire on the lower right of the panel ( yellow block). All is good. My first thought that it was the LH, but since it wasn't that old ( 35pin) I needed to check all options before sending it out for repair. It could be a loose wire or something behind the big board ( which gives me a headache just looking at the back of it).
10-28-2018, 01:59 PM
#17
Rennlist Member
So, the voltage from the LH is not sufficient to close the relay and send 12 volts to the FP?
10-28-2018, 10:26 PM
#18
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Kevin--
The LH doesn't source voltage to close the relay. The relay coil gets power from the 15 bus (hot with key in RUN or START). The LH controller **GROUNDS the other side of the relay coil, causing the relay to close.
The "fix" was to the hot side wiring so power gets to the relay coil. The ground (LH) side of the relay coil wiring was fine.
** the LH actually pulls its side of the relay coil almost but not quite to ground. It ends up floating somewhere around 0.6 Volts above ground, thanks to the silicon transistor used for the switching inside. Probably not important unless you are in there with the DMM trying to figure out why that side of the relay isn't "properly" grounded.
The LH doesn't source voltage to close the relay. The relay coil gets power from the 15 bus (hot with key in RUN or START). The LH controller **GROUNDS the other side of the relay coil, causing the relay to close.
The "fix" was to the hot side wiring so power gets to the relay coil. The ground (LH) side of the relay coil wiring was fine.
** the LH actually pulls its side of the relay coil almost but not quite to ground. It ends up floating somewhere around 0.6 Volts above ground, thanks to the silicon transistor used for the switching inside. Probably not important unless you are in there with the DMM trying to figure out why that side of the relay isn't "properly" grounded.
10-28-2018, 10:30 PM
#19
Rennlist Member
Kevin--
The LH doesn't source voltage to close the relay. The relay coil gets power from the 15 bus (hot with key in RUN or START). The LH controller **GROUNDS the other side of the relay coil, causing the relay to close.
The "fix" was to the hot side wiring so power gets to the relay coil. The ground (LH) side of the relay coil wiring was fine.
** the LH actually pulls its side of the relay coil almost but not quite to ground. It ends up floating somewhere around 0.6 Volts above ground, thanks to the silicon transistor used for the switching inside. Probably not important unless you are in there with the DMM trying to figure out why that side of the relay isn't "properly" grounded.
The LH doesn't source voltage to close the relay. The relay coil gets power from the 15 bus (hot with key in RUN or START). The LH controller **GROUNDS the other side of the relay coil, causing the relay to close.
The "fix" was to the hot side wiring so power gets to the relay coil. The ground (LH) side of the relay coil wiring was fine.
** the LH actually pulls its side of the relay coil almost but not quite to ground. It ends up floating somewhere around 0.6 Volts above ground, thanks to the silicon transistor used for the switching inside. Probably not important unless you are in there with the DMM trying to figure out why that side of the relay isn't "properly" grounded.