2010, shorted ground causing misfires and ac problems

[withku]

Hey all, I’ve been having some weird problems lately with my 2010. Extremely erratic a/c, low system voltage (alternator only pushing 13.3 volts, doesn’t change under load or while revving) , and a voltage drop on startup which causes all my injectors to fault / misfire. ForScan says Low Side INJ Short Gnd. I’ve checked all grounds I can see and they read < 5 ohms. I don’t have the electrical expertise to tackle this. Can anyone point me in the right direction?

 

[SHOrod]

How old is the battery in the car? If it's more than 3 years old, you might want to consider replacing the battery and resetting the Battery Monitor before spending too much money and time on chasing the issues. The charging system on these cars is computer controlled, so the function of the alternator is adjusted based on load and perceived battery condition.

The injectors receive battery voltage and are opened by controlling the ground, so when you measured the less than 5 ohms on grounds I assume you were not checking ground signals of the individual injectors. If you were, I need to take a look at the schematics rather than going off memory.

-Rod

 

[withku]

How old is the battery in the car? If it's more than 3 years old, you might want to consider replacing the battery and resetting the Battery Monitor before spending too much money and time on chasing the issues. The charging system on these cars is computer controlled, so the function of the alternator is adjusted based on load and perceived battery condition.

The injectors receive battery voltage and are opened by controlling the ground, so when you measured the less than 5 ohms on grounds I assume you were not checking ground signals of the individual injectors. If you were, I need to take a look at the schematics rather than going off memory.

-Rod

Battery is ~8 months old. I did say I checked all my grounds, but didn’t realize that has nothing to do with a short to ground. Like I said right after startup my injector harness gets shorted.

 

[76FoMoCo]

how are the connectors at the battery terminals? lift the lid on the red cover and take a look. corroded connections can give you this problem too

 

[withku]

how are the connectors at the battery terminals? lift the lid on the red cover and take a look. corroded connections can give you this problem too

I’ve checked pretty much all visible wiring. No signs of corrosion. I’m thinking it’s a shorted harness or ecu but as it’s intermittent I can’t properly diagnose it.

 

[robert francis]

Years ago, I had an 8 month old MotorCraft battery fail on my 01 Lightning. I'd charge it up - it would read about 13 volts, but as soon as I turned the key, it wouldn't do anything. Finally I had a"load test" done on the battery - and sure enough, a dead cell in it.

 

[SHOrod]

I just pulled up the wiring diagram for the fuel injectors. Unlike some of the older Fords, in the 2010 SHO all injector wires originate and terminate at the PCM. In several slightly older models, common power was provided an only the injector returns connected to the PCM, and the fuel injectors were pulsed by the PCM switching the return/ground. That's why I was asking a question about you checking injector grounds. The question still applies, since if you're measuring less than 5 ohms on the injector return to chassis ground with the key off, that would seem incorrect, unless now the injectors are common ground within the PCM, which I doubt.

Are you willing to share the exact diagnostic code or codes that your car is storing? The factory service manual should have diagnostic procedures for specific codes, and maybe those will shed more light on where you should be checking next.

-Rod