f150 won't start on just 1 battery

[gsdanno1]

So after all the trials and tribulations with the balancer , everything back together and in the water , I have a hard starting/very slow cranking issue. I thought I had it solved right before I started on the balancer issue -I found a loose connection at the positive power post , and that seemed to cure the problem . I have 2 starting batteries and 2 *****ing motor batteries. I have separate on board chargers for both. Starting batteries were pulled and load tested last fall by 2 separate people and batteries were said to be good . I am getting 13.1 volts at the battery while everything is turned off. Voltage fluctuates between 13.8-14.1 on the YDS at idle . fresh off the charger ,neither battery will crank the motor , I have to put the battery switch in the "both" position in order for the boat to start , and even then it cranks sluggishly. I checked and tightened all battery connections and power post connections today . Power post nuts were extremely rusted , so they will be replaced tomorrow . My thought is a bad connection somewhere , p[possibly a starter relay going bad ?

[fairdeal]

if you haven't removed and inspected the back side of the lug where the battery cable ground bolts to the block, do that -

as for the relay, that is easily tested - slide the rubber boots down and short across the terminals

[rodbolt17]

how could a starter relay cause slow cranking???????????

[rodbolt17]

yall really understand why the starter relay is there and why it is foolish to suspect it?

it is a simple switch.
it is on or off.
has nothing to do with starter current.

now would be a good time to dust off the multi meter and do a simple voltage drop test on the cables.

[pstephens46]

Curious as to the "power post". What is it?

These connection issues can cost some cash by chasing ghosts.

Betting the batteries are fine. Right up until the point of cranking.

[gsdanno1]

power post/junction block. batteries less than 2 years old

[pstephens46]

yall really understand why the starter relay is there and why it is foolish to suspect it?

it is a simple switch.
it is on or off.
has nothing to do with starter current.

now would be a good time to dust off the multi meter and do a simple voltage drop test on the cables.

For the sake of arguement. What if the relay had shtty contacts? Could this create a voltage drop even with the relay closing?

Nor suggesting this is the OP's issue.

[pstephens46]

power post/junction block. batteries less than 2 years old

Is it in the bilge? Batteries mid boat?

[99yam40]

I believe most are confusing a starter relay with a stater solenoid maybe.
relay is a lower current device , that is why Rod is saying what he does.
solenoid is the high current unit that feeds the starter motor the high current


OP with the battery switch there are a lot more connections to check.
and even cables can go bad internally, so take Rods advice and do the voltage drop test while things are loaded to see where the bad connection is located

[rodbolt17]

that is why thinking is a critical part of trouble shooting.
that relay could cause a no start but cannot cause a slow cranking.
the solenoid could but it is doubtful.
most likely a cable or cable connection.
can be easily tested with a multimeter and a simple voltage drop test.
so with this knowledge I can eliminate the relay from the list of things to check.

[Reel Kahuna]

On my previous boat I had the same thing happened that one battery wouldn't start the F150 but switching the Perko switch to "both", the motor would start.
I ended up changing the battery cables from motor to Perko and then the positives and negatives on each batteries. Solved the problem.

[rodbolt17]

run down to the bank.
get 500 bucks in quarters.
place quarters in a bucket.
stand back 15 ft and toss one handful at it every ten min.

OR

use a simple voltage drop test and find the poor connection/cable/switch.

they sell DVM's at K mart for less than 25 bucks.

you do not need a 300 dollar fluke.

a ten dollar radio shack meter will work just fine.

[rodbolt17]

I see it almost daily.
you would not believe how many chances I have to sell coils and CDI's and such.

I typically ask them why do you think this part is bad??

cause my neighbors uncle was married to a girl who's brother managed to fix a tractor once said it was bad.

I try not to waste folks money.
I do not mind spending other folks money I just try not to waste it.

[boscoe99]

Two guys have the exact same model Yamaha.

Guy one's Yamaha had a stumble at 3647 RPM. A replacement CDI solved the problem.

Guy two's Yamaha has a stumble at 3647. It stands to reason that a replacement CDI will solve the problem. How can it possibly be anything else.

Or so the thinking goes.

Yamaha loves selling replacement spare parts.

[99yam40]

I am curious as to how big of a bucket is needed to hold $500 of quarters.

Do a web search or maybe a forum search for voltage drop test , to make sure you understand the need to measure with a load on the circuit