8.7 Volts at the Coil

[Bondo]

It's brand new.

Ayuh,..... A 26 year old boat ain't brand new,.....

You have corroded connections,..... Somewhere,.....

 

[04fxdwgi25]

Drew, Is yours a TB 4 or TB5? I have diagrams for both (and the shop manual for the 92-98 big block engines if you need it), if you need them

Check
1. The big round plug that connects the engine harness to the boat for tightness / corrosion on the pins. (Had to replace the one I had on my 2550 SX)
2. Ignition switch / wiring for same and if the switch is good. See if you have 12 volts coming out of it.
3. Engine ground to batteries.
4. TB mounting bolts are clean and tight.
5. See if there is 12 volts coming out of the 50 amp breaker on the engine.

If TB5, here is the ts chart for it.

 

[Scott Danforth]

It's brand new.

with 2024 boats coming out, your 1997 boat is 27 years old.

start at the battery, take every connection apart, clean everything with 150 grit sand paper (or a wire wheel in the drill) until they shine enough for your mother-in-law to eat her sunday brunch off of them.

then tighen them, seal them with marine electrical varnish.

do this for every connection in the boat from the battery thru the big cannon plug to the adapter in the harness under the gunwale to the helm and back.

if you come across a wire that the conductors are green, replace it.

only then can you say you cleaned the connections

 

[drewm3i]

Ayuh,..... A 26 year old boat ain't brand new,.....

You have corroded connections,..... Somewhere,.....

The ignition sensor*

 

[drewm3i]

Drew, Is yours a TB 4 or TB5? I have diagrams for both (and the shop manual for the 92-98 big block engines if you need it), if you need them

Check
1. The big round plug that connects the engine harness to the boat for tightness / corrosion on the pins. (Had to replace the one I had on my 2550 SX)
2. Ignition switch / wiring for same and if the switch is good. See if you have 12 volts coming out of it.
3. Engine ground to batteries.
4. TB mounting bolts are clean and tight.
5. See if there is 12 volts coming out of the 50 amp breaker on the engine.

If TB5, here is the ts chart for it.
View attachment 382983

Hey man, this is a different boat, not mine, but a client's. It is a 1997 WellCraft with a 5.7 2 BBL Mercarb. The ignition is Thunderbolt V.

I have gone through this diagram. It is helpful, but doesn't account for low voltage. I'm going to check all of the grounds, tach connections, and the main breaker today. Hopefully I find the fault.

 

[nola mike]

Hey man, this is a different boat, not mine, but a client's. It is a 1997 WellCraft with a 5.7 2 BBL Mercarb. The ignition is Thunderbolt V.

Wait, you're *charging* someone for this?

 

[dubs283]

How is the ignition module grounded?

You told us earlier

It's attached to the main engine ground.

 

[drewm3i]

You told us earlier

I meant the sensor inside the distributor. The module looks to be grounded through the harness.

 

[drewm3i]

Update:

Measuring around 28 ohms at main breaker. With a loose pole. Will replace.

Found a loose ground at the main bus too. Now have 8.8 volts at the coil. Tach was also loose at the I terminal.

Cables at the starter solenoid are very corroded. Will clean.

Measuring 7-8.5 ohms at the perko switch. Within spec?

Measuring .02 ohms of resistance at the kill switch, but only around 11 volts going to the kill switch wires.

Dash voltmeter pegs like 9 volts.

With the new key switch I'm now measuring 11.7 volts at the b terminal in the on position and 11.6 at the I terminal.

Only 10.1 volts at tachometer I terminal with key on!

 

[Scott Danforth]

Keep cleaning... including the ground buss under the helm and ground stud on the block

 

[drewm3i]

Update 2:

Alright so I have 12.6 coming out of the I terminal at the switch. Found the harness for the kill switch and have 12.54 there with .01 ohms. Have 11 volts at the kill switch and 10.54 at the harness that heads back to the engine where I'm seeing 8.6 volts at the coil. I'm starting to think the main issue is the main breaker having too much internal resistance causing voltage to drop off rapidly. All the connections look fine IMO.

 

[Scott Danforth]

The main breaker is before the key switch. So that isnt it

Power goes from:
battery to main breaker
Main breaker to cannon plug
Cannon plug up harness thru adapter harness connection to ignition switch

Once ignition switch is turned on, power goes back to motor thru MOB switch to adapter harness connection to cannon plug to coil.


Clean every connection, you will find the bad one

 

[drewm3i]

The main breaker is before the key switch. So that isnt it

Power goes from:
battery to main breaker
Main breaker to cannon plug
Cannon plug up harness thru adapter harness connection to ignition switch

Once ignition switch is turned on, power goes back to motor thru MOB switch to adapter harness connection to cannon plug to coil.


Clean every connection, you will find the bad one

I know this, but this is helpful information nonetheless.

I'm tracing the purple wires coming out of the I terminal on the switch and have found that the voltage steadily drops out. At the tach it is around 10 volts. Back at the coil, 8.7. All of the connections are clean and secure, but the voltage drops nonetheless. The exact readings were as follows:

"12.6 coming out of the I terminal at the switch. Found the harness heading to the kill switch and have 12.54 there with .01 ohms. Have 11 volts at the kill switch wires and then 10.54 at the harness that begins to head back to the engine where I'm seeing 8.6 volts at the coil."

I think I'm going to run new wires to bypass it all to start fresh. It's not a grounding issue. The engine is grounded well as proven by multimeter testing.

 

[Scott Danforth]

Check the plug in the harness by the MOB switch, check the plug in the harness by the Starboard aft corner

 

[drewm3i]

Check the plug in the harness by the MOB switch, check the plug in the harness by the Starboard aft corner

This has a non-OEM dash-mounted kill switch that I installed last year. The wire connections are all heat shrunk and the kill switch only has .01 ohms of resistance. I have also had it bypassed for a long while with a jumper wire to rule it out for testing. It seems the actual wires themselves are the problem here because I'm seeing the voltage drop off for the entirety of the wire run.