2003 Mercruiser 8.1 HO No Crank No Start Fuel Pump Running

[mckaras]

Hello,

I'm having an issue trying to start my engine on a stand. There's enough juice in the batteries. Cranks and Starts when the starter is jumped. Fuel pump turns on when the key is turned. I changed out the starter relay with a new one and still the same issue. I've used this ignition switch set up on a dozen engines without any issues.

My question is what is the next thing to check on the engine? Could it be the 50 AMP breaker on the engine causing issues? I have another starter on the way just in case and will be picking up another ignition to change out with this one.

 

[Bondo]

My question is what is the next thing to check on the engine? Could it be the 50 AMP breaker on the engine causing issues? I have another starter on the way just in case and will be picking up another ignition to change out with this one.

Ayuh,...... Instead of replacing stuff, Test the connections with a test light or multimeter,.....

 

[alldodge]

Agree
See if there is power on both sides of the breaker

Can also do it direct at the plug

 

[Scott Danforth]

If the fuel pump is running, then the ignition circuit is powered

Since it's not cranking:
Check the ignition switch
Check the neutral safety switch
Check the cannon plug terminal
Check the starter pilot relay

 

[mckaras]

If the fuel pump is running, then the ignition circuit is powered

Since it's not cranking:
Check the ignition switch
Check the neutral safety switch
Check the cannon plug terminal
Check the starter pilot relay

Got it all sorted, I ran the wire back to the starter solenoid 8M0185149. No voltage at the wire connected to the solenoid when ignition was turned to start and no voltage at the solenoid where the starter solenoid wire connected. Thanks for all the help!

 

[mckaras]

Agree
See if there is power on both sides of the breaker

Can also do it direct at the plug
View attachment 405416

Got it all sorted, I ran the wire back to the starter solenoid 8M0185149. No voltage at the wire connected to the solenoid when ignition was turned to start and no voltage at the solenoid where the starter solenoid wire connected. Thanks for all the help!

 

[mckaras]

If the fuel pump is running, then the ignition circuit is powered

Since it's not cranking:
Check the ignition switch
Check the neutral safety switch
Check the cannon plug terminal
Check the starter pilot relay

Well, I still the same issue. No voltage at the wire going to the solenoid. I checked voltage going to the ignition switch, cannon plug terminal, 50 amp breaker, and starter pilot relay and it has enough voltage.

The solenoid that the starter solenoid wire runs to has no voltage at the starter solenoid or the solenoid that the wire runs to.

The neutral safety switch I still need to check since it's still wrapped up.

 

[mckaras]

Agree
See if there is power on both sides of the breaker

Can also do it direct at the plug
View attachment 405416

One place I haven't checked power at is the neutral safety switch. I'm just getting 0 voltage at the yellow/red wire going to the starter solenoid from the solenoid that's mounted under the ECU. Changed it out for a new one and I was still having the same issue with 0 voltage with key turned in the on position.

 

[alldodge]

One place I haven't checked power at is the neutral safety switch. I'm just getting 0 voltage at the yellow/red wire going to the starter solenoid from the solenoid that's mounted under the ECU. Changed it out for a new one and I was still having the same issue with 0 voltage with key turned in the on position.

With the motor on a stand there will be no neutral safety switch

Find the relays on the motor and find the one with a small and large Yel/Red wires.
When pin seven on the 10 pin plug has 12V applied to it it will go to the smaller of the 2 wires on the relay. The relay should energize sending power on the larger of the yel/red wires down to the starter.

The relay will have 2 yel/red, one black and one red/pur wires


The only change in this is if your motor is early enough to not use a square relay and in that case it would use the old slave relay

 

[alldodge]

BTW do you have a voltmeter and know how to use it?

 

[mckaras]

BTW do you have a voltmeter and know how to use it?

Yes I do, I was checking power with a voltmeter

 

[mckaras]

With the motor on a stand there will be no neutral safety switch

Find the relays on the motor and find the one with a small and large Yel/Red wires.
When pin seven on the 10 pin plug has 12V applied to it it will go to the smaller of the 2 wires on the relay. The relay should energize sending power on the larger of the yel/red wires down to the starter.

The relay will have 2 yel/red, one black and one red/pur wires

View attachment 405473
The only change in this is if your motor is early enough to not use a square relay and in that case it would use the old slave relay
View attachment 405472

It's a 2003 engine, it has the 3 square relays. There's no relay with a yellow/red wire going to it. I swapped over 3 relays from my other 8.1 with the 3 on this engine. Still the same issue, that engine starts.

I have the wiring diagram for this engine and there's a yellow/red going from the ignition switch/barrel connector to the slave relay (above) and one yellow red going from the slave relay (above) to the starter solenoid.

 

[mckaras]

With the motor on a stand there will be no neutral safety switch

Find the relays on the motor and find the one with a small and large Yel/Red wires.
When pin seven on the 10 pin plug has 12V applied to it it will go to the smaller of the 2 wires on the relay. The relay should energize sending power on the larger of the yel/red wires down to the starter.

The relay will have 2 yel/red, one black and one red/pur wires

View attachment 405473
The only change in this is if your motor is early enough to not use a square relay and in that case it would use the old slave relay
View attachment 405472

The only spot that I did not have 12.4/.5 Volts going to was the red/yellow connection at the slave relay and where the red/yellow wire leads to on the starter solenoid. Every other connection with the yellow/red wire had 12V to it and I checked the positive connections at the starter, slave relay, and the 50 AMP breaker they all had 12V going to it. Key was in the off/on/start positions. No power at the slave relay and starter solenoid in start position.

 

[alldodge]

There's no relay with a yellow/red wire going to it

That's not right, Merc has uses standard colors and hasn't changed them since maybe the 70's

I have the wiring diagram for this engine and there's a yellow/red going from the ignition switch/barrel connector to the slave relay (above) and one yellow red going from the slave relay (above) to the starter solenoid.

Some things are not clear for this old guy
I will assume you have the slave relay which I posted above
In that case all good

The only spot that I did not have 12.4/.5 Volts going to was the red/yellow connection at the slave relay and where the red/yellow wire leads to on the starter solenoid. Every other connection with the yellow/red wire had 12V to it and I checked the positive connections at the starter, slave relay, and the 50 AMP breaker they all had 12V going to it. Key was in the off/on/start positions. No power at the slave relay and starter solenoid in start position.

A Red/Yellow?
Post pic of this wire showing where it's coming from

496 wiring with slave relay

 

[alldodge]

I'll add a possible change, if this motor came out of a boat which has Vee or direct shaft drive, then the connections going to the transmission need to be jumped together

 

[mckaras]

The only spot that I did not have 12.4/.5 Volts going to was the red/yellow connection at the slave relay and where the red/yellow wire leads to on the starter solenoid.

I'll add a possible change, if this motor came out of a boat which has Vee or direct shaft drive, then the connections going to the transmission need to be jumped together

It did have a ZF 63 transmission attached. I think that might be my issue then! I started the other engine when the transmission was attached still... I can't believe I missed it. Do I need to change anything electrical since I'm converting it for a sternboard? I have the other engine I will be taking out to swap over the old bellhousing, starter, etc.

 

[alldodge]

It did have a ZF 63 transmission attached. I think that might be my issue then! I started the other engine when the transmission was attached still... I can't believe I missed it. Do I need to change anything electrical since I'm converting it for a sternboard? I have the other engine I will be taking out to swap over the old bellhousing, starter, etc.

Only change need going from trans to I/O needed, connect trans wires together and make sure the neutral safety switch is connected to yel/red wire coming from ignition switch goes thru it on throttle handle

 

[mckaras]

I'll add a possible change, if this motor came out of a boat which has Vee or direct shaft drive, then the connections going to the transmission need to be jumped together

If you can send me what connections need to be jumped since I detached the transmissions to list one of these 8.1s for sale and one for install that'd be great.

 

[mckaras]

Only change need going from trans to I/O needed, connect trans wires together and make sure the neutral safety switch is connected to yel/red wire coming from ignition switch goes thru it on throttle handle

Good to know. Thank you very much

 

[alldodge]

If you can send me what connections need to be jumped since I detached the transmissions to list one of these 8.1s for sale and one for install that'd be great.

Wiring diagram in post 14 shows a Yel/Blk and Blk get jumped together

The wires should be at rear of motor