Help with Mercruiser ignition 1994 series, new motor

[scottpak]

I am fairly mechanical, just super stumped on this.

1983 Aquasport 23 foot repowered in 1994 with mercruiser 305

now repowered with generic long block marine 350.

everything was directly swapped over, only sensor not connected is knock sensor.

No spark.

New plugs, coil, and ignition pick up, cap/rotor only 1 year old

any thoughts? I am sure i messed something up.

Distributor has white/red, white/green, and black out of the sensor
coil has Purple + and tan - purple into harness, tan into harness

Thanks a ton

 

[alldodge]

Re: Help with Mercruiser ignition 1994 series, new motor

Going from a 305 to a 350 is going to cause some ECM issues with fuel and torque curve, but should not keep it from starting. I take it you have an EFI system since you have a knock sensor.

Purple goes to + side of Coil
Gray goes to - side of coil
Tan is for water temp sensor

What is the engine serial number for the harness your working with.

 

[scottpak]

Re: Help with Mercruiser ignition 1994 series, new motor

whoops your right grey wire to neg.

not efi 2 barrel carb.

serial number plate off old motor reads------L625872

 

[Don S]

Re: Help with Mercruiser ignition 1994 series, new motor

serial number plate off old motor reads------L625872

Are you sure about that serial number? That would make that a 2000 model engine, not a 94, and it would have a Thunderbolt V ignition, not a IV.

 

[alldodge]

Re: Help with Mercruiser ignition 1994 series, new motor

The serial number comes out to be 5.0L (2 BBL.) GM 305 V-8 1998-2001. As before there are differences between 5.0 and 5.7 engines and require different ICM's. Don't know if you have a TB4 or 5 but I'm guessing 5 here is both

 

[scottpak]

Re: Help with Mercruiser ignition 1994 series, new motor

Hhmm. What would be the unique identifier for the TB5? The diagnosing looks close. I will run through the 5 and see where we go. Thanks for all the help guys. If it comes down to the icm are there any sources for them? Besides full retail mercury?

 

[scottpak]

Re: Help with Mercruiser ignition 1994 series, new motor

ok ran through both test.......all lead to a bad ICM coil was removed and bench tested. that works fine.

seems like the grey wire at coil is not breaking to let coil fire--as if points were stuck closed--if it had points.

i can make the grey wire open if i unplug harness at ICM

 

[Don S]

Re: Help with Mercruiser ignition 1994 series, new motor

Disconnect the gray wire from the - terminal of the coil, or if it doesn't have a separate wire, disconnect the gray wire on the back of the tachometer itself.
A shorted tach is one of the first things you should have checked for.

 

[alldodge]

Re: Help with Mercruiser ignition 1994 series, new motor

You said everything is hooked up except the knock sensor, and as Don mentioned your serial number comes out to be a 2000 model. I On my engine if the knock sensor wire is removed it will still run but mine is an EFI, so I figure yours should also. Do you have the knock control module hooked up?

 

[scottpak]

Re: Help with Mercruiser ignition 1994 series, new motor

Don. I did remove grey wire from tach. Still nothing. In fact I have left it off. Even went so far as to disconnect the ground that goes up to the instruments.

Alldodge. I have reinstalled the knock sensor hoping that might have been my missing link. But no. Yes the knock module is still hooked into the harness.

someone mentioned grounding to me. What items need clean and solid grounding? Does the icm plate need to be grounded?

THanks again.