Mercruser 1898 5.7 with thunderbolt ign problem

[dmiles452]

I have a 1989 5.7 sterndrive that will not accelerate above 2,000 rpm. The ignition module was changed recently. I now find out that I may have paid for the wrong module as there are two different types. One has advance and one does not. The new module has three wires where the one that was replaced only had two wires. If the module is my rpm problem can I see the lack of advance with a timing light? I dont think the carb is the problem I believe it is in the ignition, but I could be wrong.

 

[Scott Danforth]

most of the time its the carb.

2 wire vs 3 wire you are talking about the ignition sensor or trigger assembly. which is a glorified set of breaker points

 

[alldodge]

The 3 wire pickup module is the correct one. The extra wire is for ground

Have you checked compression?
Did this just start happening?

 

[dubs283]

As others have stated on a t bolt ignition the 2/3 wire electrical component you're referring to is most likely the ignition sensor in the distributor.

I recommend using only the oem sensor as I've seen many aftermarket ones fail quickly.

The ignition module (which is the component that controls timing advance) is most likely either located mounted to the port side exhaust riser or the distributor depending on vintage/style and is unfortunately NLA new from mercury

Yes, you can verify timing advance with a timing light. Preferably an advance timing light but a standard one will work too. You're looking for ~20-26° of total advance for proper performance depending on engine model

 

[nola mike]

Also, the sensor that you got doesn't control advance, it's the actual module. Unlikely to be the problem