Mercruiser Thunderbolt ignition Question

pbruley1116

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Jul 10, 2022
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I have a 2010 Mercruiser 4.3 TKS with Alpha Sterndrive. V6 with 2 BBL Carb and Thunderbolt V Ignition (Engine s/n 1A612644)

Recently I have been troubleshooting the TB V ignition system. I have a question about how https://forums.iboats.com/threads/how-mercruiser-thunderbolt-ignition-systems-work.676476/ long it should take for spark to start when cranking over the engine. Very nice write up here: but does not answer my question.

When I first start my engine (after boat has been sitting overnight) my engine always has to crank over for 3-4 seconds before starting. I always thought this was an issue with fuel needing time to get to carburetor; however after trouble shooting my ignition system I noticed that I don't get any spark for 3-4 seconds when attempting to start. Once ignition system finally sends a spark the engine starts just fine.
When the engine is warmed up it only takes about 1-second to start.

Is this normal behavior?

Is there a way I can get the ignition system to send spark right away? Why is there a delay?
 
Last edited:

poconojoe

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Sep 10, 2010
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1,805
You may be right about the spark, but make sure your choke is working properly.

Recently, my choke was not closing when cold and it was real difficult to start. When hot it was fine, it was just when it was cold.

I adjusted the choke and it starts right up when it's cold.
 

pbruley1116

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The TKS carb has an automatic choke system.
I am using a timing gun to watch for spark.
It is very consistent in the way it starts.. I have to hold the starter on for 4-5 seconds.. as soon as the ignition sends the spark the engine fires up right away.
 

alldodge

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Look at the module inside the distributor and see if it has 2 wires or 3. If it has 2 wires, it might be worth getting the replacement 3 wire version. The 2 wire type has a grounding issue
 

pbruley1116

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I have the 3-wire.
I was having sporadic no-spark issues
So replaced the following parts
-Spark Plugs
-Coil (this was the ittermitant culprit)
-Distributor Cap & Rotor
-Rotor position sensor (3-wire) in Distributor
That is how I noticed the long spark delay when starting.
The engine has done this since the day I bought it brand new (12 years ago)
But like I said I always thought it was a fuel issue as there is an electric fuel pump the comes on and fills the carb bowl when starting.
Now I know it is a delayed spark .... like the system has to wait for a couple of revolutions before it decides to send a spark. The TB V write up I have read does not talk about what happens during the first few seconds of starting so I thought I would ask if this spark delay is normal. If not how can I get it to spark right away when I start?
 

alldodge

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Not sure about a 2010 TBV but the old ones didn't have a delay. When I start my MPI and its cold, the ECM has it crank over about 2 full revolutions befoe it will start. When warm it doesn't even turn over 1/2 a Rev before firing up

Could be, its built into the system. I don't know, just an idea
 

pbruley1116

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My TB V is similar to your MPI as it only does the long spark delay when engine is cold then once engine is warm it fires up right away. There is no ECM on my set up so it must be the TB V doing it.

Is there a sensor on the side of the engine that sends a RPM/Tach signal to the TB V? If so maybe it's acting up.
 

alldodge

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With it only doing when cold I would let it go and not bother with it. The good thing about the 2 Rev's is it has times to build a bit of oil pressure before starting
 
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