87 4.3 Mercruiser - No Start after tune up

[carfreak_84]

Hi all, first post here. Bought this boat last week, noticed that it was misfiring a bit, I could see the coil arcing from the main post to one of the smaller posts. Decided to replace the wires, cap and rotor and coil. Now that this is done, the boat won't run. It is definitely getting fuel. While cranking it is almost starting but won't stay running. I have checked and double checked all the wires. I replaced them one by one to make sure they are in the right order.

My first thought was timing, but I am unsure of how I would have messed it up.

I have put all the old parts back on one by and still nothing. Reaching the end of my rope and will be calling in a mechanic if i can't figure it out.

 

[alldodge]

While cranking it is almost starting but won't stay running.

There should be 2 wires on the + side which are purple and purple/yellow. The - side may have 2 wires if you have a tachometer

 

[poconojoe]

The last time my 4.3 exhibited the symptoms that you describe, cranking and almost starting, it was the lanyard kill switch. I must have disturbed it while we were hanging out. As I cranked it, it would sputter and almost start. I reset the switch and it started right up. Sometimes it's just a simple thing and I hope this is your case. Good luck. Others will chime in with more ideas I'm sure.

 

[carfreak_84]

There are 2 purple wires on the positive side and 2 grey on the negative.
I don't believe my boat has a kill switch. If it did it would be at the helm, correct?

 

[alldodge]

Being a 87 it wouldn't have a kill switch. Turn key ON and see what voltage you have on the + side of coil

Disconnect one or both wires going to the shift interrupter

Remove the distributor cap and check the points

 

[carfreak_84]

Forgive my newbie question. it's thunderbolt ignition. It has the ignition sensor in the distributor. Where would the point be?

 

[alldodge]

Forgive my newbie question. it's thunderbolt ignition. It has the ignition sensor in the distributor. Where would the point be?

No points being a TB4, disregard point check

 

[carfreak_84]

Thanks! I will head down and check it out with the voltmeter. I will also unhook the shift interrupter and see if that points me in the right direction.

I double checked the spark plug wires. Numbers on the dist cap are matching the numbers cast into the intake.

 

[poconojoe]

When my sensor under the distributor cap went bad, it only cranked, no "almost starting". There wasn't spark at any of the spark plugs. So, I'm assuming it isn't your sensor. But...you know what they say about assuming.

 

[carfreak_84]

Yes for sure.
The sensor looks new. But that doesn’t necessarily mean anything.
Guy I bought it from said it was replaced last year.

 

[poconojoe]

Just as a note...my original OEM sensor was not a sealed unit. It was an exposed circuit board that was all corroded from moisture under the distributor cap. Crazy...right? The new one is completely sealed.

 

[carfreak_84]

Whats going through my head is that it was running before I replaced the parts. So what could have I messed up to cause it to not run? (my poor pride)

 

[alldodge]

Its probably something real simple, but what.
The interrupter could have just moved so it is grounding the dizzy
Look real close at the coil connections (purple and gray wires). Are the wires on the wrong post?

 

[carfreak_84]

Got it running. Carb choke plate was jammed shut oddly enough.
thanks everyone for your help!