How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Jason Your Own Question
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16214
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
Type Your Boat Question Here...
Jason is online now
A new question is answered every 9 seconds

Boat will not fire. I have 93 mercruiser 4.3l thunderbolt IV

This answer was rated:

Boat will not fire. I have 93 mercruiser 4.3l thunderbolt IV ignition, I have replaced the coil, ignition sensor, rotor, cap, ignition module an still will not fire. I do not get 12v from red an white wire coming off of the ignition module. there is 12 volts at coil positive terminal. I am at a loss.
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else important you think the Marine Mechanic should know?
Customer: no

H​ello my name is ***** ***** am I speaking with? I read what you wrote. Did you replace the parts with new or used parts?

Customer: replied 29 days ago.

Are you near the boat now?

Customer: replied 29 days ago.

Start with this. Pop the distributor cap off. Crank the engine over. Let me know if the rotor is spinning or not.

Customer: replied 29 days ago.
it is spinning

Are you familiar with where the shift interrupt switch is on the engine?

Customer: replied 29 days ago.
I disconnect that also to see if I would get the voltage if from the red and white wire if it was disconnected.

Got it. Does your TB4 ignition module have a separate ground wire, or is it grounded through the module? (there are a few different styles of that module and I don't know which one you have)

Customer: replied 29 days ago.
grounded through module

Is the module mounted to the distributor or to the exhaust manifold?

Customer: replied 29 days ago.

Get a jumper cable, like automotive, and clamp 1 end to the distributor and the other ends to the battery negative terminal, crank the engine over, and see if spark returns or not.

Customer: replied 29 days ago.
where on the distributor?

Just on the middle of it. Clean it off and make sure its' free of paint. Also make sure where the ignition module mounts to the distributor is free of corrosion as well.

Customer: replied 29 days ago.
it did fire when I did that
Customer: replied 29 days ago.
what next?

Good morning and sorry for the delay. When you replied back last night I had already logged off for the night. Can you take a picture of your ignition module and distributor for me so I can see what it looks like.

Customer: replied 28 days ago.
I rook harness off so you could see module. Did you get the picture?
Customer: replied 28 days ago.
Did you get the picture?

Sorry, went out for a morning walk with the wifey. I see the picture. Ultimately the problem is the module needs to be grounded in order to work, and it's not getting a good ground from the distributor. This is why it works when you improve the distributor ground with the jumper cable. The right way to fix this would be to remove the distributor from engine and clean the base of it, as well as clean up the top of the intake manifold in order to provide a good ground, reinstall the distributor, and retime the engine. That is the right way, but realistically speaking that is way to much work for a problem like this. What I would do instead is get a length of 12 to 14 gauge stranded wire, and crimp on some eyelet style terminals on each end of that wire. Then attach 1 end of that wire to one of the bolts that hold the module in place, then run the other end of that wire to anyplace there is a good clean ground on the engine block. If you can't find a clean ground, you can bring the other end back to the battery negative terminal. This will properly ground the module (just like the jumper cable was doing) and get your spark back. Does that all make sense. That is where you stand on your end and what the problem is. I think that should do it but I work for tips so I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Please note that our question sessions never close out, so if you need to come back later down the road with follow up questions to the issue, you can do so at any time, even after putting through a rating.

Thanks in advance, and good luck

Jason and other Boat Specialists are ready to help you