1993 mercruiser 5.7 with thunderbolt ign. problems

Johnny Blaze

Recruit
Joined
Sep 4, 2013
Messages
2
Hey guys,
I have power to + side of coil with key on, but get no spark to distributer from coil when cranking. I checked the coil wire, and that is fine. All wires have been traced and are all connected and in perfect shape, replaced the coil, no luck, then changed the cap and rotor, still no spark frm coil wire, what gives? any ideas? Please help, I am at my wits end!
 
Last edited:

alldodge

Moderator
Staff member
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Mar 8, 2009
Messages
40,582
Re: 1993 mercruiser 5.7 with thunderbolt ign. problems

Hey guys,
I have power to + side of coil with key on, but get no spark to distributer from coil when cranking. I checked the coil wire, and that is fine. All wires have been traced and are all connected and in perfect shape, replaced the coil, no luck, then changed the cap and rotor, still no spark frm coil wire, what gives? any ideas? Please help, I am at my wits end!

:welcome: to iboats

Sure could use a serial number to help but until then.
If you have a tach there will be a Gray wire on the back, remove it and try to start.
Here is the TB-4 troubleshooter, go through it exactly and it will find your issue.

TB5 Ignition.jpg
 

81 Checkmate

Lieutenant
Joined
Jul 20, 2010
Messages
1,360
Re: 1993 mercruiser 5.7 with thunderbolt ign. problems

Welcome to iboats........

Look in the adult only section at the top of the i/o forum by Don S.....there is a trouble shooting chart for your system.

P.S. you will get better results by posting your engine serial number..!
 

camalot

Petty Officer 2nd Class
Joined
Jul 24, 2012
Messages
144
Re: 1993 mercruiser 5.7 with thunderbolt ign. problems


Good steps to follow but you can get a false result following that trouble shoot. How do you test the ignition amplifier?

Help a dude out last week with the same problem, which still had the old style sensor in the dissy. After going doing that very trouble shoot ^^^^ it was pointing to the ignition amplifier was toast, problem is these are NLA.
All the wires to the ignition amplifier looked good (purple had 12v) plug looked clean, but using a spark gap tester from the coil to ground with the iggy ON and wiggling the plug to the ignition amplifier I would get a spark jumping a 7/16 gap.
All I did was disassemble the plug and clean it along with the ignition amplifier and hey presto it was working and still is. In my haste I wish I had measured the iggy sensor out put to find a way to check the ignition amplifier as my gut feeling is they are not always to blame.
 

Johnny Blaze

Recruit
Joined
Sep 4, 2013
Messages
2
Re: 1993 mercruiser 5.7 with thunderbolt ign. problems

Welcome to iboats........

Look in the adult only section at the top of the i/o forum by Don S.....there is a trouble shooting chart for your system.

P.S. you will get better results by posting your engine serial number..!

Ok guys, i disconnected the gray wire from the tack. still nothing. by the way. with the key on i noticed when i checked this before, that i have power to both sides of the coil, with the key on. this is still the same with the gray tack wire disconnected from the tack. I find it odd that i get power to both sides of the coil. is this normal? also my serial # is 0F019137.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Re: 1993 mercruiser 5.7 with thunderbolt ign. problems

Ok guys, i disconnected the gray wire from the tack. still nothing. by the way. with the key on i noticed when i checked this before, that i have power to both sides of the coil, with the key on. this is still the same with the gray tack wire disconnected from the tack. I find it odd that i get power to both sides of the coil. is this normal? also my serial # is 0F019137.

Ayuh,.... Power goes through the coil to the ignition,...

When the ignition grounds out the coil, it Fires off,...
 
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