Thunder Bolt ignition sensor replacement gone bad

[radiotoaster]

Hello,
I have a 1995 Chapperal Deckboat... 26ft . It has a 1999 5.0L mercruiser with thunderbolt 5 ignition system. I have had a random stalling issue that I am trying to fix. Basically once it gets to operating tempfor about 30 minutes it just shuts down, It fires right back up, no other symptoms and runs for another 20 - 30 minutes then shuts down again... rinse and repeat and annoying.

I went ahead and replaced the coil as well as the ignition sensor located in the distributer. As most of you may know the old sensor had 2 leads, the new generation sensor has 2 leads plus a ground.

After replacing both the boat fired right up however, if I turned any accessories on the RPMS would dramatically drop. For example if I turn on my blower while at idle the motor would die. If I have the throttle up a bit the RPMS would drop dramatically yet it may not die.

Thinking a bad ground connection I ran a wire all the way to the grounding block and same issue. I put the old part back in and I have no RPM drop. Anyone know what else I can try to fix this issue?


Thanks

 

[alldodge]

Thinking a bad ground connection

Agree, but don't think its the ignition module connection

if I turned any accessories on the RPMS would dramatically drop. For example if I turn on my blower while at idle the motor would die. If I have the throttle up a bit the RPMS would drop dramatically yet it may not die.

I think you have a bad ground back to the battery. Put a voltmeter on the starter post and see what reading you get. Then increase roms and turn the blower on and see what changes. If all good. do same thing at the + side of the coil

 

[radiotoaster]

Thanks AllDodge, I appreciate the response, I will try to source the issue.

 

[sk7499]

If the old sensor works then you might have a bad sensor or an incorrect sensor. or a ground issue. when you connect the new sensor and turn on accessories what is the battery voltage does it also go down

 

[Scott Danforth]

the old trigger assembly in the TB5's was unpotted and they failed . the upgraded ones have an extra ground wire and are fully conformal coated.

its never the coil (only 3 out of a million changed coils are ever bad)

the RPM's dropping when you turn something on is a sign of a bad connection somewhere.

 

[radiotoaster]

Thanks for helpful insight. The wifey wanted to go on the boat yesterday so we took a spin around the lake. The boat ran okay, I normally dont push it over 3800 RPMs, however on the way back I figured I would go WOT. A couple things I noticed, My voltmeter (on the boat) was reading just above 8 volts and the boat seemed to hesitate then surge but would not get over 4K RPM. Normally when I go WOT it gets to about 4300 MAX. I think I am paying much more closer attention to the Voltmeter and was much lower than I remember. Then the motor cut out, and the voltmeter pinged back up to 13.5. I am assuming this stuff is all connected... The boat fired right back up and I got back to the dock. Anyway once I get a minute I will do some more searching for anything that is not properly connected and keep cleaning terminals.. Thanks.

 

[alldodge]

With 8V the motor will barely run, it has a bad connection somewhere

 

[radiotoaster]

Could a blown starter fuse be causing my issue if I am jumping the slave solenoid to my battery?

 

[alldodge]

There is a fuse on top the starter which feeds power to the motor and alternator, its 90 amps



But if it blows, normally there is no power for anything.
Why are you running power from the battery to the slave?

 

[radiotoaster]

One morning I tried to start the boat and it would not turn over... just a faint click from the solenoid. While trouble shooting I realized the red and purple wire was not hot. At first thought it was because a wire burned out so I just ran another wire to the slave and it started right up and was planning on fixing it properly when I pulled the boat out of the water. Then I figured I would try to fix my stalling issue by replacing the ignition sensor and coil.....

 

[alldodge]

Sounds like the fuse above

 

[radiotoaster]

Alright so I wanted to regroup here. I pulled the 90 AMP fuse off the starter and it was blown. I replaced the fuse, then I installed the new ignition sensor again and ran the ground from the sensor to the neg. on the battery. The boat is now running as it was before the starter fuse issue, meaning it still has a stalling issue.

After the boat runs for about 15 -20 minutes, once it is up to temperature the motor will stall. Whether the motor is running at 2K, 3K or WOT. The motor shuts down, like the kill switch was pulled. After the first time it stalls of the day it will continue to stall intermittently, sometimes 5 minutes of running to 20 minutes of running. After the boat stalls, I put the gear back to neutral, and the motor will start right back up.

So far I replaced the ignition switch, the ignition sensor, the coil and the rotor. Does anyone have any other thoughts on what I should look at/ replace?

.

Thanks.

 

[achris]

Have you proved it's a spark issue? ie, have you put a timing light on a spark plug lead and watched it lose spark? Next, put an LED (with a resistor) on the coil positive and watch, see if the light goes out as the engine stalls. Do the instruments drop dead when it happens?

So many ways to troubleshoot this problem... And the shotgun approach of just replacing parts that MIGHT be the cause, isn't it.

Chris........