Help with Thunderbolt IV

[Forestrytodd]

I'm about to pull what little hair I have left out!

1991 Sea Ray with Mercruiser 5.7L Alpha and a Thunderbolt IV. I winterized the boat last fall and I had to let it sit due to two house payments. Now one house sold and its time to get my kids back on the water so I run through the check list of stuff to make sure things are right and she will not crank.

I first replaced both batteries since they were 7 years old and would not hold a charge. Then she would not fire. I pulled the Dist cap and there was some corrosion in there so she got a new cap and rotor....still nothing. So we start with the search on here and the flow charts and we start testing. I have now replaced the sensor in the distributor, the ignition module, the coil and run new ground wires from the module and the distributor to the back of the block just to make sure that was not the problem. I have isolated the tach and the interrupter switch too. 12 volts to the coil on the purple and gray sides with the key on and while cranking.

I don't have a spark gap tester but I used a spark plug in the coil wire and grounded it and then grounded the green/white wire and nothing. will this work like a gap tester or not?

There is nothing else to replace and I still have no spark. The motor will turn over just fine, it just will not crank! All the parts are new and not used and I'm at a loss. Help before my kids miss the whole summer off our boat.:facepalm:

 

[Eric 3.7LX Alpha 1]

Re: Help with Thunderbolt IV

Here is a service bulletin on troubleshooting the IV ignition:
http://www.boatfix.com/merc/Bullet/83/83_24.pdf

 

[Forestrytodd]

Re: Help with Thunderbolt IV

Thanks Eric. Very informative but I think I have been through all these. The only thing I did not do was the lock tight on the distributor.

Any other suggestions to look at?

 

[Bondo]

Re: Help with Thunderbolt IV

Thanks Eric. Very informative but I think I have been through all these. The only thing I did not do was the lock tight on the distributor.

Any other suggestions to look at?

Ayuh,... Welcome Aboard,.... You have to go through the diagnostic tree, step by step, in order, to find the bad component,...

There ain't no Easy button,...

 

[tank1949]

Re: Help with Thunderbolt IV

Forestry, I'd check for good gound, and I'd also get ready for the next problem: stale crap *** gassohol. I learned the hardway to solder all connections and I still have one motor that is slow in first truning and then speeds up and ingites. Run a good 40 ground from block to battery or use jumper cables after you clean contacts going to coil/distributor. Heck, cleaning them may solve your problems.

 

[Forestrytodd]

Re: Help with Thunderbolt IV

Bond-O, I have gone through the tree many, many times. That's why all the stuff is new in there.

Tank - No gas-a-crud stuff in my boat! I use only pure gas in my stuff. I'm lucky that I now live in Louisiana and there is an amply supply of real stuff here since they refine it just on the other side of town.

I have checked all the grounds, cleaned them put them back on, and even ran some new ones. That's why I'm puzzled.

Is there something else I'm missing?

 

[Fun Times]

Re: Help with Thunderbolt IV

I don't have a spark gap tester but I used a spark plug in the coil wire and grounded it and then grounded the green/white wire and nothing. will this work like a gap tester or not?

There is nothing else to replace and I still have no spark.

No not really, One of the reasons you should use a gap tester vs the coil wire and spark plug is due to the fact that the coil wire itself could be bad as well.

new cap and rotor....still nothing. I have now replaced the sensor in the distributor, the ignition module, the coil and run new ground wires from the module and the distributor, isolated the tach and the interrupter switch, 12 volts to the coil on the purple and gray sides with the key on and while cranking.

So you do have up to 12-Volts at WHT/RED Terminal on Distributor?

You're version of the ignition module is their version of ignition amplifier correct? You have to make sure the wiring to ignition amplifier is making contact. Don't assume that it is. Problems have been accidentally found by back probing while testing with multimeters and such. Sometimes the fix was installing a new ignition amplifier wiring harness.

One last test for you to try is, if you set your multimeter to dc volts and connect the positive lead of the multimeter to the negative side of the coil and the negative lead of the multimeter to a good ground, with the ignition "on" hold the white/green wire from the module/amplifier to ground for a few seconds, if the voltage drops to 7-9 volts, then returns to 12, the module is good.

 

[Forestrytodd]

Re: Help with Thunderbolt IV

Fun times - Thanks. I'll do the test on the module and let you know the outcome. I've checked the new harness connections many times and yes I do have 12 volts on the red/white wire on the module in the dist.

 

[Forestrytodd]

Re: Help with Thunderbolt IV

No voltage change. Pos of meter to neg coil and neg on the meter to a ground brings me 12 volts. When I ground the white/green wire there is no change in the reading. So you think that I got a bad ignition module strait out of the box? This was from a dealership in FL that still had one on the shelf since its not made anymore by Mercruiser.

 

[Fun Times]

Re: Help with Thunderbolt IV

No voltage change. Pos of meter to neg coil and neg on the meter to a ground brings me 12 volts. When I ground the white/green wire there is no change in the reading. So you think that I got a bad ignition module strait out of the box? This was from a dealership in FL that still had one on the shelf since its not made anymore by Mercruiser.
I've checked the new harness connections many times

When you received the new ignition module, did it come with a new wire harness as well? If so, Do you still have the old harness?

In no particular order you could try ohms checking both wire harnesses and modules to see if you get about the same readings.

 

[achris]

Re: Help with Thunderbolt IV

No voltage change. Pos of meter to neg coil and neg on the meter to a ground brings me 12 volts. When I ground the white/green wire there is no change in the reading. ....

Never actually done that particular test, but looking at the circuit and how it should work, I'd say that having a constant 12 volts on the wht/red is what you'd expect... That's the wire that supplies power to the sensor in the distributor. It's the wht/green that provides the 'fire' signal. That's why you need to tap the wht/green against ground to get a spark....

Chris....

 

[NHGuy]

Re: Help with Thunderbolt IV

I hate to suggest this cause it sounds like you are a fairly intelligent person, but... Safety kill switch or lanyard? is it in the on position?
Is the shift interrupt engaged? To allow the ignition to run the roller must be nestled down in the vee.
How about the ignition switch, check that the right wires are hot in the start position and in the on position.
Is there fuel? Stupid questions, but when frustration sets in... just sayin'

 

[tank1949]

Re: Help with Thunderbolt IV

Fun times - Thanks. I'll do the test on the module and let you know the outcome. I've checked the new harness connections many times and yes I do have 12 volts on the red/white wire on the module in the dist.

Don't take this as an insult but in haste one time between arguments with my wife, I tuned up my OMC sterndrive and forgot to put the rotor back in distributor. Perhaps this happen to you?:facepalm:Also, I had a MC TB IV rotor go bad. If you are getting spark out of coil (as I understand) to dist, something is keeping curent from plug wires. If not coming out of coil, but 12 vts +- going in then bad coil or gnd. We recently replaced NEW trim "noid" with another new "noid." So, new stuff does go bad.

 

[Forestrytodd]

Re: Help with Thunderbolt IV

NHGuy I don't have a kill switch on my boat on a lanyard. I checked all the other stuff too. I even put fresh real gas in it too to rule that out. Even checked to see it squirt into the carb. even tried some either just to see. I disabled the interrupter switch by disconnecting the green/white wire from the dist to rule that out too. And no offense taken on those either, I've done some dumb stuff in my past and overlooked stuff too that's part of why I posted cause I'm stumped.

Here's the kicker last night I decided to start swaping parts new and old in every combination I could think of just to see if there was something wrong. So I cleaned all the connections with all new parts with the interrupter and tach not connected to rule that stuff out and the first thing I did was new ignition module and new coil with the old sensor in the dist and she fired up! Ran through several checks and turned her off. Connected the tach and the interrupter switch and she worked fine again. Ran great, warmed up and ran about 160 deg. I ran it for almost 20 min and cranked it a few times to check.

We decided to take her to the ramp today after church and unloaded her and she fired right up. Dropped her in reverse to back out of the way and she stalled. We spent 30 min with the kids in the boat and she would not even think about firing up again. I disconnected the tach and interrupter switch on the water and still nothing so rather than get stranded with the kids, we put it back on the trailer.

Now I'm wondering if I should just replace the sensor again or I have some other problems that are leading to the non spark. turns over fine just will not fire. So tomorrow I'm going to start again!

 

[Fun Times]

Re: Help with Thunderbolt IV

Never actually done that particular test, but looking at the circuit and how it should work, I'd say that having a constant 12 volts on the wht/red is what you'd expect... That's the wire that supplies power to the sensor in the distributor. It's the wht/green that provides the 'fire' signal. That's why you need to tap the wht/green against ground to get a spark....

Chris....

Hey Chris, I figured you would like to see the success story of an ignition module passing the test that was confirmed by the original poster. So it's interesting to see that there is one test passing while Forestrytodd's is not passing the test.
See post's, 2, 11, 17 for test results,
http://forums.iboats.com/mercruiser...drives/apha-one-v6-thunderbolt-iv-444003.html

No voltage change. Pos of meter to neg coil and neg on the meter to a ground brings me 12 volts. When I ground the white/green wire there is no change in the reading. So you think that I got a bad ignition module strait out of the box? This was from a dealership in FL that still had one on the shelf since its not made anymore by Mercruiser.

Before condemning modules, You have to ensure the all the wiring is making contact by Pulling wire connectors, inspecting them, ensuring that the wire pins are reaching/touching their respective counterparts then reconnecting and give them a wiggle while trying to start the engine if possible and even once you do get it running again, carefully wiggle them some more to make sure it stays running. As a test, you may even have to make your own wire connections between to components to see if that helps.

Dropped her in reverse to back out of the way and she stalled.

Did it die during shifting or after full engagement and some boat movement?

Now I'm wondering if I should just replace the sensor again or I have some other problems that are leading to the non spark. turns over fine just will not fire.

Once you know your wiring is 100% good, it will be up to the Ignition System test tree once again.

Also check to make sure the distributor shaft and rotor does not have enough wobble in it to hit the ignition sensor.

The reason for the Loctite on the rotor is to keep the rotor from floating upwards at speed.

While it's not starting/sparking, Do you have 12+ power still at the dash gauges?

Also when connected, do you see the tachometer registering an RPM signal while cranking ?

 

[tank1949]

Re: Help with Thunderbolt IV

Sounds like you got it running for a while but then it died? Absolutely sure getting GOOD fuel now?

 

[Forestrytodd]

Re: Help with Thunderbolt IV

Before condemning modules, You have to ensure the all the wiring is making contact by Pulling wire connectors, inspecting them, ensuring that the wire pins are reaching/touching their respective counterparts then reconnecting and give them a wiggle while trying to start the engine if possible and even once you do get it running again, carefully wiggle them some more to make sure it stays running. As a test, you may even have to make your own wire connections between to components to see if that helps.

Tried wiggling all the wires while my son cranked. I checked them with the ohm meeter as well and it checks out. I did this with the new harness and the old as well with the same results.

Did it die during shifting or after full engagement and some boat movement?

It died as soon as it dropped into gear but it was not just a kill it actually stumbled.

Also check to make sure the distributor shaft and rotor does not have enough wobble in it to hit the ignition sensor.

I don't seem to have any excessive slop in the dist. shaft

The reason for the Loctite on the rotor is to keep the rotor from floating upwards at speed.

I'll be putting some loctite on it then!

While it's not starting/sparking, Do you have 12+ power still at the dash gauges?

It drops to around 11 when cranking.

Also when connected, do you see the tachometer registering an RPM signal while cranking ?

yes it does register when cranking when I have it connected. When it ran it seemed to be correct as well.

 

[Bt Doctur]

Re: Help with Thunderbolt IV

I would suspect that there is a manoverboard switch.is there anything near the control box that looks like a lanyard switch .black housing with a red button/switch ? might say "on-off"

 

[NHGuy]

Re: Help with Thunderbolt IV

Make sure the shift interrupt is not shutting it off. Might be a sticky lower shift cable actuating the interrupt.
Then leave those parts in the motor and run down the diagnostic sequence again.

 

[Volphin]

Re: Help with Thunderbolt IV

Just for giggles check your plug wire order.