TBV ignition electronics troubleshooting....

i also want to be sure i have a firm basic understanding of what the ignition module and ignition system are designed to do to help in my trouble shooting efforts.... if anyone can confirm or correct me if needed it is appreciated....

basically the ignition module gets a 12V signal from the battery through the ignition switch and the throttle kill switch and the shift interrupt switch.....assuming the kill switch and the shift interrupt switch are working properly the module processes this 12V signal through its internal wiring and processor...if there is nothing to disrupt this signal inside of the module it will keep the 12V on the purple wire circuit at all times which includes the purple wire to the coil....as the engine is cranked over the hall effect sensor starts to ground the 12V signal on the purple wire circuit off and on as the fingers of the the rotor spin through the sensor....when the 12V signal is grounded the coil releases its high voltage energy through the coil wire into the distributor cap...the distributor cap sends the high energy from the coil to the rotor....as the rotor spins it makes contact with the different contacts inside the distributor cap....this completes the circuit and each individual distributor contact transfers the power to its associated spark plug wire which in turn fires that specific spark plug.....the processor inside the module will advance or retard the timing the 12V signal gets grounded as needed to keep the engine running within preset parameters....


if this is correct the ignition module is like a 'monitor'....it receives signals from various switches and sensors...if everything is OK the module will allow the 12V signal to pass through and keep the purple wire to the + coil terminal energized so the coil can fire when needed...this 12V signal to the + coil terminal normaly only gets disrupted as the hall effect sensor grounds the 12V signal....if the 'monitor' does not like what it is seeing from a switch, sensor, or a corroded wire it disrupts the purple wire circuit including the 12V signal to the coil and the coil does not fire properly....

i know this is a very simple description of the ignition system, but the first step to troubleshooting a problem is to understand how the system is supposed to work...without this knowledge all i can do is swap parts and hope the problem goes away....

cliff

Cliff,

It is your choice how you want to spend your time.

Based on the diagnostics you have done and their results, all indications point back to a problem in the ICM. The only thing you have said that makes me question wiring was that your tach moved when you cranked the engine. The tach can only move if the distributor signal is ok and the ICM sends the signal to the tach. That's why I wanted you to isolate and test the ICM. Normally when an ICM is bad, the tach doesn't move. It would appear that the circuit from the ICM to coil is not working but the circuit to the tach is....which is unusual.

Isn't there a neighbor or friend you can borrow a working ICM from to test it or is it possible for you to test your ICM on their boat?

You can do all the voltage drop tests you want but if the battery has enough juice to spin the engine at 200 rpm, it generally has enough to fire the coil. If you think otherwise, put a VOM on the 12+ wire feeding the ICM, crank the engine and take a reading.

My comment on the ICM on ebay was not clear enough. Is the "new" ICM you have new or used?



-JD

PlayDate said:

Cliff,

It is your choice how you want to spend your time.

Based on the diagnostics you have done and their results, all indications point back to a problem in the ICM. The only thing you have said that makes me question wiring was that your tach moved when you cranked the engine. The tach can only move if the distributor signal is ok and the ICM sends the signal to the tach. That's why I wanted you to isolate and test the ICM. Normally when an ICM is bad, the tach doesn't move. It would appear that the circuit from the ICM to coil is not working but the circuit to the tach is....which is unusual.

Isn't there a neighbor or friend you can borrow a working ICM from to test it or is it possible for you to test your ICM on their boat?

You can do all the voltage drop tests you want but if the battery has enough juice to spin the engine at 200 rpm, it generally has enough to fire the coil. If you think otherwise, put a VOM on the 12+ wire feeding the ICM, crank the engine and take a reading.

My comment on the ICM on ebay was not clear enough. Is the "new" ICM you have new or used?



-JD

Click to expand...

thanks John....i will go back and verify the movement of the tach while cranking the engine just to make sure i did not 'imagine' that it moved...don't get me wrong....i still intend to do all the testing you have recommended....i appreciate all the time you and all others have taken on this....trust me, i do not want to take the time to do any unneccessary testing.....i am new to the concept of 'voltage drop testing' so i do not know if the other test i have done so far would indicate i have sufficient voltage going through the ignition system or not....the test i was mentioning would be in addition to your test but i will not perform them if they both tell me the same thing, that the ICM is either good or bad.....unfortunately i do not know anyone that has a boat similar to mine that would have the same ICM....so i am on my own as far as testing the darn thing.....the ICM that i bought off of ebay was advertised as being 'new' but it was from an individual seller, not a company or marina....i inspected the module closely when it was delivered and could not see any obvious signs that it had been installed before so i am thinking (and hoping) the module is in fact new, but you never know.....

if you feel the test you mentioned before will give me a definitive answer if the ICM is bad or not i will perform that test next and forgo the voltage drop test....if the ICM is bad, i will not buy another TBV module....i will switch to one of the aftermarket ignition systems....

one concern i have about switching to an aftermarket system is the removal of the distributor...i may have a problem getting the old distributor out and a new one in due to interference from the height of the transom....the position of the engine in the boat has the distributor positioned just behind the edge of the transom opening....i don't know if i have enough clearance behind the edge of the transom opening to lift the distributor shaft clear of the engine.....

cliff

One of the reasons I suggested that you perform a voltage drop test on all of your GROUNDS is because a poor connection/bad ground, can not only cause the ignition system to not work properly but can also ruin, a new or known good ignition module.

techmitch said:

One of the reasons I suggested that you perform a voltage drop test on all of your GROUNDS is because a poor connection/bad ground, can not only cause the ignition system to not work properly but can also ruin, a new or known good ignition module.

Click to expand...

OK, thanks....i will check the grounds, especially the main engine ground....

cliff

Cliff,

Hopefully you can get the distributor out without the cap and rotor in place if it comes to that.

In regards to wiring, I did have a few thoughts based on your earlier working description.

1) The purple wire is a switched hot connection. In most applications the ICM does not provide 12v to the coil ...it gets 12v from another purple wire that attaches to the + side of the coil. How many purple wires are attached to the +side of the coil?

2) The trigger wire for the coil is the grey wire. It should be attached to the - side of the coil. It is the same wire that connects back to the tach. Ergo...if the tach is working .....the coil should be firing. Sometimes the tach can cause the coil not to fire because it is shorted to ground. Depending how it is wired, you can disconnect the grey wire from the back of the tach or disconnect it at the coil if you have two grey wires at the coil. How many wires do you have attached to the -side of the coil?

In summary:

1) Switched 12v puts power to the + side of the coil. Purple wire
2) The ICM gets 12v from the +side of the coil. Purple wire
3) The ICM needs a solid ground. Black wire
4) The ICM provides power to the distributor sensor. White Red
5) The ICM receives a signal back from the distributor sensor. White Green
6) The ICM triggers the coil and provides a signal to the tach. Grey wire

The ground that matters is the ICM black wire.

If you place an digital ohm meter between the grey wire and a solid ground, you should see the wire cycling to ground as you crank the engine. If the ICM is bad, there should be no signal on the grey wire.

The only thing I am fuzzy on is how the safety interrupt wire works. It appears on the schematics as a loop of two black wires for Alpha drives with a switch that breaks continuity and two wires tied together (permanent continuity) for Bravo drives. I'm speculating that those wires are part of the ICM ground circuit. If the switch is open, the ground loop of the ICM is disrupted. When the switch is closed...the connection to ground is enabled.



JD

PlayDate said:

Cliff,

Hopefully you can get the distributor out without the cap and rotor in place if it comes to that.

In regards to wiring, I did have a few thoughts based on your earlier working description.

1) The purple wire is a switched hot connection. In most applications the ICM does not provide 12v to the coil ...it gets 12v from another purple wire that attaches to the + side of the coil. How many purple wires are attached to the +side of the coil?

2) The trigger wire for the coil is the grey wire. It should be attached to the - side of the coil. It is the same wire that connects back to the tach. Ergo...if the tach is working .....the coil should be firing. Sometimes the tach can cause the coil not to fire because it is shorted to ground. Depending how it is wired, you can disconnect the grey wire from the back of the tach or disconnect it at the coil if you have two grey wires at the coil. How many wires do you have attached to the -side of the coil?

In summary:

1) Switched 12v puts power to the + side of the coil. Purple wire
2) The ICM gets 12v from the +side of the coil. Purple wire
3) The ICM needs a solid ground. Black wire
4) The ICM provides power to the distributor sensor. White Red
5) The ICM receives a signal back from the distributor sensor. White Green
6) The ICM triggers the coil and provides a signal to the tach. Grey wire

The ground that matters is the ICM black wire.

If you place an digital ohm meter between the grey wire and a solid ground, you should see the wire cycling to ground as you crank the engine. If the ICM is bad, there should be no signal on the grey wire.

The only thing I am fuzzy on is how the safety interrupt wire works. It appears on the schematics as a loop of two black wires for Alpha drives with a switch that breaks continuity and two wires tied together (permanent continuity) for Bravo drives. I'm speculating that those wires are part of the ICM ground circuit. If the switch is open, the ground loop of the ICM is disrupted. When the switch is closed...the connection to ground is enabled.



JD

Click to expand...

there is only one purple wire connected to the coil + terminal and only one grey wire connected to the coil - terminal......i did not understand that the grey wire to the coil - terminal was the 'trigger' wire.....i thought it was just a signal to the tach......since i only have one grey wire at the coil i assume this wire serves as the coil 'trigger' wire....this may be one of those 'oh sh!t' moments where i discover i have done something really stupid (unfortunately not all that uncommon).....i have been leaving the grey wire disconnected from the coil - terminal the entire time i have been testing the system....i thought i read somewhere that when troubleshooting the TBV system you should disconnect the grey wire from the coil to insure the tach is not grounding out the coil....but that could only apply to the TBIV system that i believe has two grey wires to the coil - terminal and two purple wires to the coil + terminal....by leaving the grey wire disconnected from the coil does this mean all of the testing thus far has been invalid?.....should i reconnect the grey wire to the coil and start the testing from scratch?.....i have not checked to see if the 12V signal to the coil - terminal cycles to ground as i crank the engine over, but i will do so.....i did not get a chance yesterday evening to recheck to see if the tach moves while cranking the engine....maybe i will have time this evening after work to do some more testing....

i think your understanding of the shift interrupt switch is accurate....on the Alpha drives, as the switch rocks up and down due to the movement of the shift cable during shifting the 12V signal gets grounded for a split second which allows the engine rpm's to drop which releases the pressure on the reverse cut drive gears so the gears can be separated....the interrupt system is interesting in design in that the movement of the interrupt switch can only be observed and verified while the boat is in the water which provides resistance against the prop....the interrupt switch will not move when the throttle is shifted from forward to reverse while the boat is not in the water....

if you have access to the Mercruiser Service Manual 24 that is the one for my engine and electrical system...it has the wiring diagram for the module and the entire system wiring diagram.....

cliff

You're right TB IV has 2 gray wires TB V has 1 gray wire going to pin 2 on the wire harness connector you would need to disconnect it at the tach to check for a grounded tach.
Just my opinion but if you could get the distributor out of the engine ( if there is room ) you could take it to an auto shop to have it tested if you can't I would step back from it for a day and setup a checklist of step by step procedures for testing your system now that you have a good handle on what your looking for. You have the knowledge just need to organise everything you've learned so far, I've learned a lot from this thread hope your not getting too discouraged. We can't even get our boat out of storage to work on it the last 3 days winds have been blowing 20-60mph with 2-3" of rain a day.

Bob & Sue said:

You're right TB IV has 2 gray wires TB V has 1 gray wire going to pin 2 on the wire harness connector you would need to disconnect it at the tach to check for a grounded tach.
Just my opinion but if you could get the distributor out of the engine ( if there is room ) you could take it to an auto shop to have it tested if you can't I would step back from it for a day and setup a checklist of step by step procedures for testing your system now that you have a good handle on what your looking for. You have the knowledge just need to organise everything you've learned so far, I've learned a lot from this thread hope your not getting too discouraged. We can't even get our boat out of storage to work on it the last 3 days winds have been blowing 20-60mph with 2-3" of rain a day.

Click to expand...

OK, thanks....now i understand that the TBV ignition module sends a signal through the grey wire to the tach and then to the - coil terminal through the grey wire to ground the coil so it can release its high energy charge to the distributor....i was wondering how the coil got grounded to release its charge....that is why i was thinking the module was grounding the purple wire to the + coil terminal that carries the 12v signal....i now need to confirm the signal from the ICM is not being disrupted as it travels to the tach and to the coil....this could very well be the root cause of the problem....the test that John mentioned about using an ohm meter or a test light at the coil - terminal while cranking the engine will confirm if the signal to ground the coil from the ICM (therefore also fire the coil) is cycling as needed....hopefully i will find i have had a ground at the tach all along which was causing the coil not to fire....

i can't say that i have not been somewhat discouraged, because i have...i am pretty good with a wrench and diagnosing/repairing mechanical issues with an engine but i only have a basic understanding of the electrical systems....that is why i decided to post a description of my understanding of how the ignition system works so that i would know if it is accuarate or not....as it turns out my understanding was not completely accurate.....this misunderstanding has probably caused the troubleshooting process to become somewhat confusing and last too long.....i too have learned a lot while going through this and i am grateful for those that have taken the time to guide me through the diagnosis of the issue.....

cliff

Cliff,

It is part of the game....if we stop learning how things work...that would be the tragedy.

To make you feel better....I have a 1992 Corvette and the ECU (computer) failed on it. You can't find them anywhere and if you did it still is 21 years old!!! I had to go through a process of mating an FAST XFI 2.0 computer to a 21 year old wiring harness. It took me 3 months to build a harness to make it work and pass a Virginia Emissions test so I could renew it's tags. During that time I endured the "honey, maybe you should just sell it" torture that only wife #2 could give. I got what felt like a Master's Degree in Fuel Injection mating a 2013 race car computer to 1992 car.

I drive it everyday with a smile on my face.

You will get this sorted out. Let me know how the test goes.

-JD

PlayDate said:

Cliff,

Hopefully you can get the distributor out without the cap and rotor in place if it comes to that.

In regards to wiring, I did have a few thoughts based on your earlier working description.

1) The purple wire is a switched hot connection. In most applications the ICM does not provide 12v to the coil ...it gets 12v from another purple wire that attaches to the + side of the coil. How many purple wires are attached to the +side of the coil?

2) The trigger wire for the coil is the grey wire. It should be attached to the - side of the coil. It is the same wire that connects back to the tach. Ergo...if the tach is working .....the coil should be firing. Sometimes the tach can cause the coil not to fire because it is shorted to ground. Depending how it is wired, you can disconnect the grey wire from the back of the tach or disconnect it at the coil if you have two grey wires at the coil. How many wires do you have attached to the -side of the coil?

In summary:

1) Switched 12v puts power to the + side of the coil. Purple wire
2) The ICM gets 12v from the +side of the coil. Purple wire
3) The ICM needs a solid ground. Black wire
4) The ICM provides power to the distributor sensor. White Red
5) The ICM receives a signal back from the distributor sensor. White Green
6) The ICM triggers the coil and provides a signal to the tach. Grey wire

The ground that matters is the ICM black wire.

If you place an digital ohm meter between the grey wire and a solid ground, you should see the wire cycling to ground as you crank the engine. If the ICM is bad, there should be no signal on the grey wire.

The only thing I am fuzzy on is how the safety interrupt wire works. It appears on the schematics as a loop of two black wires for Alpha drives with a switch that breaks continuity and two wires tied together (permanent continuity) for Bravo drives. I'm speculating that those wires are part of the ICM ground circuit. If the switch is open, the ground loop of the ICM is disrupted. When the switch is closed...the connection to ground is enabled.



JD

Click to expand...

i think I have verified I have two defective control modules..... i connected the grey wire back to the coil - terminal and I disconnected the grey wire from the back of the tach....I used my Ohm meter set on the lowest scale (200) and connected the red lead from the ohm meter to the coil - terminal and the black lead from the ohm meter to a ground source....I turned the ignition switch to the 'run' position.....I used a jumper wire at the starter slave solenoid to crank the engine....I watched the ohm meter and did not see any reading as the engine was cranking....I verified I had 12v coming into the coil on the purple wire during this test.....then I unplugged one of the connectors at the ICM that has the grey wire but I left the smaller connector on the ICM that has the purple supply wire....as the engine was cranking I used the red lead from the ohm meter to touch the pin in the module that the grey wire connects to and the black lead from the ohm meter stayed connected to ground.....as the engine was cranking there was no signal coming from the pin on the ICM.....

Just for giggles I did the same test with both the new and the old ICM.....so it looks like I got scammed out of $350 on eBay when I bought the 'new' ICM......I believe the eBay ICM was dead on arrival when I got it......

so unless anyone has any other ideas or thinks I did not perform the above testing correctly just let me know.....if no new ideas are offered it looks like I will be buying an aftermarket ignition system.....I think I may be OK in removing the old distributor as long as I remove the cap and if I can tilt the distributor slightly as it rises out of the engine.....there is sufficient clearance to lift the distributor free from the engine as long as I can tilt it slightly while pulling it out.....

if this is the end of this process I want to again thank all that offered assistance, especially JD.....

cliff

I have done a little research on the aftermarket ignition systems.....right now i am leaning toward the Delco Voyager EST system...it looks to be relatively easy to wire in and is compatible with the shift interrupt circuit and less expensive than some of the other systems....does anyone know if the Delco system uses the knock sensor circuit from the TBV system or does the knock sensor circuit not get used with the Delco system?

thanks...

cliff

its alive!!!

just thought i would close this thread....i installed the Delco Voyager EST ignition system this W/E....pretty easy conversion....if you read the instructions and know how things are supposed to be wired before you start the swap should take 1 - 2 hours.....then after about a month of sitting a quick turn of the ignition key and the engine roared to life before the crankshaft could even make one revolution.. what a sweet sound that was to hear.....it actually startled me for a second when it fired up so fast...luckily i did not have any clearance issues with removing and installing the distributor.....in case someone else is considering this conversion i will give a brief description of the installation for the archives...i know it is a long post but maybe it will help someone....

first either disconnect/remove the ignition coil wire or flip the toggle of the throttle 'kill' switch down....this will prevent the engine from starting as you crank the engine to find TDC (Top Dead Center)....

i made sure the #1 piston was in the compression stroke and on TDC before i removed the old distributor....this is pretty easy to do....just crank the engine over and align the TDC timing mark on the crankshaft pulley with the timing tab on the engine block....then look at the distributor rotor....if it is pointing to the #1 spark plug wire connector on the distributor cap you know the #1 piston is on TDC during the compression stroke.....if the rotor is pointing 180* in the other direction of the #1 spark plug wire connector on the distributor cap then the #1 piston is on TDC for the exhaust stroke....you will need to crank the engine to rotate the crankshaft one complete revolution to get the rotor pointing to the #1 spark plug wire connector while the timing mark on the crankshaft pulley is aligned with the timing tab....the crankshaft makes two revolutions for every one revolution of the rotor....once you find TDC on the compression stroke for the #1 piston 'DO NOT ROTATE THE CRANKSHAFT'.....if you do it is not the end of the world but you will have to go through more involved steps to find TDC....
then i removed all of the components of the old TBV system (which i admit felt pretty darn good) :smt038 .....

i installed the new distributor....you have to be sure the new distributor is seated all the way down on the engine block (don't forget the gasket like i did at first)....you will have to rotate the rotor/shaft back and forth to seat the oiler and distributor drive gears into the camshaft gears....when the distributor is seated properly wherever the new rotor is pointing is the new position for the #1 spark plug wire connector on the distributor cap....it does not matter where the new #1 position is located...you can remove and re-intsall the new distributor and rotate the distributor shaft to get the new #1 spark plug connector in any position on the new distributor cap you want......once the distributor is seated properly you rotate the distributor base to position the wiring connections in the base in a direction that is easy for you to gain access to.....then snug down the distributor locking bolt/tab to the point you can still rotate the distributor by hand with a little force....then make note of the position the rotor is pointing when the distributor cap is installed...this will be the #1 spark plug connector on the new distributor cap....i marked this connector on the cap by scratching in a '1' with a screw driver on the new distributor cap....then i locked down the distributor cap and installed the new spark plug wires between the spark plugs and the distributor cap being careful to follow the proper firing order of the ignition system, knowing the rotor turns 'clockwise'......ironically one of the hardest parts of the install i ran into was installing the new spark plug wires on the new distributor.....it was very difficult to get the plug wire to stay snapped onto the distributor cap because the rubber boot of the plug wire end was pushing up on the connection....i tried using dielectric grease and everything else i could think of....finally i decided to cut about 1/16" off the bottom of the plug wire end rubber boot and the plug wire connectors then snapped easily onto the distributor.....it turns out the plug wire rubber boots were a little too long and they would bottom out on the body of the distributor cap before the plug connection was made on the distributor cap.....once i figured that out installing and routing the new plug wires and coil wire was easy.....

i mounted the new coil to the plate on the port side engine exhaust elbow that the old TBV ignition control module and knock module were mounted to before...i just used one of the existing mounting bolts for the plate to mount the new coil to the plate......

the shift interrupt switch was wired in easily and works properly....the new interrupt system requires a switched 12V source connected to one of the interrupt switch wires...the new interrupt system uses a 12V signal to the distributor to 'interrupt' (kill) the igniton to the engine when shifting gears...the old interrupt system sent the 12V signal to ground to disrupt the ignition to the enigne when shifting gears....i cut both black wires from the interrupt switch loose from the wiring harness...i used the purple 12V supply wire for the old TBV ICM to provide power to the shift interrupt switch (it does not matter which of the black wires of the interrupt switch is used for the power wire)...the other interrupt switch wire gets connected to the black wire from the distributor....i used red wires to splice in for the for the new interrupt switch circuit to remind me the new circuit uses a positve 12V signal to the distributor.....

i used the purple 12V supply wire for the old TBV coil to provide 12V power to the new coil purple wire....

i connected the new coil to the distributor via the provided double wire and connectors....

the grey wire from the new coil gets connected to the existing grey wire for the tach feed....

the TBV knock module circuit is not used by the new Delco system...

i used heat shrink butt connectors to make the wiring connections.....

setting the ignition timing was simple....after warming up the engine to normal operating temp i hooked my timing light to #1 spark plug wire....the new system comes with a special 'timing wire' that connects to the distributor and to a 12V power source to put the ignition system in 'base timing mode'......you temporarily disconect the shift interrupt wire from the distributor and connect this special timing wire in the same distributor port the shift interrupt wire uses....i attached the red alligator clip of the timing wire to one of the 12V terminals of the 50 amp master circuit breaker on top of the engine....by rotating the distributor and using the timing light as the engine was running i set the ignition timing to 10* BTDC (Before Top Dead Center) since i always use 93 octane gas (if i used 87 octane gas the timing would be set to 8* BTDC)....there is 26* of total timing advance with the new system.....then just lock the distributor down by tightening down the lock bolt/tab, unplug the special timing wire from the distributor and reconnect the shift interrupt wire to the distributor and your done.....i also had to slightly adjust the engine idle speed on the carburetor with the new ignition system installed to get the idle speed to around 700 rpm's.......


my initial impression of the new Delco system is very good....it may be my imagination but the engine seems to idle smoother than before and certainly seems to crank faster than before.....maybe we will have an opportunity to test the boat in the water in the next few weeks before i put her to sleep for the winter...if so i will post back how it goes.....

cliff

Congrats Cliff.......mystery solved!!

-JD

thought i would close this old thread out with a report on the new Delco ignition system....after i replaced the Mercruiser TBV ignition system with the Delco system last year i did not have a chance to run the boat in the water.....we took the boat out for several hours this past WE both Saturday and Sunday and i am VERY happy to report i believe my ignition problems are finally over....the boat ran perfectly all WE....the throttle response from the engine was much quicker and the engine just seemed to have more power and idled smoother....the boat jumps out of the water and on plane now with only about 1/2 throttle.....with the new ignition system and the switch to a 4 blade prop i can now cruise on plane at 20 mph with an engine speed of 2,800 rpm's which is pretty economical fuel burn wise and easy on the engine......this is with a 'fully' loaded boat including two adults, a full fuel tank, full water tank, and lots of food and drink and other 'stuff' since we camped on the water Saturday night.....

we finally had a very enjoyable WE without worrying about being stranded due to the engine shutting down....thanks again to all that contributed to this thread last year during my 'diagnostic period'......

for anyone that may read this post at some point in the future that is having troulbe with the Thunderbolt ingnition system i can HIGHLY recommend the Delco Voyager EST marine ignition system as a replacement system.....

cliff

I like happy endings!!! Enjoy your boat!

-John

wow
I always thought the thunderbolt system was a good set up? who make it? i thought it was made by delco GM? BTW I learned a while ago DELCO stands for detroit electric company

Saverio said:

wow
I always thought the thunderbolt system was a good set up? who make it? i thought it was made by delco GM? BTW I learned a while ago DELCO stands for detroit electric company

Click to expand...

i think that the Thunderbolt ignition is a good system overall, but some of the replacement parts are WAY too expensive....as was mentioned in the thread i bought the entire Delco system for less than what the new Thunderbolt control module alone would have cost....the older Thunderbolt systems have some weak areas such as the ignition sensor inside the distributor.....the original sensors have exposed circuit boards and are subject to corrosion.....also the Thunderbolt control modules seem to be more sensative to engine compartment heat.....the Delco system has fewer components and seems to be a little simpler in operation......not sure who actually makes the Thunderbolt system for Mercruiser.....

cliff