RPMs wont go above 4k...not overpropped.

[bfeils]

I'm in the exact same.... situation. You thought i was going to say boat haha. I just finished rebuilding my little 3.0 mercruiser. On mine the ignition module seems fine, set base timing it initially advances to 12 degrees which is 2 degrees off but in the ballpark. The problem comes when I rev it up to 3 grand to check total advance it only goes up to 18 instead of the 25 it's suppose to be. I should be able to hit 42 mph with my 14.5x19 prop but I can't get the motor past 4100 rpm and 25 mph. I think its the timing problem causing a lack of power at high rpm. Maybe your experiencing the same thing. Unless the carb fixes it of course.

 

[Railroader12]

I'm in the exact same.... situation. You thought i was going to say boat haha. I just finished rebuilding my little 3.0 mercruiser. On mine the ignition module seems fine, set base timing it initially advances to 12 degrees which is 2 degrees off but in the ballpark. The problem comes when I rev it up to 3 grand to check total advance it only goes up to 18 instead of the 25 it's suppose to be. I should be able to hit 42 mph with my 14.5x19 prop but I can't get the motor past 4100 rpm and 25 mph. I think its the timing problem causing a lack of power at high rpm. Maybe your experiencing the same thing. Unless the carb fixes it of course.

I was sure it was a timing/ignition issue at first but to be dead honest I still havent checked to see if Im getting full advance. I fixed the base timing from 4 to 10 and it helped but still didnt fix the issue. When I set the base timing correctly I didnt even consider the ignition NOT giving me full advance so I never checked it, I just revved it up slightly and confirmed it was advancing before buttoning up and heading to the lake. If the carb float doesent fix it I will check full advance next time out. Im hesitant the more I think about it to assume the carb float could cause it all on its own since I had no other lean issues whatsoever but it is MUCH harder to tell the telltale signs of a lean engine on the street vs in the water on a boat. Well see.....I should have the boat on the water sunday afternoon so expect to see an update by monday.

 

[Railroader12]

Got the carb installed, still havent got it out on the water but it idles great. Thoroughly inspected the coupler, checked the exhaust for obstructions and changed the fuel filter. I was worried that maybe the "new" long block they put in was an old 1929 non-vortec crusty truck motor with 3 million miles and 26HP after reading some horror stories in the webz. So naturally I wasted the better part of the day referencing and checking my casting numbers to verify it was what its supposed to be...it is.

Now that this is all done......if Im still having issues when I get it out on the water Im going to go skeet shooting and grenade every single thunderbolt ignition component with a 12g. buck shot and replace with pertronix or MSD. This is just silly the more I look into how often there are problems, how EXPENSIVE and just how DIFFICULT it is to troubleshoot this system. Oh...and how you WILL have to pay for a tow if something goes wrong with it all. At least MSD has a bypass plug for "just in case".

/Rant over....back to your regularly scheduled weekend:lol:

 

[Scott06]

The Tbolt is a good ignition system, but yes parts are pricey. Do you check if you are getting full advance? Google Tbolt troubleshooting and you can find troubleshooting tree to work through before you junk it


https://www.boote-forum.de/attachment.fphp?attachmentid=114582&d=1231576181

 

[Railroader12]

Finally took it out. Carb cleaning only helped it run slightly smoother but still had no power at all and topped out around 31 mph around 3800 rpm.

I brought my timing light with me this time.......base timing was looked good but I had Zero advance all the way up to 3000rpm, reached over and was able to turn the dizzy by hand...oops. Re-set base timing while pur/wht grounded and cranked the dizzy down HARD and it finally advanced a bit, but still only gave me maybe 8 degrees on top of the base so a total of maybe 18-20 in super early, less than 2000rpm. After that the boat opened UP, felt like an entirely different engine but still only gave me 36mph and 4200rpm. If that garbage can ICM would do the rest of its job and give me another 10 degrees this would be a success story but it seems to only be halfway working.

at least I figured out what the problem is so there's that!

 

[Railroader12]

Pretty sure, at this point Im just going to put in a MSD dizzy. Which brings me to my next question....running exclusively fresh water is there any reason I can't use a street dizzy like a pro billet MSD vs the "marine" version at double the cost to me? I can get auto parts for dirt cheap.

 

[Maclin]

Go Marine. It is not about Salt v Fresh. It is about errant spark arresting in a closed engine compartment, no matter on land or lake or sea.

 

[Railroader12]

Decided to troubleshoot one more time with the TB ignition tonight. Didnt end well and Ill most likely be ordering MSD or pertronix tomorrow.

Timing set at 10 BTDC with wire grounded. Results in 16 BTDC at idle when out of base timing mode. Timing RETARDS to roughly 10BTDC until about 2500RPM then just goes right back to the 16 it had at idle. Seems to me the ICM is shot and I have ZERO plans of replacing it at a cool $200. The warning alarm system is functioning correctly, Buzzes with key turn and stops after oil psi goes above 6-8psi just as the book states and never makes a single blip while running.

So...pretty sure the ICM is toast. Pretty sure Ive covered all the bases at this point but wont hurt to ask. If theres anything I didn't try Please chime in before I scrap the TB forever. Thanks guys.

One final note. I did set the Dizzy to give me about 30 total advance then buzzed around the lake for a few minutes knowing it wasnt going to give me anymore. Nearly got all my RPM and speed back. Been the ignition the whole time.

 

[tank1949]

In natural and out of gear and with hose on, rev motor to about 3 grand and see if distributor advances max.

 

[Railroader12]

I revved all the way up to 3500-4k in the lake, in neutral with zero advance whatsoever. I guess that wasnt very clearly written. What I meant was after 2500 rpm there is no change, at 2500 the 5 or 6 degrees it retards are back in for a total advance of 16 which is the same it sits at idle.

 

[Scott Danforth]

the TB-V is an adaptive / active (not fixed) advance curve. your trying to troubleshoot it incorrectly. use the troubleshooting guides in the stickies.

if you have a knock sensor, it is most likely retarding the ignition to save your motor from detonation.

here is a snippet from the manual.

 

[Railroader12]

No knock sensor on my engine. The TB V for the 5.0 carby just has a shift cut out switch. Ive read every single piece of documentation from merc on the thunderbolt (or close to it) and also forum chats regarding it. Havent found anything whatsoever stating the timing will show zero advance like mine is doing. The troubleshooting "tree" merc put out is for a no spark, no start situation which does absolutely nothing for me or this scenario.

i sat there for as long as I felt comfortable with the engine steady at 3500RPM, head stuck under the hatch with that timing light waiting........not a single degree advanced.

Also, even assuming the MBT stage of the ignition was "adapting" slowly considering im in neutral, it should already have 10-16 degrees from the ICM from the first 2-3 stages in by that point according to the manual.

 

[hoowahfun]

I don't know much about this type of system, but the snippet Scott sent starts out saying "During light load cruising".....is there a chance the advance works differently while in neutral and not cruising? Seems like a load on the engine will cause it to behave differently, thus the timing would adjust to compensate. Maybe it behaves differently in/out of gear?

Could be nothing, and I could be barking up the wrong tree. Just wanted to put it out there just in case.

 

[Railroader12]

I emailed merc. Not gonna hold my breath but just incase they have something or some way to verify the ICM (or amplifier as they call it) is bad before I swap anything out, they want over $500 for the TB V.

I was able to find another thread describing something very similar on a TB 4 system and it turned out to be a blown fuse. I'm going double/triple check the wiring to be sure before I order anything. I figured initially that the warning system tone was verification that it has power....but it really isnt. If any of the sensors fault they close, giving the alarm a ground to sound. The power to the peizo speaker is coming from the dash side behind the gauges, it would tone regardless of the ICM getting power or not with any of the (3) sensors closed to provide it a ground.

 

[Scott06]

When I repowerd my 4.3 to a 5.0 I was able
to get a good used 5.0 TBv ignition module off eBay for much less than a new one if you’re not sure in the diagnosis.

 

[Railroader12]

Welp. So much for that. Tinkered around a little bit more, still cant get it to work right and decided to hell with it, its pointless to continue wasting my time on a jurassic ignition system that is so difficult to diagnose and expensive to fix. Even Merc has no clue how to troubleshoot it minus throwing money out the window and crossing fingers until it magically works....what a joke.... Going with a pertronix ignitor 3 system, I will report back what happens once its installed just incase anyone ever stumbles across this thread in the future with a similar problem.

 

[Railroader12]

New dizzy came in...went to pull the old one out and realized everything was 180 out. I'm so lost right now.

Rotor points towards transom when on TDC where it should, the stock dizzy showed #1 plug on the cap towards front of boat and ALL plugs were plugged into the cap according to the corresponding raised cap numbers. I turned the dizzy 180 back to where it should be, unplugged ALL wires twice and replaced them in the correct order and it just backfires theough the carb now? I've tried adjusting the dizzy in each direction and it just wont start.

to be clear this is the old dizzy, new one still in box and may end up going back if it turns out the 180 out was the issue all along.

Any suggestions?

 

[Rick Stephens]

Doesn't matter where a distributor points, it matters that at #1 TDC on compression the rotor points at the #1 wire.

You cannot fire an engine with timing 180 out. At all. No gasp at all. It will just puff out the intake.


You must determine #1 TDC compression stroke, then everything is golden.

 

[Railroader12]

Doesn't matter where a distributor points, it matters that at #1 TDC on compression the rotor points at the #1 wire.

You cannot fire an engine with timing 180 out. At all. No gasp at all. It will just puff out the intake.


You must determine #1 TDC compression stroke, then everything is golden.

Thank you Rick!!. I had #1 on exhaust....oops lol. All is well now and fires right up but the wife wont let me check timing until the morning. "Neighbors blah blah sleeping blah.....
:facepalm::target::target::smash:

 

[hoowahfun]

Thank you Rick!!. I had #1 on exhaust....oops lol. All is well now and fires right up but the wife wont let me check timing until the morning. "Neighbors blah blah sleeping blah.....
:facepalm::target::target::smash:

Are you saying you had it at #1 on exhaust stroke BEFORE you messed with it, or AFTER?