Max RPM Problem

[Rick Stephens]

I would probably be taking a digital advance timing light with me and observing RPM and timing advance while under way. Don't think I would be changing the timing without knowing how the ignition was advancing.

 

[johnrmclean]

I would probably be taking a digital advance timing light with me and observing RPM and timing advance while under way. Don't think I would be changing the timing without knowing how the ignition was advancing.

Thanks for that feed back ...

 

[NHGuy]

You can increase the rpms at the dock, by 3000 rpm it should be around 32 degrees advanced.

If it's advancing and timed then it's carburetor time.

Either tear that Quadarajet all the way down or get a new Edelbrock 1410 marine 750 cfm.
There are a LOT of things to do in a qjet. If you haven't done one it will take too long and you'll lose the summer.
They are awesome carburetors but they are not quick for us home mechanic types. I have done one the right way. I spent weeks on it following Cliff Ruggles book. It came out perfect, but I did it during the winter so I had time to double check everything.
I'd recommend buying a carb if it's not timing.

 

[johnrmclean]

Thanks for the feedback ..working on determining if timing is working ok right now. I love Edelbrock carbs..replaced all my holleys on my rods with them.. pretty much bolt on and go ..unless your racing and special tuning the only carb to use

 

[johnrmclean]

Well ...Today I ran the boat and tested the advance. It runs at 9 at idle but does not advance uniformally. At one point I was running 1500 RPM at just under 30 degrees, later I ran up to 2500 then 3000 but it did not advance over 30, then back down to 1500 and up again to 2500 but not change in timing as I did this . I was told this however indicates the timing module is working but not sure what my next move is.

 

[achris]

As you have Thunderbolt V, there is no 'defined' curve. There is a curve programmed into the module, but the internal microcontroller can (and does) modify the timing according to a variety of inputs. The fuels' low octane will only cause the timing to be retarded when there is load on the engine, you probably will not see anything by just revving it in neutral.

If you haven't cleaned every bit of the fuel system, including the tank, that would have been my previous move.

Chris.......

 

[NHGuy]

I apologize, I was describing the previous ignition system (TB IV) which advances timing on in relation to engine speed.
In the Thunderbolt V there is advance based on rpm that is then further advanced by acceleration and retarded by knock. So observing it can seem as if timing is moving randomly, but it's actually following inputs.

 

[johnrmclean]

As you have Thunderbolt V, there is no 'defined' curve. There is a curve programmed into the module, but the internal microcontroller can (and does) modify the timing according to a variety of inputs. The fuels' low octane will only cause the timing to be retarded when there is load on the engine, you probably will not see anything by just revving it in neutral.

If you haven't cleaned every bit of the fuel system, including the tank, that would have been my previous move.

Chris.......

Thanks ..really good to know ..now that it seems the ignition module is not the culprit I guess its time to move on to fuel system . Carb and fuel pump first as they are the easiest to access.

 

[johnrmclean]

I apologize, I was describing the previous ignition system (TB IV) which advances timing on in relation to engine speed.
In the Thunderbolt V there is advance based on rpm that is then further advanced by acceleration and retarded by knock. So observing it can seem as if timing is moving randomly, but it's actually following inputs.

Thanks BTW ..."Speed changes you " ...got the shirt ..;-)

 

[NHGuy]

Yah my Baja was kinda fast. Little though, so I sold it on and got a bigger wave smasher.

 

[johnrmclean]

You have ...."the BUG!" ..Thanks

 

[johnrmclean]

Ok ..So I had a mechanic check the boat today. he confirmed the ignition module is ka put. The next step is finding the right part to replace it with.
The module is mounted to the back of the distributor. The motor has the original heads which are 1994 Mag heads but the block is a 1996 up Gen iV block. The module itself was made by Nippondenso and has these numbers on it 13100-2230 and T34984.14 . Problem is I can' cross reference these numbers to any Mercury numbers. The best I have done so far is identified part number 806745T-5 as the module for 94 through 97 mag engines. Also, anybody know if 806745T-6 would just be a newer replacement for the 806745T-5?

 

[achris]

You need the exact part number. The different last digit indicates a program for a different engine.

 

[johnrmclean]

After some investigation trying to cross reference the Nippondenso part number it looks to me like the ignition module that was in the engine was for a 5.7 engine not a 454 mag. Can't find the Denso number for a 454 Mag, Bravo one,Thunderbolt V system but the Merc number was 806745t-5 for a 91 to 97 . It was replaced by a -6 which was replaced by a conversion kit. 806745A01....-6 is no longer available from Merc unless you can find someone who still has one in stock.

 

[johnrmclean]

Going to be calling Merc in the morning for some further clarification.

 

[achris]

After some investigation trying to cross reference the Nippondenso part number it looks to me like the ignition module that was in the engine was for a 5.7 engine not a 454 mag. Can't find the Denso number for a 454 Mag, Bravo one,Thunderbolt V system but the Merc number was 806745t-5 for a 91 to 97 . It was replaced by a -6 which was replaced by a conversion kit. 806745A01....-6 is no longer available from Merc unless you can find someone who still has one in stock.

I don't know who been telling you what, but it's a load of cods. And forget the Nippondenso number on the module, often that's just a batch number, or a number used internally.

The original number for the TB-V module for your engine (by the serial number) was -806745T1. That has been superseded to -806745A01, which is still available.

The numbers you quoted, 806745T5 is for Gen V and Gen VI 454 Mag and 7.4 Bravo engines from 1992 to 1997 (which covers your engine) and also supercedes to 806745A01.

Chris......

 

[NHGuy]

Load of cod! love it. Seafarer talk for pile of sheet!

 

[achris]

Pile of sheet! Love it.Haberdashery talk for a heap of cobblers! :rofl:

 

[johnrmclean]

I was able to talk with the builder of the remanufactured engine in my boat, who is the biggest re-manufacturer in Ontario, that a 806745T-6 which supersedes -5 will work fine for this engine and scored one from another source who had a new one still in stock. It was substantially cheaper than going with a 806745A01 conversion kit which replaces the others that are now out of production and doesn't require cutting and splicing in a bunch of new wires and harnesses. It arrives Thursday.

 

[johnrmclean]

Well new ignition module in.. it works!! Special thanks to everyone who posted and tried to help!! Much appreciated. Have a great boating weekend!