Thunderbolt V question

[HawkX66]

I'm about to fire up my 454 tomorrow and need to verify a wire for the ignition. I know with the TB V you need to ground a purple wire with white tracer to put the ignition in base timing mode. I don't seem to have a data link connector. It's because I have a carb probably.
I have three wires left and one is purple/white with a bullet connector so I think this is the wire. Any way to confirm it? Does it terminate at the knock module? I don't like to ground wires I'm not sure of. The other two are for the trim sender.

 

[hughespat57]

Purple white to ground is base timing mode

if you are going to check timing it has to be grounded before you turn ignition on

 

[HawkX66]

Purple white to ground is base timing mode

if you are going to check timing it has to be grounded before you turn ignition on

Thank you. I understand that. I'm trying to confirm that I have the correct purple with white tracer wire.

 

[HawkX66]

Unfortunately I think this is the purple with white tracer I found. It's with two other wires, Brown with white (Trim Sender to gauge) and Black (ground).

 

[hughespat57]

If it doesnt connect to the knock sensor module then no

see the modules descriptions on page 4B-10
http://download.brunswick-marine.co...n/mercruiser/gasoline/861328-1/8613281_4b.pdf
the purple white wire is looped thru the knock connector when present it carried ghe signal between the modules

 

[HawkX66]

Ok. So it is the one to the knock sensor. Do I unplug the harness from the module to ground it? Seems odd if so.
Here is my wiring diagram.

 

[hughespat57]

Sorry cant send images from my phone well, had to run in to desktop...
So that diagram doesnt show the knock sensor module, its the basic TB V
This is typical with the individual modules (later had them integrated into a single larger off distributor module)

 

[HawkX66]

Sorry cant send images from my phone well, had to run in to desktop...
So that diagram doesnt show the knock sensor module, its the basic TB V
This is typical with the individual modules (later had them integrated into a single larger off distributor module)

Thanks for the schematic. I have Manuals 16 and 23 because my 97 seems to pull from both on certain things. It's interesting and frustrating though. I can't find where either talk about the knock module.

 

[hughespat57]

yeah, 97-98 is on the cusp with both the 5.7 and the 7.4 they started having knock problems, with carbs they just added a knock module and linked back to the IM to retard the timing. When the went to TBI and later MPI/MIE they combined the modules into the off distributor ECM

That Mercruiser diagram is actually a 5.7 but it says on the bottom 1992-1997 5.7 (7.4/8.2 similar)

 

[HawkX66]

yeah, 97-98 is on the cusp with both the 5.7 and the 7.4 they started having knock problems, with carbs they just added a knock module and linked back to the IM to retard the timing. When the went to TBI and later MPI/MIE they combined the modules into the off distributor ECM

That Mercruiser diagram is actually a 5.7 but it says on the bottom 1992-1997 5.7 (7.4/8.2 similar)

So with that said, do I still need to ground the purple/white wire?

 

[hughespat57]

To check base timing yes
It will stil put the ICM in base mode

 

[HawkX66]

I traced the one purple/white wire I found. It did go back to the knock module so I'm good to go.

 

[2016FLD]

I've been having problems with my TB V, ordered and looking forward to switching to the DUI (David Unified Ignition) Marine HEI set up that doesn't require an ICM or Knock sensor/module. Will be so glad to simplify the set-up!

 

[hughespat57]

But does it still have a knock sensor?

Without some type of knock sensor and timing retard system you can destroy the pistons.

As they increased the compression ratio and standard fuel got poorer anti knock additives you can get preignition or detonation. Which if it goes on unchecked will eat the tops of the pistons to destruction.

 

[2016FLD]

Nope, won't need one. It's a proven set up, check it out.

 

[markrsimon]

does that unit use springs and weights to handle the advance?

 

[hughespat57]

Good luck with that, just because its electronic doesnt mean it solves all problems. By the way these say Not CG approved they are racing distributors

I doubt your 85 is a high compression version and even has a knock sensor.
They weren't introduced until about 1992

 

[HawkX66]

If the DUI is just a basic dizzy and doesn't have any advance provision, it just means you'll have to run with retarded timing. It won't advance. Alot of guys mistakenly lock their distributors out and remove their vacuum advance on the street because they think they're running a race car. Without some sort of advance your leaving a lot of power and efficiency on the table.

 

[markrsimon]

“Performance is also enhanced from the super smooth advance curve tuned into the DUI. A special weight and spring assembly is hand fitted and dialed-in using a distributor machine for a precise timing curve that will match the specifications of your engine and boat”

 

[2016FLD]

The DUI Marine distributor has been around for several years as an alternative to the TB IV and V. As @markrsimon mentioned, it uses a mechanical advance tuned for marine applications. The mechanical advance essentially replicates what the IV's timing advance features via mechanical rather than an ICM. knock / detonation risk is the same as with the IV, e.g. set base timing and should be good as long as not running low octane gas.

The increased knock risks with TB V were driven more by added timing advance features built into the V ICM vs. the IV than by compression, per the Mercury service manual, the 5.0, 5.7 and Mag 350's were 9.4:1.

My TB V ICM is failing (a 1996), $800+ to replace that little box and would still have several other old TB V components that could fail vs. the DUI package for less than $400. The TB V is a good set-up till it fails, then things get expensive. If I don't like the DUI, then I'll try the Delco EST option, both combined cost less than the TB V ICM