Strange Previous Owner Hack Job..?

[Mark R.]

Attempting to resurrect 1996 SeaRay 175 BRXL with 4.3LX Gen+ engine (S/N: 0F803561).
All new outdrive seals, impeller, gimbal bearing, bellows, shift cable, battery, fluids, etc.
Unknown history. Preparing for a lake trial this week. It runs really well on the garden hose.
But I just noticed an odd looking modification to the distributor wires (see the attached pics).
Someone has chopped off the top five wires on the ignition module connector.
Also there's a blue "squeeze-on" splice connector that is clearly not original either.
Does anyone have any ideas or suggestions about what might have been done here..?!?
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[Bt Doctur]

just a guess but a green/white wire is usually for the shift interupt,Looks like a different module was installed

 

[Mark R.]

just a guess but a green/white wire is usually for the shift interupt,Looks like a different module was installed

I'm wondering if it's a Thunderbolt V distributor on a Thunderbolt IV system...
The engine is currently being controlled by a Thunderbolt IV module (see pic).
Is there a way to tell from the serial number which system it originally came with.?

 

[alldodge]

What is the connector with the cut wires connected to?

 

[Mark R.]

What is the connector with the cut wires connected to?

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I believe it is actually connected to a Thunderbolt V ignition module...
It's a small flat square mounted on the rear of the distributor housing.
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[Scott06]

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I believe it is actually connected to a Thunderbolt V ignition module...
It's a small flat square mounted on the rear of the distributor housing.
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With spliced connections did someone swap in a delco est ? Or it is a TB maybe spliced a differnt generation igntion module as many are no longer available

 

[Fun Times]

Yes by your engine year the ignition module was a thunderbolt 5 system…you show a 4 system…

Item 34 would of been original,

Genuine Mercury Marine parts, large inventory, fast shipping

Genuine Mercury Marine, Mercruiser and Mercury Racing engines, parts, propellers. Authorized dealer with large inventory, great prices, fast shipping!

www.mercruiserparts.com

Here’s the Merc parts catalog to your serial number,

Genuine Mercury Marine parts, large inventory, fast shipping. 4.3LX (GEN +) (2 BBL.) GM 262 V-6 1996-1997 0F803000 THRU 0K999999

4.3LX (GEN +) (2 BBL.) GM 262 V-6 1996-1997 0F803000 THRU 0K999999

www.mercruiserparts.com

 

[Mark R.]

Yes by your engine year the ignition module was a thunderbolt 5 system…you show a 4 system…

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Yes. It's looking like it originally came with a TB-5 and someone converted (retrograded?) it to a TB-4.

The odd part is it appears there is no knock sensor anywhere on it, and no knock sensor module.
I suppose those could have been removed when they performed this modification..?

It DOES have the purple/white jumper wire pigtail coming out of the wire harness on top of the engine.
Plus, the three mounting bosses on the port side exhaust manifold have NOT been tapped with threads.
Instead, the metal plate with the TB-4 ignition module has been mounted on a side panel next to the engine.

The first picture below shows the ignition module that is mounted to the side of the distributor.
The second picture shows the butchered up wiring connector that is plugged into the module.
Only two of the eight wires are still connected...

So it's clear they have disabled some of the TB-5 features and functions.
Is there some way to tell which ones.? And how concerned should I be.?
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[Scott06]

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Yes. It's looking like it originally came with a TB-5 and someone converted (retrograded?) it to a TB-4.

The odd part is it appears there is no knock sensor anywhere on it, and no knock sensor module.
I suppose those could have been removed when they performed this modification..?

It DOES have the purple/white jumper wire pigtail coming out of the wire harness on top of the engine.
Plus, the three mounting bosses on the port side exhaust manifold have NOT been tapped with threads.
Instead, the TB-4 ignition module has been mounted on the side panel next to the engine.

The first picture below shows the ignition module that is mounted to the side of the distributor.
The second picture shows the butchered up wiring connector that is plugged into the module.
Only two of the eight wires are still connected...

So it's clear they have disabled some of the TB-5 features and functions.
Is there some way to tell which ones.? And how concerned should I be.?
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not all TBV setups used a knock sensor. I dont think I have ever seen one on a 4.3 or carbed 5.0's

I wouldnt be concerned at all if your total timing is correct for the engine.

I dont think 4.3s use much more than 24 total degrees (maybe less) , maybe even less . With an advance light I would see what you intial and total advance is. off the cuff I would think 8 intal and no more than 24 is ok in terms of preventing detonation

 

[nola mike]

There's a write up in the stickies going over the TB-IV and V. Agree with scott, if the 4.3s had knock sensors, they're rare. The TB-V has a bit more sophisticated advance map, but without a knock sensor I'm not sure how much of an upgrade it is. Bottom line is the TB-IV is just fine. I thought I was going to pick up a TBV as a spare a while ago, and was trying to see if the KS module from a V8 TBV would work, since I couldn't find one for the IV.

 

[Scott06]

There's a write up in the stickies going over the TB-IV and V. Agree with scott, if the 4.3s had knock sensors, they're rare. The TB-V has a bit more sophisticated advance map, but without a knock sensor I'm not sure how much of an upgrade it is. Bottom line is the TB-IV is just fine. I thought I was going to pick up a TBV as a spare a while ago, and was trying to see if the KS module from a V8 TBV would work, since I couldn't find one for the IV.

I think the main difference between a TB 4 and 5 is the active timing where it constantly adds advance, watching for how much rpm increase the engine responds with until it stops increasing rpm (mean Best Timing) . there is a graph in factory manual - shown in post #8 here https://www.offshoreonly.com/forums/general-q/324380-thunderbolt-v-ignitition.html

This is why you have to put a 5 into base mode to set initial timing.

The only knock controls I have seen are on 5.7 4 bbl engines. I looked to see if could add it to my repower years back but decided it was a dumb idea. The one thing they did stupid is the knock module needs to send a constant 9V to the ICM otherwise it goes in to retard mode. To me I would rather have it fail in non retard mode... Bottom line I dont think the 4.3 and 5.0 base engines have enough advance to be pushing it enough to warrant needing to pull back timing

 

[Mark R.]

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OK. Thanks guys.! I guess I don't really have much choice but to live with it the way it is.
And I'm fine with that as long as the commanded spark advance is roughly in the proper ballpark.

Unfortunately I have not had an opportunity to check any of the spark advance yet.
I own two inductive timing lights, but neither is currently in my possession.
Each of my sons has one of them, so as soon as I can get one of them back, I'll check it.

And yes, it appears I will be missing the following Thunderbolt V features:
- Idle Speed Spark Control
- Acceleration Spark Advance
- Mean-Best-Timing Spark Advance
- Over-Speed Control (Rev-Limiter)
- Knock Retard Spark Control

New Question regarding Base Timing and Carb Settings:
Knowing it has now been converted to Thunderbolt 4, should I still ground the PUR/WHT pigtail wire.?
I'm guessing I probably don't need to..?
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