1999 MerCruiser 4.3 Alpha 1 Gen 2 Ignition Type and Timing Question....

[lintmann]

I'm trying to verify which ignition system I have, Thunderbolt IV or V. I think it's a V but what is throwing me off is the lack of a knock sensor.

This is what I know...

Only two wires coming out of the distributor housing(no module attached to the housing), both wires are white, one has a red tracer and the other a green tracer. They both to this module P/N 131800-7071 which I believe is only used on the Thunderbolt V ignition, correct?



It also has this purple with white tracer timing lead.

This tells me that I have the Thunderbolt V ignition and that you ground this lead to retain base ignition timing, correct? I believe that I read on this forum that knock sensors are "if equipped" so even though I may have the Thunderbolt V, it's acceptable that I don't have a knock sensor?

The other important question I have is...what does locking it in base timing actually do?? I'm asking because since I didn't 100% know which system I had, I checked timing with and without the timing lead grounded and with it grounded the timing still advanced with engine rpm and yes, I did ground it before turning the ignition on.

Your guidance is really appreciated. Thanks

 

[Pmt133]

I don't believe car applications got knock sensors. But yes, that is TBV.

In base timing, you get some advance but no idle compensation and a few other things. If it's set correctly, your timing mark won't even hit with a standard light without it disconnected at idle. With throttle you still get some advance I believe but not much. Been a while since I played with it.

Also, scrap those batwing manifolds before they take out your engine.

 

[lintmann]

Sorry, what do you mean by Car Applications?

 

[lintmann]

So how do I know if I actually have the timing lead properly grounded? Yes you can jump the lead to a ground and it look okay but how would you know that the timing lead isn't broken somewhere back in the harness?

Not trying to be a pain with these questions but I just want to make sure the timing is properly set and like I say, it doesn't seem to make much if any difference at all whether I ground that lead or not. I've worked on lots of older engines where you ground this or jumper that for a base timing and you could see a difference, not so obvious on this engine....

Advice appreciated before I take it on the lake and inadvertently burn a hole in a piston.

 

[Scott06]

I'm trying to verify which ignition system I have, Thunderbolt IV or V. I think it's a V but what is throwing me off is the lack of a knock sensor.

This is what I know...

Only two wires coming out of the distributor housing(no module attached to the housing), both wires are white, one has a red tracer and the other a green tracer. They both to this module P/N 131800-7071 which I believe is only used on the Thunderbolt V ignition, correct?

View attachment 418145

It also has this purple with white tracer timing lead.View attachment 418146

This tells me that I have the Thunderbolt V ignition and that you ground this lead to retain base ignition timing, correct? I believe that I read on this forum that knock sensors are "if equipped" so even though I may have the Thunderbolt V, it's acceptable that I don't have a knock sensor?

The other important question I have is...what does locking it in base timing actually do?? I'm asking because since I didn't 100% know which system I had, I checked timing with and without the timing lead grounded and with it grounded the timing still advanced with engine rpm and yes, I did ground it before turning the ignition on.

Your guidance is really appreciated. Thanks

Yes that is a TBV without a Knock sensor. yet to see a knock sensor on a 2 bbl engine. Knock sensors will have a knock module piggy backed to the ignition module.
in base mode the timing will not move as the TBV will constantly be advancing the igntion to get best idle and power when advancing the throttle. You will see it be static on the timing light so you can set intial advance typically at 8 or 10 deg BTDC

another way to feel safe with timing is to check total advance , a 4.3 should have about 24 degrees total advance at say 2800 rpm or so. 4.3 s didn’t get a lot of advance. If total timing is correct there is not chance of detonation