Knock sensor for Thunderbolt V

[MichaelBC]

Hello,

my name is Michael, I am 54 years old and I am from Germany. I have searched a while now in forums and internet but wasn't able to solve the mistery about the knock sensors yet.
Last year I bought a Bayliner 2050 with a 4.3 Mercruiser engine. It was not in the best shape and in November I decided to buy a factory new engine. On this I didn't want to reuse the old Thunderbolt IV ECU anymore and bought a pre owned Tthunderbolt V (see pictures).

So I also wanted to have the knock module with sensor and here is where my confusion starts. I found a spreadsheet on the internet that says for the V6 there are no knock sensors available. Other pages tell that it is very important to use the correct module and sensor but they won't tell you which one.

So I hope the experts here could help me with my questions.

- This ECU was sold to me as a Thinderbolt V. Is this true ?
- Is there a knock module available for this ECU and which number would that have ?

Then there is another thing that confuses me. I got this wiring plan that looks like it would match to my module. After hours of searching I also found the numbers of the wiring harness and ordered both in the US.

This plan shows cable number 6 for Audio warning system. This wire is missing in my original Mercruiser plug. Does anyone know why ?
Today the water temperature swith and the oil pressure switch are both connected directly to the buzzer. So if I connect the water temperature switch now to wire 8 how will the Audio warning system work if there is no wire to connect it ?

Thank you very much in advance for your help.

Regards
Michael

 

[Fun Times]

Hi there, Welcome to iboats forums...Lets see if we can help you out some here.

While I'll just mention you probably don't need the knock system I can understand the desire to try and use it if possible and Yes your new to you ICM is an TB_5 version.

So in order to try and make this work you'd have to start following the next almost similar engine model/type of the 4.3L that used the knock system which would be the 5.0L Carbureted engine.

Those parts for the 5.0L can be found in the following link for you for reference points, https://www.mercruiserparts.com/bam/subassembly/31863/1939/40

Since you most likely didn't get a new complete module kit as mentioned in the following guide with a new ICM bracket and wire harness assembly description, https://www.perfprotech.com/blog/wp-content/uploads/2014/06/sb4.jpg
+ https://www.mercruiserparts.com/807264a01-icm-conversion-kt

I'd have to at least think you'd need most everything in the boxed parts image of that first link above to help mount the system.

Was your old TB_4 system mounted to the exhaust system or the rear distributor assembly?

What year is the old engine and boat too?

Plus should you truly want to (but just know you don't have to) "add" the warning horn system inline with the TB_5 module for the module to work, 'It appears you would have to add your own wire and wire "pin" in the 2 prong wire plug should you want to add the Tan/Blue Audio out option for the temperature in Yellow warning wire that would be coming from a 2 wire temperature sender 805218T mounted on the thermostat housing of newer designs which should/may be a bit different type housing & sender then what came with your older TB_4 engine.

Does your older engine have any warning system components that were connected such as the oil psi, Engine temperature, Stern drive gear lube monitor?

A side note for you too:...: Sierra Marine part # 18-7677 = KNOCK SENSOR.... Replaces: Mercrusier #'s 806612T; OMC # 3850357... Fits: GM V8 (305, 350 & 377 cid) engines. Sierra Marine Knock Sensor is an equivalent part:

 

[MichaelBC]

Hello,

thank you very very much for your reply.

First I will try to answer your questions.
The boat and the old engine are from 1994 with a Thunderbolt IV ECU mounted to the distributor.
It has a warning system connected to a water temperature switch, an oil pressure switch and the oil monitor of the sterndrive.
My thermostate housing is a little changed as I did install a closed cooling system.

I bought a new engine and found out afterwards that I did not have to. Last year after I bought the boat I decided to order a closed cooling system kin in USA. The thought behind is that this is a holiday boat and it runs in saltwater of the mediteranian sea. I just don't feel comfortable to pumpt salwater through an iron cast engine block. As the parts were rusty already I also installed new risers and exhaust manifolds. After about 20 hours on operation I had white smoke in the back when I started the engine. So I suspected a broken head gasket or a crack in the block somewhere and I excluded the exhaust part as everything was new. So when I was back home I started to take the cylinder heads of and all looked good. Meanwhile I decided to make everything new and ordered a factory new engine. Afterwards I found out the the gasket that seperates the manifold from the riser didn't hold the water pressure in the closed cooling and was pushed through on both sides, even though it was designed for this and OEM Mercruiser. So water ran through and created white smoke on start. Anyway, the new engine is here and I will make all new now with starter, generatorm steering pump, intake manifold, carburetor and so on. And this also includes a more modern ECU . But this just as a side note so you understand what I am doing.

So the new unit will be installed on the exhaust ellbow and I will make this part of wire harness new. Many years ago I became an electric engineer, so I can read wiring diagrams and to build a new harness is not a challenge. I also do not like this round 1 pin connectors everywhere in the boat. Wherever possible I cut them off and replace them with waterproof connectors. So it is not a problem if my kit is not complete.

Coming back to the knock sensor. I found one post in this great forum here which contains numbers for a module and sensor on the V6.

Thunderbolt IV ==> Thunderbolt V?

So I'm wasting my Sat. afternoon time pipe dreaming, and probably will be wasting some of your time too. I'm wondering if my '96 4.3LX could be converted from it's Thunderbolt IV to a V. Assuming the graybeards don't answer "Nope", I have questions. First mine is working fine, and hopefully...

forums.iboats.com

But the ECU number is completely different even though I understood it is also a Thunderbolt V. Do you think this combination of knock module and sensor would also match with my ECU ?

I also found this page, but my trust in this information is limited as they list my module as TB IV instead of V.

Knock Modules,Mercruiser Kits, Tune-up Kits, Carb Kits, Gasket Sets

Sterndrive-Information for marine parts suppliers to provide good outdrive and sterndrive prices world-wide.

www.sterndrives.com

It says at the beginning
The Knock Module monitors the Knock Sensor's AC voltage signal
and supplies an 8-10 volt signal to the ICM if no knock is present.
Do all Mercruiser knock modules work the same ? If yes, I could choose anything I can get as the ECU should not care where the 8 Volts come from.

About the audio warning I have new information. After some hours with google I found a service bulletin that looks like it refers to my ECU. It also contains a wiring diagram where the cable colors do match with what I have. Here the port for the water temperature switch is not connected to the ECU but directly to the alarm buzzer like it was before. I don't see a reason for the Tan/Blu wire being connected to the ECU, but maybe the ECU does something when an alarm is triggered or it can also send an alarm, even I do not know for which event. At least my original cable set has neither a Tan/Blu nor a yellow cable. I jsut thought from the setup of the other plan that I posted before that the ECU would need this signal of the water temperature and would shut of the engine or reduce power on overheat. But this all doesn't seem to be neccessary.

So if you think that the numbers in the above mentioned post for knock module and sensor would work with my ECU my problem would be solved and I will start to search for those.

Thank you very much again !

Regards
Michael

 

[Scott06]

Is your new engine carburated you mention a newer ecm? Is it fuel injected ?
Ive never seen a knock sensor on a carbed V6, and the mercruiser electrical manual (4D) doesn’t show a V6 wiring diagram with a knock sensor. most 5.0 s don't have them either.
as AD outlined you could wire it up and make it work, but i think you may not accomplish much. Yes i think all merc knock sensors are the same, i think the same that GM uses. It might be more practical to just read the sparkplugs and see they are not lean.

 

[achris]

The only V6s with knock sensors are the MPIs. Even if you wired it all up it's unlikely to work properly (with 5L engine sensors) as the sensors are engine family specific (V6, SBC, BBC). You'd have to use a sensor from the MPI engine, and I don't know how compatible they'd be to the TB-V module, or even if the TB-V module for the V6 has the circuitry to utilize knock sensors.

 

[achris]

...If yes, I could choose anything I can get as the ECU should not care where the 8 Volts come from.
...

The 8 volts comes from the ECU. The sensors are 'single wire' and presents either a high resistance or a low resistance to the ECU. When a detonation event occurs ('knock') the sensor resonates at the frequency of the knock (hence why the sensors are engine family 'tuned') and it's resistance drops. When the ECU sees that resistance drop, it retards the ignition timing until the resistance goes back up. As I said in my ptrevious post, I don't even know if the V6 TB-V modules have the circuitry to use the sensors, as they were never designed to have the sensors in the first place.

Chris......

 

[Fun Times]

First I will try to answer your questions.
The boat and the old engine are from 1994 with a Thunderbolt IV ECU mounted to the distributor... With a side note so you understand what I am doing.

Thank you. It always helps knowing the back history like these.

It has a warning system connected to a water temperature switch, an oil pressure switch and the oil monitor of the stern drive..

I believe it would be easiest & best to just continue using the old warning system design vs integrating into the TB-5 design as there have been some reports of unexpected/unexplained warning horn faults going off for no apparent reason which have been linked back to the ICM/Yellow temp wiring system. No need to add an extra potential issue.

Coming back to the knock sensor. I found one post in this great forum here which contains numbers for a module and sensor on the V6.

Thunderbolt IV ==> Thunderbolt V?

So I'm wasting my Sat. afternoon time pipe dreaming, and probably will be wasting some of your time too. I'm wondering if my '96 4.3LX could be converted from it's Thunderbolt IV to a V. Assuming the graybeards don't answer "Nope", I have questions. First mine is working fine, and hopefully...

forums.iboats.com

But the ECU number is completely different even though I understood it is also a Thunderbolt V. Do you think this combination of knock module and sensor would also match with my ECU ?

Yes those part numbers that Chris already found back in 2018 for a V6 are a match up for the same part numbers i located last night in the parts link with the components in the "boxed" images....Part numbers for the knock module is 806611T and the knock sensor is 806612T.

The most important to bear in mind in finding these modules and sensors are they have to be an exact match so they work in work in uniform with each other. There are many Merc part numbers with each engine type and they all read different frequencies....Yes the V6 EFI's used different frequency modules and sensors but i believe that had to do more in some cases, (not all) is because some of these systems tied into the digital frequency read platforms vs an analog type read system making a match important as mentioned in the link you don't really trust.
(Always use the correct Knock Module WITH the correct
knock sensor or you will have problems.)
Some knock systems where tied directly into the ECM while others used external modules.

So armed with this info, should you want to use a V6 EFI design because it was already used/trusted on a V6 engine vs an V8, that should be just as possible too by just picking an V6 EFI engine and matching the 2 itemed part numbers in question as an starting point.

So if you think that the numbers in the above mentioned post for knock module and sensor would work with my ECU my problem would be solved and I will start to search for those.

I'm with Chris the first time around and think the numbers listed

806611T

&

806612T

ought to do just fine, https://forums.iboats.com/threads/thunderbolt-iv-thunderbolt-v.711870/post-5379869

 

[MichaelBC]

Thank you very much to all of you for your replies.
Yes, the new engine will get a carburetor again, but new one.
The comments of Chris that the V6 TB-V modules might not have the internal circuitry to connect the sensor makes me rethink the knock sensor project again. Also there is not realiable way to test this as I hope that, with todays fuel quality, it would never enter into a knocking state. The lowest fuel you can get in Europe today is 95.
So I will think about it again and if I find the parts for a reasonable price I might add them. Even if I know that most probably I will not need it. But it makes me feel better ....

I have some more weeks of time as I had to take out the wooden block where the fron engine mounts are screwed on to. It was all rotten and I have to make something new. So until then I have time to think.

I will also leave the audio wiring system as it is and not connect the ECU.

Regards
Michael

 

[MichaelBC]

I have another question. It is a little of topic but now I told you the history you might just give some quick advice.

The new engine came with spark plugs
AC Delco 41-101
12568387
ITR4A15

The Mercruiser service manual says NGK BPR6EFS

Should I use the AC Delco spark plugs on the carburated engine or replace them by NGK ?

 

[achris]

The 41-101 et al are for MPI engines. If you're using TB-IV or TB-V with vortec heads, then use the NGK BPR6EFS.

 

[todhunter]

The 41-101 et al are for MPI engines. If you're using TB-IV or TB-V with vortec heads, then use the NGK BPR6EFS.

Chris - does this recommendation of NGK BPR6EFS plugs also apply to a carb'd TB-IV 350 with non-vortec heads? I read somewhere to use BR6FS for non-vortec heads, and to use BPR6EFS for vortec heads.

 

[MichaelBC]

Chris - does this recommendation of NGK BPR6EFS plugs also apply to a carb'd TB-IV 350 with non-vortec heads? I read somewhere to use BR6FS for non-vortec heads, and to use BPR6EFS for vortec heads.

You are right as the non Votec heads have shorter threads for the spark plugs.
The EFS has a thread length of 17,5 mm
The FS has only 11.2 mm threadreach

 

[achris]

... use BR6FS for non-vortec heads, and to use BPR6EFS for vortec heads.

This is correct...