Merc 5.7L LX with Governor???

[SuperNova]

Re: Merc 5.7L LX with Governor???

I would like to weigh in here with some personal experience. I had an '86 wellcraft Elan 197 which originally came with a 205 hp 4.3 v6 and the 1.62/1 outdrive gears. I removed the 4.3 and installed a very high performance 350 with aluminum heads and intake, etc. I kept the original gears and the original distributor and TBIV box for the v6. I replaced the cap and rotor with the v8 ones. I ran everything from a 19p 3 blade to a 23 pitch 3 blade cleaver, including a 21p 4 blade s.s. trophy. I ran that outdrive up to 5700 rpm for extended periods(1.5 hrs straight sometimes). With the 19 and the 21 the boat didn't have any plane time, it just launched right out of the water onto plane, even with a full load. Up top it would hit 53- 5500 rpm and then I/d trim it to get the extra couple of mph and 200 rpm or so. With the 23 you'd start to notice some plane time with a full load of people, but it'd still run over 5000 rpm up top without trimming. I never hit a limiter and I nver had any problem getting onto plane. I even tried a 26p bravo 4 blade s.s. and could use it for skiing and tubing.
They tell me at the performance marine shop that the v6 ignition box is the preferred unit for performance as it has a more aggressive advance curve. I also set the base timing at 14d btdc. I swapped the outdrive for a 1.5 unit off a 26' wellcraft with twin 260's, put the 23 cleaver on it and with just me in the boat it was good for 74.3 mph on the gps at 5400 rpm, but with eight people in the boat it took a little while to plane and I sheared the teeth right off the upper gearset after about 15 dead water starts with a full load. Granted it was the light duty 1.5 gears (I tore the outdrive down and put the 1.5 h.d. set in for the guy I borrowed it from). I re-installed the 1.62 drive and it has been running happily ever since. The guy I sold it to is thrilled with it. That was 2 yrs ago.
Point is the problems you are having shouldn't be and I don't think its the ignition box unless it is known to be one with a rev limiter and then I would agree with Don that your tach is probably incorrectly calibrated. Also his advice is probably best for getting as close to the factory setup as possible. i was just trying to illustrate the point that things don't necessarily have to be factory conceived to work properly, but you do have to know what you are doing.
--
Stan

 

[Mjust]

Re: Merc 5.7L LX with Governor???

Well after reading everyones comments I am definetly thinking since the old motor was a 4.3L with the thunderbolt V ignition and has been upgraded to a 350 with the thunderbolt V ignition that I may have the wrong ICM causing my boat to hit a rev limiter at 4000RPMs. I also think my pitch of my prop may need to be adjusted and I dont know much about the Weber/AFB Carter 4 BRL carbs but it may need to be tuned up. I may need the trim tabs also but the ICM issue has my main concern.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

BTW some pics of the boat and motor!

 

[180shabah]

Re: Merc 5.7L LX with Governor???

Somebody correct me if I am wrong, although Stans experience above make think that I am right.

Doesn't the ICM pick up it's referrence from the hall effect sensor under the distributor cap and would there for make no difference if the rotor hit 6 or 8 contacts as it spun?

 

[John_S]

Re: Merc 5.7L LX with Governor???

The Thunderbolt IV does not have a rev limiter. It is just electronicly controlled advance.

I would expect the ICM to be a pulse counter over time. If you read Merc's description of the main functions of T5 (see below), and look at what few inputs it has to work with, I think it is the only way it could monitor/adjust timing. Please note that all T5 do not have knock control sensors/modules, which does come into play with the last function.

If the input is the Hall effect, the ratio stays the same. The V8 will produce two more pulses over the same time as a V6. My earlier (quick) calculation was in error. It actually takes 2 revolutions to see all 6 or 8 pulses. But it doesn't change the result.



From Merc manual:
General Description
The Thunderbolt V ignition system has several spark
control features that will be described following:
Idle Speed Spark Control
Acceleration Spark Advance
Mean-Best-Timing Spark Advance
Over-Speed Control (Rev-Limiter)
Knock Retard Spark Control
NOTE: The Ski models do not have the Mean Best
Timing feature.

Idle Speed Spark Control
The ignition module will control ignition timing to
maintain a calibrated idle speed. This is accomplished
by making small spark advance adjustments.
This feature is only active within a certain RPM
range. This range may be slightly different from one
engine model to another. The approximate range is
400-700 RPM.

Acceleration Spark Advance
This feature is active during acceleration only. When
accelerating, the ignition module may add more
spark advance to the ?Base Spark Timing Curve?.
The amount of spark advance added, is totally dependant
on how fast RPM increases (how fast the
throttle is moved). This feature is also active within a
certain RPM range. This range may be slightly different
from one engine model to another. The approximate
RPM range for this feature is 1200-4000 RPM.
Within this range, the module can add approximately
10 degrees of spark advance to the base spark timing
curve.

Mean-Best-Timing (MBT)
Spark Advance
During light load cruising, the ignition module
searches for the optimal ignition timing. This is also
accomplished by small changes to the spark advance.
At a given RPM, the module will try to add a
small amount of advance and wait to see if there is
an RPM change. If RPM increases, it will try to increase
timing more. The module will continue to advance
timing until it no longer gets an increase in
RPM. Conversely, if it senses an RPM drop, it will
start to retard some of the spark timing. The approximate
RPM range for this feature is 1200-4000 RPM.
Within this range, the ignition module can add
approximately 10-15 degrees of spark advance to
the base spark timing curve.
NOTE: The Audio Warning System is also connected
into the ignition module circuit. If the audio warning
system becomes activated by the closing of one of
the audio warning system switches, the MBT feature
is deactivated.

Over-Speed Control
The ignition module will prevent the engine speed
from exceeding a preset limit by stopping the spark.
This feature has an RPM range that varies from model
to model. The over-speed limit for a particular engine
is set slightly higher than the top end of the RPM
range for that model. For example, if the recommended
range is 4600-5000 RPM, the over-speed
limit would be set at 5100 RPM. When RPM reaches
this limit, spark is turned-off until engine RPM drops
down to a ?Reset RPM?, which would be approximately
4750 RPM for this example. At this point,
spark comes back on.

Knock Retard Spark Control
The knock control feature helps provide protection
from harmful detonation. Knock control is handled by
the Knock Control Module. This module receives a
signal from a sensor that is mounted on the engine
block. The knock control module works in conjunction
with the ignition module to retard the timing if
spark knock is present.

 

[John_S]

Re: Merc 5.7L LX with Governor???

"They tell me at the performance marine shop that the v6 ignition box is the preferred unit for performance as it has a more aggressive advance curve. I also set the base timing at 14d btdc."

The T4 V6 module is sought after for performance engines that need an initial timing more than the standard 8-10 degrees BTDC to get a reasonable idle. The standard V8 module of 22 or 24, would take them past the desired 32 Total.

T4's are sought after because they don't have rev limiter and don't have adaptive features that can't be controlled.

 

[Don S]

Re: Merc 5.7L LX with Governor???

Well after reading everyones comments I am definetly thinking since the old motor was a 4.3L with the thunderbolt V ignition and has been upgraded to a 350 with the thunderbolt V ignition that I may have the wrong ICM causing my boat to hit a rev limiter at 4000RPMs. I also think my pitch of my prop may need to be adjusted and I dont know much about the Weber/AFB Carter 4 BRL carbs but it may need to be tuned up. I may need the trim tabs also but the ICM issue has my main concern.

I can't bring my self to believe that the previous owner would replace the complete 4.3 with a 5.7 and not change the ICM. Think about it. Everything including the wiring harness had to be changed. Why would he buy a long block then search for all the pieces to make it work. The guy probably bought a bobtail engine complete and installed it with the V6 drive. Plugged it in and went boating. Since he forgot to change the tach, he pegged it a couple times too many and now it doesn't work ......Wouldn't plane, low speed, in all, it didn't work right and he sold it to an unsuspecting buyer.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

The Thunderbolt IV does not have a rev limiter. It is just electronicly controlled advance.

I would expect the ICM to be a pulse counter over time. If you read Merc's description of the main functions of T5 (see below), and look at what few inputs it has to work with, I think it is the only way it could monitor/adjust timing. Please note that all T5 do not have knock control sensors/modules, which does come into play with the last function.

If the input is the Hall effect, the ratio stays the same. The V8 will produce two more pulses over the same time as a V6. My earlier (quick) calculation was in error. It actually takes 2 revolutions to see all 6 or 8 pulses. But it doesn't change the result.


So are you saying that if it has the V6 ICM still then it may be my problem of hitting the rev limiter at 4000 RPMS?? Im going to drive out to the boat tomorrow and get that info, is there anything else I should write down or check for??


From Merc manual:
General Description
The Thunderbolt V ignition system has several spark
control features that will be described following:
Idle Speed Spark Control
Acceleration Spark Advance
Mean-Best-Timing Spark Advance
Over-Speed Control (Rev-Limiter)
Knock Retard Spark Control
NOTE: The Ski models do not have the Mean Best
Timing feature.

Idle Speed Spark Control
The ignition module will control ignition timing to
maintain a calibrated idle speed. This is accomplished
by making small spark advance adjustments.
This feature is only active within a certain RPM
range. This range may be slightly different from one
engine model to another. The approximate range is
400-700 RPM.

Acceleration Spark Advance
This feature is active during acceleration only. When
accelerating, the ignition module may add more
spark advance to the ?Base Spark Timing Curve?.
The amount of spark advance added, is totally dependant
on how fast RPM increases (how fast the
throttle is moved). This feature is also active within a
certain RPM range. This range may be slightly different
from one engine model to another. The approximate
RPM range for this feature is 1200-4000 RPM.
Within this range, the module can add approximately
10 degrees of spark advance to the base spark timing
curve.

Mean-Best-Timing (MBT)
Spark Advance
During light load cruising, the ignition module
searches for the optimal ignition timing. This is also
accomplished by small changes to the spark advance.
At a given RPM, the module will try to add a
small amount of advance and wait to see if there is
an RPM change. If RPM increases, it will try to increase
timing more. The module will continue to advance
timing until it no longer gets an increase in
RPM. Conversely, if it senses an RPM drop, it will
start to retard some of the spark timing. The approximate
RPM range for this feature is 1200-4000 RPM.
Within this range, the ignition module can add
approximately 10-15 degrees of spark advance to
the base spark timing curve.
NOTE: The Audio Warning System is also connected
into the ignition module circuit. If the audio warning
system becomes activated by the closing of one of
the audio warning system switches, the MBT feature
is deactivated.

Over-Speed Control
The ignition module will prevent the engine speed
from exceeding a preset limit by stopping the spark.
This feature has an RPM range that varies from model
to model. The over-speed limit for a particular engine
is set slightly higher than the top end of the RPM
range for that model. For example, if the recommended
range is 4600-5000 RPM, the over-speed
limit would be set at 5100 RPM. When RPM reaches
this limit, spark is turned-off until engine RPM drops
down to a ?Reset RPM?, which would be approximately
4750 RPM for this example. At this point,
spark comes back on.

Knock Retard Spark Control
The knock control feature helps provide protection
from harmful detonation. Knock control is handled by
the Knock Control Module. This module receives a
signal from a sensor that is mounted on the engine
block. The knock control module works in conjunction
with the ignition module to retard the timing if
spark knock is present.

So are you saying that if it has the V6 ICM still then it may be my problem of hitting the rev limiter at 4000 RPMS?? Im going to drive out to the boat tomorrow and get that info, is there anything else I should write down or check for??

 

[MikDee]

Re: Merc 5.7L LX with Governor???

Just a side note here, the basic Carter AFB carb is a very simple effective design, it's been around for years, in fact it is way easier to take apart, & work on, then a Quadrajet, with less to go wrong I really doubt there is anything wrong with this carb, unless it's clogged up somewhere, or it's not opening completely, has anyone checked for this? Mjust, with the engine off, put it in gear, and push your controls all the way to full throttle, and look into the carburetor to see if it's opening all the way? Another thing, what is your original static timing set at, is it set according to specs?

 

[John_S]

Re: Merc 5.7L LX with Governor???

"So are you saying that if it has the V6 ICM still then it may be my problem of hitting the rev limiter at 4000 RPMS??"

Yes, it is still a possibility. You don't want to be running with a T5 V6 module on a V8.

Don's comments on bobtail make sense, especially after seeing your engine picture. Too many other pieces seem to fit the puzzle though. It is a quick and painless check. Take your camera and get some more, especially with flame arrestor cover off.

Also, look on each side of the block for a knock sensor. Should be by the drain petcocks, if you have one. It should, if it is a LX. And it should have a knock module mounted on the ICM.

But, you should take a shop tach and varify the boat tach. The real question is it hitting the rev limiter at 4k or the tach is 1k low, and you are really at 5k.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

"So are you saying that if it has the V6 ICM still then it may be my problem of hitting the rev limiter at 4000 RPMS??"

Yes, it is still a possibility. You don't want to be running with a T5 V6 module on a V8.

Don's comments on bobtail make sense, especially after seeing your engine picture. Too many other pieces seem to fit the puzzle though. It is a quick and painless check. Take your camera and get some more, especially with flame arrestor cover off.

Also, look on each side of the block for a knock sensor. Should be by the drain petcocks, if you have one. It should, if it is a LX. And it should have a knock module mounted on the ICM.

But, you should take a shop tach and varify the boat tach. The real question is it hitting the rev limiter at 4k or the tach is 1k low, and you are really at 5k.

After doing some research on what the knock sensor looks like I do know that my engine does have one installed on it. The history on the motor swap is the guy that I bought it from had this boat in Tennessee and always payed to have it winterized ( I have all the records) then he tried to do it himself 3 years ago and ended up with a cracked block the next year so he took it to a place near Nashville called Hot Boats and was going to order a new 4.3L for it. The owner of the shop had the 5.7L LX sitting on a crate and made the guy a deal of $4800 for the motor and to install it (got the invoice for this to). The outdrive still hast the V6 Stickers and serial on it so Don is right on this. The boat is now in Texas and runs at 700' above sea level which I dont know if that matters or not. Im going to go get more pics today and get some ID numbers from the sensors. Also after looking as the serial number of the motor it looks as this motor is the Bravo 5.7L LX if that makes a difference.

 

[John_S]

Re: Merc 5.7L LX with Governor???

Up until your last statement, it was getting less and less likely you have a V6 module.

"Also after looking as the serial number of the motor it looks as this motor is the Bravo 5.7L LX if that makes a difference."

A 5.7LX/Bravo ICM is different part number than a 5.7LX/Alpha. I believe the main diffence is the shift interupter on the alpha. Running a Bravo module would slam outdrive gears. I would think the dealer would have known better to sub the V6 ICM, but it is still a possibility.

 

[Don S]

Re: Merc 5.7L LX with Governor???

What is the SN, so far, all you have given us is the 0K part, and on the parts lists, it gives both Alpha and Bravo on the same drawings.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

What is the SN, so far, all you have given us is the 0K part, and on the parts lists, it gives both Alpha and Bravo on the same drawings.

Ok heres what I got, The motor is a 1996 5.7L LX Bravo. The ICM is for a 5.7L LX Brovo part numbers T4398A 6.32 made by Nippondenso other part number on the module was 131300-2360 and the barcode had 806956-4 on it. The knock sensor module has a part number of BCTU 16184069.

The out drive is a Alpha One Serial 0F470543 on the upper and 0L12210 on the lower with a 1.62R Gear and a 13.75 X 21 Pitch 3 blade Prop.

I have pics of the wire harness and colors of wires if you need those.

Also the transmission shift int drive and reverse really smooth so i dont think the Bravo ICM is slamming the gears.

I know the motor runs great, I know the boat floats, and I know It goes pretty fast once i get it planed. I just need to figure out what is the problem with my tach only getting to 4000RPM and then hitting some kinda rev limitter, and why does it not want to plane when i put people in the back seats???

 

[SuperNova]

Re: Merc 5.7L LX with Governor???

I can't bring my self to believe that the previous owner would replace the complete 4.3 with a 5.7 and not change the ICM. Think about it. Everything including the wiring harness had to be changed. Why would he buy a long block then search for all the pieces to make it work. .

I didn't have to change any of the wiring harness when I did my conversion; it all fit perfectly. Motor mounts, bell housing, flywheel starte etc all the same. One hose I had to change for the v8.
--
Stan

 

[tommays]

Re: Merc 5.7L LX with Governor???

and why does it not want to plane when i put people in the back seats???


Trust me my BIL had the same 350 in a 18' Donzi right from the factory

But the donzi has a bow mounted fuel tank AND the seating is all well forward of the engine


These things keep the basic balance of the boat much better

Most new boats have those seats right in the stern which puts the weight in the worst possable place as well as a fuel tank that is usally as far to the stern as possable



you will need trim tabs


Tommays

 

[Mjust]

Re: Merc 5.7L LX with Governor???

and why does it not want to plane when i put people in the back seats???


Trust me my BIL had the same 350 in a 18' Donzi right from the factory

But the donzi has a bow mounted fuel tank AND the seating is all well forward of the engine


These things keep the basic balance of the boat much better

Most new boats have those seats right in the stern which puts the weight in the worst possable place as well as a fuel tank that is usally as far to the stern as possable



you will need trim tabs


Tommays

What about the Nauticus SX Smart Tabs?? They look like they dont require any electrical hook up and install easy. Also the T4 ICM Bravo that I have shouldnt have a rev limiter if im reading correctly so Im guessing i need to get my tach checked??

 

[Don S]

Re: Merc 5.7L LX with Governor???

That T4 does not stand for Thunderbolt 4, you still have a Thunderbolt V system and it does have the rev limiter in it.
BTW, the new superceded ICM number is now 806956T 5

 

[Mjust]

Re: Merc 5.7L LX with Governor???

That T4 does not stand for Thunderbolt 4, you still have a Thunderbolt V system and it does have the rev limiter in it.
BTW, the new superceded ICM number is now 806956T 5

Ok so if I do have a rev limiter im sure they wouldn't have a Bravo set for 4000RPM unless a shop can reprogram the ICM. Wouldn't you still think it would be the tach that is off my 1000RPMS??

 

[Don S]

Re: Merc 5.7L LX with Governor???

No, they are not reprogramable.
Regarding the tach, read replies 3 and 7 of this thread.