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Engine will not go over 2000RPM

1marc1 said:
Its not that i don't completely understand. I get it. If my sticker is incorrectly placed my timing will be incorrectly set. If my timing doesn't advance my ecm could be pooched. If there is something wrong with my knock sensor or tps, it could be throwing my engine into a safe mode or something. But long story short everything we transferred from my old engine worked before at WOT and should be working now. My fuel pump is new and was replaced when i was having issues with my first engine, the marine shop did zero trouble shooting and replaced my entire fuel system when the real culprit was zero compression on 2 cylinders. So the pump thats on my engine even tho is new.....its still untested and it sat for 2 years which is why we just want to try this fuel test out. I would run a gauge but i do not have a guage to see if the pump is producing the correct psi. I Already spent 7000 dollars in parts or unwanted and useless labour in the repair of this boat, and im done trying to spend any more money than i have to now on test guages or anything else for that matter.

But I get that my timing could be the main culprit......but we just want to try to throw some fuel down the throttle body........just to see what that does. If it does nothing, we'll run a light while giving it throttle to see if my timing is advancing. I get the basics of everything here to find out how to find the answers i need and i thank you guys for that! But it gets to a point to where youre sending me graphs and attempting to make me understand very techinal things i don't have the knowledge for.......and it is falling on deaf ears. But i appreciate your help none the less, the more information i can get is only going to help me more. I tip my hat to everyone who took that time to help me with this issue so far! Im hoping to have some kind of concrete asnwer to what is happening thursday night once we try again. I will keep you all posted.
Click to expand...

THERE ARE only a few possible reasons for not reaching wide open throttle under load.

process of elimination and don't rule anything out such as things you may already think are ok, double check everything. Missing ground, loose connection, partial connection........bad connection.......



bad coupler (outdrive drive shaft goes into it)
Bad prop hub
loss or lack of fuel
no timing advance
too much fuel (over rich) but you should see excess black smoke out the exhaust


Other possibilities would be lots of growth on bottom of boat
over weighted boat
something in water path causing cavitation at outdrive
Tachometer may be interfering with ignition...

Bad internal motor issue such as valve issues etc.

So start somewhere see what result you get, then either move to another possibility or come back and post results and ask more questions.
 
Kghost said:
THERE ARE only a few possible reasons for not reaching wide open throttle under load.
bad coupler (outdrive drive shaft goes into it)
Bad prop hub
loss or lack of fuel
no timing advance
too much fuel (over rich) but you should see excess black smoke out the exhaust

Other possibilities would be lots of growth on bottom of boat
over weighted boat
something in water path causing cavitation at outdrive
Tachometer may be interfering with ignition...
Bad internal motor issue such as valve issues etc.
Click to expand...
No disagreement here if we're talking about a WOT RPM issue ONLY!

See post #1 below.

1marc1 said:
I have a 4.3L throttle body injected Mercruiser (s/n M093527), we just installed a brand new long block. Ever since installation the boat runs good at idle and on muffs but under load it will not go over 2000rpm.
Click to expand...
As you can see, Marc at this time is not concerned about WOT RPM. Marc is unable to even reach 2,000 RPM.
He needs to first figure out why he is unable to reach 2k RPM. Then if WOT RPM cannot be achieved, he'll want to go onto the next issue(s)!


MikDee said:
If you put a timing tape on the vibration damper/ balancer, I believe you can do this with an average timing light. Otherwise, you need an advance timing light. Speed shops usually have this self stick timing tape.
Click to expand...
Marc, is your harmonic balancer factory marked off...... or has someone installed a "decal" (aka timing tape)?
If "decal", is the decal correct for the balancer diameter?

1marc1 said:
Firing order was correct, and i have 150lbs on every hole. But upon pulling my plugs out i noticed cylinders number 1,3,2,4 are all burning and are black..... but cylinders 5 and 6 came out still looking like new.
Click to expand...
Cylinders 5 and 6 are you two aft-most cylinders and are oposite one another.
If TBI, these two cylinders are separated via the elevation of the intake manifold "planes", which means that each cylinder pulls from the oposite injector.

1marc1 said:
It says there that the ignition module may supply more spark advance. But in my circumstance isn't it my ecm that controls my spark advance? So if my ecm isn't working or working properly it's not going to adjust for the spark advance.
Click to expand...
Correct!



Marc, this info that you posted is important to understand:

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.

IMPORTANT: The graph below shows the typical advance ranges for a Thunderbolt
V ignition control module. The numbers plotted on the graph are not representative
of any particular model. It is only presented to provide an understanding of how the
system functions.



*****************************
kghost said:
I agree.
Simply put inorder for a motor to achive wide open throttle under load the timing must advance.
So with a base of 8 and the timing control adding ~ 22 more you should see about 30 total degrees advance (btdc). This should occur by 2000 rpms if the timing spec is the same as prior year v6 motors.
All due respect to your knowledge here...... but I'd like to see an OEM curve graph whereby it shows an advance of 30* @ 2,000 RPM!

Kghost, you asked me earlier to "loose the acronyms"! Aren't "ECM", "BTDC" and "RPM" abreviations? Are abreviations allowed in this discussion? :rolleyes:

So if you are not getting any advance either there is a ecm issue or a sensor it telling the ecm to retard the timing.
A very likely posibility!

Did you reinstall the knock sensor? If all the wiring connected to the correct places?
Thats my best guess
Again.... a very likely posibility!
Click to expand...


Marc...... I think that we're all assuming that your engine is equipped with Throttle Body Injection (aka TBI).... is this correct?



.
 
A TPS Is mentioned and poo-pooed but I don't believe it should be discounted so quickly.
No, a TPS won't affect engine timing directly per say but it does affect it in that the computer looks at how quickly the throttle is advanced.
All that aside, a defective TPS (say one that reads wide open at half throttle) could readily limit engine rpm to 2000. And that's the OP's problem, right?

What kind of scanner do these boats use? Will a standard automotive OBD II work or are they more proprietary?
 
DaveG55 said:
All that aside, a defective TPS (say one that reads wide open at half throttle) could readily limit engine rpm to 2000. And that's the OP's problem, right?
Click to expand...
Yes..... agreed.
It would appear that it's never been a WOT RPM problem, since Marc has not even been able to get into that RPM range!


.
 
RicardoMarine said:
No disagreement here if we're talking about a WOT RPM issue ONLY!

See post #1 below.


As you can see, Marc at this time is not concerned about WOT RPM. Marc is unable to even reach 2,000 RPM.
He needs to first figure out why he is unable to reach 2k RPM. Then if WOT RPM cannot be achieved, he'll want to go onto the next issue(s)!


Marc, is your harmonic balancer factory marked off...... or has someone installed a "decal" (aka timing tape)?
If "decal", is the decal correct for the balancer diameter?

Cylinders 5 and 6 are you two aft-most cylinders and are oposite one another.
If TBI, these two cylinders are separated via the elevation of the intake manifold "planes", which means that each cylinder pulls from the oposite injector.

Correct!



Marc, this info that you posted is important to understand:

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.

IMPORTANT: The graph below shows the typical advance ranges for a Thunderbolt
V ignition control module. The numbers plotted on the graph are not representative
of any particular model. It is only presented to provide an understanding of how the
system functions.



*****************************



Marc...... I think that we're all assuming that your engine is equipped with Throttle Body Injection (aka TBI).... is this correct?



.
Click to expand...

Yes my boat is a TBI! And tonight we ruled out that this isnt a fuel issue 100%. Yes we went about it the incorrect manor but we can easily say that the extra fuel we were adding to the throttle body did nothing. It showed no sign off life no matter how little or how much we put in. We took it to the point to where we over fueled it a bit and it bogged down. My ecm is working, we adjusted the timing a bit out on the water and no matter what we did it.......it didn't improve anything. We also didn't exactly take the timing back to where it was initially, but the timing was probably a hair under 8 at the time and then when we hit the throttle and at around the 2000 perhaps a little over rpm range we were showing around 28* or 29* (ish) on my damper. We didn't have the boat out for long, and we didn't push it to too hard, we definitely had it up at operating temp and after coming in i noticed my top riser was hot on my starboard side meanwhile my port side was barely even warm. I understand that one side runs warmer than the other but this was a pretty big difference between the 2. Even after about 20+ minutes of not running the starboard riser was still pretty damn hot. Does that sound normal??
 
kghost said:
THERE ARE only a few possible reasons for not reaching wide open throttle under load.

process of elimination and don't rule anything out such as things you may already think are ok, double check everything. Missing ground, loose connection, partial connection........bad connection.......



bad coupler (outdrive drive shaft goes into it)
Bad prop hub
loss or lack of fuel
no timing advance
too much fuel (over rich) but you should see excess black smoke out the exhaust


Other possibilities would be lots of growth on bottom of boat
over weighted boat
something in water path causing cavitation at outdrive
Tachometer may be interfering with ignition...

Bad internal motor issue such as valve issues etc.

So start somewhere see what result you get, then either move to another possibility or come back and post results and ask more questions.
Click to expand...

Hey, not sure if you get a notification if i don't reply to you but we got some answers tonight. I posted them on Ricardo's comment.
 
Popped off my elbows tonite from my risers hoping to see if perhaps one of my flappers failed and fell into my y pipe restricting my exhaust and perhaps making the one run hotter but no. Still intact, functioning and working fine on both sides. Engine temp was normal too, always around 150.

So perhaps it is TPS? Or possibly some bad plug wires??
 
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