Mercruiser 4.3L EFI Rev Limiter

[Fish Bin Laden]

Re: Mercruiser 4.3L EFI Rev Limiter

There are codes on your ecu post them if you would like to save a few dollars or a pic would be fine. However if your somewhat comp savy you may want to unplug your ecu and under a good glass check out the pins for uniformity and free of corision.Litte note e-proms are a solid state device and are either on or off..I doubt very much you have a bad ecu

Heres a link that will show you how to make a basic tester..if that works you dont or its highly unlikely your ecu is bad

http://www.offshoreonly.com/forums/...ke-marine-efi-code-tool-less-than-1-00-a.html

All accessible electrical plugs have been inspected and all look ok. Whilst doing this I found a spare earth terminal which was hidden tucked under a loom. It was cable tied to the loom and originates in the area of the reset button for the circuit breaker. The length of the wire and the size of terminal indicate to me that this should be connected to the mounting bolt of the distributor cap. Would this be the case and could it be the cause of the problem? I have not reconnected it yet as I thought I would wait for the problem to occur and then connect it and see if it makes any difference. I guess if it is a earth wire it can do no harm. Opinions please
The code on the ECU is 860371KA00031238

 

[Pete104]

Re: Mercruiser 4.3L EFI Rev Limiter

Have you had the ECM scanned? Probably not!
That ground wire belongs right where it's at. Ty-rapped under the rest.
And try running with the main harnes disconnected.

 

[Tail_Gunner]

Re: Mercruiser 4.3L EFI Rev Limiter

All accessible electrical plugs have been inspected and all look ok. Whilst doing this I found a spare earth terminal which was hidden tucked under a loom. It was cable tied to the loom and originates in the area of the reset button for the circuit breaker. The length of the wire and the size of terminal indicate to me that this should be connected to the mounting bolt of the distributor cap. Would this be the case and could it be the cause of the problem? I have not reconnected it yet as I thought I would wait for the problem to occur and then connect it and see if it makes any difference. I guess if it is a earth wire it can do no harm. Opinions please
The code on the ECU is 860371KA00031238

Ok make that home made tester and see if there is continuity with your ecm. That is the first step if it can communicate then its a down line issue..Its just that simple

 

[dubs283]

Re: Mercruiser 4.3L EFI Rev Limiter

is this engine using a t-bolt ignition??

 

[Don S]

Re: Mercruiser 4.3L EFI Rev Limiter

is this engine using a t-bolt ignition??

Nope, he has the Delco EST distributor.

 

[dubs283]

Re: Mercruiser 4.3L EFI Rev Limiter

okay, was thinking if t-bolt perhaps an ignition sensor issue, i know merc claims they either work or they dont but i have seen some funky things happen with the older style ones

 

[Fish Bin Laden]

Re: Mercruiser 4.3L EFI Rev Limiter

Ok make that home made tester and see if there is continuity with your ecm. That is the first step if it can communicate then its a down line issue..Its just that simple

Yes I intend doing this, just having a little trouble sourcing a suitable LED. Sorry this is taking so long but work keeps getting in the way.

 

[Fish Bin Laden]

Re: Mercruiser 4.3L EFI Rev Limiter

Have you had the ECM scanned? Probably not!
That ground wire belongs right where it's at. Ty-rapped under the rest.
And try running with the main harnes disconnected.

Sorry could you please explained what you mean by the main harness and how and where I disconnect it.

 

[Pete104]

Re: Mercruiser 4.3L EFI Rev Limiter

If you remove the flame arrestor cover. Behind the distributor cap, in that area, you'll see a big plug. Should have a hose clamp on it. That sometimes gets overtightened. Don't let that happen! The plug has the majority of the wires that go to the dash. Unplug it & hot wire the engine. B+ to + side of the coil, energize the solenoid via 12v to the small yellow/red wire. Then drive it! Nothing on the dash will work as far as gauges. Switches will. Just drive & see how acts.
What this is doing is letting the motor do everything it should, without any boat builder issues. There may still be a problem but this just says it ain't at the dash.
While your at it, put a fresh water sep filter on & run it a remote tank.

 

[Fish Bin Laden]

Re: Mercruiser 4.3L EFI Rev Limiter

Ok make that home made tester and see if there is continuity with your ecm. That is the first step if it can communicate then its a down line issue..Its just that simple

OK. Have done the home tester thing successfully. I am getting the code 12 i.e. one flash, pause, 2 flashes, long pause repeatedly - no other code showing. What does this mean?

 

[Don S]

Re: Mercruiser 4.3L EFI Rev Limiter

12 means nothing is wrong that the sensors can detect. ie. there are no codes.

 

[Fish Bin Laden]

Re: Mercruiser 4.3L EFI Rev Limiter

If you remove the flame arrestor cover. Behind the distributor cap, in that area, you'll see a big plug. Should have a hose clamp on it. That sometimes gets overtightened. Don't let that happen! The plug has the majority of the wires that go to the dash. Unplug it & hot wire the engine. B+ to + side of the coil, energize the solenoid via 12v to the small yellow/red wire. Then drive it! Nothing on the dash will work as far as gauges. Switches will. Just drive & see how acts.
What this is doing is letting the motor do everything it should, without any boat builder issues. There may still be a problem but this just says it ain't at the dash.
While your at it, put a fresh water sep filter on & run it a remote tank.

Thanks for that Pete, I would like to try and isolate the dash but you lost me after I unpluged the big plug- sorry but I am not particualy mechanically minded especialy when it comes to electrics.

 

[Tail_Gunner]

Re: Mercruiser 4.3L EFI Rev Limiter

I have a 4.3L EFI Mercruiser serial number OL 034997. It appears that the rev limiter is activating prematurely and randomly. After a short period of use the tacometer needle will oscillate wildly usually between 4500 & 5000 revs although I normally run the engine at cruising about 3800 - 3900. When this occurs the motor will tend to de-rate and although without any input from the throttle or noticable increase in revs, the problem will get worse to the point where the rev counter will touch maximum of 6000 at which stage there will be noticable misfiring and back firing. The only way to proceed when this happens is to reduce the revs to well below 3000 and even then the motor runs erratically, seemingly in sync with the oscillation of tacometer. I have fitted a new distributor module and cap, also HT leads, fuel pump, coil, tacometer etc etc. Ideas please

Ok a few things...First your ecu does have a rpm limiter and you engine cannot go to 6000.....Unless the ecu is indeed bad

Are you saying you cruisng at 3800 rpm and the engine jumps up to 5000 (built int rev limit) with no throttle input aka a runaway engine

Or are you saying when you reach 4500 rpm then the engine runs erractic and jumps to 5000 rpm again with no throttle input

The key here is building up rpm with no throttle input and at what rpm,,If this is happening then you might have a bad ecu..it is possible that injectors are not switching and running at full cycle.

Give these guys a call they are very comptent and can help you if you do have a mefi ecu you could ask them if it is possilbe for mefi ecu to all of sudden just run the injectors at full duty cycle that is they do not switch on and off.

http://www.obd2allinone.com/sc/details.asp?item=mefitune

 

[Fish Bin Laden]

Re: Mercruiser 4.3L EFI Rev Limiter

Ok a few things...First your ecu does have a rpm limiter and you engine cannot go to 6000.....Unless the ecu is indeed bad

Are you saying you cruisng at 3800 rpm and the engine jumps up to 5000 (built int rev limit) with no throttle input aka a runaway engine

Or are you saying when you reach 4500 rpm then the engine runs erractic and jumps to 5000 rpm again with no throttle input

The key here is building up rpm with no throttle input and at what rpm,,If this is happening then you might have a bad ecu..it is possible that injectors are not switching and running at full cycle.

Give these guys a call they are very comptent and can help you if you do have a mefi ecu you could ask them if it is possilbe for mefi ecu to all of sudden just run the injectors at full duty cycle that is they do not switch on and off.

http://www.obd2allinone.com/sc/details.asp?item=mefitune

No the engine does not increase revs at all, rather the opposite. The Tacho simply indicates it is over revving and consequently derates the engine. It appears to me that either the signal from the sensor to the ECU (and tacho) is incorrect or the ECU is misinterpreting the signal.

 

[Pete104]

Re: Mercruiser 4.3L EFI Rev Limiter

Energize the positive (+) side of the coil, it's the purple wire terminal.
Crank the engine by energizing the small yellow w/red tracer wire. If you have too much difficulty getting the slave solenoid, try doing it at the starter. Same principle, just different location.

 

[Fish Bin Laden]

Re: Mercruiser 4.3L EFI Rev Limiter

Energize the positive (+) side of the coil, it's the purple wire terminal.
Crank the engine by energizing the small yellow w/red tracer wire. If you have too much difficulty getting the slave solenoid, try doing it at the starter. Same principle, just different location.

Did the isolated dash test today and the problem persisted so I guess that elimenates that.

 

[Tail_Gunner]

Re: Mercruiser 4.3L EFI Rev Limiter

Very odd the limiter seems to work at the 5000 point...yet you say it can peak to 6000> id give OBD a call and ask them if the ecu can behave like that

(After a short period of use the tacometer needle will oscillate wildly usually between 4500 & 5000 revs)
That sounds normal its preset for 5000....the oscialltion should be very breif almost like a slight miss.. which it is...

If that motor is running to 6000 your way under propped..I doubt very much it is turning 6000..Could there be something in the drive system that is letting go occasionally..Not a spun hub

 

[dubs283]

Re: Mercruiser 4.3L EFI Rev Limiter

Did the isolated dash test today and the problem persisted so I guess that elimenates that.

at this point you are down to two possible culprits:

a) bad ecm - pretty spendy, although if all it needs is a reflash it is fairly simple and cheaper than a new one

b) faulty crank position sensor (the ecm gets the rpm signal from this) - it is located next to the balancer and connects to the harness above the balancer, maybe there is some corrosion in the harness connection or the sensor got bumped and is rubbing, etc... - try removing it, unplugging it, cleaning connections, etc...and lake test again

 

[Pete104]

Re: Mercruiser 4.3L EFI Rev Limiter

at this point you are down to two possible culprits:

a) bad ecm - pretty spendy, although if all it needs is a reflash it is fairly simple and cheaper than a new one

b) faulty crank position sensor (the ecm gets the rpm signal from this) - it is located next to the balancer and connects to the harness above the balancer, maybe there is some corrosion in the harness connection or the sensor got bumped and is rubbing, etc... - try removing it, unplugging it, cleaning connections, etc...and lake test again

Not in this configuration! There is an "ECM" for the fuel system & there is an "ECU" for the ignition system.
The only real troubleshoot for an "ECU" is a no start/no spark issue similar to Thunder V. Anything else is process of elimination.

 

[dubs283]

Re: Mercruiser 4.3L EFI Rev Limiter

Not in this configuration! There is an "ECM" for the fuel system & there is an "ECU" for the ignition system.
The only real troubleshoot for an "ECU" is a no start/no spark issue similar to Thunder V. Anything else is process of elimination.

oh gosh!!

thats right!!

i keep getting confused on this thread! - i was thinking mpi when this is tbi