Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

[dryan117]

Folks,
I have a 1998 Mercruiser 5.0 with TBI. The boat will not start, and has set DTC43, which is continous knock. I have replaced the cap/rotor, ICM, KCM, and verified solid 30psi fuel pressure.

I can reset the code via Rinda Codemate tool. but it resets with the first few attempts to restart.

If I remove the spark arrestor cover, I can watch the TBI injectors "fire" and spray fuel into the manifold for the first few seconds, then they stop.

Does it make sense that DTC 43 would shut off the fuel injection system?

What else could it be? I have been through all the ignition system, the fuel system, and diagnostic tests, and am pretty darn stumped...

Help!

Dan

 

[Gary H NC]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

From what i have found is code 43 is the knock sensor.
Don S. or one of the Merc techs should chime in soon...

 

[JustJason]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

Have you tried disconnecting the knock sensor and trying it again?

 

[vegasphotoman]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

you havent mentioned if you have spark..........

go back to the basics......Fuel / spark / compression / timing
if you have all of the above it should atleast run

Im no "tune up" master, but Im pretty sure the inital "spray" is normal....

when you key on do you hear the fuel pump whine? you may need someone to key on for you....

Ive heard some of these boats have the electric fuel pumps connected to the oil pressure sensor....if the pressure doesnt stay up on the oil it cuts the fuel pump off.

the knock sensor from what I know....is there to let the electronics know if the motor is to far advanced....so it can adjust etc

and some fuels have more additives especially in winter....oxygenators and such...unplugging the knock sensor should reset the electronics to a preset OEM base setting, but wont completely fix anything, if it helps at all.

hope this helps! post more info as you figure through it

 

[Maclin]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

When was the last time the engine ran correctly? What all has happened since then?

 

[Don S]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

And what is your engines Mercruiser SN. While you may have a 98 boat, that doesn't mean the engine is. We might as well be looking at the correct manual when trying to help you.

 

[dryan117]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

The engine sn is OL261265. I am definitely getting spark, and I just ohmed out the pickup coil in the distributor - 809ohms and stable with the wiggle test. The battery is brand new today, and cranks over the engine quite well. I am getting intermittent "firing" of the fuel injectors. After a much cranking and intermittent fuel pulsing, it will get a strong sequence of fuel pulses such that the engine will start, and it will achieve idle for about ~5seconds and then the injectors suddenly stop.

I am getting no other DTC codes but 43, and I have performed all the checkout and replacement of the knock sensor circuit.

The last time it ran was over the summer, where it was "sputtering" a little with some hesitation, but overall ran strong. I died as I was pulling it out, so I didn't think much of it and it sat on the trailer since. Trying to run it on the earmuffs...

I don't have a noid tester, so I cannot tell if the injectors are getting proper "firing pulses" or not.

As for the quality of fuel, it doesn't look bad, and I changed the fuel filter and added about 10gallons of fresh gas to the ~20 in the tank.

Dan

 

[dryan117]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

One other theory - It could be possible that the ECM is shutting off the fuel pump after 3-5 secs after starting, and I am losing fuel pressure. It then takes turning the key on/off a few times and a few moments of cranking to get fuel back into injectors. Then, it will pulse fuel into the engine, start, and idle for another 3-5 secs.

What could cause the fuel pump to stop running? I have no other trouble code being set other than code 43, which is continuous knock, which I have yet to understand.

I am going to check the oil pressure sender and transom oil level senders tonight.

The only thing I will mention is that after the engine "dies out" after the 3-5 secs, if I "bump" the starter one of the injectors will fire 1 pulse - thats it. If I crank, no fuel pulses. It "looks" like a full single pulse. - This is making me believe the ECM is cutting the electrical "pulses" to the injectors. But why????

 

[Glastron_V210]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

It sounds like your oil pressure sensor is toast.

If you get a prime pulse of fuel, then nothing, that 's likely what it is.

What happens is that the ecm gives you a bit of fuel to start (the prime pulse), then as the engine starts and oil pressure builds, the fuel continues. loose the oil pressure, the fuel quits.

So, if is fires, then dies, you've got to look for a bad oil pressure switch.

It could very well be a bad fuel pump as well. They will sometimes mess around a bit before dying. Use a fuel pressure guage at your pressure port and jumper the fuel pump to run....any deviation in pressure from stock? If it holds steady then the ecm is shutting the fuel down.

This will NOT be due to a knock sensor...the sensor will retard the ignition advance, but it won't killl the engine.


C

 

[dubs283]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

another quick check is to see if the tachometer is giving a solid RPM reading when running or when cranking

the ecm gets the signal to "wake up" and turn everything on, spark, fuel, etc. from the ignition sensor in the distributor

if the sensor is failing or has failed the engine will not run or run poorly for a few seconds then die

check your mercuiser manual for troubleshooting the ignition system and the tests will indicate if the sensor is bad or not

i would say if the sensor is original, go ahead and replace it anyway, the older ones are junk

 

[Fun Times]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

First off you need to figure out if you have a EFI problem or a real engine problem giving the engine a knock code 43. Does/Did the engine seem louder that the knock sensor is really picking something up and giving you a code? Pull your spark plugs just to be safe. Sorry if this seems dum to you It's just that we are not there at the engine with you so it kind of hard to do over a web site.

Also have you checked and rechecked all the ground wires to the back side of the engine block to make sure they are clean & tight, And not broken in anyway, There is a stud at the back of the engine where the ground wires go for the ecm, ect, You may need a flash light to really get back there to check them out real good.

Then try disconnecting the knock sensor down at the block and trying it again?

Yes you may have a bad ECM, Or ignition module. [See below for what to look for, I think this may help know what to start looking at anyways.

Yes it still could be a bad pick up coil under the distributor cap.

If you have a mercruiser service manaul for your engine set up, Look to see if any of the wires goes from the knock module to either the ECM or to the ignition module under the cap, If the wires go to #9 in this link then there is a chance the ignition module is bad, And if they go the ECM then it may be bad also.
http://www.mercruiserparts.com/Show...=70&bdesc=DISTRIBUTOR+AND+IGNITION+COMPONENTS

 

[Fun Times]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

It sounds like your oil pressure sensor is toast.

If you get a prime pulse of fuel, then nothing, that 's likely what it is.

What happens is that the ecm gives you a bit of fuel to start (the prime pulse), then as the engine starts and oil pressure builds, the fuel continues. loose the oil pressure, the fuel quits.

So, if is fires, then dies, you've got to look for a bad oil pressure switch.

It could very well be a bad fuel pump as well. They will sometimes mess around a bit before dying. Use a fuel pressure guage at your pressure port and jumper the fuel pump to run....any deviation in pressure from stock? If it holds steady then the ecm is shutting the fuel down.

This will NOT be due to a knock sensor...the sensor will retard the ignition advance, but it won't killl the engine.


C

Hi, I just wanted to say back in 1998, I do not believe mercruiser was using the oil pressure switch yet to run the power for the fuel pump power yet, I believe the oil pressure switch for the fuel pump came out in some where around 04ish and up but I can not remember exactly when they started using it.

 

[Don S]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

OL261265 is the serial number for the outdrive, not the engine.

Hi, I just wanted to say back in 1998, I do not believe mercruiser was using the oil pressure switch yet to run the power for the fuel pump power yet, I believe the oil pressure switch for the fuel pump came out in some where around 04ish and up but I can not remember exactly when they started using it.

The oil pressure switch is used for controlling the fuel pump on the carbed engine ONLY, since the electric fuel pump has been in use. But it is not used on EFI engines. The ECM controls the fuel pumps on EFI engines.

 

[Fun Times]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

OL261265 is the serial number for the outdrive, not the engine.



The oil pressure switch is used for controlling the fuel pump on the carbed engine ONLY, since the electric fuel pump has been in use. But it is not used on EFI engines. The ECM controls the fuel pumps on EFI engines.

Thank you Don I forgot about the use of this switch back then, It may be because I myself have never seen one go bad and never needed to check it for any reason, Have you or anyone eles ever found one go bad out there?:redface:

 

[Don S]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

Thank you Don I forgot about the use of this switch back then, It may be because I myself have never seen one go bad and never needed to check it for any reason, Have you or anyone eles ever found one go bad out there?:redface:

Not familiar with the term "Switch back", could you explain? And, I'm not axactly sure you you have never seen go bad ...... ECM or oil pressure switch. I have replaced both.

 

[dryan117]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

Good info on the pressure switch theory. Being an MEFI2, i just unplugged the oil switch (normally closed, open indicates oil pressure), and it had absolutely no effect. Success! Not the switch.

The fuel pulsations are definitely erratic. I will sometimes produce fuel spray only on one side, then jump back and forth between the other side. Seems quite random on when the fuel spray pulses. I am still thinking it is not getting consistent pulses from the ECM, as opposed to a fuel pressure/supply problem.

Time for a set of Noid lights.

Would water in the fuel be causing any of this?

Engine SN is L058534, I think - hard to read the numbers backwards in a mirror.

Dan

 

[Don S]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

Is the battery fully charged, the cables clean an TIGHT (not with wing nuts) and is the engine turning over at normal cranking speeds?
EFI engines that don't see proper cranking speeds WILL NOT start.

 

[dryan117]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

Absolutely. Brand new battery (with good charge) installed yesterday. Cranking over the best it ever has.

I dumped a crappy video up on youtube, not sure you can see the fuel pulses, but they are very sporatic.

http://www.youtube.com/watch?v=6qoEWUVscIo

Dan

 

[Don S]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

This is where you really need a scan tool of some sort to see what is happening. You could have a sensor gone bad that will not set a code of any kind, the the scan tool will show what is going on.
And to a previous question I forgot to answer, YES, water will DESTROY an EFI system.

 

[dryan117]

Re: Mercruiser 5.0 - Won't Start, Continuous Knock Code 43

Don - Thanks for all the info. I am using a codemate, but that is just giving me the DTC codes stored in the eeprom. Nothing realtime.

Next move... I am going for a noid tester to separate the electrical from the mechanical here... If the solenoids are getting electrical pulses to fire, I'll know I have a fuel supply or fuel injector problem. I also might "T" the fuel pressure gauge in line while cranking over to measure pressure during the noid light pulses.

If they don't, I am back to figuring out why the ECM is not getting all the sensor input (or it's toast too) to pulse the injectors.

I have been through service manual 24 backwards and forwards - nothing is jumping out. I have replaced all ignition system parts, with the exception of the pickup coil - but that ohm'd out fine.

Dan