ECM for 1999 Mercruiser MCM 5.0L EFI / 305 CID

[ToboFan]

Hi there,

I am desperately searching for a replacement/spare part/alternative solution for a possibly failing ECM.
Boat: 1999 Searay Sundeck 240.
Motor: Mercruiser MCM 5.0L EFI / 305 CID
Engine Serial Number 0L379916

Symptoms are: A) Engine in idle runs a bit rough, B) In the water would not go above 3000 RPM Engine, and backfires.
Replaced spark plugs, ignition cables, checked for bad fuel, replaced distributor cap and rotor. In another thread I read ECM may be the issue. I cannot find a replacement. Does anyone have a solution/source?

Many thanks

Tobo

 

[Scott Danforth]

First, welcome aboard

the fact that your motor is running rules out the ECM.

The fact its backfiring means you are running lean or your timing is off.
Not going above 3000 RPM could be you are running out of fuel or the motor doesnt know its in gear

First, empty the contents of your water-separating filter into a clear container and make sure you do not have water or cloudy fuel in there.
Second, replace the filter
Third, measure your fuel pressure. You didnt state which one of many different EFI systems you have. however make sure you are getting correct fuel pressure for your engine.

However most likely TBI. so your fuel pressure is either 15psi or 30 psi.

 

[alldodge]

As Scott mention fuel pressure may be out of spec, should be 30 psi at 1800 RPM

You have EST ignition, might have an issue with the modules (item 8 or 9). Have you tested the items?

https://www.mercruiserparts.com/bam/subassembly/31844/2704/70

 

[ToboFan]

First, welcome aboard

the fact that your motor is running rules out the ECM.

The fact its backfiring means you are running lean or your timing is off.
Not going above 3000 RPM could be you are running out of fuel or the motor doesnt know its in gear

First, empty the contents of your water-separating filter into a clear container and make sure you do not have water or cloudy fuel in there.
Second, replace the filter
Third, measure your fuel pressure. You didnt state which one of many different EFI systems you have. however make sure you are getting correct fuel pressure for your engine.

However most likely TBI. so your fuel pressure is either 15psi or 30 psi.

Thank you! This was quick! How do I identify which EFI system I have?

 

[ToboFan]

As Scott mention fuel pressure may be out of spec, should be 30 psi at 1800 RPM

You have EST ignition, might have an issue with the modules (item 8 or 9). Have you tested the items?

https://www.mercruiserparts.com/bam/subassembly/31844/2704/70

Thank you, will do shortly

 

[alldodge]

Thank you! This was quick! How do I identify which EFI system I have?

Your serial number shows it's a MEFI-1 TBI motor.
Timing should be 8* BTDC set in base timing mode
Plugs MR43LTS Gap 0.045

 

[muc]

Mercury Marine EPC (electronic parts catalog) shows this engine to have MEFI3 but it could have been updated to MEFI4 because MEFI3 has been NLA (no longer available) for a long time, MEFI4 is also NLA for many years. Here is how you tell what you have. Here's a picture of the MEFI4 conversion kit.The ECM is on the left. MEFI3 and 4 ECMs look the same. What's different is the adapter harness on the right. If you still have MEFI3 you won't have this extra harness.
I agree with @Scott Danforth that the chances of you having a Bad ECM are near zero and I would inspect the fuel in the filter like he advised. Also check fuel pressure, should be 30 psi. The local auto parts store will probably loan you the gauge for free. You could also use your timing light to watch the injector fuel pattern when the engine is running (should have a nice cone shaped pattern). ----- Just be sure to be safe and wear face protection and have a fire extinguisher handy ----- etcetera ---- because you don't want a fire from a backfire.
After these tests I recommend a compression test before replacing any more parts.
I also show your engine to have a Thunderbolt ignition system. Most likely not the source of these symptoms.
Yes 8° is your timing spec Engine must be at idle when checking this.

 

[ToboFan]

Your serial number shows it's a MEFI-1 TBI motor.
Timing should be 8* BTDC set in base timing mode
Plugs MR43LTS Gap 0.045

Thank you for your support! There is another odd thing that I have seen: The whole distributor unit can easily be turned, without any significant resistance. I do not know how to lock in a specific position.

 

[ToboFan]

Mercury Marine EPC (electronic parts catalog) shows this engine to have MEFI3 but it could have been updated to MEFI4 because MEFI3 has been NLA (no longer available) for a long time, MEFI4 is also NLA for many years. Here is how you tell what you have. Here's a picture of the MEFI4 conversion kit.View attachment 378212The ECM is on the left. MEFI3 and 4 ECMs look the same. What's different is the adapter harness on the right. If you still have MEFI3 you won't have this extra harness.
I agree with @Scott Danforth that the chances of you having a Bad ECM are near zero and I would inspect the fuel in the filter like he advised. Also check fuel pressure, should be 30 psi. The local auto parts store will probably loan you the gauge for free. You could also use your timing light to watch the injector fuel pattern when the engine is running (should have a nice cone shaped pattern). ----- Just be sure to be safe and wear face protection and have a fire extinguisher handy ----- etcetera ---- because you don't want a fire from a backfire.
After these tests I recommend a compression test before replacing any more parts.
I also show your engine to have a Thunderbolt ignition system. Most likely not the source of these symptoms.
Yes 8° is your timing spec Engine must be at idle when checking this.

Thank you for help! I am truly impressed by the support I am getting here!

 

[ToboFan]

There is another odd thing that I have seen: The whole distributor unit can easily be turned, without any significant resistance. I do not know how to lock in a specific position.

 

[alldodge]

There is another odd thing that I have seen: The whole distributor unit can easily be turned, without any significant resistance. I do not know how to lock in a specific position.

That's the problem right there. Time motor and clamp the dizzy in place

 

[ToboFan]

That's the problem right there. Time motor and clamp the dizzy in place

I really do not know how. It is not very accessible, and I do not see or feel a way to lock it in place. I know it sounds stupid, but I tried, without success!

 

[alldodge]

At the base there should be a clamp with one bolt going into the intake. Clamp resembles a Y

If it's not there then need to get one. Can obtain from most auto parts store or a junk yard.


To time need a timing light (might be able to get a loaner from parts store). If you don't feel up to it find a dealer or other

 

[ToboFan]

Is this it? I assume I will have to tighten bolt 28?

 

[Scott Danforth]

View attachment 378215 Is this it? I assume I will have to tighten bolt 28?

Only after you follow the manual and properly set timing

 

[Scott Danforth]

I really do not know how. It is not very accessible, and I do not see or feel a way to lock it in place. I know it sounds stupid, but I tried, without success!

If you can't set timing correctly, I suggest taking it to a qualified marine mechanic

 

[ToboFan]

The boat did not come with a motor manual, but manuals can be found here: http://publications.brunswick.com/
Alternative online sources may be scam or phishing!
Thank you, Scott!

 

[Scott Danforth]

The boat did not come with a motor manual, but I believe I found one online: http://www.atlanticmobilemarine.com/service manual 5&57.pdf

No, that is most likely a scam site

Due to copyright laws, you can only get manuals from Mercruiser. Sites claiming manuals are usually phishing and scam sites

Get the manual from http://publications.brunswick.com/

 

[alldodge]

View attachment 378215 Is this it? I assume I will have to tighten bolt 28?

Yes, that's it

You need manual 24,

To set timing motor must be placed in base timing mode. To do this find the DLC (Data Link Connector). It will have a plastic cover on it that is removed to gain access to the pins. Take a paper clip or small wire and jump pins A and B which places motor in base timing.

 

[ToboFan]

Mercury Marine EPC (electronic parts catalog) shows this engine to have MEFI3 but it could have been updated to MEFI4 because MEFI3 has been NLA (no longer available) for a long time, MEFI4 is also NLA for many years. Here is how you tell what you have. Here's a picture of the MEFI4 conversion kit.View attachment 378212The ECM is on the left. MEFI3 and 4 ECMs look the same. What's different is the adapter harness on the right. If you still have MEFI3 you won't have this extra harness.
I agree with @Scott Danforth that the chances of you having a Bad ECM are near zero and I would inspect the fuel in the filter like he advised. Also check fuel pressure, should be 30 psi. The local auto parts store will probably loan you the gauge for free. You could also use your timing light to watch the injector fuel pattern when the engine is running (should have a nice cone shaped pattern). ----- Just be sure to be safe and wear face protection and have a fire extinguisher handy ----- etcetera ---- because you don't want a fire from a backfire.
After these tests I recommend a compression test before replacing any more parts.
I also show your engine to have a Thunderbolt ignition system. Most likely not the source of these symptoms.
Yes 8° is your timing spec Engine must be at idle when checking this.

Mine looks just like this. It is either MEFI 3 or MEFI 4. I am now looking at a diagnostic tool that does not cost an arm and a leg. I have been searching for an hour now, and only find 700 USD models. Can anyone recommend a more reasonable priced MEFI Scan tool?