Mercruiser 5.7mpi horizon single cylinder burning lean

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woodworker2001

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I have got a 2000 5.7 horizon mpi. When i pulled the plugs on it cylinder 4 was white on the porcelain with some black on the metal. Definaly burning lean from the other 7.

Immediately lead me to a possible bad injector so i changed it out. I was pretty positive that was the problem since there was some rust on the injector and looked like it had issues, but the problem continued. Swapped that injector with another one just to test and same issue.

Hooked motor up to computer and don’t see any codes or any abnormal fuel burn between the engines.

I have good compression on this cylinder and also installed a new plug in it.

Looking for suggestions. Wondering about maybe a bad harness to that injector.
 
nola mike

nola mike

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woodworker2001 said:
I have got a 2000 5.7 horizon mpi. When i pulled the plugs on it cylinder 4 was white on the porcelain with some black on the metal. Definaly burning lean from the other 7.

Immediately lead me to a possible bad injector so i changed it out. I was pretty positive that was the problem since there was some rust on the injector and looked like it had issues, but the problem continued. Swapped that injector with another one just to test and same issue.

Hooked motor up to computer and don’t see any codes or any abnormal fuel burn between the engines.

I have good compression on this cylinder and also installed a new plug in it.

Looking for suggestions. Wondering about maybe a bad harness to that injector.
Click to expand...
Are you sure it's firing? First step for me would be to put a noid light on it. Also need to make sure you're getting spark to that cylinder
 
alldodge

alldodge

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Your motor should have a MEFI-3 ECM (SN needed to verify) and it uses batch firing of the injectors. Batch firing means 4 injectors are fired at one time and normally fire at least twice for each revolution.

Injector 2 and 4 are fired at the same time by the ECM. Swap 2 and 4 connectors to see if it moves to 2

Edit: change 6 to 2
 
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woodworker2001

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alldodge said:
Your motor should have a MEFI-3 ECM (SN needed to verify) and it uses batch firing of the injectors. Batch firing means 4 injectors are fired at one time and normally fire at least twice for each revolution.

Injector 2 and 4 are fired at the same time by the ECM. Swap 2 and 4 connectors to see if it moves to 6
Click to expand...
Did you mean see if it moves to 2?
 
alldodge

alldodge

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Your SN comes up as a MEFI-3 ECM, your pic is for a MEFI-1
Hard to see but this is YOURS
Smitty on Offshore only has said many times that it doesn't matter with batch firing, so for testing swap which ever one you can
 
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woodworker2001

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alldodge said:
Your SN comes up as a MEFI-3 ECM, your pic is for a MEFI-1
Hard to see but this is YOURS
Smitty on Offshore only has said many times that it doesn't matter with batch firing, so for testing swap which ever one you can
Click to expand...
Ok thanks!!! And I wondered if batch fired even mattered with testing since it is firing multiples together. I will check this this week hopefully
 
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woodworker2001

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Ok I am trying to get photos of the plug, but here is the update.

Changed the injector wires and ran the boat for a mile at 3200 and idled another 10 minutes minimum and no change in plug at all. So to date I have done the following basically eliminating a fuel deliver issue as far as I can tell…..

  • New injector
  • Switch new injector with a known good cylinder
  • Switched injector wires with another cylinder
  • New spark plug
  • 150psi compression on that cylinder
I am trying to get photos of the plug to share but struggling as I can’t get them to upload.
I did switch the plug wire with an old one I still had tonight but have not had a chance to run it.
 
alldodge

alldodge

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Photo's don't work, MODs have been trying to get it fixed for a long time but iBoat Admins don't care.

I'm out out ideas, it looks white so running a bit lean, but might not be enough to cause damage
 
alldodge

alldodge

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Left is white but does show some black , so not bad

The other looks like not burning clean, maybe cold. If all others are this way, check your cap, rotor and wires
 
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woodworker2001

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alldodge said:
Left is white but does show some black , so not bad

The other looks like not burning clean, maybe cold. If all others are this way, check your cap, rotor and wires
Click to expand...
Just put new cap and rotor on. Have not done wires in a few years.
 
alldodge

alldodge

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Get a one or more cheap spark gap testers. Place on each wire and see what the results are
 
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woodworker2001

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Finally found time to get down there and test. Bright light same on all cylinders tested. I am at a loss right now.
 
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