5.0 Mercruiser Problems

[nola mike]

There are *a lot* of suggestions on this thread that you never reported back on...have you tried them?

 

[dsull]

There are *a lot* of suggestions on this thread that you never reported back on...have you tried them?

Mike, I've done all but the cylinder drop test. I'm a little wary of that process. When I've done it in the past, I've been popped a few times. Not fun.

Edit to add I also haven't successfully tested the TKS module. I'm not positive how to do it and it's not economical to replace.

 

[nola mike]

Mike, I've done all but the cylinder drop test. I'm a little wary of that process. When I've done it in the past, I've been popped a few times. Not fun.

Ha, true. Thick gloves + pliers

Edit to add I also haven't successfully tested the TKS module. I'm not positive how to do it and it's not economical to replace.

This was the biggest concern waaaay at the beginning of the thread. Are your plugs black again? It's plenty economical to junk it and throw on a standard carb. I've never mucked with one, but jumping 12v to it with the engine off should let you hear if it's at least trying to work. Too late for me to go looking through the manual to see how to test it, but would probably be good homework for you...

 

[Lou C]

The pic looked like you weren’t getting enough cooling water, also the driveshaft/ujoints are always spinning whenever the engine is running. Put the drive at least half way down. What’s your engine temp?

 

[dsull]

Anyone who is much more mechanically savvy than I want to tell me what these plugs are telling me. They're about two weeks old and maybe four hours engine run time. They look too rich to me but it's not consistent across the cylinders.

 

[Rick Stephens]

Wow, all over the map. 1 has carbon from the piston stuck to it - caused by detonation blasting the carbon deposits off the piston top. 2, 3 and 8 look like you have oil burn. Weird one is 6 - hot, oil and carbon specks all at once.

 

[dsull]

I can't get the timing set, either. I don't understand it. I ground the purple white wire and I've checked to make sure I'm on the compression stroke and, even using an advance timing light, setting the timing to 10* BTC makes the motor sound like it's barely running. I have to run the idle speed screw all the way in to get it to idle. The fuel/air mixture screw is supposed to be backed out 1.5 turns from factory but my motor sounds like it runs better backed out 3-4 full turns. I can back the screw almost all the way out and it won't choke and die like I'd expect. I don't know if that means it's a fuel delivery issue or what. The timing light also looks like the engine is missing somehow. It will flash consistently and then periodically it doesn't flash and the motor sounds like it kinda sputters and then goes back to running correctly. I'm clearly punching above my weight class but no on will be able to look at it for me professionally for months.

 

[Rick Stephens]

Try running a hose from a gas can to the fuel pump and run it on fresh gas.

Idle jet adjustment is a suggested starting point, not a tuned setting. However, I have yet to see a carburetor that was up to spec need to be 3 or 4 turns out.

One of the ways to determine TDC is pull all the plugs so the motor manually turns easier. Remove the pulley off the harmonic balancer and stick a bit longer bolts in the balancer's threaded holes. Use those with a bar to manually and controlled turn the motor. Use a rod, or pencil or whatever will stick through the spark plug hole a fixed distance. Turn the motor to where the #1 piston is coming up on compression but still 10 to 20º shy of TDC. Mark your pencil. Use a felt pen to mark the balancer where the timing mark is. Use the bar to turn the motor past TDC about the same amount and then fine tune position so the pencil mark is at the same place. Mark the balancer. Halfway between is actual TDC. At least you won't be guessing.

 

[Rick Stephens]

Next time you get the motor warm, I'd redo the compression test.

 

[dsull]

Try running a hose from a gas can to the fuel pump and run it on fresh gas.

Idle jet adjustment is a suggested starting point, not a tuned setting. However, I have yet to see a carburetor that was up to spec need to be 3 or 4 turns out.

One of the ways to determine TDC is pull all the plugs so the motor manually turns easier. Remove the pulley off the harmonic balancer and stick a bit longer bolts in the balancer's threaded holes. Use those with a bar to manually and controlled turn the motor. Use a rod, or pencil or whatever will stick through the spark plug hole a fixed distance. Turn the motor to where the #1 piston is coming up on compression but still 10 to 20º shy of TDC. Mark your pencil. Use a felt pen to mark the balancer where the timing mark is. Use the bar to turn the motor past TDC about the same amount and then fine tune position so the pencil mark is at the same place. Mark the balancer. Halfway between is actual TDC. At least you won't be guessing.

Thanks, Rick. I'm going to get a piston stop and mark true TDC, as you recommended. I've also done significant reading on the TKS and it appears that the plunger inside the TKS retracts when the engine is cold and enriched fuel is pulled into the intake and, when the engine gets warm, the plunger inside extends and closes off the enrichment process. I'm going to pull my TKS module and see if I can apply 12v and see how it behaves.

 

[dsull]

Probably a long shot but does anyone have any idea what these wires are for? They are unhooked. They are orange/pink, brown, and black. There's a capped pair of wires labeled Mercathode that look orange/pink and brown but they are just terminated at a cap, not plugged into anything.

 

[dubs283]

Those wires are most likely for a mercathode controller. They would connect on studs along with a fused constant 12 volt lead and the capped orange and brown wires would connect to a harness for the unit mounted under the gimbal housing. Apparently your engine does not have a mercathode system but the engine harness contains the wiring to add it

 

[dsull]

This boat is the devil. Nothing works the way I think it will... I purchased a piston stop and placed it in the #1 cylinder. Removed all the spark plugs. Found the compression stroke and manually backed the motor away from the compression stroke. Inserted the piston stop and manually advanced the motor until it stopped. Marked my balancer. Rotated it backwards to find the exhaust TDC mark and the motor continues to rotate... It never stopped. I pulled the piston stop and I have these marks on the threaded part that inserts into the motor. I don't understand what's going on.

 

[Scott06]

This boat is the devil. Nothing works the way I think it will... I purchased a piston stop and placed it in the #1 cylinder. Removed all the spark plugs. Found the compression stroke and manually backed the motor away from the compression stroke. Inserted the piston stop and manually advanced the motor until it stopped. Marked my balancer. Rotated it backwards to find the exhaust TDC mark and the motor continues to rotate... It never stopped. I pulled the piston stop and I have these marks on the threaded part that inserts into the motor. I don't understand what's going on.

Would think one of the valves made that mark when it opened.