Ongoing 8.1 Issue Still Unresolved

Lots of good info there, but Before you get too deep into this, I would swap all 8 coils from one motor to the other. Label them with a sharpie or paint pen to keep things organized.

See if the popping moves to the other motor.

Also closely inspect the wire harness connectors that go to the coils, look for damaged, corroded, or loose crimps.

Instead of removing all 8 coils from the other motor why not just remove 1 and replace one coil at a time to see the misfire goes away. If it does you know which coils is bad. If it doesn't go away then you only have one coil to reinstall back on the other motor. BTW use dialectric grease on the connections.
 
It seems I should just see if my marina can put a scan tool on it, run it and see if there any codes that will narrow it down?
 
Instead of removing all 8 coils from the other motor why not just remove 1 and replace one coil at a time to see the misfire goes away. If it does you know which coils is bad. If it doesn't go away then you only have one coil to reinstall back on the other motor. BTW use dialectric grease on the connections.

Only problem with this is that you have take the boat out and run it between each coil. That's going to take a lot of time and make that engine compartment smoking hot!
 
Only problem with this is that you have take the boat out and run it between each coil. That's going to take a lot of time and make that engine compartment smoking hot!

This is the reason to swap all 8 at once.
One trip will tell you if a coil(s) are the issue.
 
Scheduled a meeting with a tech next Tuesday to take him out for a spin and run the codes. Figured I've passed my level of usefulness on this and need to stop chasing my tail.

I'll post back when I know more.
 
First thing that comes to my mind when you say heavy load, large throttle opening and "popping" noise is "pinking" or "pinging", which is uncontrolled detonation of the fuel air mixture, usually caused by either substandard fuel, excess compression, a lean mixture, or very advanced ignition timing.

Before you tear down parts of the engine, first you need to confirm the kind of fault - step one, get the fault history downloaded from the ECU and examined by someone who knows what they are looking at.
 
First thing that comes to my mind when you say heavy load, large throttle opening and "popping" noise is "pinking" or "pinging", which is uncontrolled detonation of the fuel air mixture, usually caused by either substandard fuel, excess compression, a lean mixture, or very advanced ignition timing.

Before you tear down parts of the engine, first you need to confirm the kind of fault - step one, get the fault history downloaded from the ECU and examined by someone who knows what they are looking at.
CHECK THE COMPRESSION. i HAVE CHASED AROUND ALL KINDS OF ISSUES AND ALWAYS FOUND OUT THE COMPRESSION WAS OFF IN THE END.nOW , WHEN i HAVE AN ISSUE i CHECK PLUGS AND WHILE THEY ARE OUT,CHECK THE COMPRESSION.
 
Scheduled a meeting with a tech next Tuesday to take him out for a spin and run the codes. Figured I've passed my level of usefulness on this and need to stop chasing my tail.

I'll post back when I know more.


This is the right course.

You have already chased the simple things. Hopefully the scanner will provide a clue or clues if it is a part to be replaced.

Depending on the engine hours it seems you might have an intake valve not sealing at higher rpms. That would create a popping sound at higher rpms. Typically electrical issues like coils/wires/plugs fit into the loss of power world. Rhythmic noises on the other hand tend to be mechanical. It could be something as simple as a broken valve spring or a sticking guide.

Hopefully he can narrow it down.
 
CHECK THE COMPRESSION. i HAVE CHASED AROUND ALL KINDS OF ISSUES AND ALWAYS FOUND OUT THE COMPRESSION WAS OFF IN THE END.nOW , WHEN i HAVE AN ISSUE i CHECK PLUGS AND WHILE THEY ARE OUT,CHECK THE COMPRESSION.

X1000
 
A running compression test will detect a broken valve spring or bent push rod. Although I would not normally advocate engine oil additives as I usually say "There's no such thing as Mitch in a can" this stuff https://www.walmart.com/ip/Rislone-...24214&wl11=online&wl12=22578974&wl13=&veh=sem
will almost free stickey valves.

I remember in the "OLD DAYS" we would replace valve stem seals on an engine by using compressed air in the cylinder to hold the valve in place while using a valve spring compressor to remove the springs and replace the seal. I would think the same procedure could be used to replace a broken valve spring in a marine engine without having to remove the heads and doing a complete top end overhaul.
 
I remember in the "OLD DAYS" we would replace valve stem seals on an engine by using compressed air in the cylinder to hold the valve in place while using a valve spring compressor to remove the springs and replace the seal. I would think the same procedure could be used to replace a broken valve spring in a marine engine without having to remove the heads and doing a complete top end overhaul.

You still can....the only problem is as we have gotten older and wiser.....we realize that finding one problem usually means there are more waiting to be found.

I had client who said he had a "lifter noise". We pulled the valve cover and found a bent push rod. The owner just wanted to replace the push rod. Well, something bent the push rod and would in all likelihood would bend the new one. A bore-scope showed the piston had come in contact with the valve. In the end....the guides were shot from poor maintenance (never changing the oil) and the heads had to be rebuilt.
 
I remember in the "OLD DAYS" we would replace valve stem seals on an engine by using compressed air in the cylinder to hold the valve in place while using a valve spring compressor to remove the springs and replace the seal. I would think the same procedure could be used to replace a broken valve spring in a marine engine without having to remove the heads and doing a complete top end overhaul.

The old days were when we many times we didn't have compressed air and you would put the piston at BDC and feed a piece of rope into the cylinder then slowly brought the piston up to hold the valves up to complete the job.
 
MY GUESS

Popping at higher rpm indicates a INTAKE valve not seating, allowing the explosion created at the next stroke to be heard back out through the intake manifold and throttle body, bent pushrod, broken valve spring, dirty valve stem, loose or missing keepers, bad/gummed up lifter, broken or loose valve seat.
 
Have you put this motor on a computer yet? I chased around a similar intermittent issue for a year, spend $1000 bucks changing this -that and the other. Finally, had it put on the computer. Took the tech 15 minutes total to find the problem and fix it. Ended up being a loose pin in the harness. He repaired the pin and charged me a total of $150.00. Money well spent as he also did the other motor and found a small ignition issue as well and repaired that. All for the $150.00
 
Engine has 420 hours on it. Oil changed every year, even the flood year when I only put 4 hours on the boat. Just put 3rd set of plugs in it since I've owned it the last 7.5 years. Freshwater lake boat that is typically cruised at 3400-3500rpms to a destination 3 to 10 miles away. In other words it's had a easy life.

Hopefully we'll know a lot more tomorrow after it's had the codes read. Obviously praying for something simple but whatever it is I just look forward to having a more clear plan of action.

What are your guys thought that it could be a faulty throttle position sensor. My very mechanically inclined friend bet me a case of beer that the TPS is bad. I really hope I owe him some beer.
 
So good news today. Tech said that the #5 ignition coil pack shows to be throwing a fault code intermittently. He's pretty sure that's the issue. We took the boat out and ran it through its paces and he said he's positive it's not a mechanical issue and that is either fuel or fire.

Only other option he feels it could be is the fuel pump system that has a Mercruiser TSB out on it for flaking paint.

So I've got my fingers crossed he's right and will wait for the final fix.

Thanks all!
 
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