2 engines = 2 different problems
 

So I have 2 8.1 HO engines (from 2014) in my boat with 200 hours.

Port side. I changed plugs and they seemed pretty rich looking. Engine runs perfect though. I thought my fuel gauge was off all of this time but now I realize the port side burns maybe 15% more fuel than the starboard side. I have all new fuel lines and filters. No leaks anywhere. I am about to change spark plug wires. What else should I check? I think fuel is being wasted somehow. Would the fuel cool system cause this?

Starboard side.
I had a lot of missing at mid-high RPM & the boat would shake even at low rpm. Turns out it was a spark plug that was cracked and the wire was totally OFF. I changed all spark plugs and no more bad shake. It runs way smoother now. BUT, at over 3600 RPM I get a small popping sound so there's still a misfire. I can tell the engine isn't as smooth as the other. I am about to change all spark plug wires on this one too. I'm wondering if a misfire is bad for the engine if I run it? (want to go out this weekend) and if changing the plugs and wires doesn't fix it, would the next step be the coil being bad? (the coil where the spark plug wire was off). I'm tempted to buy the Rinda engine code reader although I do have vessel view. Vessel view shows no error codes though! And it won't show any misfire info.

At anything under 3600 rpm the engine seems perfect and I never go that high in RPM but I was testing some stuff so I cranked it up one day and found it misfiring.

thanks for any help

I'm not sure if you have the paint issue with the cool fuel units on 2014 motors. But burning more fuel than you expect is a tell tale sign that you have a pressure problem on that port motor. See what the rail pressure is and pull the fuel regulator, the screen could be clogged up with paint.

Ive read about the paint issue for the gen 3 and not sure if mine is like that either. I did buy new filters for the cooler and need to put them in. I need to figure out where the regulator is also. I bet that screen is clogged!

You need access to a scanner with those motors. The motor has 8 coils, and while one might have an issue, we need to do some testing before replacing anything. If parts are replaced without testing, it can cause other issues to show up.

The misfire at higher RPM's could be many things, plug, wire, coil, injector, valve, preignition from a lean condition

Burning more fuel could be a few things, MAP for one, and a scanner will tell if the output is off

ok I think I'll just buy the Rinda scanner. One thing to note, the engines ran full throttle fine when I bought it (maybe 10 engine hours ago) but we changed out risers and manifolds causing that plug to crack. (weight of the manifold resting on plugs during install) which is why I switched them all out. I was getting a Beep which led me to find the spark plug wire crack and wire was off. I replaced that plug and no more beep. Engine runs better. But I THINK ... this caused another issue or a plug wire was pinched. Maybe the wire being off arched or something. So the next obvious step is to replace all spark plug wires.

That's where I am now. So its possible that one coil went bad from a spark plug wire hanging down. I don't think its anything else since this all happened in like 2 months time.
I will find out this weekend on that one. I have all new wires ready to go.

For the other one, with fuel issue, I'm trying to figure out where this regulator "screen" is. I see the exploded view but there is no screen. I know there are 2 fuel filters in the fuel cooler. Is this the thing I need to check? I actually have 2 brand new sets of these because I planned on changing them.

What is the motor serial number?
Need to look up its configuration

It is 1G300338

Comes up as a Merc reman, all good

If your looking for a screen like was used on the earlier Regs on the fuel cooler tube, this model doesn't use one like that.
https://www.mercruiserparts.com/bam/...32022/16439/60

Not having the problem before riser changes, you could be right on wires and plugs. Still I wouldn't change a coil out unless it can be determined which one(s)

ok, thanks for all of the help so far!
I mentioned screen because the other person responded that the engine may be getting too much fuel and screen may be clogged. So if there is no screen, what do you suggest I look for if engines are running rich and it seems to use 10-15% more fuel than the other side? I guess the regulator could be bad and I should test fuel pressure. Other than that, not sure what would cause it.

Would an engine scanner check for fuel pressure? I'm assuming no.

Scanner can read a fuel pressure sensor (IF installed) but your motor doesn't have one that I've found

There is a screen filter below the filter, but that is normally replaced when doing a filter change

Fuel pressure should be 39 PSI at idle and 43 PSI at WOT. Can check for high pressure output by removing the vacuum line from the Reg at idle

My guess (only a guess) is if pressure is within spec, then I would think of the MAP sensor. If they go out of spec, they can make the fuel mix go rich or lean. The scanner will tell if its out of spec

It might have damaged the ecu with an arcing wire.

ok thanks! You've been really helpful. I know where to start at least. Have a good memorial weekend.

IF you end up going to buy wires, you’ll see merc sets are like $600 snd once your heart attack is over, look here. We’ve given part #’s that are less than $100. Some OEM and some good aftermarket like Moroso.

There is a recent thread too.

How did you determine the extra 15% fuel burn, Smartcraft? Or was is based on actual gallons used from fill up to fill up? If you are missing 15% of your fuel from that motor then it's going somewhere either a fuel leak or that motor is dumping fuel in at a rapid rate. Do you have excessive exhaust odor when running?

You need to get a pressure gauge on the fuel rail at the schraeder valve. I bet its reading way high.

Each time I fill the tanks I always need to put in more in the port side just to get the guages even. Then I can run the boat for a weekend and the gauge is showing a lot less fuel on the port side. Also, I have some other clues. The part plugs were black. I see a film in the water when the engine is running. But most of all, that engine has a bad exhaust smell. I thought it was just the way the boat is until one day I decided to run just the starboard motor and we had NO exhaust smell the whole time crusing around.

I just bought a new fuel regulator hoping that's it. I will also get a fuel pressure gauge.
If its not the regulator what else could it be?

Note, the boat has done this since I bought it 9 months ago. But I had all fuel lines and filters replaced 3 months ago. I keep hearing about some sort of screen that gets clogged but Idon't know where this is at. I have a gen 3 fuel cooler so its not there.

The symptoms you describe are all indicative of the cool fuel paint problem. Check the fuel pressure with a mechanical gauge and check the regulator/damper for clogging with paint. Have you pulled the cool fuel filter assembly on the problem motor? You can see telltale signs in there as well.

But I would bet you have the paint in your fuel system and its made its mess. If so, you need new cool fuel$ unit, thorough cleaning of the rail, new regulator damper, and send out all 8 injectors for service. If one motor has it, the other is close behind.

Sorry.....

Man, that would be a bummer.
My engines are remanufactured 2014s. So do think the paint issue even existed from that time? I thought it was earlier.
I did do the other engine cool fuel filters and they actually looked pretty clean. But I didn't look to see if it was painted inside.

Does that regulator just pull right out? its on top of the unit with a vacuum line right? I didn't see how it would come out when I glanced at it and the diagram doesn't show.

According to Merc this affects all sterndrive 496 models equipped with Gen III cool fuel 1A349420 and below

The regulator/dampener thingy is on the fuel rail and you have to pull some parts off to get at it. If you pull it you have to install a new o-ring to reinstall.

I would get the mechanical reading before you start digging.

Search the web and OSO...this issue has been covered to death.

ok thanks. I have a Rinda scanner on order. Also a fuel pressure gauge and a few of those dampener orings.
maybe I'll get lucky and it won't be a paint issue. Funny thing is, the engine runs strong. Full RPMs and never a problem. It just uses more fuel and smells. I would think if its the paint problem I've been reading about, I would get misfires, restricted fuel, or something of that nature.

So if the fuel reading is fine and the dampener looks clean (and cool fuel housing isn't flaking) then I assume I'm safe for now and it's some other problem right?

Btw, my serial # is 1G300338
and their bulletin is saying 1A349420 and below . So I'm in the clear with the paint issue?

I wouldn't say yes or no until you do some more digging. The symptoms are saying one thing, now you need to do more forensics to rule things out.

Fixed
 

I fixed both issues today but have a new one because nothing is easy. So I don’t have the painted fuel coolers. I was getting too much fuel pressure. Almost 90 psi. I replaced the fuel cooler filters and the fuel regulator. Fuel pressure is normal now. Bounces around 40 T idle

The regulator had some crud on the white plastic piece so I’m not sure if that was the issue. I bought a regulator the other day just hoping it would be that.

for the starboard misfire. Ran the Rinda scanner and if found no codes. Checked each coil one by one with a spark gap tester and all looked fine. Just for the hell of it, i replaced a coil that I suspected was bad because I had a new one here. Took the boat out and no Misfire at high rpm any more. Not sure if ir was the coil or maybe me taking off spark plug wires for testing fixed something (like a loose spark plug wire)

now the bad news. When replacing that fuel Regulator it’s held on by 2 bolts. One of them snapped inside. I tried ez out and end up drilling it out so I can tap a new bolt in. Well. The tap broke off inside the hole now

I’m going to see if I can just take off that top part and then take it to a machine shop or jusr Buy a new top piece. Or a whole new fuel cooler. Ugghh

im still working on getting the tap out because I was pretty much there. I just went too far with cheap ass taps

so overall I’m pretty happy. The Rinda scanner works great!

Easy outs are carbide and that size are brittle. Take it to a machine shop with a TIG machine and they can fix

Glad you made progress! I had a feeling that your problem was ski high fuel pressure.

I found a new top for it for $140. I figured its probably better than a machine shop fix and around here they probably would want $200 anyway.

Yes, thanks for all of the help. Without this thread I wouldn't really have known what to do. Having an idea on where to start goes a long way! I do all of the work myself and learned a LOT this weekend. Even though I have the good gen 3 coolers, I did find some sludge under the fuel pumps sitting on the bottom. Not paint, just sludge. I'm wondering if this caused the clog in the regulator (assuming it was clogged). And now thinking I should check the other side.

Do you have plastic fuel tanks? I would want to find the source of the sludging.

metal tanks. But the boat is 25 years old. I had all fuel lines replaced because they were horrible.
It wasn't a lot of sludge, maybe a spoonful at the bottom under the fuel pumps. Maybe just crappy fuel, who knows.