Mercruiser 5.0 MPI #3 cylinder ignition miss

[Searay205]

Hello,
My Rinda indicates #3 cylinder misfire (2011 5.0 MPI with 255 hrs). I get about 100 misses in 3 minute? No code but I can feel it. I checked plug wire for resistance it appeared good. I will order a new plug, but my question is what is the best distributor cap to buy. I hear the automotive are the same as the mercruiser. In the end I looking for best quality.

On a side note I changed my filter after 4? years and 150 hrs. What PIA to get off. Anyway cut it open looked perfect, zero water. Surprised as I leave my boat sit all winter with only a 1/2 tank of fuel at times.

 

[itsathepete]

Do you know how long it had been since plugs, wires, distributor cap, and rotor have been changed? Probably want to do it all if you don't know. Inspect the plugs to determine running condition

 

[Searay205]

I not a proponent of changing parts. That why I spent $600 on a Rinda. All other cylinders look perfect, only #3 shows misfires. Plugs, cap, wires total about $325. I probably swap plugs with another cylinder. Plug about $8 but that still hurts. I wasted 90 minutes changing a perfectly good fuel filter yesterday in miserable Houston heat. It was like new after 100 hours and 4 years when I cut it open.

 

[achris]

Swap a couple of plug wires at the cap and the plugs. That may give you an idea of where the problem is.

 

[dubs283]

I get about 100 misses in 3 minute?

Suspiciously specific

Swap a couple of plug wires at the cap and the plugs. That may give you an idea of where the problem is.

Wtf, no idea your troubleshooting effort here

OP: Delco/hvs distributor caps from a generation or two ago had issues cross firing, is tune up stuffs in order, aka new?

 

[Searay205]

I found an interesting video on YouTube on these crab style caps. It appears overtime due to the close proximity of the conductors in the cap and at times porosity in the "plastic' they will jump terminals internally. I pretty sure its the cap as I saw more than one post (GM cars/trucks) with ignition misses even after plug and wire replacement and the cap was the issue. An item I left out was the misses on #3 weren't constant, at times it would run a couple minutes without any than all the sudden they would stack up. I don't know if a plug or spark plug wire would be so sporadic.

Option two is as achris suggested, swap plugs/wires.

 

[dubs283]

I not a proponent of changing parts.

Tune up parts are supposed to changed on a regular basis. Engine hours or number of seasons, whichever spec is reached first.

I understand the theory of just "throwing parts at it" and agree a diagnostic tool is necessary for some issues. It has helped you locate an issue that many boaters, mechanics, and even mercury is well aware of. The solution is to install new cap/rotor. Possibly wires and plugs too, i.e., perform a full tune up, it's time

 

[Searay205]

255 hours at 70 mph is 17,850 miles on my ignition components worse case scenario for a car with the same hours as my boat. Is this 1965? where tune are required annually? I wish it was 1965 I would not have $3K in cat manifolds on my boat and I could see the Doors.

 

[dubs283]

255 hours at 70 mph is 17,850 miles on my ignition components worse case scenario for a car with the same hours as my boat.

Your car is not your boat, other than same theory of engine operation there is very little to use as a comparison between the two.

You can do what you like with your boat and asking questions related to your boat will garner quality answers from experienced persons on this site. Nobody is trying to steer you in the wrong direction here, tune ups are a part of regular boat engine maintenance regardless of the vintage/hours. My recommendation is tune up every 2-3 years under normal use which equates to every 100-150 hours of operation, ymmv

 

[QBhoy]

Stick another cap on it. Keep one spare too…or change every year. They are that bad…I’ve had one fail out the box.

 

[Searay205]

Please don't take my questions as "pointed". I ask/challenge here because of the experience of the members. I always wonder why "boats" deserve shorter maintenance intervals. When I say boats I am referring to mine which is only outside when used and stored in enclosed storage. Thanks again to all, especially the moderators they are a WEALTH of knowledge. I going to order a cap and probably plugs. My last boat the plug wires were 30 years old with points and condenser. Ran like a champ. Only issue it ever had was the carburetor would "load" up while idling like when I was blowing up an inflatable for the kids and the bride wouldn't throttle up even after I had asked over 10 years, lol.

 

[dubs283]

Please don't take my questions as "pointed". I ask/challenge here because of the experience of the members. I always wonder why "boats" deserve shorter maintenance intervals.

I belive pointed questions are the only ones to ask in this forum. The issues deserve concise answers with pertinent info regarding analysis and repair. e.g., I wouldn't recommend a member replace the prop due to a no start issue....the direction does require knowledge of known situations and probable causes of said situation. Yes, we can get esoteric with our answers because at times the issue warrants the detail required for solving.

I think boats, specifically engines and running gear require shorter maintenance intervals due to the operating environments. Heavy, increased load often repeated means more demand on performance from the engines and running gear. High torque demand and a higher running rpm mean there is more wear and expectancy from the power package, which means a more watchful eye on every aspect of the propulsion system including battery/DC systems and helm operation from instruments, steering, accessory operation and engine/drive controls.

Sounds like you take very good care of all your equipment, cheers! And please, keep up with the maintenance and any questions regarding boating, we like to help

 

[achris]

Car engine - load during acceleration. Once at speed, throttle pulled back, load actually quite light.
Boat engine - higher operating rpm, much much higher load, all the time.

If you want to equate the load on a boat engine with a car, then the car needs to be going up a steep hill at 70 mph, towing the boat! And it's doing that ALL THE TIME...

Chris....

 

[dubs283]

And it's doing that ALL THE TIME...

Yep, think your buddy in the tube getting pulled around at a reasonable rpm, just enough to be on step with a bit of trim for handling.

This scenario is how your boat, engine, drive and related power supply systems operate. Yer car just gets you to 70 and then the motor chills, overdrive n all....your boat has one forward gear, no overdrive. Sorry for the digression, I care not much for automobile use/repair and comparing them to boats in my mind is a no no

 

[Searay205]

I changed the distributor cap and rotor with Quicksilver yesterday. The one on the engine was original 2011 with 260 hours, I am 100% sure. A lot of white corrosion on terminals. No difference in misfires, lol. Still #3 getting about 15 misses a minute at idle. I will go after plugs next. (I can't believe my stupid ass didn't at least order one plug when I got the cap and rotor). I am 100% sure it is not fuel as I filled up yesterday and went on 120 mile ride over 5 hours, lol. Probably have 1/3 tank left. Boat runs great but I do feel a surge sometimes around 3K rpms if I bury the throttle from stop, if accelerate aggressively then it ramps up perfect. 80% of trip was pretty smooth 20% was a ruthless beating of 2-4 foot chop, If anything was loose on that boat it laying in the bilge, lol


On a side note experiencing my boat running constantly at 3300 rpm under load yesterday for hours I am beginning to understand the more aggressive maintenance schedules for oil and gear lube. What grind for the engine. My guesstimate is an hour on boat engine is equivalent to 3 or 4 for a car engine.

 

[dubs283]

Replaced just the cap....

Not rotor, plugs, wires or fuel filters

I get you dislike the fact you have to perform routine maintenance on your boat. Unfortunately, it is a part of boating. Ya gotta maintain it so you have a baseline. Your boat will fail you at some point, it's inevitable. The best you can do is keep up with the dumb, sometimes brutal maintenance. Or, you can replace one part every few months, cross your fingers, continue to dislike maintenance and go 120 miles in your (seemingly unkempt) boat

This reminds me of customers at the dealership who's number one concern was fuel economy. If that's your hangup, boating isn't for you......

 

[Scott Danforth]

Swap plugs between 3 and 5

Recheck

Swap plug wires between 3 and 4

Recheck

 

[alldodge]

I would check the clocking on the Dizzy. Best method is to make the $10 tool in the bulletin

Can also be caused by yellow flag circuit breaker (50 amp) but you should not have one of those
Edit: don't know your serial number

 

[QBhoy]

Any sign of water at the plugs on that side of the engine ? Could be just a lead. But I’d swap over the leads like AD says. See if it replicates on number 5

 

[Searay205]

I like the idea of swapping the leads and plugs, but I ordered 8 plugs so I will install those. I should have realized if it was the distributor cap it would probably have caused misfires on more than one cylinder. One unique characteristic is no misfires for a minute or two then misfires start racking up. The other 7 cylinders I would be lucky to see 1 misfire in 5 minutes between all of them.
Fuel filter was changed before the distributor cap and was also found to be in perfect condition when cut open and inspecting the fuel that was in it. Resistance on plug wire was within spec and I yanked and pulled to try to expose a "loose" connection.

$1700 manifolds were replaced earlier this year and when inspecting the exhaust passages for grins, they were bone dry and looked perfect. I seriously doubt I getting water into the cylinder but when I pull plugs. will know.