2011 Merc 4.3L MPI power loss issue

[cam29906]

I have been chasing this issue for a season already. Thought I had bad gas end of last season always use startron and sea foam. I ran all the gas out the boat last September and filled with non ethanol 91 with starteon. Same issue when putting in back in last earlier this week.

it’s starts fine, has no power and will
not exceed ~2K rpm until engine hits 150 Deg. If I put around the lake for half hour it will start to surge up and down then plane and run about 4K WOT. Boat use to do 4800 rpm and 45 mph. Now it barely does 25/30 @ 4K. Very much has a hesitation issue. It seems like if I slam it to WOt while warming it up it just runs like crap and is bogged down. If I walk it up over the course of 10 minutes it will usually get to 150-160 Deg and all the sudden plane and run the new norm with plenty of hesitation if you come back down to idle forward. I checked the TPS it’s good, I replaced the IAC because I did start to notice I couldn’t hear the IAC whistling until it started hitting the 4K time line and I checked fuel pressure and it’s 40 idling and 45 under throttle. New fuel filter annually, 3 last season at the end as I thought for sure it was fuel related (didn’t use boat much). Any ideas would be appreciated I’m at a loss.

 

[cam29906]

Sorry 140 hours on the boat had it since new.

 

[alldodge]

Howdy
You need to have the motor scanned for codes

What is the motor serial number?

 

[tpenfield]

Fuel injected engines are extremely difficult to diagnose without the computer software. They don't follow the 'rules' of carburetor engines.

See if you can get the engine scanned for codes, but more likely you will have to run the engine with the computer attached and record the data to see what is really going on.

Was there any incident or maintenance done last season that preceded the power loss?

 

[cam29906]

Howdy
You need to have the motor scanned for codes

What is the motor serial number?

Hi there S/N is 1A624495
My service manual #32 calls for AC Delco 41-932 plugs gapped .060. I took a stab and swapped plugs. Power is incredible.
From what I could tell AC 41-932 plugs were discontinued and replaced with AC 41-993 plugs so that is what i used. Neither of those are what was in the engine..... AC 41-101 were in the engine. So did I just follow the manual correctly or am i missing something. I did notice the idle was immediately excellent when i hit the key. Boat had plenty of power, it actually went over 5K rpm so I'm concerned if I really know what rpm it use to hit. Anyone that can tell me the correct spark plug and WOT rpm for my engine would be appreciated. Either way this was definently the issue, the books says plugs every 300 hours so should I be concerned these only made it 120 hrs and 7 years? I'm in NW NJ and only sits in the lake so it doesn't get much abuse IMO. I use Merc Oil annually and/or sea foam and startron with each fuel fill.

pics of the plugs:

 

[cam29906]

Fuel injected engines are extremely difficult to diagnose without the computer software. They don't follow the 'rules' of carburetor engines.

See if you can get the engine scanned for codes, but more likely you will have to run the engine with the computer attached and record the data to see what is really going on.

Was there any incident or maintenance done last season that preceded the power loss?

Hi there nothing really generated this. I usually pull the boat in September, change the engine oil, filter, gear lube, fuel filter, suck in pink antifreeze, remove the batteries and unbolt the alternator to free up the serp belt. In May I uncover it, throw batteries in, bolt up alternator, clean it and she's in the lake. With all the ethanol talk i assumed bad fuel all last year so i ran it like i mentioned in opening post. Thanks for the help!

 

[alldodge]

41-993 are the correct plugs

WOT rpms should be 4400-4800. Your motor may not have reached 5K rpms it could be just the tachometer. The boat Tach can be accurate, but in most cases its not over the entire rpm band

Boat had plenty of power, it actually went over 5K rpm so I'm concerned if I really know what rpm it use to hit.

Are you saying your motor is running good now?

Your motor distributor cap is known to have issues and cause problems. Yours may be fine, but its always good to have one on hand because they can go out without a warning. Can also just cause misfirings

 

[cam29906]

41-993 are the correct plugs

Thanks for confirming the plugs are right, should I change these periodically or was this a fluke?

WOT rpms should be 4400-4800. Your motor may not have reached 5K rpms it could be just the tachometer. The boat Tach can be accurate, but in most cases its not over the entire rpm band



Are you saying your motor is running good now?

Boat ran great. I think my tach on the dash may be a bit off, it use to show 600 rpm for idle (which is correct) and today it showed 1200-1500 rpm (maybe i didn't let it warm up at this point if that is a thing).

Your motor distributor cap is known to have issues and cause problems. Yours may be fine, but its always good to have one on hand because they can go out without a warning. Can also just cause misfirings

I ordered a mercrusier rotor and flat cap. No wires at this point. So I'll throw those in the boat and swap them at the end of the season or if i get the need unless you think it makes sense to swap them this week. They seem fairly easy. My lake is small that I'm fortuante that I can call a neighbor to tow me back to my dock. Thanks

 

[alldodge]

The plugs should last longer IMO. Many think they don't last long but I've had motors with original plugs, wires cap and rotor and be fine for many years. Its about maintenance, have a look every now and then and listen to the motor for anything that starts to get your attention.

Getting a new cap and rotor to have on hand is a good plan with your motor. Replace if you like or just keep it for when needed. Some have had the same cap and rotor last years without issue, but these are not as many as have had problems.

About the only thing that I'm seeing where not tracking is was the original cap replaced with aftermarket or OEM. We don't know enough right now, just seeing comments

 

[cam29906]

I ordered this one:

898253T28 Cap & Rotor Kit

 

[QBhoy]

Agree about replacing the cap either way. One day they can be fine and the next terrible. All because of the cap.
if I was being fussy...those 993 platinum plugs aren’t very good at all. They will get you by, but my mpi never ran well with them at all. Although more expensive, the best specified plugs for these Mpi is the NGK full iridium plugs. Without looking it up, they are NGK 5599 plugs.