454 MAG MPI Tune Up

[burtonrider11]

Hi all, it's been awhile. Thanks for all the help over the years. Disregard my signature at the bottom, my new boat is a 2000 Powerquest 260, with 454 Mag MPI - 0L611921. Just purchased this past fall with around 450 hours, freshwater only. Had a lot of conversations with other owners and same set up. While it isn't a race boat, I still want to get every HP and MPH I can. That said, I think the best place to begin is with a full tune up, otherwise, I can't baseline any potential upgrades/prop changes.

The boat starts and idles great. Gets on plane real nice, cruises great and has phenomenal midrange giddy up from 2800-4000 RPM with our labbed 22" 4 blade Bravo 1. Runs out of gas and is only getting up to 4600rpm with that prop. WOT is 4600-5000 and with that prop, we should be getting there. I don't have a lot of service history so a tune up this spring is in order. Here is what I plan to do:

-New plugs
-New wires
-New cap
-New rotor
-THOROUGHLY clean flame arrester - was black when I got it and I'm sure is still needing cleaning
- Oil change (done at winterization)
- New fuel water seperator
- New raw water impeller and housing
- Test and replace thermostat if faulty
- New serpentine belt

Just wondering if there is anything else I consider such as:

- New IAC?
- New fuel regulator?
- New fuel pump?
- Clean/replace injectors?
- Pull intake and clean?

The skeg on the Bravo has taken some abuse over the years as well. I am at the very least going to clean up the sharp edges with a hand rasp. I am also thinking that it might cut the broken parts of the skeg off and add a Skeg Gard. It's bent to the side just a bit, so that can't be helping either.

If there is anything else that can/should be done while waist deep in the engine bay this spring, please let me know. I'll be going thru the Merc manual for annual service stuff as well.

Thanks in advance!

 

[Scott Danforth]

prior to the shot-gun parts replacing (wallet draining) approach. I suggest a bit of troubleshooting

start with a compression test

then inspect the contents of the fuel filter

then read fuel pressure both at idle, and under WOT

then weigh the boat and compare to specs

 

[burtonrider11]

Thanks Scott, good advice to be sure. The things I’m planning to do above, I want to do regardless of how she runs. The PO had owned for 10 years and didn’t keep service records. He just had a mobile mechanic come up each year to winterize, scan for any fault codes and do the basics. I asked when he last did some of the tune up stuff and his repossessed was “I’m not sure”. So (at least for me) I’ll sleep better at night knowing many of the parts are fresh and new. We are planning to take some longer trips with her next year, so a new serpentine belt gives me some piece of mind. Mental insurance I suppose.

Ill for sure do a compression test to baseline that.

for the fuel PSI test, I believe there is a Schrader (presta maybe?) valve on the fuel rail somewhere. I’m assuming I just need to hook a gauge to that?

thanks for the insight!

 

[scoflaw]

I've got that same boat with a 502 mag, 65mph on a stock rebuild with a mirage plus 23. Do have those injectors serviced. It's a 4200# boat.

 

[wingless]

The 454 MAG MPI Horizon engines on my boat requires annual plenum removal to permit thorough internal cleaning, along w/ cleaning of the vacuum hoses, including / especially the skinny vacuum hose going to the fuel pressure regulator.

When I do that service I also clean the flame arrestor. I find garden hose water and Simple Green works great for keeping these parts clean.

Prior to discovering / implementing this service I was having performance issues, now I don't.

 

[burtonrider11]

Thanks Wingless and Scoflaw! Scoflaw, are you a Lake Michigan boater? I’m on the PQ owners forum on Facebook also. I love that boat with a 502Mag. We looked at a couple but couldn’t find one with low hours and/or good shape as our boat now....Besides, with forged internals, we can just throw a blower on it later if it’s that important lol.

could a typical auto repair shop do the injector service? I’ve seen DIY ideas online to clean injectors, but I think I’d rather have it done right versus messing with sensitive equipment.

wingless, so you pull the whole intake plenum off and clean that as well I’m assuming? The flame arrester is filthy so I have to assume some of that is in the plenum. I’m winterizing everything tomorrow, so that would be a good time to start pulling parts....I’ll clean all the vacuum hoses as well. I believe the IAC and MAP sensors are to be removed prior to ANY cleaning to be done on this?

thanks again guys, this is all great stuff.

 

[wingless]

Yes, remove the whole intake plenum for internal cleaning.

The first few times I yanked the sensors, now I just clean w/ those in-place. I have had zero issue from water and soap on those parts.

My throttle body is also removed and cleaned at that time. Everything is shaken, then blown dry prior to installation.

My experience is that the plenum to intake manifold gaskets are durable, permitting reuse for many cycles. I replace those after they break, but I usually get over six cycles on those gaskets.

FWIW, when I initially had performance problems I sent my injectors to a professional for cleaning / testing. They documented before / after improvements and identified problem parts that were replaced.

Don't forget to properly verify the ignition timing.

 

[tpenfield]

If I understand you correctly, you are getting 4600 RPM out of a boat/engine combo that should run in the 4600 - 5000 RPM range. (right?) :noidea:

You may not actually have any issues and a 'tune-up' will be more wallet draining than beneficial as mentioned.

I'd go with Scott's recommendations. See if you can hook up the computer engine analyzer and get some data from the MPI system while running, etc. But . . . there may be nothing wrong.

 

[QBhoy]

Hull clean helps.

 

[burtonrider11]

Hull clean helps.

Roger that, hull is clean. Boat never stays in water and is very clean.

 

[burtonrider11]

If I understand you correctly, you are getting 4600 RPM out of a boat/engine combo that should run in the 4600 - 5000 RPM range. (right?) :noidea:

You may not actually have any issues and a 'tune-up' will be more wallet draining than beneficial as mentioned.

I'd go with Scott's recommendations. See if you can hook up the computer engine analyzer and get some data from the MPI system while running, etc. But . . . there may be nothing wrong.

Very valid point and I don’t want to be argumentative in anyway. However, I did a ton of research on this boat/motor combination and even spoke with Brett at Bblades who did the lab work on the prop for the previous owner. My numbers just aren’t in line with identical setups out there. I do understand there are certainly variables that affect the equation and you may even be right. But I also have a 20 year old boat that I feel was maintained to a very basic level and it’s due for some routine maintenance, like plugs wires cap rotor etc. I did it for the last boat I bought and it made a world of difference, albeit it was a carbed motor.

I do think it would be a great idea to get some data as she is running though. I think the only tools that can do that are the Mercury scan tools?? I’d be wide open to any suggestions regarding getting data from the MPI system.

And a compression test is definitely in order as well.

Again, I appreciate the input. A lot of the things I want to do I’m going to file under “maintenance that I don’t know when it was done, so I’m going to do it to make sure it’s done “ And things like cleaning require nothing more than mild detergents and elbow grease

And I will say that I stick some $$ in here and it does absolutely nothing, I’ll be back to say so and let me story guide others

 

[Scott Danforth]

Rinda diacom is the only tool out there for boats.

https://www.rinda.com/marine/

 

[scoflaw]

I'd do a compression test and a leak down now so you have all winter to do something about it. 20 year old engine is probably due for a valve job.

 

[burtonrider11]

Rinda diacom is the only tool out there for boats.

https://www.rinda.com/marine/

Awesome thank you, definitely not cheap, but probably after a couple scans from a mechanic it would pay for itself....

 

[burtonrider11]

I'd do a compression test and a leak down now so you have all winter to do something about it. 20 year old engine is probably due for a valve job.

Good call. I'm thinking a compression test is in order for sure. I've never done a leak down test, I'll have to do some googling.

 

[wingless]

The tool I use for my engines is my Quicksilver DDT.

 

[burtonrider11]

The tool I use for my engines is my Quicksilver DDT.

Awesome, looks like I can snag one on EBay for $300. Any reason to spend more to get the Rinda tool IE features one has that that other does not???

 

[Scott Danforth]

Rinda allows you to connect with nearly every other marine ECM out there in existence. the Mercruiser tool works on Mercruiser.

 

[wingless]

The tool I use for my engines is my Quicksilver DDT.

Mine has the Mercruiser Diagnostics Ver 2.0 '98 Quicksilver module.

It is not clear which module or which interface cable is included w/ that $300 tool.