Tune up schedule for 2004 Mercruiser 4.3L 225hp 4bbl

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ShoalSurvivor

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I found "Ignition system - Clean and Inspect condition" = every 100 hours.

If it's running fine, is there a time frame or running hours where a full tune up is really required (including replacing Cap/rotor, etc)

Thanks



original engine SN: L332123 replaced with: 2004 Mercruiser 4.3L 225hp 4bbl Quicksilver repower SN: 90004747 (#807736R11 / 03252004)
Alpha 1 Gen II - Transom: 0L517680 Drive: 0L192679 1.62 R (1.81R scratched on top) original drive may have been SN: L40356
 
harringtondav

harringtondav

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Pretty sure you have Thunderbolt V. A robust ignition system. I'd start by pulling a spark plug or two and check their condition. Actually not a bad idea to crack and re-torque all plugs so they don't freeze up when you need to replace them, which is normally a long time. You can also remove the dist. cap and check for significant arcing on the rotor and contacts. If everything looks OK, and if you don't have any performance issues I'd run it until you do.
 
P

poconojoe

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Yep, agree. Pull the spark plugs and the distributor cap for inspection. My 4.3 Mercruiser (2003) had a no spark condition due to the ignition sensor under the distributor cap. When I removed the distributor cap, I was shocked at the condition of the rotor and cap contacts. There were literally stalagtites (like in a cave) hanging from the contacts. No copper was visible. It was all green clumps.
 
achris

achris

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Here's what I did on my '94 4.3LX...

Replace genuine wire plug leads with 8mm silicone. Ensure the gasket for the distributor cap is good. Make sure you have the updated sensor (flying leads, not screw terminals). Do that, set the timing and forget it. Every 200 hours, new spark plugs...

Pull, strip and clean the carb every 7 or 8 years.

Pull the drive annually and check everything on the gimbal housing (bellows, alignment, etc), check/change the impeller and gear oil every 3 years.

Keep up the annual engine oil and filter changes.

Check manifold and elbows every 4 or 5 years.

Do all that, and that engine will last longer than you. :D

Chris
 
Lou C

Lou C

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Yep!
What about this, some say that fogging a carb engine will result in the plugs being fouled next season. What I've done is after the spring smoky start up I pull the plugs and clean em with carb cleaner and an old toothbrush lol. Put them back in and they seem to work fine. Of course if you have good plugs in it, then want to winterize it you can put in a old set of plugs to fog it and then replace them with your good ones after the spring start up. It is good to remove them regularly to avoid corrosion locking them in.

I have found more signs of wear on the dist cap terminals than on plugs. The plugs if clean will last a long time. That may be because my boat has lived on a salt water mooring for many seasons so its exposed to salt air for 6 months each season.

Even if I don't change the drive oil at the end of the season I pull the drain plug just enough to see if any water or milky oil comes out, that's important esp if you store the boat in freezing temps.
 
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poconojoe

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When I replaced my cap, rotor and ignition sensor, I also did the spark plugs and wires. And just like Chris did...8mm silicone. The thicker ignition wires didn't fit so well in the wire looms, but I managed to loosely secure them with tie wraps in strategic locations.
I'd like to mention that the original ignition sensor had an exposed circuit board which was all corroded. The new one was completely sealed.
Great peace of mind having everything new. Plus that 4.3 runs smooth now!
 
Q

QBhoy

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HI
great am good advice above here. Oil, filter, fuel filter and plugs every year and check the cap and rotor every other year are the basics.
Just as a mention. Your engine isn’t 225hp. There isn’t such a 4.3 merc. It will be either 175, 190 or rarely just over 200 if the heads have been changed for vortec. The most powerful 4.3 is 220hp, but that’s an MPI
 
achris

achris

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QBhoy said:
.... Your engine isn’t 225hp. There isn’t such a 4.3 merc. It will be either 175, 190 or rarely just over 200 if the heads have been changed for vortec. The most powerful 4.3 is 220hp, but that’s an MPI
Click to expand...

Nope. Go to the Merc repower site. The 4.3 V4 (carb) is indeed rated at 225hp....

Chris...
 
JoLin

JoLin

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poconojoe said:
Yep, agree. Pull the spark plugs and the distributor cap for inspection. My 4.3 Mercruiser (2003) had a no spark condition due to the ignition sensor under the distributor cap. When I removed the distributor cap, I was shocked at the condition of the rotor and cap contacts. There were literally stalagtites (like in a cave) hanging from the contacts. No copper was visible. It was all green clumps.
Click to expand...

Don't know what year Merc started cheaping out on the caps, but they did. No brass coating on the contacts anymore. The cap on my 2014 reman looked like yours after one season. On the advice of my mechanic, I changed to Sierra- they still have the brass coated contacts.
My .02
 
Lou C

Lou C

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achris said:
And the average injection system shirts on a carb for both reliability and efficiency...
Click to expand...

Sorry I am going to disagree with you Chris. A properly tuned Q-Jet is the next best thing to fuel injection. As long as you have a good core that is not a Franken Carb, a top quality rebuild kit and 2 hrs of your time will put it back to new. Add up the cost of EFI sensors, injectors and fuel pumps. While EFI fuel pumps are very reliable in vehicles, in boats they seem not to be as much, perhaps because they must pull fuel from the tank, instead of pushing it out of the tank as in an auto application. Look at the grief Volvo's pump issues caused their owners for YEARS. Some owners in disgust, pulled off the EFI Stuff in disgust and installed a carb!

https://cliffshighperformance.com/

we had a Quadrajet in my parents' 1975 Olds 5.7 V8. They had that car 15 years and I took care of it all that time. It always started up just fine, much better than other carbed vehicles of that era and only needed an occasional choke cleaning one a year. I never had to have that one apart (ran it on straight gas not E10 which is what we are stuck with).

And what pray tell, do you do when either Merc or Volvo decides to make you EFI computer NLA? It has happened to a number of people with boats in the 12-15 year old range.
With the carb and mechanical fuel pump, you get a new pump (my first one lasted 30 years yes that's right 30 years) for $100 or so and a $60 rebuild kit from Cliff's. Back in business. Easy repair-ability trumps efficiency every time.
 
Last edited:
Lou C

Lou C

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JoLin said:
Don't know what year Merc started cheaping out on the caps, but they did. No brass coating on the contacts anymore. The cap on my 2014 reman looked like yours after one season. On the advice of my mechanic, I changed to Sierra- they still have the brass coated contacts.
My .02
Click to expand...

Agreed, the original OMC caps were good and the Sierras seem as good. I get at least 3 seasons out of them.
 
P

poconojoe

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JoLin said:
Don't know what year Merc started cheaping out on the caps, but they did. No brass coating on the contacts anymore. The cap on my 2014 reman looked like yours after one season. On the advice of my mechanic, I changed to Sierra- they still have the brass coated contacts.
My .02
Click to expand...

Good to know...thanks for the info.. I used Sierra cap, rotor and ignition wires. So I guess I'm good. The ignition sensor I bought was Mallory.
 
Q

QBhoy

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achris said:
Nope. Go to the Merc repower site. The 4.3 V4 (carb) is indeed rated at 225hp....

Chris...
Click to expand...

Show me Chris. I’m sure there isn’t any 4.3 with a carb at 225. There ain’t a carb 4.3 with more HP than the MPI.
Sorry.
 
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