2005 Mercruiser 5.0 260HP running/smells rich

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GregR

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2005 Monterey 302 with twin Mercruiser 5.0s, 260 HP, 67 original hours on both. Bravo 3 outdrives. Boat has had very little use in the past 3 years and was stored on land for a long time before then.

I bought the boat 4 weeks ago and have put 10+ hours on the engines since. I am starting to notice what I call a rich fuel smell, like what I used to smell on previous carburated boats. I noticed some smoking at idle at the outdrives this weekend. When I come down off plane to a hull speed or idle cruise I can smell that "too rich" fuel smell.

Engines run well, 4800 WOT, port engine is difficult to start, acts like it needs gas. Both tachs bounce around from 600 RPMs to 800 RPMs on a cold start. Fresh gas added 2 times since I purchased it.

Fuel injectors and fuel pumps replaced approximately 2 years ago after the boat had been stored on land for a long period of time.

If the engines were carburated I'd adjust the air mixture screws. I am not sure what to check on these engines though.
 
These are MPI engines, not TBI, right ?
Is the odor clearly gassy, not burned oil or coolant. Oil and coolant levels remaining steady?

A fuel pressure test gauge could show if an injector was leaking by noticing if pressure drops quickly after turning the engine off. the gauge connector screws onto a Schrader valve on the fuel rail or a crossover with engine NOT running. Be careful if you do attach the gauge , as the rail could still have over 45 psi of gas that can squirt at your eyes or a hot engine.

And a marine scan device could reveal if the IAC or MAP(if yours has one) or other sensor was sending faulty response to the computer compared to reading from the good engine.

If you do suspect a leaking injector, before starting you could try moving the throttle lever to WOT position which prevents either spark or injector pulse until the engine fires up. But be ready to close the throttle immediately when it does start. Maybe momentarily remove the flame arrestor and sniff the throttle body before touching the throttle before starting too.

If you smell gassy odor in the boat be sure to look at the engine, filters , tank, etc. to rule out a direct leak , then use the blower before cranking.

At N idle after startup, do you notice any fuel sheen in the exhaust wake?

Have you noticed if the port engine's tank requires more fuel at each fillup than the stbd , if they have independent tanks w/ crossover closed?

Dirty spark plugs or corroded dist cap electrodes could also cause hard starting and poor initial combustion. If your engines have the flat "crab" style dist caps, check them often as they tend to have short life.
 
Hi Sandy, i am not sure if it's MPI or TBI, how can I check?

It's a gassy smell. Raw water cooled, recent oil samples show no fuel or water in the oil. Oil levels are good, i actually changed the oil/filters yesterday as well.

I do not own a fuel pressure gauage, so i may have to turn this over the the service shop to do.

No gas smell in the engine compartment, no gas leaks, it's a fumey smell at idle, no sheen on the water. Single gas tank. When the tank is low the port engine will not start, I'm guessing it pulls at a higher level on the tank. My 2000 302 did this as well.
 
The fuel pressure test gauge with pressure release, adapters and case are not very spendy. But the scan devices are ( check Rinda Technologies.)
https://www.sears.com/search=craftsman tools fuel pressure gauge

If smelling transom gas fumey smell at idle I'm a little surprised there is no sheen, though gas sheen dissipates much more rapidly than oil , and A/F mixes so well with water it really doesn't show.

Gas MPI's don't inject directly into the combustion chamber, so ...if... an injector is leaking I should expect there could be noticeable gas odor ( compared to the "good engine") at the throttle body before starting or shortly after shutdown. Odds are low both engines would have that issue .
 
Is the rich smell coming from the exhaust...as in black smoke and outside the boat or raw gas in the engine compartment.
 
Shopped checked it out for me. All spark plugs had soot on them. They replaced all the plugs, replaced the fuel pressure regulator on one motor, replaced IAC on both motors, problem resolved.
 
I misspoke, the shop has yet to replace the IAC valves. They quoted me $175 per part per engine and $100 labor per engine.

It look to be a fairly simple job, removed to hex bolts, two hoses, a wire plug then reinstall. Is it that simple?
 
I believe there can be a BIG difference in part cost for the exact same IAC depending on how many hands it goes through before you and how, ah, "profit motivated" the owners of those hands may be.

You might be able to save $300 or more by doing it yourself in a very few minutes with your eyes closed. And learn a bit more about your engines in the process.

Just get the right one for your motor's model & serial # range.
 
Thanks, I did exactly that. I found the part online, using my engines serial #'s, OEM, for about $40 less each and plan to do it myself. And yes, I love to learn, which is the main reason I want to do this myself.
 
Still putting off having the engine scanned? The scanners like Diacom SW which allow scanning both engines at once to be able to compare parameters on both simultaneously can help see any anomalies on the troubled engine. But a single engine scan device can suffice if you have an ignition diagnostic manual to which you can refer, so you know what value ranges are normal for that engine/ign. .

But note, the scan devices can only display items controlled by, and data output by, the ECC/ECM.
 
Hi Sandy, the IACs that were shipped to me were supposed to be Mercruiser. They were not. They had a pin and a spring in them, the ones on my boat did not. Per the shop they have had issues with aftermarket IACs so they always go thru Mercruiser. The shop adjusted the idles up to 620 I think on both engines (from 570) which has helped with the cold starting issue.
 
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