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Thread: Mercruiser Performance Issues/Need Advice

  1. #1
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    Default Mercruiser Performance Issues/Need Advice

    So here it is. I have a 2005 Trophy Pro 2359 with a Mercruiser 5.0L carburated. When I bought the boat this winter it only had about 83 hours on it. I took it in to Odie's marine to have it checked out and winterized again so it was ready for the season. On the first trip out, the thing purred like a kitten, ran real smooth and did great. The only issue was when turning it off the motor would diesel. I took it back to Odie and he reset the timing. The next time I took it out, no more dieseling but it seemed as though the idle was set too low; it would not stay running without some throttle untill it was fully warmed up. On one trip I had spent the night in Sunny Cove. When we got up in the morning, we took off out of the cove and after about a minute or two on step the boat began to loose power and almost died. I could keep it about half throttle and it would do fine, but at full throttle it would sputter and loose power. It did this about three times and then all was fine.

    I got it back to Anchorage and was going to replace the fuel water separator. I couldn't get the filter off, so I called around and took it to Boat Works of Alaska who happen to squeeze me in just in time. They had to replace the filter and housing, plus they did some carb adjustment because the idle was low. Took the boat out the next day and headed to Montague. She ran like a dream all the way out and back, however, she started to diesel again on a few occasions. The next day, we had a bunch of people on the boat, so we just took slow cruise around the bay.

    Three weeks had passed and I finally got the boat back in the water this weekend. Hit Seward on Saturday morning. Launched the boat, started up fine, warmed up nicely and then headed out. Got outside the harbor and hit the throttle and it seemed like I wasn't getting enough power to get up on step. Throttled back down, adjusted trim tabs and off we went. Got up on step but still a little slower than normal, then all of the sudden, it started to loose power. After a few minutes it sputtered and died. It took a few minutes and playing with the throttle and she started again. I had to pump the throttle to keep her going and there was a weird clanking sound coming from the engine. I was able to limp back into port, and at idle the engine sounded normal and ran fine, but as soon as I tried to throttle up, it would spit and sputter.

    Got back to Anchorage, hooked her up to the hose to flush her out and she started fine. However, there was a slight winning sound coming from the belt. I began to play with the throttle a little and rev her up and got it to back fire once or twice. Other than that, she sat there and idled fine and warmed up to temp while it flushed and I shut her off, no deiseling.

    So here's the question. After that long story and all the symptoms, what do you suspect this could be and how would you fix it?

    When I got her back from Boat Works, I was told it was time for a tune up and that the electric fuel pump was weak. I'm thinking I have some bad gas coupled with a weak fuel pump and maybe a timing belt issue. What do you think?
    TIGHT LINES...ALASKA!!
    2005 Trophy Pro 2359
    "Nut-N-Honey"

  2. #2
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    I suspect it has carb issues, ignition issues and fuel pump issues and possible water contamination in the fuel tank. It does not have a timing belt, the cam is chain driven by the crank. I am curious what kind of distributor it has in it. Also, wondering why it has a electric fuel pump on a carbureted engine?

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    Member OKElkHunter's Avatar
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    I had a similar issue with my 5.0 Merc. Thought it needed a tune up and new fuel filter. Replaced Disrtibuter cap, rotor, wires, plugs and set timing. Replaced fuel filter and checked fuel pressure. She purred like a kitten until she was fully warmed up, then started dieseling and lost power under throttle. Under load, shed get up on step, until warmed up, then no power. I took her home and did a compression check and found out I had dropped 2 cylinders and had low compression the other cylinders. Boat Works has her now; putting a new 5.8 Merc in. I'd do a compression check if I were you, before spending any more chasing your issue. I dumped over $500 into tuning and filters just to find out I have wasted my time and money. I hope you don't have the same issue. Lesson learned, I'll never buy another used boat without checking compression. Compression on the 5.0 should be between 130 and 150.
    “Don't expect to build up the weak by pulling down the strong." ~Calvin Coolidge~

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    Member Frostbitten's Avatar
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    I hate to say it, but I too had the same boat (2003), with the same motor and many of the same problems. I was thinking it was carb related, but just like OKElk, turns out I lost two cylinders. I repowered with a Merc 350 MAG.

  5. #5

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    So what was there verdict?

  6. #6

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    Quote Originally Posted by Cresent Hills View Post
    So what was there verdict?
    Timing problem. He tells me it was out by 13*. The engine had a minor timing problem in the early season so that leaves a couple reasons for the problem. The first reason IMO is they didn't tighten the distributor when setting the timing or a timing chain issue. Not really likely on the timing chain due to super low hours.


    Heavy Hitter Fishing
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    Yeah, it seems it was just timing. Like Charlie said, off by 13 degrees according to Burkshore. I took it out on the lake and it ran perfect. Not sure about timing belt/chain; was told it does not have that. Took her out last weekend on Saturday and she ran fine. Did have an issue at the first try to take off where we were at full throttle and it would not get up on step then acted like it was gonna die. I backed off, had a few guys move forward then tried again and got up on step no problems. I'm thinking that having the weight in the back was too much for the motor and having so much load on the engine maybe started to flood her our or something. It seems to do that only when it's pushing real hard to get on step but just can't get their. Oh the headaches of under powered boats. When this one blows up, I'm putting a bigger horse power motor in her.
    TIGHT LINES...ALASKA!!
    2005 Trophy Pro 2359
    "Nut-N-Honey"

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    So another update...

    Took her down to Seward again and she fired right up only to spit and sputter a little before dying. Could not for the life of me get her started. Tried starter fluid and not even a cough. Checked to make sure I had spark by taking the coil wire off the distributor and put a screw driver in it. Laid it next to a ground and had good spark. My buddy Charlie and his friend Jim came to the rescue. He loosened the distributor and turned the distributor while cranking and bam, started right up. Tighted in down then after a minute it died out again. Had to do the same thing to start her up. Looks like it's jumping timing, but not sure. Like Charlie said below, very low hours on this motor. I'm wondering if it's something to do with a component in the distributor itself? Maybe something loose in the assembly causing it to raddle out of timing. Oh well, dropped it off to Burkeshore yesterday. Hope they can work their magic and fix it for the last time. Hey Tom, I know you are reading this...can I have her back before Thursday next week
    TIGHT LINES...ALASKA!!
    2005 Trophy Pro 2359
    "Nut-N-Honey"

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    Member Sobie2's Avatar
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    Lock-tite, or spot weld that dam thing in place. I have never head of a distributor walking so quickly. Maybe replace the bolts and washers and clean the thread holes.

    Sobie2

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    Member OKElkHunter's Avatar
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    Did you ever do a compression test on your cylinders? While its in the shop, you should have them check all the cylinder compression. Sounds exactly like the problems I was having. could play with the distributer and get her going, but that was only temporary and after checking compression, I discovered that I had dropped 2 cylinders.
    “Don't expect to build up the weak by pulling down the strong." ~Calvin Coolidge~

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    I had a similar problem on my old boat and mechanics tried almost tried everything. The problem was intermittent for the most part. It wouldn't throttle up with the prop in gear but would throttle up in neutral. Replaced the high pressure fuel pump and never had a problem again.
    Ryan
    Kingfisher 2525 Honda 225 & 20

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    Timing could also be an issue with the gear on the distributor if it seems to be jumping.
    Maybe mark the block and distributor to see if it's actually walking or if the issue is elsewhere.
    As said do a compression test as well.
    Also fuel pressure test (be good if you could do it while out running).
    Could be a fuel, timing or electrical issue or a combination of issues.
    On an old bike I owned It had a similar gremlin that turned out to be a bad electrical connector.
    Took forever to figure out that one.

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