Engine trouble shooting

[4Wins]

1995 OMC SX COBRA 502APHUE Four Winns 195 Sundowner

I am trouble shooting my engine because I have less than desired WOT speed 3800 RPM and 27 MPH. I also have serious problems planing out under a full boat load.(MPH verified w/ Garmin)


*** I have also noticed that when I am at WOT or in hard turns (heavy load) I am getting a surge and then lag. The RPM's start to increase but quickly begins to decrease again. This happens continuously when I induce it. It creates a back and forth motion. Kinda like if you were pressing your gas pedal in your car very gently and letting off again.***

-I am going to be doing a compression check and fuel pressure check this weekend. I believe that these procedures are pretty cut n dry. However any advice would be appreciated. I know it is especially hard to remove the spark plugs. Any tips there?
-I will be replacing the distributor cap and wires as well.
-I have a mechanical fuel pump going to my 2 barrel holley carb. I will be checking for 3-7 psi their during cranking and during on water operation.
-Can I use the compression guage with a t-fitting to read the PSI at the fuel pump?
-I will also be test running a new prop. Current prop is 14 and 3/4 x 21 stainless steel viper. The new prop is a 14 and 1/2 x 19 solas aluminum.
- I also want to attempt to check my throttle cable rigging. Is the complicated as it sounds in the manual?

 

[bonzoscott]

Re: Engine trouble shooting

Is the boat new to you? 21 pitch prop is a bit high for 19-20 footer. You may try that first. I don't think you can use a compression gauge for fuel pressure, but if the boat isn't missing or cutting out, don't think pump is the problem. I would check and make sure the throttle plates are fully open with full throttle at the shifter, and try the 19" prop. Personally I wouldn't go throwing parts at it unless I've check them and are faulty. Cap and wires get back to "Is it mis-firing"? Do compression test with all plugs out and don't mix up your wires. Most important, has it ever ran well for you - history?

 

[4Wins]

Re: Engine trouble shooting

Is the boat new to you? 21 pitch prop is a bit high for 19-20 footer. You may try that first. I don't think you can use a compression gauge for fuel pressure, but if the boat isn't missing or cutting out, don't think pump is the problem. I would check and make sure the throttle plates are fully open with full throttle at the shifter, and try the 19" prop. Personally I wouldn't go throwing parts at it unless I've check them and are faulty. Cap and wires get back to "Is it mis-firing"? Do compression test with all plugs out and don't mix up your wires. Most important, has it ever ran well for you - history?

It's never ran good for me. I should be flying on the water with a 5.0. Even by myself I can't get up past 30mph. I am borrowing a compression gauge from a friend tomorrow and I am going to buy a fuel pressure gauge. I am only changing out the wires and caps because they are seriously gummed up. And i'm changing the prop because I feel it may be over pitched at 21.
Here is a video.

4 Winns 5.0 - YouTube

 

[bonzoscott]

Re: Engine trouble shooting

It doesn't sound like it's running bad. Boat speedos and tachs are known for being inaccurate. Try and locate a shop tach and verify RPMs. Let us know how it turns out with the 19 prop.

 

[diveman05]

Re: Engine trouble shooting

It's never ran good for me. I should be flying on the water with a 5.0. Even by myself I can't get up past 30mph. I am borrowing a compression gauge from a friend tomorrow and I am going to buy a fuel pressure gauge. I am only changing out the wires and caps because they are seriously gummed up. And i'm changing the prop because I feel it may be over pitched at 21.
Here is a video.

4 Winns 5.0 - YouTube

on your one video you have water leaking from the back, maybe exhaust or transom, did you ever figure that out? are you also leaking exhaust into the engine compartment?

Prop i would be curious to see how the change helps, I'm pretty sure i have a 19 on my 205 sundowner with the 5.0 and i can do around 50 with it, its a 1989 so that is fast enough for me!

 

[4Wins]

Re: Engine trouble shooting

on your one video you have water leaking from the back, maybe exhaust or transom, did you ever figure that out? are you also leaking exhaust into the engine compartment?

Prop i would be curious to see how the change helps, I'm pretty sure i have a 19 on my 205 sundowner with the 5.0 and i can do around 50 with it, its a 1989 so that is fast enough for me!

One of the clamps was really loose and allowing the water to leak out. I just tightened it down.

 

[4Wins]

Re: Engine trouble shooting

It doesn't sound like it's running bad. Boat speedos and tachs are known for being inaccurate. Try and locate a shop tach and verify RPMs. Let us know how it turns out with the 19 prop.

It's not running bad per say. No obvious systoms from the engine and that is why I am trying the prop. But it's not running good either. It's a 5.0. I should be getting much better performance.

 

[4Wins]

WOT Fluctuations

WOT Fluctuations

1995 OMC SX COBRA 502APHUE Four Winns 195 Sundowner

*** I have noticed that when I am at WOT or in hard turns (heavy load) I am getting a surge and then lag. The RPM's start to increase but quickly begins to decrease again. This happens continuously when I induce it. It creates a back and forth motion. Kinda like if you were pressing your gas pedal in your car very gently and letting off again.***

 

[Levinz11]

Re: WOT Fluctuations

Re: WOT Fluctuations

Is the prop ventilating in turns (coming out of the water)?

 

[Levinz11]

Re: Engine trouble shooting

Have you read this? http://forums.iboats.com/mercruiser...ives/list-possible-causes-low-wot-295070.html

 

[4Wins]

Re: WOT Fluctuations

Re: WOT Fluctuations

Is the prop ventilating in turns (coming out of the water)?

I don't believe so... I will have to take a look.

 

[Silvertip]

Re: WOT Fluctuations

Re: WOT Fluctuations

I don't believe so... I will have to take a look.

Nothing to look at except the tach. What is it doing when this problem occurs. If the rpm rises and then falls but holds steady going straight, the prop is ventilating.

 

[4Wins]

Re: WOT Fluctuations

Re: WOT Fluctuations

Nothing to look at except the tach. What is it doing when this problem occurs. If the rpm rises and then falls but holds steady going straight, the prop is ventilating.

It does it when I am going straight as well.WOT

 

[81 Checkmate]

Re: Engine trouble shooting

^^^^^^^^^^^ Check all those things listed first...............Or its water loged and you now have a heavy boat!

 

[Levinz11]

Re: WOT Fluctuations

Re: WOT Fluctuations

Could be a spun prop hub. From my reading when they go that's usually it but maybe yours is letting go...then catching again?? Mark the prop and the shaft with a sharpie. Make the situation you describe happen again. Then check to see if your marks are still aligned.

 

[Celtichawk]

Re: Engine trouble shooting

Was it me or when you throttled up your MPH gauge didn't move right away! You have GPS to calculate speed and it seemed spot on with MPH when you got it going.

Anyways have you checked the structure areas of boat for water logged? Previously stated but that's a idea maybe under deck is full of water and rot. Hope not but its a thought. How bad is your compression? And your cap does it appear to have a arch and not firing correctly on all contact points?

Had a 4cyl Merc that I never noticed the cap didn't sit on straight so when I pulled it off to check for signs of points bad I discovered it was not firing correctly which was reasons for my backfires on plane.

 

[bonzoscott]

Re: Engine trouble shooting

Is the boat new to you? 21 pitch prop is a bit high for 19-20 footer. You may try that first. I don't think you can use a compression gauge for fuel pressure, but if the boat isn't missing or cutting out, don't think pump is the problem. I would check and make sure the throttle plates are fully open with full throttle at the shifter, and try the 19" prop. Personally I wouldn't go throwing parts at it unless I've check them and are faulty. Cap and wires get back to "Is it mis-firing"? Do compression test with all plugs out and don't mix up your wires. Most important, has it ever ran well for you - history?

Did you ever look at that?

 

[4Wins]

Re: Engine trouble shooting

Was it me or when you throttled up your MPH gauge didn't move right away! You have GPS to calculate speed and it seemed spot on with MPH when you got it going.

Anyways have you checked the structure areas of boat for water logged? Previously stated but that's a idea maybe under deck is full of water and rot. Hope not but its a thought. How bad is your compression? And your cap does it appear to have a arch and not firing correctly on all contact points?

Had a 4cyl Merc that I never noticed the cap didn't sit on straight so when I pulled it off to check for signs of points bad I discovered it was not firing correctly which was reasons for my backfires on plane.

I am replacing my distributor cap this weekend and will be check all of the that. I have looked at it already though and all is as it should be other than it being gummed up.
As far as MPH it takes a while to get up speed and thats part of my issue of poor performance in WOT. The MPH does seem to be accurate when compared to the GPS. What do I look for to see if my boat is water logged? I will be checking compression and fuel pressure this weekend.

 

[Celtichawk]

Re: Engine trouble shooting

Your gonna need to drill holes into your stringers below deck and check for dry wood shavings. Also drill holes into transom without going trough the fiber glass hull and again checking for dry shavings. Many others will chime in and provide the proper drill depth and specifics. Check around in the restorations threads its got some good reads.

 

[4Wins]

Re: Engine trouble shooting

Is the boat new to you? 21 pitch prop is a bit high for 19-20 footer. You may try that first. I don't think you can use a compression gauge for fuel pressure, but if the boat isn't missing or cutting out, don't think pump is the problem. I would check and make sure the throttle plates are fully open with full throttle at the shifter, and try the 19" prop. Personally I wouldn't go throwing parts at it unless I've check them and are faulty. Cap and wires get back to "Is it mis-firing"? Do compression test with all plugs out and don't mix up your wires. Most important, has it ever ran well for you - history?

The throttle is one of the first things I will be looking at bonzoscott. I am very interested to see what the WOT plates are looking like. I feel like this could very much be my problem. Unfortunately, I have no idea how to verify the throttle is rigged correctly. There are procedures in my Clymer but they are confusing. Is there any guidance you can give me on how to do this? (Step by step procedure, a link, or video) I would like to check this before I start really tearing into everything ( i.e. fuel press check & compression check).