Learning my lesson

[PitDr13]

I purchased a 1991 Chris Craft Crowne 252 with 5.8l cobra OMC last July. My family and I love the boat for heading out of the marina and cruising to a cove and hanging out for the day but if we want to go down the lake 10 miles it is a nightmare. Basically my issues is power. When there is four of us on board (myself-230, wife-120, boys 150 each) and I attempt to get up on plane it takes everyone in the nose of the boat and close to a mile of playing with the trim and finally it will come up. If there is one more adult in the boat it is a 2000 RPM cruising kind of day. If it is just my family or less once it is on plane it tops out at 3800 rpm and if you come off of WOT 10% it falls back down into the water.

When I purchased the boat it came with a 15.5 x 14 prop and the last owner said that it was always on it from the day he bought the boat and it always ran great. I tried a few different props but the one on it performs the best (tried a 14.25 x 17, a 15 x 19, 15 x 13 ) with the one that is one there. All of them were aluminum to find the right one before i got stainless, never found the right one. Next we emptied the boat except life jackets and seats - the same. Upgraded the fuel system to EFI - the same.

I cant even sell the boat to buy a new one because it is not what I expected when I purchased it and I couldn’t do that to someone else. Nevertheless where do I go from here?

 

[southkogs]

To my - less than mechanically excellent - line of thinking, you're not getting enough oomph from the engine. Have you tested compression and made sure you're getting all the power out of it?

WOT should get you closer to 4000 RPM I would think.

Welcome aboard.

 

[Maclin]

I am confused as to what prop is on there now, what pitch.

Next thing, BIG boat for a single 5.8. Low pitch prop is certainly indicated. Do you know what the drive ratio is.

Does the boat have trim tabs.

 

[PitDr13]

Compression was checked at the beginning of the season by a mechanic and said it was good?

Motor stamp says it should be running between 4000 and 4400

The current prop is a 14 pitch prop 15.5 diameter. I agree about the low pitch however if I drop to a 13 pitch prop there should be an increase in RPM but will there be enough thrust?

Yes it has trim tabs and they must be utilized to get out of the water no matter what. I do not know what the drive ratio is.

 

[Maclin]

I meant that the low pitch prop, the 14, is what was needed. I missed the part where you had reinstalled that one.

Thrust is basically the same between differently pitched props with same diameter and blade count. Lower pitch will effectilve amplify the torque at the expense of top speed. More blades increase thrust but load the engine more. A 14 pitch should do it, not sure what is going on now.

Do you ever get past the 3800 rpms in any of the scenarios you tried? If not, almost sounds like an ignition rev limiter is in play?

 

[kenny nunez]

It is always better to be under propped pitch wise on a combination like you have. Even if it turned up to 4600 would be better than straining it to 3800. The wear on an engine overloaded is a lot more than one that can turn up .
It is a common practiced for boat builders to put smaller engines in the boats they build to keep the cost down. I have seen some pretty ridiculous engine combinations that I finally repowered for customers because the engines were worn out from being overloaded.

 

[Scott Danforth]

something may be wrong with your motor, however with that boat at 5800# and a 14P prop, you should be well above 3800 RPM

start with taking compression readings yourself
then measure fuel pressure yourself

 

[PitDr13]

Yes the engine will rev well over 4000 rpm when trimmed to much but the boat will slow down. I will check the compression when I get to the boat again and the fuel pressure is @ 60 psi.

 

[tpenfield]

Having an OMC 5.8 Cobra is certainly learning a lesson.

Have you established that the boat is not water logged? The symptoms seem to match that condition.

 

[PitDr13]

Not sure if it is water logged. I would not know how to tell.

This weekend the boat ran good all weekend. Got up on plane with no issues and ran about 4000 rpm. Not quite where it should be but better than it has and I made no changes. Just started up and went.

She is driving me a touch crazy. I will be trying one last prop this weekend..

 

[Bt Doctur]

Upgraded the fuel system to EFI - the same.
Care to describe how this was done. Usually 41 psi is the standard for MPI and 31 psi for throttle body.

 

[PitDr13]

I installed a Holley Sniper EFI system. It requires 60psi on the fuel system then regulates it done to 58psi. I used a Holley Sniper retrofit in tank fuel pump. Also needed to add an O2 sensor plate to the exhaust riser.

I do like the system but it only eliminated cold starting. Everything else performs exactly the same as before.

 

[Maclin]

Hate to go there, but is this Marine compliant system? There are some USCG regulations on distance of the fuel pump from the engine. Also fuel pump cutoff when engine dies but ignition is on.

I mean, you won't get arrested or anything, but the regs are for safety of self and passengers (on your boat or any close to you!)

First thought was, is there a full 60psi from inside the tank to the filter outside the tank and on into the regulator? What materials are you using for the fuel lines.

Next is, what cuts off the fuel pump when the engine dies but ignition stays on.

 

[Lou C]

Agreed, I think I'd have contacted Holley and asked them if this system meets marine specs. I have never seen a marine EFI set up where there is a pump in the tank and it pushes the fuel forward to the EFI system, all the stock marine systems use a pump or combination of pumps that suck the fuel from the tank, this may be safer in a marine set up. Did the boat have EFI on it originally or was it a carb?

 

[Bt Doctur]

I used a Holley Sniper retrofit in tank fuel pump
how did you get it to fit thru the tank sender hole thats like 2 1/4 inches?

 

[Bt Doctur]

$1600 and the motor does the same thing as a carb`d motor ? No gain there

 

[Bt Doctur]

With 240 Hp ,thats a BIG boat to push around. Most are shown with the 383 stroker motor and a Bravo III

 

[PitDr13]

Let’s see if I can avoid forgetting any of the questions... As far as USCG compliance the regulations are for the spark arrester and fuel shut off (from what I have read). I am still using the stock spark arrester and the rest of the system is pretty much stock.
I did have a conversation with a tech from Holley berfore I purchased the system and he assured me that the system has been used for marine application many times before me.
The in tank fuel pump was the most recommended for the fuel system and the inline pumps are very loud so I chose the in take pump. There is a digital display that reads all of the connected sensors and a read out of 60psi for fuel pressure. The readout comes from the onboard computer and has a dedicated 40 amp relay that controls the fuel pump so when the motor stops running the fuel pump shuts down. It’s goes through a 2.5 second prim when the key is initially turned on.
Original equipment was a 4 barrel Holley carb with a mechanical fuel pump.
The new fuel pump would not fit in the original fuel outlet (obviously) so I used a 3 1/4” hole saw and made it work. Tank was almost empty when cut the hole so I used a vacuum and towels to clean out any debris before I put the new pump in.
Absolutely agree on the $1600 = zero change. I have considered putting it all back to stock and selling it.
Finally I was very surprised that a company would build a solid boat like this one and not put enough power in it to get on plane. This boat sleep 6, it should run perfect with at least 6.

 

[Maclin]

There are specific regs covering the placement of fuel pumps, ultimately aimed at limiting length of pressurized line. I scooped this out of the Fuel and Emissions Compliance guideline a while back for another project for reference, peruse or not...:

183.566 Fuel pumps: Placement.
Each fuel pump must be on the engine it serves or within 12 inches of the engine, unless it is a fuel pump used to transfer fuel between tanks.

Most engines are equipped by the engine manufacturer with a fuel pump as an installed engine component. For engines that are not so equipped, a remote fuel pump, usually electric, may be used. In order to keep the length of the pressurized portion of the fuel distribution line at a minimum, it is required that a remote fuel pump be installed within 12-inches of the engine. The 12-inches are measured directly to the engine, not along the fuel line. Pumps used to transfer fuel from one tank to another may be installed in other locations, and are not required to be within 12 inches of the engine.

TO COMPLY If the fuel pump is not on the engine, is it within 12 inches of the engine? If the fuel pump is not on the engine or within 12 inches of the engine, is it used only to transfer fuel from tank to tank?


United States Coast Guard and
Environmental Protection Agency
Compliance Guideline
-How to Comply with the Law-
Fuel and Emissions

Prepared by the American Boat & Yacht Council, Inc.
613 Third Street, Suite 10 Annapolis, MD 21403 (410) 990-4460
www.abycinc.org

 

[PitDr13]

Perfect. I am 12” from the engine.