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Just bought a Signature 240 2001 and need advice please

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Hi fellow Chaparral owners.

I have recently acquired a signature 240 fitted with the 5.0 Efi Mercruiser (240hp and only 600 hrs with Bravo 3 leg). She is a beautiful boat but really struggles to get on the plane. Had her fully antifouled and load is usually only 2 (lightish) people, 10 gals water and 30 gallons fuel plus luggage as we live aboard occasionally.

At best had 25mph (following sea and wind) but usually about 10 mph because she will just not get up! Changed the 24p prop for a high tech s/s 4 blade 20p with negligible difference. 4000 rpm is about best we can achieve.

Engine sounds sweet but smell unburnt fuel so suspect we may not be getting full power? Have there been any upgrades for this engine on fuel systems, engine management or whatever? Or perhaps we can re-chip for more power

Also concerned about erosion. She is based in salt water in Playa Blanca Lanzarote. However, new sacrificial anodes fitted only weeks ago are being attacked wholesale and notice some damage to the leg. How can this be addressed?

Can anybody out there help with these issues? I would love to get this boat running correctly so we can safely cruise to other islands. When I read about others achieving 35 mph I am sceptical as she is a heavy boat and perhaps underpowered but am sure we are not getting the best out of her.

Thank you in anticipation


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First, welcome to the forum and congrats on the new to you boat!

The 240 hp engine on Sig 240 might not be the optimum setup. With 300 or 320 hp power plant she would jump on plane in no time. There are others Sig 240 owners here that can share their experience. Related questions ... Does it have trim tabs? Do you use them?

Smell of gasoline fumes in exhaust ... is the engine running on all cylinders?

The rapid corrosion is a concern ... it's a complex issue, could be a number of things. Are you connected to shore power? Do you have galvanic isolator, and what does it indicate? How is the marina installations in general? Do other boats around you have similar problem?

You can search the forum for "galvanic corrosion" and find a lot of info on the subject and potential causes/remedies.

Just FYI ... my Sig 270 (nearly 9000 lbs loaded) gets consistently 45+ mph at WOT, reaching 50 mph on a good day with a clean bottom.

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I too have a Sig240 with the 5.0 (GXI) and she jumps on plane quickly. 40-41mph with 270HP.

Here's what I would do with a new to me boat:

1. Change the oil and filter.

2. Change the spark plugs and wires. INSPECT THE PLUGS. You can learn A LOT about your motor from inspecting the plugs.

3. Inspect the rotor and cap. Change if needed.

4. Seriously consider a new battery. You'll have a fresh starting point knowing it's new and you'll have a warranty on it.

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Many thanks guys.

I guess there may be something wrong with the motor and I will certainly be following both your advice and check plugs etc. Have just fitted a new battery but a full service is in order.

We do have trim tabs fitted, should these be down to help get on the plane? Someone has fitted the sacrificial anodes underneath tabs which seems wrong to me as they cause additional drag?

Yes we do have shore power and electrics in the Canary Islands is a bit iffy so may not have a proper earth? Is there something I can do to stop the degradation of the leg and anodes so fast?

I guess I have much to learn as this is the first inboard boat after a number of outboards!


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The anodes being eaten alive. COULD be electrical currents from other boats & dock electricity. Sometimes paradise is not.

I would check ALL the anodes on the sterndrive Maybe just replace them. 2001 boat should have been changed long ago in salt water. A problem can occur if the ANODES are too old. The bare aluminum UNDER the Anodes starts to be attacked. Real problem to do right

Is there a WORKING cathodic unit in the boat ? May need a fast adjustment or repairs. Is it turned on & working correctly ?

Disconnect your power cord from dock electricity until your protection system is operating correctly. That may slow down the leg from dissolving.

Why does a 5.0 240 HP motor not sound right in your boat.

Get GOOD PEOPLE ON THE ANODES NOW !! That problem will ruin the drive housing.

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You did not give the prop diameter of the 4 SS 20 pitch..........Diameter Causes overloading VERY quickly. My 5.0 L 220 hp with a Power Tech 14.25 dia. X 21 P Would almost stop the engine if floored at a stop. Now have a 17 P & it is a sweetheart boat. Very raked & cupped propeller . WOT is 4400 rpms & about 46 GPS

YOur fuel odor COULD be from the fact your engine has too much prop ( 4000 rpms max ) & the engine can not burn the fuel due to the load on it.

Ken at www.propgods.com can get you into a loaner prop setup. With only you paying shipping charges back & forth for each testing prop. Worked for me.

Could all be a overloaded engine by the prop. Correct that first.

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1. I guess there may be something wrong with the motor and I will certainly be following both your advice and check plugs etc. Have just fitted a new battery but a full service is in order.

2. We do have trim tabs fitted, should these be down to help get on the plane? Someone has fitted the sacrificial anodes underneath tabs which seems wrong to me as they cause additional drag?

3. Yes we do have shore power and electrics in the Canary Islands is a bit iffy so may not have a proper earth? Is there something I can do to stop the degradation of the leg and anodes so fast?

1. It does really sound like the engine is underperforming. Look into it before spending time and funds on props, etc.

2. Yes, the trim tabs help to raise the stern and get it over the hump (bow wake). Try 3/4 down first and see what happens.

Correct, the anodes should be mounted on the top side of the tabs but I would not implicate them in poor boat performance.

3. Disconnect from shore power or use it sparingly until you have the time to troubleshoot.

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Well thanks everyone. I am really impressed by the interest from other owners and wish I had found you all before flailing around in the dark and spending £1000 on new props! I will be following up on all this advice just as soon as I get back down to the Canaries. Meantime she won't be plugged in again to shore power!

Whilst we have the momentum, there are some minor issues on the gauges which you may be able to help with and sourcing parts in UK may be easier and take them down with me.

The trim gauge is dead. Where is this sensor or fuse or how does should it work?

The Rev counter parks at about 1500 rpm and is a bit erratic. Is it serviceable?

The speedo is dead. Are they pressure sensitive on these boats and where might the pitot head be, if that is the way it works?

Thanks guys, Nick

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The pitot is on the front is the b3 leg, and very susceptible to plugging up. Use a small drill bit by hand to clear it.

Bravo units often have failing trim sensors on the leg. There are two sensors, the one on Starbord is the trim indicator, the one on port is the trim stop, to keep yo from going to high when on the water. With the boat out of water, I've been able to rebuild mine by using some silicone to repeal water, and cleaning the sensor by taking apart and cleaning it and putting it back together.

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  • 5 months later...


Thanks for all the advice, weve fitted the electrical isolator and sorted the gauges etc but we've still hit a wall on the most important issue - engine power!

We eventually found someone on the island with a diagnostic tool & the engineer now suggests we have a dodgy water flow sensor causing the engine to limit power, explaining fuel smell at WOT and not getting on plane. Going into troll mode??

Also she wont start when hot. Cool down and hey presto, no problem.

What is a water flow sensor (I guess cooling water) and does anyone know about these? Engine is 5L EFI 2001

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My buddy has the same boat with a 5.0 Volvo. His boat is OK getting on plane until there's more than 2 people on board. With a full boat load, some people need to lay up in the front of the cabin or else it'll never get on plane no matter how long it's at full throttle. Once on plane it's OK but it's a heavy boat for a 5.0. What are your RPM readings when you have her at full throttle?

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Thanks for that, I appreciate it may be a bit underpowered but when I first had her she planed OK. I am lucky to get 2500 rpm at WOT.

The power is definitely down and need to find out from someone what this safety mode is that limits the power when there is a problem (ie low water cooling flow??)


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Hi Nick,

Your particular engine, the 5.0L EFI - 240 hp throttle body injection, (not the later 5.0L MPI - 260 hp multi-port injection) didn't have a water pressure sensor like the later MPI engines did - at least that I know of. 5.0L EFI/MPI power is just adequate for that boat in my experience, even with a twin prop drive.

Any alarm when the boat is cruising along? If you get a beep when you start the boat, but none afterwards, that simply means the ECM has done a check, and found nothing wrong. In such a scenario, the problem would be mechanical in nature, such as low or high fuel pressure, blocked fuel filter screen (item # 16 in the picture below) under the fuel pressure regulator, reference hose off the fuel pressure regulator, base engine timing is not correct, (special procedure) or something else mechanical in nature such as blocked exhaust (flappers blocking the bottom of the Y pipe) poor ignition, crap fuel, etc. etc.



If you get no beep anytime, that probably means you're audio alarm horn (item # 8 in the picture below - mounted under the dash) is NFG (or covered with tape), and needs to be replaced so you can hear when the ECM signals a problem.

Send me the engine serial #. Can be found on top of the plastic engine cover piece, or on a plate riveted to the block directly above the starter motor. That will make it easier to see exactly what you've got.


If you have the MerCruiser made Thunderbolt style ignition on your engine (which I believe you do) than along with new spark plugs, distributor cap and rotor, I HIGHLY recommend replacing the ignition sensor under the rotor. New style came out around 2005, and is a far better piece. Item # 5.

If you have the Thunderbolt ignition, than get the following parts:

805759T3 or Q3. MerCruiser/Quicksilver V8 Thunderbolt cap and rotor kit.

87-892150K02 or Q02. MerCruiser/Quicksilver ignition sensor (new style)

84-816608K83 or Q83. MerCruiser/Quicksilver spark plug wire set.

8 of NGK TR6IX spark plugs from an auto parts supplier - stock # 3689 (be VERY careful when checking the gap or you'll damage or break off the Iridium electrode)

4 of 10-90926 hold down screws seeing you're in salt water





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hi First Sea Lord

Thank you so much you've clearly gone to a lot of trouble.

My big problem is I am 1500 miles away from my boat and cannot get back until end of this month. However, the engineer in Lanzarote (Spanish Canary Island) assures me, as far as I could understand, that his diagnostic gadget showed a dodgy sensor (water flow?) that can limit the power and instigate a limp home type of mode? Is that possible?

The alarm you describe sounds when first switching on the ignition but never again after that, even when trying to get on the plane at WOT. Engine always starts first time from cold and sounds really sweet. However, does not when hot! Let her cool for 1/2 hr and off she goes.

Recent service, new oil, plugs, battery etc. Made no difference. Even tried some 20 pitch props (instead of the 24s fitted); again no difference.

I have a copy of the boat manual here in UK and it quotes Serial No: OM064990 and Transom No: OM248949

thanks again, I wonder what parts the Spanish guy has ordered?. All very frustrating as I bought the boat over a year ago and have trying since to get her right.


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You do indeed have a 5.0L EFI (throttle body injection) with the Thunderbolt ignition. From your description, it sounds like your EFI system believes everything is okay, or else an audio alarm would sound.

Believe your issue is mechanical in nature. 20" pitch props should have allowed the boat to leap up on plane with a 2.20 gear ratio.

Is there a shield in place over the fuel filter? Item # 10 in the link below. Sounds like you're experiencing vapour lock, which could mean a fuel restriction.


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Thanks Shep (is that your real name?)

Not sure about the shield over the fuel filter, I will ask my buddy there to take a look.

What is the relevance of this, do we need to take apart and clean out?

Would this cause my symptoms and engine not starting when hot. Plus safety mode on revs or whatever it's called?

Just wondering now what the mechanic has ordered in terms of sensors, perhaps I am being wound up?

It's late here now so signing off but thanks again,


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Hi Nick,

There is a plastic shroud that goes around the spin-on fuel filter; it's job is to help keep as much engine compartment heat away from the fuel in the fuel filter as possible. In my area, we have a temperate climate, thus a lot of techs remove them from a boat for easier future servicing as we don't really run into vapour lock issues. (I don't subscribe to the practice of removing parts from people's boats unless required)



NOTE: the engine compartment is hottest roughly an hour after the engine was last run. Hot water in the manifolds and block can no longer be replaced with cooler water as the engine is no longer running and pushing water through itself. I personally have not seen true vapour lock in our area - only at service school by inducing too much vacuum.

Your RPM range at wide open throttle is 4400-4800. Seeing the problem is mechanical in nature, you may need to have a compression test done once the engine is warm. Another test I highly recommend is pulling each spark plug wire off one at a time to see if the engine stumbles at all. You could be down a cylinder.

At idle, if the engine is down a cylinder, the ECM tells the other 7 cylinders to simply work harder. In the marine environment, 7 cylinders usually results in 4000 RPM at WOT for a small block V8. The amount of raw fuel that marine engines can pour into the cylinders is simply staggering vs. that same engine in say a 1997 North American 1/2 ton truck running essentially the same engine. You don't want to have a cylinder get washed out, as this will require having the engine rebuilt, or replaced.

Lastly, if the worst should happen, and you need a new longblock for any reason, have a a 5.7L longblock of the same era installed, and simply get your ECM reflashed - everything else will bolt right on. Better fuel economy, and superior performance vs. the 305 cid.

I wish you nothing but success. I honestly don't know the problem with your boat, just trying to supply you with some possibilities. Best approach is to start with the basics; fuel, compression, spark.


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