Low Voltage at RPM?

[twerth]

I've got a semi-intermittent problem that I hope the group can help me with. 1991 SeaRay BR17 with a 3.0 Mercruiser. It runs great for the first 10-15 minutes, but once it's good and warmed up it starts to bog and generally run poorly at higher RPMs. When it starts to run bad I've notice that the voltage meter also shows lower than normal voltage. It normally runs at just below 14V, but it drops to ~12V or less when the poor performance shows up. I haven't been able to correlate it to a switched electrical draw (bilge pump, blower, trim, stereo), but it does seem to be RPM related. It only occurs when the engine (engine compartment) is warm and I'm running over about half throttle. If I go back to idle, it runs fine and the voltage jumps back up to where it should be.

My first thought was voltage regulator, but I replaced that and no improvement. I've also made sure all my connections at the battery, alternator and volt meter are clean and shiny. Before I spend money on a new alternator, is there something else I should look at?

TIA

 

[ESGWheel]

If I may, suggest your priority is the bogging and running poorly at higher RPM. While you seemingly have a concurrent issue with voltage regulation / output that may be impacting the poor running I am struggling to connect those dots unless there is a severe short somewhere which I suspect would have shown itself already.

Can you provide a little more history on the boat, type of maintenance performed before the issue, along with what RPM range is it bogging down. Also given its age, I am assuming a points / condenser type of ignition. Is that correct? Thanks.

 

[Bt Doctur]

losing voltage at rpm could indicate a winding opening up at high rpm inside the alternator

 

[twerth]

If I may, suggest your priority is the bogging and running poorly at higher RPM. While you seemingly have a concurrent issue with voltage regulation / output that may be impacting the poor running I am struggling to connect those dots unless there is a severe short somewhere which I suspect would have shown itself already.

Can you provide a little more history on the boat, type of maintenance performed before the issue, along with what RPM range is it bogging down. Also given its age, I am assuming a points / condenser type of ignition. Is that correct? Thanks.

Thanks for the quick replies!

History: This is my second full summer with this boat. It's a 1991, but it has a 2001 engine. Presumably, someone froze it at some point. It has electronic ignition.

It's run like this the whole time I've owned it. It has always run great for the first 10-15 minutes, so I initially blamed it on temperature in the engine compartment. I'm evidently not very observant because I didn't notice the correlation between bogging and voltage until recently, but I think that's always been the case.

Last summer I fired the parts cannon at it and replaced plugs, wires, distributor cap, ignition coil, ECU and pick-up coil. I also cleaned and regasketed the carb and replaced the manifold gasket. Last time out last year after I'd replaced the ECU and pick-up coil it seemed to run pretty well.

I thought I had it licked, but this summer it was back to its old ways. This year I noticed I was getting water in my fuel, so I thought that might be the culprit. I drained the tank, added a water separator and dumped it and my carb after each outing. I continued to find water, so I took it into a shop. They also drained the tank and rerouted the fuel tank vent line. That seems to have solved the water in the fuel problem. They also made sure the carb was adjusted correctly and checked the timing. They gave it a clean bill of health.

But it still runs like $#!@%, and now I've noticed the voltage issue. My battery is fairly new and load tests ok. If it was simply the alternator dropping out, battery voltage should keep me at or slightly above 12V for awhile, correct? I've seen voltage drop to 10 or less, and the engine will die when that happens. That makes me think something is shorting, but as you mentioned, that should have exposed itself by now (blown fuse, melted wire, fried component). Could an open winding like Bt Doctor suggested cause that?

I've probably got one more weekend this year before it gets stored, and I'd like to have it solved by then. Thanks for the input.

 

[cyclops222]

Should be the SLIP RINGS on a alternator / generator.

 

[ESGWheel]

Thanks for the extensive background. But only is causing me to ask more questions

I am surprised at the need to move the fuel tank vent to preclude water. It just seems odd to me that the original boat designers would place it in such a position as to be able to ingest water. Thinking out loud I am wondering if the boat is waterlogged and causing it to sit lower than normal….

Your parts cannon contained a lot of regular maintenance items so do not beat yourself up too much on that.

You state “cleaned and regasketed the carb”. Does that mean you rebuilt it? Rebuild = complete teardown and internal cleaning and ensuring every passage is free and clear of all debris and put back together with a rebuild kit.

I read that this new to you boat has never run properly after warming up. That it has always bogged down after 10 or 15 mins. Is this correct? Prior to it bogging down can you get to WOT RPM, like 4500 or so and it sounds & runs great?

If the voltage does drop to 10 or less, it makes sense it dies > the electronics in the ign cannot handle that.

And from my knowledge I agree a fully charged and healthy battery would carry you for a bit (unless a short)

My suggestions are to start with some basics:

• Given a history of water in fuel, start by dumping your fuel filter (or pump gas) into a glass jar. It should be clear.
• Conduct a compression test. Best if warm. And have the ign disabled and throttle wide open.
• Provide serail no. of engine, answers to the questions above and we’ll go from there.

Here is what I do know: with your help and follow thru on the suggestions this forum will get you on the water with a great running boat. And I looked at some pics and u tube of the ’91 SeaRay 170 > it is a sweet ride, so congrats on your purchase!

 

[twerth]

Thanks ESG. Lots of good stuff here, so I've inserted my responses in blue font below.

I am surprised at the need to move the fuel tank vent to preclude water. It just seems odd to me that the original boat designers would place it in such a position as to be able to ingest water. Thinking out loud I am wondering if the boat is waterlogged and causing it to sit lower than normal…. The vent inlet (outlet?) is below the rub rail on my boat, and the hose has a loop in it that goes higher than the inlet. The guys at the shop thought splashing in rough water or when crossing wakes could force water into the hose and on to the tank. They made the loop bigger and higher, and so far it seems to be helping.

Your parts cannon contained a lot of regular maintenance items so do not beat yourself up too much on that. One thing I forgot to mention, I also replaced the fuel pump. I had intended to just disassemble, clean and check for cracked or damaged components. It was so gummed up I'm surprised it worked at all. But that didn't improve the issue.

You state “cleaned and regasketed the carb”. Does that mean you rebuilt it? Rebuild = complete teardown and internal cleaning and ensuring every passage is free and clear of all debris and put back together with a rebuild kit. Yes, complete disassembly, blew carb cleaner and air through all the passages and put it back together with a new kit.

I read that this new to you boat has never run properly after warming up. That it has always bogged down after 10 or 15 mins. Is this correct? Prior to it bogging down can you get to WOT RPM, like 4500 or so and it sounds & runs great? Correct on both counts. When it's running properly it'll wind out to ~4500 rpm and I can get ~35 mph on smooth water.

If the voltage does drop to 10 or less, it makes sense it dies > the electronics in the ign cannot handle that.

And from my knowledge I agree a fully charged and healthy battery would carry you for a bit (unless a short)

My suggestions are to start with some basics:

• Given a history of water in fuel, start by dumping your fuel filter (or pump gas) into a glass jar. It should be clear. Starting about halfway through this summer, I've been dumping the separator, the filter bowl on the pump and the carb after every outing. Since the shop modified the vent line, I haven't found any water.
• Conduct a compression test. Best if warm. And have the ign disabled and throttle wide open. 160 +/-3 on all cylinders.
• Provide serail no. of engine, answers to the questions above and we’ll go from there. As I'd mentioned, the engine had been replaced in about 2001. The new engine doesn't have any stampings where they're supposed to be. Maybe it's a warranty engine?

Here is what I do know: with your help and follow thru on the suggestions this forum will get you on the water with a great running boat. And I looked at some pics and u tube of the ’91 SeaRay 170 > it is a sweet ride, so congrats on your purchase!

Thanks again!

 

[ESGWheel]

Ok, so no water in fuel > good news. And carb rebuilt. And compression good.

Given the 2 symptoms of electrical and poor performance I am going to suggest a couple of directions, starting with the poor performance. Assuming your carb has an electric choke (per the diagrams I looked at it does) need to make sure its working properly. Others may know better, but I think with key ‘On’ the choke gets power and thus will open over a short period of time. One test can be to pull off the flame arrestor on a cold engine, turn key to “On” and check to see if +12V on hot wire (purple?) and that the ground wire is a good ground. Assuming have +12V watch the choke and see if it pulls off over about 5 min or less.

If all that is good, and you can get out on the water again, run around till warm and have it bog out on you and (assuming in a safe spot), kill the engine right away and pull a spark plug. If looks black somehow it is getting too rich, and this is the probable cause of the bog.

For the electrical, my suggestion is a new alt. Make sure it’s a marine alt.

And please be open to other suggestions / ideas from the forum as i may be all wet

 

[twerth]

Thanks again ESG.
I've checked the choke (electric as you mentioned), and it opens as it should and stays open. That was one of the first things I thought of. Also, pretty easy to test.

I think I'll bite the bullet and buy a new alternator, but one thing to bounce off you before I pull the trigger. Is it possible the battery has an internal short that only shows up once it's warm or after it's been bounced around a bit?