1987 Mercury 150- Stator??

[coastalrichard]

Hi Folks:

I've rummaged through the threads for help with my issues and can't seem to find it. We're talking about a 1986/7 Mercury 150 (SN 933516). Here's the lowdown and some background:

Just got it back from the shop where it received a rebuilt (entire) lower unit, rebuilt carbs and fuel pump, and a poppet kit (OUCH!).

Prior to sending to the shop I had replaced t-stats, water pump/impeller to alleviate a hot running condition. Engine started well, idled OK (had trouble with cutting out while trying to load on the trailer - which is why I elected a carb/fuel pump rebuild) and ran very well (until the gear case failed).

On my first sea trial I have no trouble with cranking or idling. The shifter is smooth, tell-tale is strong and temp appears normal (although at a slightly higher idle temp than that associated with the previous lower unit).

The problem comes when I attempt to plane off. When advancing the throttle to WOT, the motor does not develop enough RPM's to get on plane and the temp gauge goes nuts (pegs to HOT!). When I back down to idle, the temp recedes again to it's slightly elevated level.

BTW, compression is 120-122 all six, battery is fully charged, ALL fuel lines, filters, water separater, bulbs are newly replaced, new fuel


Any comments?

 

[sschefer]

Re: 1987 Mercury 150- Stator??

I'm not totally familiar with your engine so this may not apply.

If you have the 16amp red stator then you should also have a voltage regulator along with with a rectifier. On mine the regulator was stuffed in behind the oil tank. At low RPM's the voltage from the stator is probably close to normal but as you increase RPM's it rises and at some point will be high enough to make the gauges read wrong. Most of the gauges work using a balance between voltage and resistance. If either one is out of specs for the guage it will read wrong. Since the resistance provided by the sender in the block likely isn't changing beyond specs then the voltage might be and this is what is pegging the gauge.

 

[Chris1956]

Re: 1987 Mercury 150- Stator??

Rich, You need to find out if you have an overheat condition. Put you hand on the block and rev her up. See if both sides are warm or hot. if it is overheating, you need to fix that.

Take a spark test to assure it is running on all six. Ohm out the stator if you lose spark above idle.

 

[coastalrichard]

Re: 1987 Mercury 150- Stator??

Thanks to both of you!

Chris, I don't have alot of fancy diagnostic temperature wizards, so I (re)calibrated my meat thermometer (I cater for a living...) and, once the t-stats opened, it read a consistant 140 at the tell-tale throughout a nominal range of RPMS. Water flowed from the prop and the tell-tale was strong (2-3 ft). The t-stats are recommended replacements (143).

Master Chief, you're suggesting then, my problem is the voltage regulator?

 

[sschefer]

Re: 1987 Mercury 150- Stator??

Thanks to both of you!

Chris, I don't have alot of fancy diagnostic temperature wizards, so I (re)calibrated my meat thermometer (I cater for a living...) and, once the t-stats opened, it read a consistant 140 at the tell-tale throughout a nominal range of RPMS. Water flowed from the prop and the tell-tale was strong (2-3 ft). The t-stats are recommended replacements (143).

Master Chief, you're suggesting then, my problem is the voltage regulator?

It won't hurt to check it. Since I don't know your engine that well, I don't know if your regulator just regulates voltage to the switch box or if it regulates both switch box and battery voltage. Do you have a voltage gauge on the boat? If you're showing more than 14.5 volts when running then you might have a problem. I

 

[coastalrichard]

Re: 1987 Mercury 150- Stator??

Master Chief

I have the 16 amp system. The regulator/rectifier is located on the starboard cylinder bank. It is fed by a red coming into it which then continues to the switch box. I also see a red and a tan wire leading from the regulator/retifier to another smaller box located at the top of the motor behind the flywheel(??).

I have a battery voltage gauge that reads slightly above 12v while running and it does not appear to vary with the RPMs.

I'm not a great electrical wizard, but I guess I need a volt meter and another set of hands to determine if the voltage regulator is working properly?

 

[CharlieB]

Re: 1987 Mercury 150- Stator??

IF, and you notice that I used caps, IF the stator is weak and fails to produce the required voltage, then engine RPM is limited UNDER LOAD, but will still be able to rev freely in Neutral.

Because the Stator is a spendy item you really want to be SURE that you need it before spending a chunk of money on one.

Since you want a volt meter, spend a few more $ and get a DVA Meter. This is THE tool needed to prove any ignition part good/bad.

Use the well spelled out step by step directions in the (FREE) Ignition Troubleshooting Guide found thru the link at

www.rapair.com

You do NOT have to be a Rocket Scientist to do this!

 

[coastalrichard]

Re: 1987 Mercury 150- Stator??

Good Morning All!

Well a friend lent me his DVM and I checked the rectifier according to a procedure found on this forum. It checks out OK.

CharlieB, thanks for your information, I will take your suggestion. And, if I understand your IF, then that may explain why I can't get enough RPMs to achieve plane. However, since the rectifier tests OK and the water temp at the tell-tale is a consistant 140, why would my temp gauge be pegging when I throttle up?

A big thanks to all for your patience!!

 

[coastalrichard]

Re: 1987 Mercury 150- Stator??

I'm still wondering why the temp gauge would spike to HOT when the water temp at the telltale is OK?

Also, I checked resistance on the two yellow wires from the stator and got a reading that fluctuated between 0.9 and 1.0.

I'm reluctant to put the motor in the water and check for dropping cylinders (under load) since I don't have a clear understanding of why the temp gauge is acting up.

HHHEEELLLPPP!!!

 

[j_martin]

Re: 1987 Mercury 150- Stator??

I'm still wondering why the temp gauge would spike to HOT when the water temp at the telltale is OK?

Also, I checked resistance on the two yellow wires from the stator and got a reading that fluctuated between 0.9 and 1.0.

I'm reluctant to put the motor in the water and check for dropping cylinders (under load) since I don't have a clear understanding of why the temp gauge is acting up.

HHHEEELLLPPP!!!

What will make the temp gauge spike like that is one of 3 things.

1. A bubble of steam develops in the block because cooling water is not sufficient for the load. The tell-tale will sputter and be hot under those conditions.

2. A bubble of exhaust develops in the block because of a gasket failure. The tell-tale will sputter, and often be visibly smokey.

3. The engine is running a combination of overloaded (wrong prop) and maybe lean. The tell-tale will be strong under those conditions.

Normally, misfiring won't overheat the engine. There is less fire within the engine when it misfires of course.

If, when the gauge is spiking hot, the tell-tale is strong and at 140 degrees or so, then you have plugged water passages in the head that has the temp sensor on it. If you put your hand on the head in question and it sticks, you found the problem. If a hack mechanic used sealer on a head gasket, that could easily happen. It will eventually be fatal if not corrected.

Water born debris can also plug various passages in the engine. I once sawed a rotten log in half with my boat. I barely felt the hit. Temp pegged and the overheat alarm went off. Took me a couple of hours, and head gaskets and exhaust pan gaskets to clean all the toothpicks out of it.

hope it helps
John

 

[sschefer]

Re: 1987 Mercury 150- Stator??

I don't know why I didn't think of this earlier. You probably have the wrong temp sensor in it or it's faulty. I'm thinking about what might happen if it's too long and making metal to metal contact some how.
Of course this then trips the overtemp alarm and reduces your max RPM to 2000.

 

[coastalrichard]

Re: 1987 Mercury 150- Stator??

Please let me recap as I'm now TOTALLY CONFUSED (I know absolutely nothing about electrical matters)!

The motor cranks, starts and idles like a champ on muffs. Water exiting telltale is 140 and stream is strong. Temp gauge reads in the "normal" range(not digital). Tach works OK sometimes and not at all other times.

Rectifier check is OK. Stator resistance is reading 0.9 to 1.0 when touched to both yellow wires (when disconnected from rectifier).

The problem is in the water when I try to take off! Give it throttle and it won't develop enough rpm's to get on plane and the temp gauge pegs HOT.

What is my problem (other than tremendous ignorance)?

 

[cell]

Re: 1987 Mercury 150- Stator??

Sounds like you have a blockage.The temp will peg under throttle if theres no water hitting the temp sensor.Thus its getting hot and probably causing you not to hit wot rpm.

 

[sschefer]

Re: 1987 Mercury 150- Stator??

Well, ignorance is not you problem, if it were, you wouldn't be here looking for answers.

That recap makes a lot of sense now. I show your sender as part number 97465. I don't think there is anything wrong with the voltage. Let's take that out of the equation for now.

What is throwing us is that you are being limited on RPM's and that normally will happen if you're low on oil or have an overheat condition. Since the temp gauge is pegging I think this is the best circuit to suspect for now.

Since the gauge is pegging, I'm going to suggest that you disconnect the lead to the gauge at the engine harness, if you can. I think it is one of the bullet connector wires that is not part of the main connector. If you can't then you need to trace back the main harness from the ignition to the engine and look for any cuts or abrasions. Look closely around the throttle/shift control and cables.

Here's what I'm thinking - Some how, when you accelerate and move the control it is causing a short in the temp sensor wiring to the gauge. This is setting off the temp alarm module and you're being limited to 2000 rpm max. This might sound a little goofy but I'm beginning to think it's something really simple like this.

 

[j_martin]

Re: 1987 Mercury 150- Stator??

Well, ignorance is not you problem, if it were, you wouldn't be here looking for answers.

That recap makes a lot of sense now. I show your sender as part number 97465. I don't think there is anything wrong with the voltage. Let's take that out of the equation for now.

What is throwing us is that you are being limited on RPM's and that normally will happen if you're low on oil or have an overheat condition. Since the temp gauge is pegging I think this is the best circuit to suspect for now.

Since the gauge is pegging, I'm going to suggest that you disconnect the lead to the gauge at the engine harness, if you can. I think it is one of the bullet connector wires that is not part of the main connector. If you can't then you need to trace back the main harness from the ignition to the engine and look for any cuts or abrasions. Look closely around the throttle/shift control and cables.

Here's what I'm thinking - Some how, when you accelerate and move the control it is causing a short in the temp sensor wiring to the gauge. This is setting off the temp alarm module and you're being limited to 2000 rpm max. This might sound a little goofy but I'm beginning to think it's something really simple like this.

I thought we were talking about a 1987 motor, which would be a carb motor. Correct me if I'm wrong. Carb motors don't have any electrical limit to rpm except at WOT by the so called advance module.

The combination of overheat and flameout makes me want to suspect that the wrong carbs, or carbs set up wrong are causing an all cylinder lean condition above idle. That might create this set of symptoms. Read item 3 on my last post.

hope it helps
John

 

[j_martin]

Re: 1987 Mercury 150- Stator??

Master Chief

I have the 16 amp system. The regulator/rectifier is located on the starboard cylinder bank. It is fed by a red coming into it which then continues to the switch box. I also see a red and a tan wire leading from the regulator/retifier to another smaller box located at the top of the motor behind the flywheel(??).

I have a battery voltage gauge that reads slightly above 12v while running and it does not appear to vary with the RPMs.

I'm not a great electrical wizard, but I guess I need a volt meter and another set of hands to determine if the voltage regulator is working properly?

The item on the switchbox mounting plate is a rectifier if stock. If it's replaced with a regulator, the shunt regulator on top of the motor should be removed.

NOTHING in the charging circuit should go to the switchbox. You said there's a red wire to the switchbox. Should not be. The systems are totally isolated from each other all the time. The switchbox's do not have any battery going to them.

The rectifier should have two yellow wires from the stator going to it supplying AC. A red wire going to the battery, usually at the solenoid end of the battery cable. A grey wire going to the tachometer connected to either yellow wire, and if a shunt regulator is connected, a yellow and a red wire going to that item on top of the engine.

Check the wiring and compare it to an engine wiring diagram by color code. If it isn't correct, make it right before you continue.

hope it helps
John

 

[coastalrichard]

Re: 1987 Mercury 150- Stator??

WOW - You guys are fantastic! Let me provide some more input and clarification.

First, Cell, Schefer and CharlieB: I was incorrect about the wiring I mentioned earlier. From the stator, I have a (large) blue and a (large) red going to the port switch and a (large)blue/white stripe and (large) red/white stripe going to the starboard switch. Two yellow wires lead from the stator to the rectifier, one on each "side" post (I will refer to those posts as "side" and the remaining post as "middle" - I'm sure someone will let me know the proper references!). The red is coming from a large bundle of wires leading from the boat into the motor and leads to the "middle" post. From the "middle" post, a red wire, along with another white (could be white, could be tan - hard to tell) connected to the left "side" post go together to a box located on the top of the powerhead, behind the flywheel (not anywhere near the switches), and terminate (Is this the regulator?). I also see a gray wire (tach?) leading from that same large bundle to the left "side" post. Only the large (red, red/white stripe, blue, blue/whitestripe) wires go to the switches.

I disconnected the tan/blue stripe wire from the temp sensor (located just below the plug on the #2 cylinder) and removed the sensor to find the "Leaning Tower of Pisa". The sensor appears to have been "compressed", as if the piston has hit it! I will, of course, replace the sensor, but that condition itself raises the question: Why do these symptoms with the temp arise now and not previously? No work was performed on the powerhead (ie pistons). Yes, the sensor is slightly bent, but it's obviously been that way for a while!

Would a faulty temp sensor cause my issues?

John, I noted your earlier remarks about the water circulation and initially wanted to discount blockage as a potential cause of the current temp issue in view of the fact that I did not encounter it after I replaced the water pump/impeller on the old lower unit. I continued to discount blockage as a culprit since I now have an entirely rebuilt lower unit (I know, I know, there are hacks out there!). At any rate, I will be pulling the port water jacket for inspection/cleaning while I'm working on the sensor replacement. Never done that; anything extraordinary about that? I notice the many lugs have different markings on the heads. Should I label each lug as I remove it to make sure they go back in the same location? I also note your #3 comment and sure hope that the (just completed) carb rebuild is not a contributory factor, as well.

Geez guys, I never knew outboards could be so much "fun"!

 

[j_martin]

Re: 1987 Mercury 150- Stator??

The little box on top is a shunt regulator.

Wiring seems right.

Temp senders go bad all the time. Not to expensive, try replaceing it. Could be the whole problem.

As I suspected, you may have two seperate problems. The bad temp sender can not possibly limit engine speed. Only fuel and spark can. Forget about opening up the cooling system for now.

If when it balks, you squeeze the primer bulb and it picks up, you have a fuel delivery problem.

Stator output to the switchboxes, especially the high side, should be checked with a DVA. A rough check of the stator can be done with an ohmmeter. Neg results here is definitive, but positive isn't. An ohmmeter cannot detect a shorted turn which will kill the output. A bad high speed winding will drop 3 cylinders at about 1500 - 2000 rpm.

If spark is good, and fuel is being delivered, you have a carburetion problem.\

Have fun.
John

 

[coastalrichard]

Re: 1987 Mercury 150- Stator??

Hey John:

Thanks for keeping watch on this thread - I can't tell you how much help all of you are!

And, I know I admitted to ignorance earlier; I was wrong - I'm just stupid! Once I removed the port side water jacket it was instantly apparent that no piston has ever crunched my water temp sensor!

BTW John, no blockage in the cooling jacket, so I guess i'm back to square one.

I also cranked the motor and let it idle to temp; removed the port sending wire and the gauge went dead. Not that sensor anyway!

Why is there another sensor on the starboard side leading to a rubber-insulated post and then on to the oil injector warning module? That makes no sense to me but, remember, I am stupid!

(I can prepare, cook and serve a five-course meal to 300 guests in my sleep! Why can I not get one outboard motor to work?) UGGHH!

While hunting the replacement sensors and water jacket gaskets I learned (ahem, was told!) that this motor features a "limp mode" that is triggered by excessive temp to prevent major damage from overheating. Is this true and, if so, is it the starboard water temp sensor (mentioned above) that initiates the signal for "limp mode"?

I did quite alot of research on the mechanic that I used for the carb and fuel pump rebuild - his credentials are tremendous and ALL of the references gave him accolades (he supplied some references and I personally knew the others). He has been suggesting stator since day one but, as CharlieB pointed out in an earlier post, that's a pricey one. So are the trigger assy, switches, coils/wires, etc (I'm looking at about $1K to just replace all of them - and still no "warm and fuzzy" feeling that any of it will correct my issue.

When I acquired the boat several months ago, the first thing I did was drain and clean the fuel tank, installed new pickup and anti-siphon barb, replaced ALL fuel lines with ethanol-rated ones, installed a new fuel/water separator, new primer bumb (and line) and new connector at the motor. I just had the carbs and fuel pump rebuilt and a (newly) rebuilt lower unit. I'm running the same prop that came on the motor. The fuel is fresh and contains NO ETHANOL.

I just don't understand how this can be fuel related. Carb issue, maybe, but until I can get some rpms under load, how will I know? Doesn't the finetuning process need to be done under an actual load?

What is causing this (darn!) water temp issue

 

[coastalrichard]

Re: 1987 Mercury 150- Stator??

bump