175 BlackMax idles good, but lost 800RPM on top end

[MarshMan73]

I have had a time with this motor. It is a 1986, 175HP, V6. Found a few water drops on #3 cylinder and replaced cracked, rusting head gasket. Compression was down 10psi in that cylinder, now all are at 105. Took it out yesterday and ran it but would idle rough and was low on top end. Only got 5000RPM at WOT. Took it back home to flush it out and wouldn't start. Ohmmed out all ignition componets possible and found stator had open in blue wire for front switchbox.

Got a known good stator (THANK YOU DONNIE!) and put it on it today and disconnected the 3 wire idle stabilizer module. Started right away and idled beautiful on the hose. Took to the launch and cranked instantly. Idled very good. Went out and still no top end. Even had my good buddy pump the primer buld while running and no change. Sometimes it was lugging a bit to get on plane, sometimes not. Still would not get over 5000RPM. It used to go 5800-6000. It does not sound like it's missing. Just for giggles, I hooked back up the idle stabilizer and it ran like crap at idle and would stall out. So obviously it is shot.

Took it back off and brought it home and it cranked right away on the hose. What am I missing here? All carbs are feeding, compression is OK, and the lower unit feels good. What else can I check? I really want to go out this weekend with my buddies, but not in a motor I don't trust.

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

The module you took off might have had an advance function to it. Do a link n sync, especially checking your WOT timing. I'll bet a dollar to a doughnut that it's about 19 degrees. (advance module would take it to 23 at 5000 rpm.) Fix is to set WOT timing to 23 degrees. Unless you do a lot of high torque mush driving, it won't hurt you.

I would check the plugs to be sure you aren't running one cylinder lean. That will hurt you.

hope it helps
John

 

[MarshMan73]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Thank you JMartin. You are confirming something I suspected. My book kept calling it idle stabilizer, so figured it only affected idle. There was also another box mounted up there next to it with 2 posts and much smaller and rusted out. Nothing was connected to it. But it sounds like something ignition related to me too. It idles Ok so far just lost that top end.
Does one turn in or out increase the timing 1 degree?
Advancing means turning the trigger base counterclockwise right?
I don't have a timing light yet so I will have to just have to wing it by sound and performance until then. I do know which one it is just don't won't to turn it too much and blow it!
My expertise is refrigeration, not boat mechanics, so I have only limited knowledge of the functions of the modules and various functions in the switchboxes themselves. The books I have don't seem to do a good job explaining the actual workings or circuitry in one single book either, just how to ohm and replace usually.
Also does the alarm module send signals to the switchboxes for timing? Don't want to get it running good and then have the alarm module kick in the advance another 9 degrees and blow up.
Thanks JMartin.

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Thank you JMartin. You are confirming something I suspected. My book kept calling it idle stabilizer, so figured it only affected idle. There was also another box mounted up there next to it with 2 posts and much smaller and rusted out. Nothing was connected to it. But it sounds like something ignition related to me too. It idles Ok so far just lost that top end.
Does one turn in or out increase the timing 1 degree?
Advancing means turning the trigger base counterclockwise right?
I don't have a timing light yet so I will have to just have to wing it by sound and performance until then. I do know which one it is just don't won't to turn it too much and blow it!
My expertise is refrigeration, not boat mechanics, so I have only limited knowledge of the functions of the modules and various functions in the switchboxes themselves. The books I have don't seem to do a good job explaining the actual workings or circuitry in one single book either, just how to ohm and replace usually.
Also does the alarm module send signals to the switchboxes for timing? Don't want to get it running good and then have the alarm module kick in the advance another 9 degrees and blow up.
Thanks JMartin.

The little box is a shunt voltage regulator, basically useless. You must have a 16 amp system with a rectifier mounted near the switchboxes.

Do not guess on the timing. You will either suffer poor performance or grenade your power head. This is high performance, high HP density stuff. Yer talking controlling about a 2 million BTUH fire in a 2.4 CU ft motor. That's enough energy to heat 20 average houses in a Minnesota winter.

It is very important you read your plugs to be sure you're not leaning out 1 or 2 cylinders.

The oil alert (alarm) module samples the coil signal from one cylinder and compares it to rotational signals from a sending unit in the VRO. If both exist, or both are missing, it is assumed good. If one is missing, it alarms. It does not affect the ignition in any way with the caveat that it is very remotely possible to kill one cylinder. A third signal, from the oil tank, will alarm if it is there (grounded) and the engine is running.

hope it helps
John

 

[sschefer]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Yup John, dead hole. Actually it's somewhat mathematical.

 

[MarshMan73]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Ok, I knew I was going to have to get a light and a dial indicator sooner or later, looks like sooner. But when I do get it, to advance the timing, I turn that screw at the top out and that will make the base turn more ccw at WOT?
My plugs don't look lean at all, in fact they are almost wet with fuel and getting darker everytime I look at them. Lean would look like clean and white, right?
John, you have been a wealth of information on this old motor. Please let me pick your brain some more as I learn how this motor works.
How does it remotely kill a cylinder? I did see a green wire going from the switchbox terminal to the alarm module it also went to #3 coil. Does it ground this wire and kill the cylinder when there is an alarm? So to bypass alarm module completely for testing I just remove the green wire?
My alarm did not work when I got the boat. No beep when turning On. Which wire is the alarm signal wire? I do not see one in my schematic. I want to find it and connect a light or horn to it at the module since I think the one in the throttle may be bad. As far as the temp sensor input it is just a normally open switch?
I want to get the alarm module back working and be able to use it for monitoring the VRO, time it, and see what happens. If it malfunctions, its all going where the idle stabilizer went and premix here I come. Probably for the best anyway.

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

What I meant is that it is very unlikely that it would kill a cylinder. If the green wire should short to ground, that is the only way it would. It isn't supposed to do that, though.

There should be a screw terminal block above the switchboxes. One screw has a wire from the overtemp sensor , and a wire from the oil alert on it. If you ground that screw, it is supposed to sound the buzzer. That's the first test.

There's a purple wire for twelve volts to the oil alert. On some engines it goes under a screw near the other one. On some, it is a bullet connector. Purple in a Murkery is key switched power.

If the oil alert is getting power, and the alarm circuit works, it should beep a couple of times on power on. Then when it's running, if you disconnect the oil pump sensor, it should sound. If you short the tank sensor, it should sound. If you disconnect the green wire, it should sound. Otherwise, except for the Power on beeps, it should be quiet.

The alarm wire is tan with a blue tracer. It goes to the controls through pin #3 of the cannon plug. There should be a copy of it coming out of the controls with the dashboard harness.

hope it helps
John

 

[MarshMan73]

Re: 175 BlackMax idles good, but lost 800RPM on top end

So now that the idle stabilizer is gone, there is nothing else that will "bias" the switchboxes? It will operate like an old school carbuerated 2 stroke now? That's what I want. What was the purpose of that stupid black box anyway, just to give mechanics a headache trying to figure out what's wrong?
I called off my fishing trip today and instead of just winging the max advance screw in, I'm off to HarborFreight to get one of those digital calipers and a timing light to set this thing. I've read the procedure in the book for indexing the flywheel pointer. Boy that sure sounds like a complex ritual. Do I need to do a dance and make an offering to the Mercury god before I start too?
I've come too far with this old motor to give up now, so just maybe I'll have a little luck and this will bring it back from its current state of junk. It doesn't know how close it was to having the mounting bolts out and rammed in reverse so it could spend the night in Davey Jones locker.
John, thanks again for your help.

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

So now that the idle stabilizer is gone, there is nothing else that will "bias" the switchboxes? It will operate like an old school carbuerated 2 stroke now? That's what I want. What was the purpose of that stupid black box anyway, just to give mechanics a headache trying to figure out what's wrong?
I called off my fishing trip today and instead of just winging the max advance screw in, I'm off to HarborFreight to get one of those digital calipers and a timing light to set this thing. I've read the procedure in the book for indexing the flywheel pointer. Boy that sure sounds like a complex ritual. Do I need to do a dance and make an offering to the Mercury god before I start too?
I've come too far with this old motor to give up now, so just maybe I'll have a little luck and this will bring it back from its current state of junk. It doesn't know how close it was to having the mounting bolts out and rammed in reverse so it could spend the night in Davey Jones locker.
John, thanks again for your help.

Hope you have a dark place to check the timing. The harbor freight timing light probably isn't bright enough for daylight. (been there, done that)

I use a cheap digital caliper for a depth gauge. Made a mount for it out of a spark plug. Tis very accurate and easy. If I can track down pictures, I'll post them.

John

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Here it is
I gutted a spark plug and welded a tab to it to mount a cheap digital caliper. Works great.

Install the depth gauge. Turn engine manually past TDC and continue about 1/2 turn. Set caliper readout to zero. Push caliper in past .462, continue turning engine manually till indicator goes to .462. Check/set the timing marker on the flywheel cover.

hope it helps
John

 

[MarshMan73]

Re: 175 BlackMax idles good, but lost 800RPM on top end

I'll bet a dollar to a doughnut that it's about 19 degrees. (advance module would take it to 23 at 5000 rpm.) Fix is to set WOT timing to 23 degrees.

Well John you get a dollar or a donut. Your choice! I went through the elaborate procedure to set the timing pointer. First I bowed my head to the east and did the Mercury dance and gave an offering to the Mercury gods!

What I did find waswhen i removed the flywheel by taking out those 7 bolts and changing the stator, it moved one screw hole and I had to remove it again and set it back. When I did and set the digital caliper to .462, the pointer was dead on!
I checked the WOT timing by pushing the throttle lever full forward and making sure the stop was against the block, then I cranked it with all but #1 plug removed and the rest grounded and guess what? It was at 19degrees! I set it just shy of 24 degrees. This was set at cranking RPM per the book instructions. I let it idle for awhile and checked the RPM with my new Harbor Freight photo tachometer. It seems to idle best around 800-900RPM in gear on the hose. I can pull back on the timing arm and get it to go down to around 550 without dying. So I guess I'm good as far as that goes now.

So just 4-5 degrees of timing can cause all this trouble? It wasn't very much turning on that screw either. I see why you said I would grenade it if I tried to wing it without a light!

One final matter is that alarm module. I do not see a tan with blue tracer coming out of the alarm module. All I have is the brown, green, black, purple, and 3 wires with quick connects to the oil sensor. When I short the terminal on the starboard side terminal strip, no alarm. I guess the horn in the control is bad. There is a white wire from the boat harness going to that terminal where the temp sensor connects. Maybe that used to be tan colored?
Let me see if I understand this alarm circuit. 12volts goes to one side of the horn, then out of the horn to the tan/blue stripe wire to the engine. When the temp sensor or module grounds that point it completes the circuit and the horn goes off?

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Another convert to systematic troubleshooting. Another power head saved. Tis been a good day.

The link n sync procedure is intimidating at first, but it's really very logical, and no big thing when you get used to it.

Some Lubealerts have a tan/blue wire, some have a tan wire. All the sensor wires are various shades of blue and white. Best bet would be the brown wire is the output. Connect a light bulb or a voltmeter between it and 12 volts. Turn on the key. If the alarm module is good, it'll blink or move a few times.

The horn wire should show up in your dash wiring. Hook a rat shack sonalert between it and 12V purple, and yer alarm is good.

hope it helps
John

 

[MarshMan73]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Well more parts down to DaveyJones locker thanks to systematic approach. But I can rest assured they were bad. What is up with Mercury electronics? So far it's been idle stabilizer/advance box, stator, voltage shunt box, and now an alarm module. I do feel much better knowing I diagnosed everything like you said.
My motor is starting to get much cleaner looking now. I've always been a fan of less electronics in an outboard = less chance of things going wrong. The two switchboxes are enough in my opinion.
But anyway I could not find a tan or tan/blue wire under my dash so I guess I'll have to run another wire when I get a new alarm module. Until then previous owner ran a tan/blue stripe wire from the other temp sender and mounted a dash temp gauge that does work. The alarm horn must be bad as I am getting a backfeed 12V on the terminal strip that the alarm brown and the temp sender are connected to but when I ground it out I get a very very faint spark and the horn does not sound.
I'm tempted to leave it like this and use the oil blockoff plate kit and mix my gas 50:1, but I like the idea of the VRO and it still works. So I guess alarm module time and a horn. Can it be any 12volt buzzer or mini horn?

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Well more parts down to DaveyJones locker thanks to systematic approach. But I can rest assured they were bad. What is up with Mercury electronics? So far it's been idle stabilizer/advance box, stator, voltage shunt box, and now an alarm module. I do feel much better knowing I diagnosed everything like you said.
My motor is starting to get much cleaner looking now. I've always been a fan of less electronics in an outboard = less chance of things going wrong. The two switchboxes are enough in my opinion.
But anyway I could not find a tan or tan/blue wire under my dash so I guess I'll have to run another wire when I get a new alarm module. Until then previous owner ran a tan/blue stripe wire from the other temp sender and mounted a dash temp gauge that does work. The alarm horn must be bad as I am getting a backfeed 12V on the terminal strip that the alarm brown and the temp sender are connected to but when I ground it out I get a very very faint spark and the horn does not sound.
I'm tempted to leave it like this and use the oil blockoff plate kit and mix my gas 50:1, but I like the idea of the VRO and it still works. So I guess alarm module time and a horn. Can it be any 12volt buzzer or mini horn?

There's a small harness coming out of the controls. The alarm circuit should be there also. Sometimes they don't include it in the boat harness.

Any reasonable 12 V load will work. It could even be a small motor vibrating against your toes.

Put a meter on that terminal and see if the voltage bounces when you turn on the key. If it does, the oil alert is OK.

On pulling the oil pump, or replacing the oil alert, I'd first inspect the Nylon Drive Worm gear on the crank under the oil pump. If it's in good shape, you can keep the oiler. If it's in tough shape, yer better off to take the oiler off.

Any V6 oil alert module will work with a little splicing. Used is fine.

hope it helps
John

 

[MarshMan73]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Well just got back from sea trials. Had a pretty good chop today so took it easy 4000RPM until I got into calmer water. I did notice on throwing down the throttle first time coming out the launch it bogged a little then cleared out. Did not do that again for the rest of the day. Made several stops and restarts. Still did not ever get back up to 5800 RPM only got 5400 out of it now, but was much peppier. I set it just shy of 24 at cranking RPM. Maybe I need to go a little more 24 or 25? Or will it never see 5800 again without the module kicking in that little extra advance?
One other thing I noticed was this stator really puts out the voltage! It was putting out 16.5 volts after cruising at 5400 for a few minutes! This was with the battery switch accidently left on 1&2 with freshly charged batteries. I guess it was a good thing for my batteries that I left it on 1&2. You I should get the regulator/rectifier module or just leave battery switch on 1&2 while running?

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

Well just got back from sea trials. Had a pretty good chop today so took it easy 4000RPM until I got into calmer water. I did notice on throwing down the throttle first time coming out the launch it bogged a little then cleared out. Did not do that again for the rest of the day. Made several stops and restarts. Still did not ever get back up to 5800 RPM only got 5400 out of it now, but was much peppier. I set it just shy of 24 at cranking RPM. Maybe I need to go a little more 24 or 25? Or will it never see 5800 again without the module kicking in that little extra advance?
One other thing I noticed was this stator really puts out the voltage! It was putting out 16.5 volts after cruising at 5400 for a few minutes! This was with the battery switch accidently left on 1&2 with freshly charged batteries. I guess it was a good thing for my batteries that I left it on 1&2. You I should get the regulator/rectifier module or just leave battery switch on 1&2 while running?

I wouldn't advance the timing any more. In fact, I'd back it down to 23 degrees. It might be OK at 24 if you consistantly run 92 octane in it.

Warmer wetter air will significantly reduce your power output. It's probably normal. You always get the screamingest performance first go in the spring.

If yer prop isn't releived (holes in it to let a little exhaust get into the blades) it might bog on the hole shot. Don't worry too much about that. If it's boggy on a slow throttle advance, you'd set the throttle pickup a bit later in the timing ramp. I run a high five, which is releived. Hole shot is basically controlled mayhem.

Another thing is that yer blasting off at 24 degrees now, instead of 19. Backing it off a bit might help the hole shot. (and it might not)

Run it a WOT for a good 5 minutes, and suddenly shut it down somewhere you can safely come to a stop and pull the plugs. They should be burning a nice shopping bag brown. If one's too clean, look for a plugged main jet, or float adjustment leaning it out in that hole.

If one's black and wet as heck, yer dropping a cylinder. Probably bad coil or wire or plug.

Yer batteries might be a little low on water, or old. They should hold the voltage down a bit better than that. You can retrofit a 20 amp regulator with no problem. Not a bad idea.

Sounds like yer closing in on it.

John

 

[MarshMan73]

Re: 175 BlackMax idles good, but lost 800RPM on top end

I did not take that weather factor into consideration. Today the water temp here was close to 89 degress and air temp close to 90 with almost 90% humidity. So that could be it? I did not hear any pinging or noises coming from it. I usually feed my beast midgrade non-ethanol fuel. There is only 1 station in town advertising no-ethanol.
The prop is relieved as you said. I don't know how big it is, just that it's a 3 blade stainless. It may be a little tall because it drops about 200-300 RPM when putting it in gear.
The bog only happened once. That was after a very clean, flawless, first crank start. I let it idle about a minute or two as I trolled out of the harbor. Then I nailed it and it bogged for a few seconds then shot off. All other hammer down blast offs were great. Coming back down on power was pretty smooth too.
I also noticed my temp gauge is running warmer now. It had been running colder than normal when it wouldn't go above 5000. Now it has moved up to where it used to run. That's got to be a good thing.
My batteries are in top shape, almost a year old, marine starting batteries. I keep them on a 2 amp tender several days, on several days off. So they are always fresh. I'm looking for a regulator now and an oil module.Would be nice to get an idle/advance box too, but shame they don't make it anymore. I can see how it could help me in an aging motor with only 105 compression at idle with a big prop. And would be nice to have that extra couple of degrees at WOT. But it will probably run a lot longer just like it is.

 

[j_martin]

Re: 175 BlackMax idles good, but lost 800RPM on top end

The idle stabilizer only compensates for poor tune. You don't need it. If the module should short out to ground, it'll advance your timing about 15 degrees and almost instantly grenade your power head. I think that's why they don't sell them any more.

You might have had a slug of oily fuel in the carbs or carboned up a coupla plugs on the first blast off. Don't worry about it. These things don't really like to idle a long time. They have a very strong ignition system and will usually clean out in a few seconds when you can it.

I'm serious about backing it down to 23 degrees. Peak timing is an engine determined thing. Some engines might want 35 degrees, and inline 6 merc better be below 20. 23 is about where yours wants to be. 24 is pushing it.

The only time the advance part of the timing module might be useful is if you're propped real steep, and want to mush along at half throttle pulling a load, like skiing. I'm not real sure it would even make a difference.

My oil-alert module chit the bit a coupla weeks ago. I had one off'n an EFI engine. With a little cutting and splicing, it went on and works fine.

I have 2 props for my XR4. A 22 and a 24. I use the 24 in the spring, and when I'm light. In the summer if I'm heavy, as in going camping, or carrying a heavy passenger, or skiing, I put the 22 on. I'm looking for a 20 for skiing, just to let the engine spin a little easier. Right now the floor is starting to delaminate, which weakens the superstructure that pulls the pylon, so the ski prop in on the back burner till I split the durned boat and put a coosa floor in it.

The regulator module is a TSR device, and doesn't give off much heat. Anywhere you can find to mount it is fine.

anyway, carry on
John