Older 150 Merc Black Max idle problem

[spocter72]

Hi Guys

I have an issue with this 150 merc that started yesterday and for the life of me,I can not seem to figure it out. When it is at idle,all of a sudden it will stop running on all the cylinders except for about 3.After a bit it will pick up and run normal again and continue to do this.The problem is that it does not cut out just 1 bank,but 2 on one side and 1 on the other. Now here's the clincher.If I just raise the idle by "a hair" with the carb bar,it runs perfectly fine indefinitely until I let it go back to idle. Just a slight increase in the rpm solves the problem. I check as best I could for bad wiring,moving wires when it is skipping,but that makes no difference. I moved wires coming from the trigger,but no difference there.Both power paks and all coils replaced last year along with the carbs being rebuilt. I cannot figure out what is going on.The electronic fast idle unit is not hooked up and hasn't been for a long time.Has an idle jet been plugged in one of the carbs? Again this just started yesterday.I sure would appreciate any input. Thank You ALL Very Much

 

[j_martin]

Re: Older 150 Merc Black Max idle problem

How many different "older" 150 mercs do you suppose there are?

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

How many different "older" 150 mercs do you suppose there are?

I would imagine quite a few now that you mention it. Problem is, I do not know the year of the engine. I do have this serial though..OB251602. Would this help in the identification of it? Thank you...Len

 

[Barnacle_Bill]

Re: Older 150 Merc Black Max idle problem

Is the idle on your 1987 motor set properly? It should be idling at 600-700 RPM. This is with the motor in the water (not muffs) and in gear. When is the last time it had a tune up? Also try running some Sea Foam thru it.

 

[Faztbullet]

Re: Older 150 Merc Black Max idle problem

Weak stator....

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

Is the idle on your 1987 motor set properly? It should be idling at 600-700 RPM. This is with the motor in the water (not muffs) and in gear. When is the last time it had a tune up? Also try running some Sea Foam thru it.

Pretty much everything was done at the beginning of last year.Plugs,wires,etc. Took a compression test today.All were around 110+_3lbs. Thank you for the year. I now know it is a 1987. I really have never heard of "Sea Foam". What is it? Yes, this started in the water yesterday in gear,but now continues in neutral in water and with the ears on it.It usually idles about 750 rpm in neutral.I never noticed what it idled at in gear.Sorry I didn't answer questions in order,but think I covered it all.

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

Weak stator....

This makes alot of sense to me.Is there a way to do a test to see if that is the problem? Also is there a way to power the motor with a battery with the stator disconnected or would that hurt something else? These may be very dumb questions,but if I knew the answers,I wouldn't be asking Thank You....Len

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

Ok,Well thanks alot

 

[j_martin]

Re: Older 150 Merc Black Max idle problem

Ok,Well thanks alot

Do you suppose there are 1000 merc nuts around the world waiting to jump on your every question in an instant. Patience, grasshopper, patience.

The engine does not run on the battery. All the power for ignition is generated in the stator in coils that are not related to battery charging. The battery is charged with a third coil in the stator, dedicated to that.

#1, it sounds like the idle speed is set a bit low. If the idle stabilizer were operational and hooked up, it would pick it up before it died. Most consider that a bit "Mickey Mouse." The best way is to have it in good tune and set at the right idle speed.

There are many things that can affect the idle. I would put the stator at about the 18th position in that list. Some people automatically replace the most expensive part first, just because. If that is your MO, go for it.

One caveat. If it isn't charging, and the rectifier (or regulator) is shorted, it could pull the charge coil current down enough to make it balk at idle. If you think this is the problem, disconnect and tape off the yellow wires and try it. If the symptoms go away, you found it fault.

It's probably due for a "tune up".

You've already done the first step which is to verify general engine health with a compression check.

Next verify spark on all six at cranking speed. It'll be good.

The next step would be to decarbon it with SeaFoam. Look in the FAQ section of this board for that procedure. That will clean out the exhaust system, and free any stuck rings. It can be tough on neighbors.

Next would be to put in a fuel pump diaphragm kit. It's 25 bucks and less than an hour of your life to verify it's good. I consider it an annual maintenance item, along with the water pump. Check the condition of the other fuel delivery items, filter, primer hose, and internal hoses.

Next would be to verify the condition and routing of the bleed hoses and their associated check valves. Again, look around on this board to figure that out.

Next would be a trial link n sync, or timing and linkage adjustment.

If it still idles a bit rough, put kits in the carbs, verifying the settings and cleaning them thoroughly.

If it's still rough, pull the carbs back off, and pull the reed plate and verify their condition. Usually bad reeds will cause a steady miss at idle. This is getting to be a long shot.

Needless to say, the factory service manual has all these procedures in it.

hope it helps.
John

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

Thanks alot John
I will try all you said and let you know the results...appreciate it...Len

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

Hi John,

Please try to bear with me on testing. I originally thought that cylendars were out on both sides. I was mistaken and the complete 1 side was out.I then swapped the red and blue wires from one switchbox to the other switchbox that had the red/white and blue/white wires and vice versa.Then the other side went dead and the side that was out now has spark.I did this after you said to do a spark plug test. So now the book says to test the stator,two tests need to use R1000 setting and two are R1 settings on the VOM. My VOM doesn't have them settings nor could I find one to buy around here today that did,so I put the VOM on R2000 for the 1000 and R200 for the R1. Anyway, it says between Bl/Rd with R1000 setting should be 5.4-6.2. I get no reading at all here. Then it says Bl/wh and Rd/wh @ R1000 setting should also be 5.4-6.2. No reading there also. It then says Rd to gnd @ R1 setting should be 125-175. Using R200 setting I get 69.8. Rd/wh to gnd same R200 setting, I get 70.9 and says should also be 125-175. Stator is still on engine.Book did not specify on or off the engine. Rectifier tested completely oposite of what it should be. When it said it should have continuity it didn't and when it said it shouldn't, it did,so I would guess the rectifier is shot(again). I believe I read one of your posts somewhere where the voltage regulator isn't really needed if you maintained your batteries correctly. I tend to believe mine is bad and pretty ragged. If I am incorrect in this please let me know so my intentions will be to do away with the regulator. Well I do not know if this testing is going correctly or not, but I am trying. I do not know if my readings will mean anything being on the wrong scale, but my meter only has 2000k,200k,20k,2000,200. So if you get a chance, would you please let me know what you think?

Thank You Very Much....Len

 

[j_martin]

Re: Older 150 Merc Black Max idle problem

Hi John,

Please try to bear with me on testing. I originally thought that cylendars were out on both sides. I was mistaken and the complete 1 side was out.I then swapped the red and blue wires from one switchbox to the other switchbox that had the red/white and blue/white wires and vice versa.Then the other side went dead and the side that was out now has spark.I did this after you said to do a spark plug test. So now the book says to test the stator,two tests need to use R1000 setting and two are R1 settings on the VOM. My VOM doesn't have them settings nor could I find one to buy around here today that did,so I put the VOM on R2000 for the 1000 and R200 for the R1. Anyway, it says between Bl/Rd with R1000 setting should be 5.4-6.2. I get no reading at all here. Then it says Bl/wh and Rd/wh @ R1000 setting should also be 5.4-6.2. No reading there also. It then says Rd to gnd @ R1 setting should be 125-175. Using R200 setting I get 69.8. Rd/wh to gnd same R200 setting, I get 70.9 and says should also be 125-175. Stator is still on engine.Book did not specify on or off the engine. Rectifier tested completely oposite of what it should be. When it said it should have continuity it didn't and when it said it shouldn't, it did,so I would guess the rectifier is shot(again). I believe I read one of your posts somewhere where the voltage regulator isn't really needed if you maintained your batteries correctly. I tend to believe mine is bad and pretty ragged. If I am incorrect in this please let me know so my intentions will be to do away with the regulator. Well I do not know if this testing is going correctly or not, but I am trying. I do not know if my readings will mean anything being on the wrong scale, but my meter only has 2000k,200k,20k,2000,200. So if you get a chance, would you please let me know what you think?

Thank You Very Much....Len

1. Stator's bad, cable swap test confirmed that.
2. Meter's wacked, but readings should be the same on both charge coils, even with an errant meter. (each charge coil has 2 taps.)
3. Your meter leads are backward. Rectifier is good.

hope it helps
john

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

Thanks for the reply John. About the leads...Please correct me if I'm wrong,Black is common on meter,Red is load/ohms. I used a digital and an older conventional meter with same results. Took all wires off of rectifier to test. Where it said there should be continuity,there wasn't and when it said there shouldn't be there was. I really do think it is good though because it does charge,but how can the readings be doing that with 2 different meters.If it was bad, would it not be charging? That is for the battery charging circuit correct or no? Also, could you confirm that removing the regulator would be a good move/or not. Thanks so much for your help. Just trying to understand this stuff....Len

 

[j_martin]

Re: Older 150 Merc Black Max idle problem

Thanks for the reply John. About the leads...Please correct me if I'm wrong,Black is common on meter,Red is load/ohms. I used a digital and an older conventional meter with same results. Took all wires off of rectifier to test. Where it said there should be continuity,there wasn't and when it said there shouldn't be there was. I really do think it is good though because it does charge,but how can the readings be doing that with 2 different meters.If it was bad, would it not be charging? That is for the battery charging circuit correct or no? Also, could you confirm that removing the regulator would be a good move/or not. Thanks so much for your help. Just trying to understand this stuff....Len

The confusion lies in the fact that the cathode in a diode is the negative pole of the diode, but when you put it in a circuit that's rectifying an AC voltage into a load, it is labeled +. In testing, for instance, the negative lead of the ohmmeter goes to the + terminal, and the positive lead to a ~ terminal.

Long story short, the 4 diodes in the bridge rectifier each conduct current in one way, and block it in the other. They may fail either open or shorted, but never reversed. Don't mess your mind up worrying about meter polarity, but just check for diode function between the output terminals (+ & -) and the input terminals(~).

hope it helps
john

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

The confusion lies in the fact that the cathode in a diode is the negative pole of the diode, but when you put it in a circuit that's rectifying an AC voltage into a load, it is labeled +. In testing, for instance, the negative lead of the ohmmeter goes to the + terminal, and the positive lead to a ~ terminal.

Long story short, the 4 diodes in the bridge rectifier each conduct current in one way, and block it in the other. They may fail either open or shorted, but never reversed. Don't mess your mind up worrying about meter polarity, but just check for diode function between the output terminals (+ & -) and the input terminals(~).

hope it helps
john

AHH...Great explanation. I understand what you are saying. I love learning things. What about the regulator John? I tend to think this all happened partially due to that regulator. It would intermittintly charge when it felt like it and the regulator itself looks pretty bad shape. When I disconnected it, It shows charging,but I sometimes get worried because the guage will show upwards of 16 volts at high rpm's.Even if I have both batteries in line , it will show high charging voltage. I keep my batteries in top shape and always fully charged. When boat is not in use, I keep float chargers on them. What do you think? Thank You again soooooo much. I know I am aggrivating.I am just an old man that has been trying to take his wife and daughter for a boat ride that has been uneventful for 2 years now. Something always goes south.

 

[j_martin]

Re: Older 150 Merc Black Max idle problem

I'm guessing you have an 87 V6 with a rectifier on the switchbox mounting plate and a little square regulator sitting on top of the motor.

If you check, you'll see that regulator is NLA.

Overcharging at 16 amps, especially into multiple batteries, won't hurt them as long as you keep the electrolyte over the plates. That regulator, however, has proven to be a fire hazard, and has many creative failure modes, most of them harmful to something else on the motor.

If you haven't guessed yet, chit can it and don't look back.

hope it helps
John

 

[spocter72]

Re: Older 150 Merc Black Max idle problem

I'm guessing you have an 87 V6 with a rectifier on the switchbox mounting plate and a little square regulator sitting on top of the motor.

If you check, you'll see that regulator is NLA.

Overcharging at 16 amps, especially into multiple batteries, won't hurt them as long as you keep the electrolyte over the plates. That regulator, however, has proven to be a fire hazard, and has many creative failure modes, most of them harmful to something else on the motor.

If you haven't guessed yet, chit can it and don't look back.

hope it helps
John

Thank you John;

You have been a lot of help and I appreciate it alot. Voltage regulator is history. Thank you soooo much again...Len

 

[powrguy]

Re: Older 150 Merc Black Max idle problem

I'm guessing you have an 87 V6 with a rectifier on the switchbox mounting plate and a little square regulator sitting on top of the motor.

If you check, you'll see that regulator is NLA.

Overcharging at 16 amps, especially into multiple batteries, won't hurt them as long as you keep the electrolyte over the plates. That regulator, however, has proven to be a fire hazard, and has many creative failure modes, most of them harmful to something else on the motor.

If you haven't guessed yet, chit can it and don't look back.

hope it helps
John

Are you saying that the regulator is an un-needed part? If removed, you will lose battery charging, and no other problems will result? What about the switchboxes?

 

[j_martin]

Re: Older 150 Merc Black Max idle problem

Are you saying that the regulator is an un-needed part? If removed, you will lose battery charging, and no other problems will result? What about the switchboxes?

Understand, this is a shunt type regulator. If removed, the maximum available current goes to the battery, limited by the electromagnetic design of the stator. The battery itself serves as the voltage regulator.

The ignition system on this engine does not depend on the charging system or battery for anything.

Now go back to your cheby inboard.

 

[powrguy]

Re: Older 150 Merc Black Max idle problem

Thanks, John. I've got a 1988 Mariner 135HP, and I am guessing it's the same setup. I have a spare regulator and rectifier, and thought my charging system was not charging my batteries. HOWEVER, some other electrical/wiring issues are resulting in my making a new instrument panel, new wiring harness, and re-wiring my entire boat, along with moving my batteries forward to the center console.

In my mind, I couldn't understand how you could charge the batteries without a voltage regulator. I guess removal of the regulator just puts full output on 'em, and as long as you don't boil 'em dry, they should charge up pretty good.