At what engine speed should the trigger voltage be tested at on a 1986 mercury classi

[Coltrickle]

I have a 86 classic fifty 45 hp.. It has a real bad miss when powering up.. I replaced the stator, rectifier, plugs and wires.. I am getting fire on all 4 cylinders.. The manual states I should get 4 volts minimum when testing the trigger wires for voltage.. When I check them at idle I am getting 1.9 volts on one side and 2.2 volts on the other side at idle... I can rev the engine and increase the voltage to 4 volts or so on both sides.. When I check all my other electrical components they pass with flying colors at idle.. Should teh trigger pass voltage at idle or what RPMs should it be at when I take my reading???? Thanks

 

[Dave1027]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Cranking speed which is about 300 rpm. How are you reading this voltage? Are you using a DVA?

 

[CharlieB]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Cranking only 1 1/2 to 3

Voltage will rise with RPM running.

If you get spark cranking it is most likely fine.

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Thanks gentlemen.. I have done some more testing per the cdi website.. Is this info accurate?? I am using a Fluke that I borrowed from my grandfather that is capable of reading dva.. It is out of my price range, I had no idea a meter to read dva was that expensive.. to the point.. per the cdi site I should be getting 800-1400 ohms across the two top trigger wires and 800-1400 across the two bottom trigger wires. I am getting 1017 ohms on top two wires and 1021 on the bottom two wires.. I also did a running voltage test at idle and from each trigger wire to ground I should get a minimum of 1 volt.. I am getting 1.7-1.8 volts on all four trigger wires to engine ground... All of the ohm measurements are done with the wires disconnected from the switchbox.. I also read the voltage across the top two trigger wires and bottom two trigger wires again.. I have to do these readings at a low idle due to my leads not being long enough to reach my console while cranking.. I again have 1.9 volts on the top two trigger wires and 2.2 on the bottom two trigger wires.. My stator is putting out 202 on the blue wires at idle and my red wires are 39.. All of the test seem to pass except the voltage test for the two top and bottom trigger wires.. Any suggestion??? please I cant take it anymore!!! I also have a cylinder that no matter which plug I put in it, it always looks new when I remove it.. Cylinder 4 on the bottom.. Compresion is 112-116 on all cylinders..

 

[oldman570]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

The coil on #4 might not be making a good ground, when the motor is running, and cause it not to fire. Try switching that coil with another and see if the trouble moves with that coil.
Oldman570

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Thanks I will try that this evening.. Seems like the simple thing to do... Sometimes you can't see the Forest for the trees!!!

 

[CharlieB]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

A remote starter button from an auto parts store will make testing a lot easier.

If all cyl's pass the 7/16 inch spark gap test with a hot blue arc, then the ignition is not your problem.

You may have a water leak at the exhaust side cover spraying water into #4 and 'steam cleaning' the plug and piston.

Look into the spark plug hole at the top of the piston, describe the color.

Is the motor having problems at speed, at idle? Or is your concern just the clean appearance of the one plug?

 

[Dave1027]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Just to add, you can make a DVA with about $2 in parts. It's only a diode and a capacitor wired together a certain way. Search this website.

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

The motor will idle all day long on muffs.. It has a rough idle though.. It will power up but has a miss in it.. when I put the boat in the lake it has a bad miss and will not plane out!! Could you please explain how the leaking exhaust cover can get water into the cylinder?? Thanks

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

OK I have not yet swapped the coils to see if that is the problem but I tested the spark gap and its doing one inch on all cylynders. I had a chance to borrow a timing light from a friend.. We marked top dead center of all the pistons on the fly wheel. When I started the engine I put the timing light on the number one(top) plug wire. I pointed the light at the timing mark indicator and It was at 9 degrees at idle.. I put the light on top of the flywheel and it was showing number 1 cylinder at the timing marker.. I walked the light around the flywheel and could read all cylinders about 90 degrees apart from each other.. How are are cylinders reading around the flywheel while my light is connected to the number one wire.. It would read all cylinders all the way around the flywheel no matter what plug wire I hooked to. they just rotated around the flywheel.. I was under the impression only the wire I am connected to will show up under the light..

 

[oldman570]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

All the marks should show up if you marked the flywheel for each cyclender at TDC as stated. They will show up every 90 dgs. around the flywheel as you move the timming light around it. The only true reading of the timming for the cyclender that the light is conected to will be at the pointer. By watching the timming light just to see if it lights up when it is moved from one plug to another will tell if that plug is getting the electricty to the plug to fire. It will not tell you if the plug itself is good and firing. As Charlie has stated, if the #4 plug is always clean, and is not colored, it is getting steam cleaned from water leaking into the exhaust section of the motor and need to be fixed inorder to solve the trouble you are having as long as EVERYTHING else test out good.
Oldman570

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Thanks gentlemen.. I went out last night and had my son control the cranking and throttle and I noticed water seeping out of the bottom of the exhaust cover and running down the foot.. Is this the water that is potentially getting in my cylinder?? Is this due to a cracked block or just a gasket problem? And also will gaskets repair the water getting into the cylinders?? I know it's a lot of questions but I am about ready to chunk it???? Thanks again!!

 

[CharlieB]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Have your model and serial #'s then go to the Merc parts pages and look at the pieces that make up your motor.

http://www.mercruiserparts.com/mercruiser_parts.asp

You will see that the exhaust side cover is really two covers, the outer and an inner plate with gaskets on both. Water fills the gap between these and helps cool the exhaust and keep from melting the side of your motor.

A leaky gasket or a crack in the inner plate will allow cooling water to spray back into the exhaust port of a cyl, causing 'steam cleaning' of the piston and spark plug. This is not a good thing as the moisture can cause the rings and to rust, rapidly wearing and ruining the cyl/piston.

Be very careful removing exhaust cover bolts, they have a nasty habit of sticking and breaking off. Do NOT force them. Finese them. Love taps on the head with a very small ball peen hammer while gently wiggling the bolt with a wrench until it turns, screw it in and out those small bits until it eventually backs out. LOTS of patience.

Once the cover and plate are off inspect closely for any warping or cracks, install with new gaskets. IF you use any silicone sealer, smear only just enough as so as barely to be there, hang the gaskets up to dry at least 20 minutes before installing. Too much or assembling too soon and the gasket can get squeezed out like a tidly-wink and tear, if squeezed out inside you will never know until you see your next 'clean' spark plug.

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Thanks gentlemen I will repost this weekend after I have it taken apart..

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Ok gentlemen here is what I found.. The bolts were very easy to remove.. Almost to easy. I found pieces of a old water pump in the bottom right water jacket of the block where the water comes from to cool the outer edge of the exhaust cover.. The whole was completely clogged. There were also pieces in the outer water jacket of the cover itself. After careful inspection I noticed Where exhaust soot was in the outer water jacket of the cover near the bottom. Could this be where water was escaping and exhaust getting into the jacket?? I also had some type of liquid seeping out around two of the bottom cover bolts and one about halfway up on the side of the cover.. I found no evidence of cracking or warping on the metal plate between the gaskets.. Does this sound like a problem you all were describing? And where do I go from here?? Just order new gaskets clean surfaces and install?? And how tight should the bolts be?? Is there a torque spec?? Thanks again!!

 

[oldman570]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Yes, parts from a old impeller will cause the water not to flow as it should and can cause an overheat problem. This will also cause the exhaust water jacket to overheat and cause the gaskets to leak, if it has not craked the plate that divides the water and exhaust. It can also cause the gasket between the block and waterjacket covering the head area to leak around the plugs. If any sign of water leakage around the plugs, now is the time to replace that gasket. The jacket bolts should tork to 165in. lbs. on motors 50hp and smaller JMO
Oldman570

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

I replaced the gasket around the plugs last week. I made a gasket out of a roll o gasket paper.. They were leaking a good bit.. I will order new gaskets for the exhaust and update you all as soon as they are installed and tested.. After removing the side cover I could see exactly what you all were explaining with how water can enter the cylinders.. Thanks for all your expertise and input!!

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Ok gentlemen it has been a few weeks but I put the new exhaust gaskets in and my plugs are no longer super clean but still not looking used a lot!!! My 2 and 4 cylinder are not as dirty looking as my 1 and 3 plugs.. I have resorted back to electrical checks.. Everything seems great except my trigger checks.. According to the manual I should get open circuits from each wire to engine ground and I am getting about 16k. I am within specs on my check from white/black to brown and my white to violet. They are around 860 each.. The book says 800-1400. So no problem there. My voltage is at 2.5 on the top two wires and 2.7 on the bottom two wires.. Book says 4 volts min. Each side.. Outboard ignition says to swap the wires around such as 1 for 3 and 2 for 4 and see if the problem changes to the other cylinders but when I do that the engine will not even turn over.. As always any help will be greatly appreciated..

 

[halmc]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

I had the same motor you have a few years ago, and the symptoms were very much the same as yours. Once in a while, it ran great for very short periods, but it usually had a bad miss, and the miss was not always on the same cylinder, and sometimes it would miss on two cylinders. Very inoccasionally, it would miss on three. Moving the coils and plug wires changed nothing. I finally bit the bullet and replaced the switch box which was not cheap. The engine ran perfectly after that.

When you're chasing water in the cylinder, you should keep in mind that many engines are equipped with water injection to reduce detonation, and it doesn't make them miss.

Incidentally, my engine had good spark on all four cylinders at cranking RPM -- with the plugs out of the engine. The ignition is much more challenged when it is trying to fire a plug under compression. its correct to think that if you have spark at cranking speed, that you probably have spark over all engine rpm's and loads. But it would be very incorrect to conclude that you absolutely do. You probably do, but you might not.

I'm not saying that you should replace the switchbox. I am saying that replacing the switch box put an end to my troubles.

 

[Coltrickle]

Re: At what engine speed should the trigger voltage be tested at on a 1986 mercury cl

Thank you I have been trying to avoid the switch box change.. I just wish there were a way to test it!!!