Mercruiser 120 2.5 Spark Issues

[acicomp]

Hey Folks,

I'm new here and just picked up a 1982 Renken with a Mercruiser 120 2.5L. The guy we got it from said he had the motor rebuilt a couple of years ago after he got it and then he updated some wiring. He supposedly "winterized" it some time last year and it's sat for the remainder. I went ahead and changed the fluids and tried to start it. It didn't want to turn over at first like the starter was seized. Finally, after a few tries, it started to turn over but that was about it. Just for giggles, I shot some starter fluid in and tried gain. It just turned over and that was it.

I put a spark tester on the coil wire and had no fire showing up. I went ahead and picked up a tune up kit and grabbed a set of plugs and changed it all out including the plugs, cap, rotor, condenser, coil and points. Set the points to .022. Still not firing. I pulled the gray tach wire just in case and still no fire. In checking for voltage, I have around 10 volts on the + side of the coil when I checked it with the key on and I have continuity between the terminals on the coil.

This is my first I/O and I'm not sure what it's supposed to sound like when it cranks, so I don't know if it's turning over too slow or if it's turning over at normal speed. I wasn't sure if slow turnover would cause no spark at all. I was thinking it would just produce low/weak spark if it was a weak starter or low battery and not turning over fast enough.

Not quite sure where to go next with this thing. Should I pulled the wires off the + side of the coil and and put a jumper between the battery and the + side of the coil or can I just put a jumper on there with the two wires that are already in place to check for voltage issues?

Any suggestions on top of what I have tried already?

Thanks!

 

[Scott Danforth]

You will need to clean or replace the points at a minimum. They oxidize from sitting

 

[Mercruiser420]

A weak/undercharged battery can do that

 

[Alumarine]

Welcome.
Here's a link to the trouble shooting section that might help.

http://forums.iboats.com/forum/engi...es-outdrives/295720-adults-only-no-exceptions

 

[acicomp]

Points have been replaced and gap set to .022. Also, battery is good. I am going to jump a lead from the battery to the + post on the coil and see what happens next.

 

[Scott Danforth]

you also replaced the condenser as well, correct?

 

[acicomp]

I went ahead and jumpered from my + battery terminal to the + terminal on the coil and still had no spark using my spark gap checker. Removed all the wires, once again, to the coil and check continuity and we are good. Checked the resistance between +/- terminals and I have 1.5ohms. Checked between center tower and - on coil and I have around 8600ohms.

Sort of at a slight loss for now as I begin to dig deeper. New points, rotor, condenser, wires and cap from Sierra. Points were set by turning motor to the highest spot on the lobes and then adjusted to .022. I have also tried several different grounding spots in case my spark tester wasn't grounded good the first 10 times.

Thanks for all the help so far...

 

[Bondo]

Ayuh,.... With everything hooked up, 'n the key On,....

Is the coil side of the points, Hot,..??
Is the other side of the points, Grounded,..?

You should be able to fire the coil, by openin', 'n closin' the points,....

 

[acicomp]

I'll double check. At least I think I know how to check that... I also want to make sure I didn't accidentally ground the lead going to the points on the plate.

 

[acicomp]

No Title

I went out and started looking things over a little closer. in particular, I was looking for the shift interrupter switch and this is what I found. I have the wires from the interrupter switch coming to a terminal. There are two wiring leaving that terminal from one of the posts and one wire from the second post. As you can see, one of the wires is cut/broken. Can someone tell me where these three wires are supposed to be going to? Seems like the broken one would be ground and the other two.... Not so sure where they should be going. I wanted to trace them back or reconnect the broken wire to the proper location. I assume that if the shift interrupter is not hooked up properly, then this might be a possible cause of a no fire condition. Is this correct?

 

[Bondo]

Ayuh,... With the interrupter unhooked, it won't come outa gear in the water, but will run,.....

The broken wire is the ground,...

The others go to the (-) side of the coil,....
The switch grounds out the coil/ points to make the motor stutter, allowin' the drive to come outa gear,....

There's 2 "Points" Threads in Don'S Adults Only section, the link is in my signature,.... Have a look,....

 

[acicomp]

I'm going to reground the the interrupt switch and ensure it is all hooked up properly. Right now, the only thing wired to the - on the coil are the points and the tach wire. I have 2 wires hooked the + side of the coil and they are together on one ring. I'll double check to make sure where they are running. I would assume one was a wire to the starter and the other should be the resistor wire. I figured I'd have some things to go through to get her going again. I've looked through the Threads you mentioned several times over the last couple of days. I'm at the point where I think I'm troubleshooting some wiring issues where I think the guy messed some things up before I got it. I'm going to double check my point settings as well here in a few too.

 

[Bt Doctur]

a quick test ti see if the points are making and breaking contact is to put a meter lead on the neg side of the coil and the other lead to ground. crank the motor . meter needle should move with the opening and closing of the points, Can also make sure the points are closed on the flat part of the dist.
The switch works by grounding out the neg coil wire and as you look at the pic, there should not be 2 wires on the outermost screw. the inner most screw is what supplies a ground thru the plate

 

[acicomp]

One of those two wires that are on the one terminal appears to head back into the main wiring harness and the other heads toward the coil. I may have to go ahead and cut the tape off in order to fan out the wires to see where they go for sure. This whole boat has been strange so far. Wiring is wrong, different kind of plugs, etc... Not to go off topic, but when I went to change the plugs, I picked up a set of MR43T plugs and they wouldn't work. I checked the old ones that came out and they were AC44XL plugs, which have a longer set of threads. I checked for any sign of previous damage such as rethreads, heli-coil, etc.. and there was no sign. Anyhow, I'll trace back the wires again and see where they lead for sure.

 

[Scott06]

As BT dr lays out check the ohms on the points, even if they are new. If points are making and breaking the circut check ohms on coil both primary and secondary sides. Don't know how it should ohm but I'm sure you can find via Google. I'm assuming the rotor on distributor is turning ??

 

[acicomp]

I found a video on how to double check the points... It's for a VW, but I am thinking that it should still work. Essentially what Bt Dr said, but it was using a test light in stead to make sure the voltage was passing. I have a digital meter that I can try as well. I should be able to notice some bouncing on the meter. if hooked up between the - post and ground, the motor can be turned and the light should light up when the points open and pass voltage. I have already tested ohms on the coil. It reads 1.5ohms between the +/- terminals and 8600ohms between the - and the center tower. I pulled the specs for the Sierra coil and it was reading within spec.

 

[acicomp]

Also, if I had to guess, I would say that the two wires are together on the terminal are the tach/interrupt bonded together on one terminal and then going to the coil. I was looking through the wiring diagram tonight and even though some colors have faded, the wire appeared to be gray going back in to the harness, which, in theory, should be the tach. I was reading through another post and a guy had the same setup with the two wires on one terminal like that. I'm going to separate them tomorrow.

 

[ihc1470]

To throw in my 2 cents. With a test light you should see a bright light on the positive side of the coil with key on. Negative side should show a light when the points are open and no light when the points are closed. When the points are closed you can open them with a screw driver and every time you do you should see a spark at the end of the coil wire going into the distributor if you hold it close to ground. The other thing you can check while cranking and cap is off the distributor is how much of a spark you have on the points contact surface. If a bunch you probably got a bad condenser. If the test light never goes out when on the negative terminal then the points are not making contact to ground. If it never lights up then you have a grounded primary wire, most likely location is where they connect to the points or shift interrupt system is not adjusted correctly. Bottom line every time you break the primary circuit on the negative side of the coil you should get a spark out of the secondary side of the coil.

 

[acicomp]

Houston.. We almost have life after two years of sitting. I have to be honest and say I cheated today. I tested the points with a test light and volt meter and they appeared to be fine with he light going on and on/off, 12v/0v as would be expected, yet, still no fire. Swapped out the coil with another 1.5ohm coil and still no fire. From a working standpoint, it seemed like it should be working, yet it wasn't. Long story short... I "cheated" and located a Pertonix 1146A conversion and a Flame Thrower 3ohm coil, removed the resistor wire and got it all hooked up and we have FIRE!! Still wouldn't start, but that was a lack of fuel. I shot a little starting fluid in the carb and it fired right up and purred for a few seconds. I'll start down the fuel road next to see what's causing that issue. Thanks to everyone for all the help trying to get this motor going.