Engine problems - MCM 165

[Iamwildman]

So I just bought this used boat, an 88 Wellcraft powered by MCM165. It started right up and ran great. I've even had it out for a run on the water and it ran way better then expected. So I figure ill do some work on it and clean some things up. I get up under the dash and its just a crazy rat nest of wires. It was basically a 10" diameter ball of wire, black tape and butt connectors. To make a long story short, I've redone all the wiring behind the dash, including new switches and added a new fuse block in place of old breakers. Everything seems to be working fine now with the exception of the engine. It turns over just fine but I but it hasn't even attempted to fire. I believe there are two wires that come off the ignition switch to run the motor. A yellow with red and a purple with red. I've looked over both wires and checked continuity as well. Everything checks out, but its still not firing. The only thing I can think of is that I've connected something to the ground that's causing a constant kill to the engine. What am I missing?

 

[Bt Doctur]

yellow w/ red stripe is the starter slave relay trigger, red with purple stripe is main power feed .the red goes to the "B" , the yellow w/ red goes to "S" ,the purple goes to "I". that's the one your missing to supply power to the coil.Is this a 4 or 6 cylinder?

 

[Iamwildman]

It's a four cylinder. Ok I'll check that out tomorrow. Thanks

 

[stonyloam]

If it turns over, it should start, even if the ignition wire is disconnected (even though it would only run as long as the switch is in the start position). That is because the coil gets its voltage from the slave when the starter is turning. I would start by the looking to see if the re is voltage on the coil + with the key in the run position. If there is, pull the center wire from the distributor cap and lay it close to bare engine metal. Hit the starter to se if you get spark. If not look at the points.

 

[Bt Doctur]

 

[Iamwildman]

That's a big help Bt doctur, do you happen to have the engine side as well? After Reviewing the diagram you provided, I think my wiring under the dash is sound. I've unplugged the harness at the engine and inspected a bit with my volt meter. What I found was that with my meter set to ohms and one lead touching the engine, if I touched the other lead to each port in the engine side harness plug, I would get a reading on all the ports but one. I hope you understand what I'm saying. I don't think I should have continuity in all but one port. So this leads me to believe that I'm getting a bad ground somewhere on the engine. Basicly killing any spark.

 

[Bt Doctur]

that's not how you test .Do you have power at the purple wire at the ign switch? Do you have power at the + side of the coil with the key "on"
Quick test: run a wire from the + side of the battery to the + side of the coil, does the motor start and run?
Where you located?

 

[Bt Doctur]

 

[Iamwildman]

Yes, I get power to the coil with ignition on. The engine turns over, but won't fire. I've pulled off the middle coil wire and placed it on a ground and couldn't see any arching while cranking. I'm starting to think I have a bad coil. I notice for some reason I was getting a connection from the + side of the coil to the ground. Even after removing the wires.

 

[Bt Doctur]

I go with a point system , remove the wire from the - side of the coil,remove the cap and run a nail file across the points to clean them . most times they get glazed and do not make a connection.
attach a ohm meter, set to ohms to the black wire going to the points, crank motor. needle should move from 0 to infinity everytime the points open and close
Then remove any others wire to the neg side of the coil for now. just leave the wire going into the dist.
Verify 12v at the + side of the coil with key on. test for spark and report back

 

[Iamwildman]

So I pulled the cap off the distributor and found that the PO had installed a digital system in there. I still did the test as you've suggested from the coil to the cap with the meter and came up with no results. I'm going to swap out the coil and see what happens. Everything is pointing to a bad coil.

 

[stonyloam]

Actually nothing points to a bad coil yet. Take the wires off of the - side of the coil. Attach a piece of insulated wire to the coil -. Turn the key on (make sure you have voltage to the coil + ) and briefly strike the wire to ground (bare engine metal ). You should get a spark from the coil center wire every time you remove the wire from ground. If you do, then your coil is OK. if no speak then it points to a bad coil. 90% of the time it as not the coil.

 

[Iamwildman]

Ok I did that test stonyloam and I actually did get spark out of the coil..... Finally. So I guess that puts me at a problem with the digital point in the distributor. Any ideas how to troubleshoot that? From what I see there are three wires going into it. A ground (black) a red (ignition) and a green (from the - side coil). It's a Mallory part 6001M.

 

[phrater]

It very well could be the electronic points that's giving you no spark from the coil. I tried putting Pertronix 91146a electronic points on my 3.7, but I had the same issue. I spent $17 on new points and the problem was fixed.

 

[stonyloam]

No idea on a Mallory. I have a Petronix. Problem is that you can't go back to points unless you have the original distributor plate for the points. If it ran well before, sounds like the wires are messed up. Here are the Mallory instructions: just scroll down to the 6001m for GM. http://info.mallory-ignition.com/support/instructions.html. Kind of looks like they use the original points plate, so as a last resort you may be able to go back to points. Have a feeling once you get the wiring figured out it will be fine. Good luck and welcome to the 470 Club!

 

[stonyloam]

Phrater, yeah, had the same problem with mine years ago till I figured out that you have to feed a full 12 V to the red wire by bypassing the resistance wire and splicing directly into the purple choke wire. If you did not do that, it could be the problem. I know, sorry for the thread, off subject, but the most common mistake with a Petronix. The Mallory is a very different setup.