mercruiser 470 dies after running 45 mins

[Dayrunner567]

I have a 1981 Four Winns w/ Merc 470 I/O. Just picked it up. checked all fluids and is clean and good. After running great for about 45 minutes it stalls. It restarts everytime and will rev up with no load on it. As soon as I put it in gear to go it dies. I can slowly put in gear and as it just catches, it will go slow. Any more throttle it will die. I check fuel filter and looked clean but old. I changed it. Put an in-line clear filter so I can watch fuel flow. I rebuilt carb w/ new needle and float. It is still doing the same thing. Fuel pressure is 8-10lbs, the spark seems to be weak. I changed the original plug wires from 1979 that the resistance was really high. Changed the points, condensor, cap, and rotor. Plugs look new. How much spark should this produce? I have an in-line spark tester and the max setting that I get any spark is less than 10k volts. And even then its a hairline blue spark that is hard to see. Same thing coming straight from coil. I did not put a new coil on it yet, but I put a used one that I think works. Does same thing as other coil. Disconected the tach to see if shorted and was no improvement. Does anyone have any suggestions?

 

[stonyloam]

Re: mercruiser 470 dies after running 45 mins

I went with a PerTronix Flame-thrower II 45,000v epoxy (for marine use) coil a few years back. I use it with OEM points and condenser and it works great!

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

What did you set the dwell at? Did you use a meter? What is the voltage at the coil with the points open and closed?

 

[Bifflefan]

Re: mercruiser 470 dies after running 45 mins

What did you set the dwell at? Did you use a meter? What is the voltage at the coil with the points open and closed?

I agree sounds like a dwell (or lack of) problem. if its not right then the coil has no time to build a spark. No coil in the world can help that.
IMO you should upgrade to some sort of electronic ignition. This is after all the 21st century.

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

IMO you should upgrade to some sort of electronic ignition. This is after all the 21st century.

Stick with the points. It should work fine.

 

[Dayrunner567]

Re: mercruiser 470 dies after running 45 mins

The dwell is at 30 degrees. The voltage at coil is 12.3 on both side with the points open, points closed it is 0 on the negative side and around 3-4 on positive side. Is this correct?

Thanks for the reply. Fishing tournament coming soon and would like to use it.

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

3-4 volts is way too low with the points closed. You have a voltage drop somewhere. Might want to trace the wire back from the coil and measure before the ballst resistor/wire and see what the voltage is there...should be full 12V. Sounds like you have a resistive connection somewhere. As a test you could run your coil with a full 12V by jumpering it to see if that solves you engine running problems and then search for your voltage drop.

 

[Dayrunner567]

Re: mercruiser 470 dies after running 45 mins

You are right. I ran direct line to ignition coil positive terminal and I get good spark. I traced the wires back and one goes to the starter solenoid and the other to electric choke. The wire between the choke and coil is getting slightly warm so there must be a short. I disconnected the choke and the prob still exists. The other wire from the choke, I am having a harder time tracking down. It goes through bulk connecter and appears to run up to the front of the boat. Does that feed my guages or is that my 12v from the ignition switch? I am still searching but I thought I would post real quick. I was trying to get a wiring diagram for it but I can't find one.

 

[Dayrunner567]

Re: mercruiser 470 dies after running 45 mins

The voltage at the choke is only around 9v with the points closed. If I disconnect the positive coil wire, the voltage is 12v everywhere. With connected, the voltage drops. Could my coil be shorted, should there be any resistance between pos and neg terminals on coil? I have 0 resistance right now.

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

If the wire between the choke and the coil is warm , that is more than likely your resistor wire unless you have ballast resistor somewhere. Not very familiar with your setup.

How did you measure 0 ohms across the primary of your coil? You do know that you would have to have the coil out of a complete circuit to do this right? Having the points open should accomplish this though.

If you have 9V at the choke, your voltage drop is between your choke and your ignition switch. It will go through the engine harness and that is where I would look first. Open up the connector and make sure all connections are clean.

Next, measure the voltage at the ignition switch. If you can, hook the ground of your meter to the battery.

 

[Dayrunner567]

Re: mercruiser 470 dies after running 45 mins

I disconnected the pos coil terminal then checked resistance. I will go check the ignition switch. With the coil connected and the points closed, I only have 9v at the choke and 3-4v at the coil. If I disconnect the pos side of coil or open the points, I get 12v at both coil and choke.

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

Your coil resistance should be very low..in the range of an ohm or so... so you have to make sure you use your meters lowest ohm range. Look up in your manual to see what it should be. No matter what, you have a voltage drop problem and you need to stop looking at the coil right now. The ballast wire is limiting your current for you. Even if the coil resistance is on the low side you shouldn't see the drop you are getting at the choke.

 

[Dayrunner567]

Re: mercruiser 470 dies after running 45 mins

I traced the wires back to under the dash. I did find a loose connection behind the temp guage. It is where the two wires meet after it feeds the guages and goes to the choke. I cleaned and tightened it and now I have 11 volts instead of 9.33 volts like before. Battery voltage is 12.8 volts. Now my coil has between 4-5 volts with the points closed. Is that where it should be? I did not see any other loose connections but I ran out of time and had to go to work before continuing any more tests. .

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

You are getting closer but still no cigar! What is the voltage when it leaves the ignition switch and this connection you are talking about?

Basically, the path is as follows:

1) battery to the starter,
2) starter through a fuse to the engine connector
3) engine connector to the fuse panel at the helm
4) fuse panel to the ignition switch
5) ignition switch to the overboard switch(if you have one)
6) overboard switch to the engine connector
7) engine connector to your choke
8) choke through the resistor wire to the coil.

By measuring at the ignition switch(you should measure both sides of the switch), you will at least be measuring at the midpoint in the circuit and then you can go whichever way that test takes you.

You should be getting darn close to battery voltage at the choke.

 

[Dayrunner567]

Re: mercruiser 470 dies after running 45 mins

ok, this is driving me crazy. I have checked all the voltages and it seems to be consistant. In desperation I isolated the wire going to the choke and applied 12v directly to it. With the points closed I still get 10.20v at the choke and 4.4v at the coil. Battery voltage is 12.14v and I also disconnected the wire to the starter solenoid coming off the coil pos. Put 12v direct from battery to the choke and I still get the same readings at choke and coil. This, I would think this would isolate the problem to: the resistor wire, coil, points, and/or condensor. Right? The points and condensor are new and I have an external ground on the distributor. Should I change it all or am I missing something stupid. Could the coil(I know you told me to leave it alone)be drawing the voltage down too low when points are closing?

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

Where are you measuring your ground at? Make all you reference measurements to the ground post of the battery or the block...no where else.

 

[Dayrunner567]

Re: mercruiser 470 dies after running 45 mins

Yes, all my grounds are straight from the battery.

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

What gauge wire are you using to jumper over to the choke and how are you connecting it? What is weird to me is that you said you jumpered straight over to the coil a while ago and got full battery voltage. Maybe not!

 

[Dayrunner567]

Re: mercruiser 470 dies after running 45 mins

I disconnected the circuit, backprobed the connector at the choke, ran a 2ft 18 guage jumper straight to battery pos. post. Using alligator clips. Still exact batt voltage with points open, and 10.2v at choke and 4.4 at coil with points closed.

 

[bruceb58]

Re: mercruiser 470 dies after running 45 mins

Seems impossible that you are having that much drop with an 18 Gauge wire. For a 2 foot wire, the resistance of the wire is only 0.01277 ohms. If you were drawing 10A that would only be a 0.13V drop.

With the alligator clips on there, use your voltmeter and place one end on one alligator clip and the other lead on the other...only touch the alligator clips. I want to see the voltage drops across your jumper wire.

I then want you to measure, with the original boat setup, between the positive terminal of the battery and the choke terminal.