Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

[Limited-Time]

02 centurion Merc 350 Mag MPI electrical issues. Ignition system problems, the ignition switch will not activate the buzzer warning system or apply the 12 volts to the coil or fuie pump. It will however engage the starter. I have ruled out the kill switch. It was bad so I bypassed it for testing purposes. (may have been fried by owner, see below)

A little back ground. On the water coming off plane engine dies, turn key, nothing. Owner checks wires to ing. switch and finds several disconnected, clips them back where he believes they belong, trys again no go. Gets a tow in and trailers boat home.

Upon inspection I find he has connected the ignition wires directly to the pos. Battery lead and also bypassed the circuit breaker in the dash. Claims he only reconnected one loose wire. Currently power is going to the ignition (purple) wire but not the positive side of the coil. 12 volts is going to the buzzer as well but I can only get the buzzer to sound if I ground the other side of the circuit. So where do I go from here??

 

[Don S]

Re: Ignition wiring issues Merc

Re: Ignition wiring issues Merc

Got a serial number for the engine? Mercruiser does not list anything about different engines by year, only by SN.

 

[Limited-Time]

Re: Ignition wiring issues Merc

Re: Ignition wiring issues Merc

Engine SN 0L671793

 

[Don S]

Re: Ignition wiring issues Merc Engine SN 0L671793

Re: Ignition wiring issues Merc Engine SN 0L671793

Look on the engine, there is a section (for lack of a better word) that has the fuses and relays that controls the power to the engine. There are fuses for both the fuel pump and ignition relays. Since you aren't sure about what was rewired, look at the fuses. If they got shorted in the repair procedures, they would blow.
You need service manual #24 for that engine, for 1998 to 2001 engines. It's also an MIE, (Inboard) not an outdrive model.

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793

Re: Ignition wiring issues Merc Engine SN 0L671793

Don you are correct on the MIE inborard part. The 3 fuses covered by a plastic cap 15 10 15 amp all OK. And I just happen to have the service manual #24. So where to from here??

 

[Don S]

Re: Ignition wiring issues Merc Engine SN 0L671793

Re: Ignition wiring issues Merc Engine SN 0L671793

Look at page 4E-17 of the manual, and start checking power with the key in the run position and see if you have power to the fuses. If not, back up till you find where the power ends. Including fuse #15 in the wiring diagram.

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793

Re: Ignition wiring issues Merc Engine SN 0L671793

I'll look at it in the AM and see what I find. I'll let ya know, thanks for the help Don.

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793

Re: Ignition wiring issues Merc Engine SN 0L671793

Update. I rechecked the fuses and circuit breaker resets no faults found. I then unplugged the starting and charging system harness (page4E-12) from the fuel and ignition system harness (page4E-17) turned on the key and checked for voltage. All checked OK. As soon as I re-connected the harnesses the system came to life, buzzers, fuel pump and gages all powered up. So even though the engine now starts and runs fine, and the lake test went without a problem. I learned nothing??? Leads me to believe there is an intermittent connection issue here. Run it till it fails again??? Or is there another course of action I can take?

 

[MJ76]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

Just thought I would chime in about a problem I had a few months back with an MPI with a no-start condition. The diagnostics program pointed to a failure at the injector banks, so I checked the relays and the fuses, and there was power at the fuse, no power at the injectors. However, with an ohmmeter, there was continuity bewteen the fuse and injector positive. Huh? Long story short, one of the little yellow fuses in the fuse pack (on the port manifold) was not blown, but had a hairline crack in it, such that when I probed it, it would complete the circuit, making it appear that everything was fine. It was only when I pulled it, and looked at it very closely, that I could see it. Three other techs I showed it to didn't see it until I pointed it out. Probably won't apply to your situation, but just something else to check. It sure flummoxed me for a couple of hours. I was ready to start unwrapping the wiring harness!

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793 Spring 07

Re: Ignition wiring issues Merc Engine SN 0L671793 Spring 07

Update. I rechecked the fuses and circuit breaker resets no faults found. I then unplugged the starting and charging system harness (page4E-12) from the fuel and ignition system harness (page4E-17) turned on the key and checked for voltage. All checked OK. As soon as I re-connected the harnesses the system came to life, buzzers, fuel pump and gages all powered up. So even though the engine now starts and runs fine, and the lake test went without a problem. I learned nothing??? Leads me to believe there is an intermittent connection issue here. Run it till it fails again??? Or is there another course of action I can take?

New year same problem. Had the boat out for about 45 min. it died while underway, same sheet. Any how, I think I screwed up the trouble shooting procedure by unplugging the above mentioned connector during my initial attempt at locating the fault.
FF to today, this time along with the original issues the key would not even engage the starter. I traced that problem to the remote starter solenoid (while holding the key in the start position if you rap on the solenoid the starter engages). I don't think the two issues are related.
So to clear my mind and make sure I'm attacking the original issue correctly. With the key in the run position I start at the farthest point back in the system looking for current and move towards the ignition switch.

 

[Haut Medoc]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

I'd start at the switch, making sure BAT had 12v+.......​

 

[Reel Poor]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

You can trace either way, from the switch until you lose power or from the fuses until you find power. Really makes no difference with the exception that the problems are more common in the engine compartment.

Check the harness connectors for dirty/corroded or loose connections.

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

OK heres what I found so far. With the key in the run position: The 2 15 amp fuses have power Fuel pump, and ECM/DLC/Batt. The 10 amp ECM/injector/ign/knock module does not. Note, the power remains after the key is turned off. And the purple wire going to the kill switch gets HOT if the key is left on. I disconnected the kill switch while checking the power to keep it from over heating. Where to now?

 

[Reel Poor]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

Did you remove the 10 amp fuse and check for power at the terminal or did you check for power at the top of the fuse? The power source to the 10 amp ECM/injector/ign/knock module fuse is the same source for the 15 amp fuel pump relay fuse. Power is supplied to the fuses via the System/Ignition relay. There may be a wire problem between the relay and the 10 amp fuse connector.

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

I checked power on both sides of the fuses. I then checked ing sys relay, # 12 only have power on the in side. If I'm reading the schematic correctly that relay supplies the fuse lacking power. What fires that relay??

 

[Reel Poor]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

The pink (relay trigger) wire to the relay should be hot with the key on. The pink wire is part of the ECM harness which is connected to the starting/charging system harness via a 4 wire connector. At this connector the pink wire (outlet side of connector) is connected to a purple wire (inlet side of connector). The purple wire is fed thru the round main engine harness connector via the ignition switch.

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

I figured the pink wire fired the relay after looking at it a little longer. I Do not have current there with the ing switch on. But I also have the kill switch disconnected (unpluged). I am assuming this kills the feed that fires the relay. I may venture back down and check. Are there not two seperate purple ing wires feeding from the ing. switch??

 

[Reel Poor]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

There may be more than one purple wire leaving the switch but only one of them will lead to the engine. The other will lead to the instrument panel. I believe the purple wire is terminal #5 in the main engine harness connector.

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

Thanks for your input Reel Poor. I'm going to go back at it tomorrow after work. Hopefully I can finish up then.

 

[Limited-Time]

Re: Ignition wiring issues Merc Engine SN 0L671793 update 9/17 PM

Happy ending . Found the problem under the dash, after systematically tracing the lost power back through the wiring harness by using the factory manual, and the help of some fine folks here. I found the ing wire (purple) cut and shorting out against the steel strap iron supporting the radio in back. There were actually 3 wires cut through and shorting, The way the original manufacture routed the wiring it was only a matter of time before the insulation rubbed through on any of the wires touching the bracket. Thanks again the help.