Mercury 402 - No Spark on Cyl 1

[cambo]

I've had this motor for years, and it's always been difficult to get it started after sitting for a long time. I had it running in June this year (just attached to the earmuffs). It was difficult to start but it did eventually run. It's been sitting in the garage since. I finally got out to the lake last weekend, and guess what.. she wouldn't start. I ended up flooding it, pulled plugs (try to dry it out) and after about an hour of trying we gave up and went home.

This is really the first time I've ever worked on any type of engine, so please bear with me.

Model: Mercury 402 (2cyl, EL - Electric Start, Long-Shaft)
Serial Number: 7102322
Year: 1983 (I think).
Problem: Motor will not fire up.

Fuel, Air, Spark.

Fuel

I assume it's ok, since the plugs were dripping with gas when I pulled them out. When it wouldn't start, I was using a new tank of fuel.

Air
Compression tested - 120PSI for each cyl. Choke is operational.

Spark

- I bought new plugs just to be sure I had good ones. It's been two years since I replaced them.
- Cyl #1 - No Spark (I used the same plug for cyl2, so I know it works)
- Cyl #2 - Good Spark

So, I have an ignition problem. I should mention that at the beginning of last season, I replaced the coil for cyl 1 as the contacts/plug cable had corroded. Engine ran good all last year after the replacement.

So, I swapped the "live" wire (green/white) from Coil #2, to Coil #1 (replacing green wire). I got spark. So, both coils work, so problem must be upstream?

From what I've read, this leaves these possibilities.
Wiring*, Stator, Trigger Plate, Switchbox
*Wires are very weathered - sheath is cracking. I've replaced parts of them, but there isn't a way to replace the whole cable without buying all new components (sealed units, with no screwdown contacts). Any suggestions how to fix these?

Stator Charge Coil - RED to GND == 52.3 Ohms (Acceptable Range = 45-60 Ohms)

Trigger - Disconnected & Between White/Brown == 841 Ohms (Acceptable Range = 800-1000 Ohms)
**Acceptable Ranges from my SELOC 1404 Manual.


So, I think I've narrowed it down to the switchbox or wiring from the switchbox. Anything else I should test before I go buy a new switchbox?



Thanks,

-Cambo

 

[Laddies]

Re: Mercury 402 - No Spark on Cyl 1

It's either the coil, switch box or their wiring for sure. Heres a ign. test for the engine.

 

[cambo]

Re: Mercury 402 - No Spark on Cyl 1

What does DVA stand for?
Are all the voltages specified in the test AC or DC?

I'm using a Fluke 85 multimeter (Max Voltage 1000). Red probe on fluke connected to Green or Green/White, and the Black probe to GND.

Green (Cyl 1) Voltage test results in pretty much nothing (0.045 volts). This is the same when the green wire is removed from Coil #1.
Green/White (Cyl 2) Voltage test resets my meter.

Am I testing this incorrectly?

 

[jarand82]

Re: Mercury 402 - No Spark on Cyl 1

DVA stands for "direct voltage adapter".

 

[Laddies]

Re: Mercury 402 - No Spark on Cyl 1

Without the DVA you can't capture the voltage so you will have to use the OHM specs although they are not as accurate.

 

[cambo]

Re: Mercury 402 - No Spark on Cyl 1

I've order the CDI Peak Reading DVA Voltage Adapter (PN: 511-9773) that was on the iboats.com store. Is this the correct device to use with my Fluke?

While I wait for it, I decided to replace some of the cracked/frayed wiring. I started with the 4 wires coming off the stator then tested. I got spark on Cyl 1 ! So I thought I had it fixed. The other side of the switchbox had one wire that needed fixing, so I fixed that one. Tested again. Now no spark

Do the components inside these switchboxes fail intermittently or is my problem likely wiring?

 

[achris]

Re: Mercury 402 - No Spark on Cyl 1

Cambo,

Firstly.... FANTASTIC!!! Thank you, thank you, thank you.... all the info we like to see, model, serial number, all the testing you've done laid out nicely and done in a very logical and methodical manner.... I wish more people would do things the way you've done them.... and you're using a Fluke... I like this man!!!

So, your problem... I don't think I have ever seen a switch-box go intermittent. It does sound like a wire somewhere, and the wiring Merc used on their earlier engines wasn't too good. It cracked and flacked off, just like yours is... That said, I have seen some people remove and replace all the crap wiring very neatly and successfully.... Judging from your first post, I think it would be a task you could undertake easily....

The easiest check would be to meter between each of the wires and ground.... Any reading there would indicate a wiring problem... Do you have decent circuit drawing?

The DVA adapter you've ordered is the right one for your meter.... Good luck...

Chris.........

 

[achris]

Re: Mercury 402 - No Spark on Cyl 1

Cambo,

You may find this useful....

 

[cambo]

Re: Mercury 402 - No Spark on Cyl 1

I replaced all the wire that had damaged sheath. I figured if this is a loose/bad wire somewhere I'd find it by "wiggling" each wire individually and then testing for spark on Cyl 1. It ended up being the Brown wire (trigger input) going into the switchbox. I cut the cable as close to the switchbox as possible and soldered on a new lead. Tested for spark on both Cyl1 & Cyl2 --> both OK.

So i turned the key... and she started up right away . Time for the water!


Thank-you all very much for your help.

 

[achris]

Re: Mercury 402 - No Spark on Cyl 1

Nice job, well done... and happy boating....