DVA-multimeter The result. Mercury 1976/50hp

ixs

Cadet
Joined
Jun 8, 2008
Messages
17
Hi
Chris and everybody.

I finally made my DVA meter. According to this diagram

http://forums.iboats.com/showthread.php?t=374544

Measured my cables, and obtained the following values.

The problem during the last two years, is that the engine been sick. Very sick.
No revs, no speed.
Earlier jobs
Changed the lower sealbox crankshaft, Gaskets changed on the carburetor, Fuelpump, etc.
etc..
Eventually discovered that the two coils did not give a spark when the engine speed increased over1500 rpm

Anyway this is what I got, sitting out in the rain.

Measurement between cable from box to the coil and earth.
Idling/High speed
Green/Black 254/260
Green/Red 253/260
Green/White 190/106
Green 190/103

Measurement of red and red/white from the stator
Plus on red/white
Idling/High speed
135/230
Minus on red/white
90/230

Measuring between blue and blue/white from the stator
Plus on blue/white
Idling/High speed
260/300
Minus on blue/white
300/270

DVA-measurement on the trigger wires was approx 8V
Then the question is, what does this tell me?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: DVA-multimeter The result. Mercury 1976/50hp

From your readings it looks as if you have a grounding issue on the the last two coil outputs,check them for cracks,broken ground strap and broken ferrites. If they seem ok flip the coil wires on pack(top to bottom) if problem stays on grn & grn/wht output, replace the pack...
 

ixs

Cadet
Joined
Jun 8, 2008
Messages
17
Re: DVA-multimeter The result. Mercury 1976/50hp

Hello

I did the earth thread, before and got good ground on all four.

From your readings it looks as if you have a grounding issue on the the last two coil outputs,check them for cracks,broken ground strap and broken ferrites. If they seem ok flip the coil wires on pack(top to bottom) if problem stays on grn & grn/wht output, replace the pack...

Run out of battery when i?d tried to start it.
Not quite sure what "flip the coil wires on pack(top to bottom)" means.
Normal position on the box from the top, is Green/Black, Green/Red, Green/White and the bottom one Green.
When doing the above test "flip the coil wires on pack(top to bottom)"
Will it be, for example Green, Green/White, Green/Red, Green/Black.
Or change them in pair like e.g Green/Red, Green/Black, Green, Green/White

Or let say 1 2 3 4 to 4 3 2 1 or 2 1 4 3.
Does it sound confusing.
I am confused.
Hope to hear from you or anybody that understand:confused:
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: DVA-multimeter The result. Mercury 1976/50hp

You have traced the problem to either 2 bad coils, or 2 bad coil drivers. (switchbox) Move the bad coils to good position, and vice versa. Then retest the green wires. If the problem follows the coils, it's the coils. If it stays in the same place, its the switchbox.

You don't have to physically move the coils, just the wires. (swap the wires) In this case you don't have to run it, so don't worry about the secondary (spark plug) wires. Just don't start it.

It's called substitution, or swap testing.

hope it helps
John
 

ixs

Cadet
Joined
Jun 8, 2008
Messages
17
Re: DVA-multimeter The result. Mercury 1976/50hp

Hi
The initial problem was, the spark died on two coils, on higher revs.
But OK on idling and up to aprox 1500 rpm.
I done test with a ohm meter and found the earth strings on the back of the coils was bad, but fixed it so all four coils was around 900 ohm on the highvolt outlet.
Changed two coils, but still bad. So its the stator or the box.
I changed the blue with blue/white and the red with the rede/white.
I was told that if it was a foulty stator, the problem would move .But would it stay on the same, it?s the box.
But when I did this the engine did not start at all.
Can I swap the top nr one wire for number three on the box, leading to the coils, without changing the cable to the sparkplug?

How do the ignition work, do nr 1 and 4 ignite on the same time or is it 1 and 3. Or don?t the light in pairs at all?
If cyl 1 fire on the same time as cyl 4, I could change the green with the green/black. and se if the problem moves.
I dont understand how I could do a DVA test without starting the engine, I have to rev it up to get the foult.:confused:
Hope I don?t missunderstand to much.
 

Dave1027

Lieutenant Junior Grade
Joined
May 25, 2010
Messages
1,078
Re: DVA-multimeter The result. Mercury 1976/50hp

Does not have to be started to do a dva test. Cranking is ok.
 

ixs

Cadet
Joined
Jun 8, 2008
Messages
17
Re: DVA-multimeter The result. Mercury 1976/50hp

Hi
But my problem is that the spark fading out at revs over ~1500rpm.
So I need to start and rev it up a bit.
 

ixs

Cadet
Joined
Jun 8, 2008
Messages
17
Engine on dry land, now.

Engine on dry land, now.

As the title says, put a stroboscoop to the plugs. 1:st cyl yellow, at tickover, and fading at revs.
2:nd same as nr 1.
Nr 3 and four, almost whiteblue in the light and getting stronger at higher revs.
Changed the red and blue from the stator with blue/white and red/white.
And the problem stayed at nr 1 and 2,.
So, do I change the box?
 

ixs

Cadet
Joined
Jun 8, 2008
Messages
17
Re: Engine on dry land, now.

Re: Engine on dry land, now.

As the title says, put a stroboscoop to the plugs. 1:st cyl yellow, at tickover, and fading at revs.
2:nd same as nr 1.
Nr 3 and four, almost whiteblue in the light and getting stronger at higher revs.
Changed the red and blue from the stator with blue/white and red/white.
And the problem stayed at nr 1 and 2,.
So, do I change the box?


Changed the box. After two years of renovating.
Engine worked fine. The boat was flying over the water.
Two weeks later it was nicked.
But got meself another Mercury 5o/Hp Thunderbolt 1976.
 
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