Electrical Problem!

[hanjae]

I have a pair of VP151's and since running her up this season we have hit a problem. Both engines have Luminition and the Stbd engine after a short while just cuts out. It is electrical. It will restart and run for a short while then just cuts out again. I have checked all the connections and all are ok. Next I had a spare brand new Luminition so fitted that and still the same. The rev counter is running fast, so to test this used the port tacho and that was fine. Could the tacho cause this problem? what else could it be. sitting on a pontoon it will not reproduce the problem it is only when under way!
HELP please I want to play! When we have some summer!

 

[No Regrets]

Have you tried a 'wiggle' test?

Start the engine and 'wiggle' the wires from the boat to the engines power and ignition circuits.


Try not to get your fingers/ loose clothing caught in the whirling bits though...

It may be a semi-broken wire or iffy connection which only breaks as the engine moves slightly under load...

 

[lenseman]

[ QUOTE ]
sitting on a pontoon it will not reproduce the problem it is only when under way!
HELP please I want to play! When we have some summer!

[/ QUOTE ]

Therein is a clue . . . /forums/images/graemlins/smile.gif

Firstly, Luminition are very reliable and I was using and supplying them in the late 60's and early 70's

You have to understand how ignition of the air/fuel system works in a -stroke engine (land based or marine)

During the combustion stroke the fuel air mixture (15:1 by weight) comes up on compression and the ignition is then told to 'fire'.

The spark generation is similar to lightening and the voltage, from the Luminition system, builds up and builds up until it exceeds the breakdown voltage (BV) inside the combustion chamber.

The fuel/air vapour mixture will (hopefully) ignite and burn causing the pressure to increase and making the engine turn.

Under no load or light load, the BV will be less. When you are up on the plane and the engine is working hard the BV will be greater.

Now this is the important bit.

As the BV under load might be a few thousand volts GREATER than when running at idle the volts will try to find the easiest way back down to earth. This route is obviously NOT via the spark plug gap inside the combustion chamber but via a different route.

This route can be the leads themselves or the rotor arm inside the distributor. A spark plug (neon tester) in the king lead can tell you when the fault starts to manifest.

Closing the spark plug gaps on the faulty engine will alleviate the problem as basically you are 'lowering' the BV required to jump the spark plug gap as the gap is smaller.

A good test is to run the engine under load and in total darkness to see if you can see any faint blue sparks leaking out of the HT ignition leads. Your eyes might have to become adjusted to the dark to fully see this phenomenon? If you suspect the leads, change them.

If in the past, you have sprayed them with WD40 or similar water inhibitor, you will have laid up an oil (SAE 5) onto the leads. This oil, sadly has the effect of collecting dirt, salt and carbon deposits. These deposits help to lower the BV outside the HT leads and can lead to their early demise.

Clean each and every lead with hot water and detergent and soap and don't replace the WD40 water inhibitor. You might find that this will cure your HT breakdown. Similarly clean every part of the distributor cap(s) inside and out and again, do not use WD40

I hope this helps?

 

[hanjae]

Hi, I don't thing you quite understand me. We run her for a good 20 mins on the pontoon. All ok left the pontoon and went down river after about 5 mins the stbd engine just cut dead, ignition light came on straight away. Turned key and engine fired up straight away and ran for another five mins and then cut dead again! No petering out of fluffing!
I have checked all wires and we have tried the wiggle test, bang and everything else but it wont reproduce it back on the pontoon!
I am going to try to run a wire direct fromt he starter motor to the coil in the morning to see what that does.
It is as if something is getting hot and makes it all cut out!

 

[brianrunyard]

I've just solved a similar problem on my volvo, engine would run forever on the pontoon, but underway would cut after about 15 mins. After a few minutes it would start and run ok for another 5 mins or so.
Turned out to be a faulty ignition switch, there was a high resistance across the contacts, under load the coil draws more current, which caused the bad contacts in the switch to get hot, which increased the resistance until the voltage at the coil was insufficient for the engine to run.
Tracked it down by monitoring the voltage at the coil, then checked back through the system to find the volt drop, turned out to be about 7 volts across the ignition switch.
Proved it by bypassing the switch.
Bought a new switch from ASAP and all is well

 

[hanjae]

Would this also account for the rev counter throwing a wobly?

 

[No Regrets]

OK, if it starts immediately, it could be a fuel pump relay, if your boat has such a thing, or perhaps a defective coil which breaks down when hot.

When it stops, do you have a spark on any of the HT leads?

(I'm a car technician and MOT tester by the way...)

 

[No Regrets]

[ QUOTE ]
Would this also account for the rev counter throwing a wobly?

[/ QUOTE ]

The older type tacho's are usually fed from the low tension wire in the distrubutor. There could be a break internally, which is exacerbated by any mechanical advance/ retard system (i.e. when the inside part of the distrutor swivels to change the spark advance, usually vacuum or centrifugally operated)

Recheck or replace the wire from the inner part of the dist. to the outer body, easy to see once the rotor arm and dust cap have been removed!

 

[hanjae]

Fuel pumps running all the time, I have Facets fitted.
It stops dead and then as soon as you turn the key she fires up again!
and runs for 5 mins or so then does it again.
It is not fuel/

 

[hanjae]

I connected the feed to the other rev counter and and it the rev counter works fine so it is in the rev counter.Jon

 

[No Regrets]

OK, so assuming disconecting the rev counter doesn't stop the problem...

Try the Distributor internals, especially that wire, which may appear to be OK on a visible only check...

It's either a semi broken wire, or component breaking down.

Also swap coils to see if the problem transfers or remains the same.

Keep swapping parts, in fact, until the problem swaps too.....

 

[hanjae]

Lastest. 2 of the 4 new plugs from Volvo are faulty! So I have told the boatyard to send the whole lot back to volvo and I am putting in NGKs.
Tacho seems to be the fault and taking off all the connections and reconnecting seems to have done the trick.
One more test in the morning!