old fault returned again tonight

[markcw]

Have been plaqued with this fault below for years now and it comes and goes, can any one give me a second view as my head tonight is screwed, started fault finding at 18-30 and still on it 00-20 midnight


Ok have had a weird electrical problem on my VP .4.3gl v6 carb engine,
battery tested and full of power, when i turn the ignition key to postion 1 my volts drop on the gauge from 12.63 to 10.01 and needel sits button with no volts even thou there is 12 on other items in the boat like lights and depth sounder, battery show no volts drop at all, the other day i removed the whole engine loom from the boat and checked all wires and connections, nothing found so placed back on the engine.

For weeks now have been checking and ohms testing all loom cables, tonight i done a continuty test across the volt gauge with wire connected and found i had a direct short, if i remove the purple wire from the back of the volt gauge that travels down the boat to energise the fuel pump relay, the volts are normal and correct on all gauges including the volt gauge, So i placed the purple wire back on the gauge and it instanlty drop to 10v and needle down fully off, remove the wire again and volts go back up.

so then i check the main engine harness loom block connector(big black one) and the meter shows a direct short between the earh pin and the purple wire pin, disconnected the coil wires completly and the dead short is gone, volt on all gauges correct, reconnected wires to coil and volts gone down to 10v and lights dim on dash.

useing a Clibrated Fluke meter

Have taken coil out on bench now and between the + and - ohms is 0.8 primary circuit v/p book says it should be 1.25 to 1.4

secondarty circuit is 10.14k ohms book says 9.4 to 11.7.

Inside the coil you can hear lots of fluid is this right could it be a cooling oil?????, all relays are energizing with this issue, fuel pump is running, choke not used and taped up

the boat runs fine or did have not tested the last few days, what confussed me is the large voltage drop when the ignition is turned, the coil is 2 years old.


Has any one got any ideas as were the fault could lie,i am now brain dead with this issue

 

[Sandyman]

Not an expert on MoBo's but sounds to me like your picking up the earth or partial earth through another wire.

 

[volvopaul]

Your engine wont be a carb engine with an electric fuel pump, its a single point mixer unit, id say the pump could be on its way out if the volts are dropping that much, does it start ok? and are the volts up to 12,5 when the engine is running, if not its a charging fault.

 

[markcw]

fuel pump is new 2 months old, for testing the pump is not connected, the engine i have has a nikki carb with a low pressure electric fuel pump, the engine is the third revision and the loom is the third revision.

boat runs fine, chargeing is fine, 13.6 volts when running and battery dial needel show correct voltage, when the ignition is at postion one i should have 12v to all dials and ignition relay wire that go down to the main engine harness loom, but currently i have with coil connected and 10.01v, if i remove the coil from the engine 12.5v returns to the dials and ignition relay and every thing works correctly again until the coil is reconnected.

i think sandy man could be right, but removing the coil removes the dead sort circuit from the engine loom and harnesses in the dash and dials.

have to admit im baffled and i am a eletrical/ mechanical field service emgineer

 

[markcw]

Good news hopefully,so far fault found, after lots of loom checking and belling out cables, found the trim beach switch wires running straight over a counter sunk screw which is 2" to long and the two wires have been slowly rubbing over the tread of the screw. this was noticed when leaving the meter buzzing away on the dead short, i accendently activated the trim beach switch and the short was interupted and then i wonderd how can that be.

The wires run to the trim indicator, which has supplied power by the purple ignition switch, this is why i was picking up the short via the ignition side and coil

lets hope this is the end of this extrely time consuming fault please wellcrafty no more