Tamd22 MD22 Earthing Thread.. Isolated Return. 55Amp Fuse.Help Needed

[jw2000uk]

Hi lads.. Followed wiring diagram.

But my block has permanent ground to it.. If i put a multi-meter + to battery +. then neg to a bolt on the engine, it shows 12.6V at all times. i take it this is not correct?

even when i disconnect all Neg terminals off the starter, it still shows 12.6

ive got more testing to do.. but any idea why this is happening lads?

also, on the chance that the 55amp fuse has gone (will be testing), could i replace with one of these
http://www.ebay.co.uk/itm/Fuse-Spann...YAAOSwmfhX2ago

I have heard control cables can ground a engine??

I unplugged all my accessories,leaving just the positive form battery selector switch,still the block was grounded.

 

[alldodge]

I'm seeing additional grounds coming from the battery terminal. Some how one or more of them has a connection back to the block. Don't see the cables being the ground but it would only be possible if a ground wire is touching it

 

[Bondo]

But my block has permanent ground to it.

Ayuh,.... Am I missin' something,..?? The block should always be grounded,....

 

[jw2000uk]

I'm seeing additional grounds coming from the battery terminal. Some how one or more of them has a connection back to the block. Don't see the cables being the ground but it would only be possible if a ground wire is touching it

Unplugged all them just incase mate.. they dont go to the engine also. Ones deck wash. Solar and tracker.

 

[jw2000uk]

Ayuh,.... Am I missin' something,..?? The block should always be grounded,....

Not this engine its isolated return.

The block should only ground to start,stop, and heat glowplugs.

 

[alldodge]

You can remove the grounds (remove battery cables on ground side) to the battery and still get 12V, correct?

Not this engine its isolated return.

you need a ground on the engine to get sensor info

 

[jw2000uk]

right, ive now disconnected every extra. leaving just the volvo stuff.

gone to single battery.

- battery to - post on starter

+ battery to + solenoid.

red mulitmeter lead on battery +
then black on a engine bolt i get 0V. perfect.

BUT as soon as i put either the negative from the alternator
or from the sensors,on the the starter - (witch is where they should go)
then i get 9v on the engine block at all times.

55amp fuse still makes no difference if connected or not. Technicaly, when i disconnect it, it should stop the pre heat, and stop solenoid working.

as i said, the engine runs fine, starts and stops fine.

 

[alldodge]

I don't see an issue. The alternator and some sensors will have voltage on them when the battery is connected. They are not drawing any current until the motor is started. The alternator output line is connected straight to the positive terminal. The only time is is turned on is when the field winding side is energized when motor is started

 

[jw2000uk]

I don't see an issue. The alternator and some sensors will have voltage on them when the battery is connected. They are not drawing any current until the motor is started. The alternator output line is connected straight to the positive terminal. The only time is is turned on is when the field winding side is energized when motor is started

Thanks for the replies mate. Heres some text on how it works the isolated earth. Im still convinced i shouldnt get any V on block..

The lower relay is energised from the glow plug circuit and the engine stop circuit in order to provide a negative path from the engine block during these two operations.

However what I think you have missed is that the glow plug circuit remains energised via the "ignition" switch during the starting phase .

The result is that the lower relay is energised during preheating and during cranking, connecting the engine block to battery negative via the fuse. That is what you observe.

If the starter motor is of the insulated negative type there should be no path from it to the engine block. The negative return should be directly back to the battery negative via the negative isolating switch.

 

[jw2000uk]

The engine block and saildrive are isolated from battery negative ('earth' or ground) when the engine is not running i.e. most of the time. There is a relay (identified by a 5 in the wiring diagram in the Owners Manual) that connects the negative to the block, through the fuse link you mention (numbered 6), when the 'ignition' is turned on. It allows the glow plugs and stop solenoid to work as they have a ground return rather than a separate wire.

The starter, like the alternator, should be insulated return, and therefore have no effect on the fuse you mention. If yours is not insulated return then the starter would certainly blow the fuse.

 

[alldodge]

Had to go find a wiring diagram for the motor to see what your issue is. If the glow plugs are staying energized then it the first place to check would be the relay. In this pic note the connections for the contacts. The coil uses contact points 85 and 86, and the power is switched using 30 and 87.




In the pic below you can see where every relay is connected to ground on 85 (other shows as 2). To energize any of the relays power is applied to pin 86 (other shows as 1). So the grounds are not made, but yet connected at all times. The glow plugs are turned on from the key switch via orange wire at pin 6

 

[jw2000uk]

Had to go find a wiring diagram for the motor to see what your issue is. If the glow plugs are staying energized then it the first place to check would be the relay. In this pic note the connections for the contacts. The coil uses contact points 85 and 86, and the power is switched using 30 and 87.




In the pic below you can see where every relay is connected to ground on 85 (other shows as 2). To energize any of the relays power is applied to pin 86 (other shows as 1). So the grounds are not made, but yet connected at all times. The glow plugs are turned on from the key switch via orange wire at pin 6

Thanks again for your help mate. Those previous 2 posts were other peoples problems,,juat explained the earth setup better

Glowplugs were fine, i.e. working on key.

The issue was the 55amp fuse that grounds the engine,but only for starting.stopping &glow plugs, made know difference when disconnected.

Hence its acting as if the blocks getting earth from something else.

Tested all the relays, checked wiring etc today. Cant find a fault. Maybe the new starter isnt insulated earth, even though its sold as that.

:/

 

[alldodge]

Sorry but guess I'm just not understanding the issue. From my way of thinking, if the positive end of the volt meter is placed on the positive post of the battery, or anything theat is connected direct to the post (such as the starter and alternator), you will always see 12V. While power is connected to the starter there is no connection to the negative side of it. The negative side is only connected when the solenoid is energized. The meter is reading another ground