earth points and earthing

[adyw]

Gents,
I'm having a few earth issues and I need some advice.
General issue is a noisy earth so have carried out a few general tests with the following results

Battery -ve to engine,
just meter on 0.2mv
ignition on 2.8mv
during cranking 0.67 Volts

Battery -ve to chassis
Just meter on 0.2mv
ignition on 2.8mv
during cranking 0.33 Volts

My question is.
Is this normal, my first thought are to change the earth cable from the engine to the chassis and see if it makes a difference, but any advice would be good.
Another question is how many cables earth the engine to the chassis, I have found the one in the offsite frount wheel arch but is there any more.

[HRG]

No idea on the values but there's an earth on the front chassis crossmember where the body bolts on, one under the centre console, one between the fuel tank and the chassis at the rear. Not sure of any others but that's four accounted for.

[adyw]

I know there most of those are, but not sure where the fuel tank one is, I've had the tank out last year with a leak and can't remember disconnected an earth cable.

[HRG]

It's there on the NS IIRC under one of the button heads. It sorta 'sticks' to the car when you remove the through bolt. That said you've got me doubting my own sanity now....

[adyw]

can't remember that one, will have a look tomorrow night

[HRG]

Found it. Offside running vertically by the looks of it. I think it's just visible in this pic lurking below the speaker.

[adyw]

thanks for the picture,
is it connected to the tank one end and the chassis the other. or does it just disapear

[HRG]

Just disappears... Possibly. Sorry I can't be more certain, I just vaguely remember seeing something there when I did the raise.

[adyw]

I think the only way I can start to narrow it down is to turn the ignition on and then pull out each fuse one buy one until the earth disapears, then it at lease gives me a clue of where to look.

[Loubaruch]

What exactly do you mean by " a noisy earth"? Is there interference on your radio?

Looking at your voltage measurements. If we assume 100 Amps cranking current (I think fairly typical with a cold engine)your measured volt drop engine to battery of 0.67 volts gives a resistance for the earth lead of 6.7 Milli-Ohms.I would have thought this quite reasonable considering the method of connection. There is a main chassis earthing point on the tunnel top member under the whale tail immediately under the dash passenger side. This is known to cause problems if loose (ref Steve Heath et Al)

[adyw]

Hi,
by noisy earth I mean bad connections causing the -ve side of the battery not being 0v but higher, therefore causing interferance with electronic componets such as the ecu that rely on -ve.
I have taken the car appart and had a look at the earth point on the passenger side of the tunnel, All seams ok, undid the bolt, gave it a scrub and then tightened it up again.

[davetherave1970]

adyw said:

earth point on the passenger side of the tunnel,

I assume you saw the drivers side one too!
My drivers side earth point was loose enough to move by hand and the only problem I had was that in traffic my speedo would bounce between 30mph and 130mph. It was actually putting the mileage up while standing still!

[spend]

I don't think there is anything wrong with those readings, you may have the courtesy light relay / alarm + remote / clock all active. Remove the positive from the battery & measure resistances if you want a sensible check IMHO.

Engine earths for sensors are at the back of the cylinder head behind no 7 pot. I think these go back to the ecu BTW.

Battery to chassis is under trans tunnel, dash / fusebox earths come from there or off the steering column.

Front loom earths from the chassis bolts under the rad.

Rear loom earths from chassis bolts under the petrol tank.

If you do the resistance check you can test the loom earths from:
- front rad fan connector
- rear tail light bulb holder
- dash fag lighter

Without knowing what problems you are having its hard to say where the faults are so you have to search through those grounds. All the grounds are just a collection of black wires all crimped to a single ring terminal bolted to the chassis, they can become mechanically stressed and need recrimping + heat shrink if they have been mis-handled.

[adyw]

doh only did the passengers side earth, will have a look at the other over the next night or two. The main issue I have is the new after market ECU is particularly earth sensitive and on occasions trips out, not all the time, just on occasions, hence need to find the earth fault.

I must admit I have been under the car many times and never notices an earth at the rear near the fuel tank.

[spend]

Bloomin MS at a guess! earth it to the battery, and sensor grounds to the cylinder head both at least 25A wires. You just need a bigger computer plug

[adyw]

everything is earthed to the battery -ve aleady, except for the edis and coils, it's just getting some interferance from something occasionally.

[spend]

Have you got a black wire going into the alt W+ by any chance. IIRC its the tacho signal for LR's but I've seen quite a few with it connected to the engine earths?

[adyw]

will have a look tonight

[adyw]

p.s what's LR's.

[spend]

Sorry LR is my lazy code for Land Rovers The alt generates a signal for their rev counters, then they use the same instrument pod for 4/5/6/8 cylinders juice or oil. IIRC its W+ on the alt