VK 355 starter motor current draw.

[Immortality]

The fact that it starts fine with a starter pack on the engine but not with it on the battery at the back suggest there is a issue with the wiring from the boot mounted battery to the engine/starter.

How did you crimp the fittings onto those welding cables?

 

[Ultravk]

The fact that it starts fine with a starter pack on the engine but not with it on the battery at the back suggest there is a issue with the wiring from the boot mounted battery to the engine/starter.

How did you crimp the fittings onto those welding cables?

Well I didn't have any of those big lug crimps so i kind of used a vise to squash lug around the cable.
It is on tight though.
No solder

 

[wamboin23]

What does the voltage at the battery drop down to under cranking?

 

[Ultravk]

What does the voltage at the battery drop down to under cranking?

Haven't checked it at the battery.
Just at the post on starter.

 

[the_boozer]

run a big negative from the negative battery post to the block as well as the big positive I once knew a bloke with the battery in the boot that manged to melt his clutch cable

 

[harrop.senator]

Long way to run an earth a good bare metal to bare metal block to chassis and chassis to battery will suffice.

 

[gtrboyy]

Yeah those red wires are 12v supply to relays in fusebox etc & ignition switch...should be fusible link before those off battery or your case starter.

Think you meant battery cable to starter motor then another wire from alternator to starter as charge wire.

As Immortality mentioned large voltage drop from your battery cable if you can jump start from front yet notably slower if jumpstart from boot...that long cable is suspicious.

Long earth cable not really needed if you run couple of good earths front & back...remember mags used to say should for efi cars with battery in boot,very few did it or had any problems.

 

[Ultravk]

Ok thanks for everyone's suggestions.
I guess I'll have to recheck all earth connections and the main batt cable connections.

How do I measure the voltage drop along this cable?
Just voltage under load at both battery then starter and take 1 from the other?

 

[vc commodore]

I do have my battery relocated to the boot....The battery earth goes straight to the boot floor via a nut and bolt. It's about 1 foot long) The block earth goes from the engine mount to the K-frame....At the K-frame it is nut and bolted and again about 1 foot long.......All battery cables and earth cables are thick ones, but unsure of thickness...

Alternator charge wire is.8 MM (from memory) and goes from the alternator to a battery isolator switch.....Prior to the isolator switch, it went to the positive post of the starter solenoid....

It might be possible your main power feed cable is cactus, being an old welding cable.....Welding cable tends to be subjected to intense sustained voltage put through it, which can lead to a voltage drop over time....Considering you can put a jump starter pack onto and get it cranking over quickly, I'd be looking closely there, because you have discounted the power feed by using it.

To double check, use the main power feed from the starter pack and use the cars earths to try and crank it, at the starter end of the power feed....To check if it is an earth, use the earth of the jumper pack and main power feed to the starter to crank....To me, this would be an easy way to determine whether it is an earth or power supply issue

 

[Ultravk]

Ok I think I have it sorted.

It had .5 volt volt drop between battery and starter.

So I went checking for earths
Used jump leads from block to chassis in exact place I had wire hooked up originally and presto everything starts cranking.

Obviously there is a lot of resistance in that piece of cable.

I'll replace it tomorrow and let you guys know.

Thanks for the help everyone!