cranking voltage

[Jason]

im having some problem getting my ecu to register that my motor is cranking.

The problem im seeing is that the voltage is droping to 6v wile its turning over, now im just scabbing power from my mums car. The plugs are not in so its just smoothly turns over.

The question im trying to ask is that i dont have my alternator attached atm. Im worired that even with the alternaotr connect during cranking its still not going to produce enough voltage for my ecu to run (9v min).

Also just adding to help, im running an external start switch insted of using the ign barrel, so the acc off function is not being used, but i have hooked a realy up so that my thermo fan turns off when i hit it. Ive got central locking, should i hook that up to the 'disconnect' relay. Although i cant see it using much power when its not active.

[rthy]

did you measure the 6v from the battery when it was cranking? if so your battery is stuffed

[Jason]

well it was 6v on the '12v' rail it was behind some fuses but that dosnt matter... hmmm

[mattysshop]

what your doing is performing a load test on the battery, whilst having a multi meter hooked up to the battery it might read 12.6 (for example) but then when you put the batter under load buy tuning the engine over etc.. your seeing it drop to 6-7V.. usually means it's dropped a cell or two..

this normally happenes to batterys that are a few years old.. (there only ment to last about 2 years!) and a cold winter snap goes through them.. OR they used to be used quite regularly once or twice each day sorta thing.. then over about 2 months never touched as the car was getting a transplant etc etc..

you might find that if you charge it up over night.. it will start her.. but not hold voltage..

you cannot hurt a car buy putting a battery in with a little more CCA (cold cranking amps) this is what it draws on to start the bastard each morning (best simplest explination)

i run 580CCA calcium sealed batterey in my 86.. you can continuously try and start the car for about 20 mins.. and she still won't go dead!!