Hey all, after some help/advice
My cars always had crap voltage, about 12.7 charging 13.2 is the best i have ever seen.
Its just had the new engine in, with, what looks like, a pretty new alternator, and still, charging at 12.7v revving, 12 idling.
Thats clearly no good for an 044 feeding 500 ponies.
I have uprated the alternator main wire to the battery with 8awg, and the engine bay earths are uprated, its got an Optima Yellow top 75ah battery too.
My reading is taken from the fuel pump terminals.
Obviously i want 14.4 or as close as i can get there, anyone got any idea's why its so crap?
Its not going to be safe to drive hard as it is, and i am running out of idea's?

 

What V are you getting at the battery? You need to start there, but sounds to me like a crappy fuel pump loom its a known fault.

 

Forgot to say, its got a rewire kit in, battery is in the boot, so run from that to the pump is about 2 ft long, and its earthed direct to the battery.

 

Are you getting too much resistance from alternator to battery?

 

Pump shud be earthed on the body of the car not the battery!

 

What voltage are you seeing at the alternator????

 

Do you have any reason behind this?
As far as my auto electrical knowledge goes, earthing directly to a battery is the best way?

 

I'll have a check with multimetre tomorrow

 

Just what I was told by msd when I rewired my pump as I was told if it was direct to battery it would read less volts! I agree with what you say as I would say battery is the best earth!

 

Correct straight to batt is better

 

Probably due to large cable run back to battery when it's up front.
If we get very technical mine is earthed to the body, but the battery earth is on the same bolt, battery is in the boot on mine.

 

If the battery is in the boot its not a problem. If its under the bonnet then straight to body. Earth problems cause so many problems. Possibly check engine to body earth. Check voltage as is, then check voltage after cleaning earths up. Worth a try.

 

Yeah I was told earths should be short as possible so yeah you right what you say!

 

Earthing direct to the battery is the best way as it will eliminate any resistance which would be caused by earthing to the body!

By earthing to the bodywork you are going to have a higher resistance than going direct to the battery.

Ideally you want to be seeing 13V+ with no load, but around 12.8-13V under load is ok, the fuel pump is a 12V device, so long as it has this power UNDER load, as this is where the power demand is, then your fine!

Martin

 

After re-wiring my fuel pump wires and new battery and better wires all round etc etc.
I only see 13.5/13.8 volts at the fuel pump and it is\as I have been told because of the length of the wire from the battery to the pump.
But as said above 12v or slightly above is perfectly fine to me.
I think the fact that the alternator to battery wire is so long is were your losing some voltage IMO. But then I am not a mechanic lol.

Hope you get it solved

 

Sounds like the alternator regulator is lazy. Check the output at the back of the alternator before you look anywhere else.

Also, the pump voltage check is meaningless unless its under boost, so check it at full boost, 4000rpm in 4th.

 

Right, been and done a bit more thorough testing with the multi meter, the gauge i have on the pump was reading a tad low to start with, proper readings are........

at idle speed........
13v @ alternator and engine bay power supply's
12.8v @ Battery in the boot
12.5v @ fuel pump

On fast idle, at a guess 2.5k
13.4v @ alternator and engine bay power supply
13.2v @ Battery in boot
13.1v @ fuel pump.

Stu, i know it never drops under full boost, always stays the same as it charges at, so about 13.0v

I still think i should be getting more?

 

Just out of curiousity, what type wire have you used for the alternator rewire ? Semi Rigid or flexible and what sort of length from the Alternator to the battery ?

 

its only 8 awg audio power lead i have used, its not a complete rewire, its known as "TB3" in car audio world, or "the big 3", which is, alternator to battery wire, battery to engine earth, and battery to body earth.
Mine goes to the engine bay power supply which is where the battery was, then the battery is in the boot via 4 awg cable.

 

Normal 8mm cable is only rate to 60amp, although im unsure about the audio type stuff.

16mm/ 5awg flexi battery cable takes nearer 110amp off the top of my head and 20mm/4awg does 130amp

I doubt it will make a huge difference but considering the alternator is 90amp, i would rather run something bigger

 

The standard cable is still there too, mate.
So its got what ever that is (smaller than 8awg standard?), plus the 8 awg i have run.

8 awg audio will do 80a over 30ft, or so i am led to believe?
could be bollocks, used an online calculator to figure that out?

Whatever it is, its still got more than ford gave it .
I seem to be getting 13.8v at the alternator now.