RV8 Hotwire 14CUX: Current for Pump, Injectors, ECU?

wesbrooks · Post by **wesbrooks** » Mon Mar 21, 2016 1:10 pm

Hi All,

Any one got reliable figures for the current that the Pump, Injectors, and ECU take on average and peak? I'm trying to size fuses and there were other components on the same fuse on the donor so those fuses are likely to be overkill!

Thanks.

DaveEFI · Post by **DaveEFI** » Mon Mar 21, 2016 1:25 pm

The purpose of a fuse is to protect the wiring in event of a short, etc. If you wish to protect an individual component, you'd use a local fuse - like say in a car radio, etc. But there's not really any point in doing this with a pump or injectors.

wesbrooks · Post by **wesbrooks** » Mon Mar 21, 2016 1:36 pm

I appreciate the purpose of the fuse is to protect the wiring. These components were on different circuits on the donor. I'd assumed this was to create some separation of the potentially electrically noisy pump and injectors from the ECU?

Either way can if any one can offer information on the expected draw of these components it would be appreciated.

I'll be using this to pick the nearest fuse, pick wire size greater than this (Fuse rating < 0.8 * rating of cable), and finally potentially re-size the cable if the expected voltage drop is greater than 3% using 12V. So when running on normal battery voltage of 13 or so volts all should be fine.

v8250 · Post by **v8250** » Mon Mar 21, 2016 5:03 pm

You don't specify which fuel pump, ECU, injectors? Find the exact model numbers and you should be able to track down the original load specs.

Re' pump, this will [should] be operated by a relay so no need for an inline fuse with new wiring.

Re' injectors...it's highly probable the ECU pcb will have safety suppression/a cap'/zenner diode to handle any line noise.

Re' injectors, it's just not necessary unless the injectors are crap at their terminals and/or the wiring's shot with a part short causing over heating to the wiring loom...and as per your post you're replacing the wiring.

To help, the more components you put in a cct the greater chance of cct failure; especially fuses. Keep your fused cct requirements to only what is required. By all means fuse each primary cct but try not to over do it, it's simply unecessary on a car. If you do fuse every cct bring each cct back to a central fusebox in the cockpit where it's nice and dry and use this as the primary test point...it's a great way of easy fault finding as you can isolate ccts i/p's & o/p's. Only draw back is that you'll need a lot more wire, but it's the correct way to wire a car.

wesbrooks · Post by **wesbrooks** » Mon Mar 21, 2016 8:28 pm

v8250 wrote:ccts i/p's & o/p's.

I'm assuming inputs and outputs for the latter but what is ccts?

It's what ever comes on the 95 Land Rover Discovery V8i.

Pump appears to be Delphi ESR3926 (FG2000412B1)in tank level sender and pump. That appears to be rated at 10.5A.

Injectors are ERR722. On the following link they list the resistance as 4.0 - 4.5 ohms per bank, and therefore a total current of 6A.

http://www.britishv8.org/articles/rover-14cux-efi.htm

Not seen much listed for the consumption of the ECU itself yet.

richardpope50 · Post by **richardpope50** » Tue Mar 22, 2016 1:53 pm

I did these calculations to work out my fuses (as I designed / made my loom) and have a spreadsheet of all requirements for day, night and max running so PM me with your e-mail address if you want all the calculations in the .XLS but ...

Injectors = 2.67 amp per bank.
Fuel pump = 6.5 amps
Alarm + ABS ECU + Megasquirt ECU + Stepper Motor all add up to 2.2 amps.

I had either measured all currents or calculated them.

wesbrooks · Post by **wesbrooks** » Tue Mar 22, 2016 1:57 pm

Hi,

Thanks for that. The rating for the pump that I saw is probably worst case end of life. I'd seen the 6.5 figure somewhere before too.

I'll PM you for your sheet. I've got a fair way though my loom now but it's always good to see fresh perspectives.

Thanks.

DaveEFI · Post by **DaveEFI** » Tue Mar 22, 2016 2:14 pm

The standard hotwire injector is given as 16 ohms. ( 15.9 if you want to be picky.

) At 13.8V that would be 0.8625A per injector. Or 6.9A total. But there will be some voltage drop in the drivers, and with batch injection and alternating, they won't all be drawing maximum current at once. So a 10 amp fuse should be just fine.

If you Google for a MegaSquirt external wiring diagram - or go to the MS site - you'll find the standard fuse values they recommend.

It's not a good idea to use a standard fuse close to the limit of the continuous current actually drawn, as thermal cycling can cause it to fail early. You'd need anti-surge types for that.