Low voltage

[pmc_3]

I've noticed the other day when using Rovergauge that the main voltage shown is low, with the engine not running it shows 11.7v (voltage is 12.7v measured across the battery) and when doing a log file on a journey home from work it's showing between 11.5v and 13.1v.

I've cleaned up the earth from the engine to the outrigger in case it was that but putting a multimeter across the battery with it idling shows just over 14v, so it's not a charging issue. I've had a look for the 80amp fuse but can't find it anywhere in the rats nest, not near the positive in the battery or near the fuse box. if I follow the positive from the battery it is just a straight cable that disappears up between the lower dash and the transmission tunnel.

Any ideas where to look next?

[taylormj4]

Hi pmc-3, the large fuse on my 450 is attached to the underside of the offside chassis rail, close to the starter motor, if that is the one you are looking for?
It is located in a small black box that just contains that single fuse.

[sixor8]

The large 100A fuse bolted to the lower chassis rail is between the alternator and the battery, this is in addition to the large fuse close to the battery that is protection for all car electrics. The thick red cable from the battery goes directly to the starter motor.

[Belle427]

If the tests at the battery are ok i dont think you have an issue as such, older cars did not have the 100 amp fuse and i seem to remember reading if the Ecu software is older then it can be a little erratic displaying the correct voltage.
Some important grounds can be located on the engine timing cover lower bolt, from memory the same one as the chassis ground is fixed to and this is always worth checking just as a maintenance item.
What year is the car?

[PabloGee]

don't know about every car, though mine is a 1995, and the 80A fuse is between the battery where a red cable meets two brown cables that go up behind the fuse board. It's in the nest of wires above the battery.

[pmc_3]

Just thought I'd update this. When the car was at Central having some trimming done the ECU shat itself. It was very odd as I drove it 115 miles over there! Something had burned out on the pins for the injector drive on one bank, they did a bit of diagnosis and couldn't find an obvious cause. Amother ECU they had was put on and it fired straight up and ran fine. Interestingly, I plugged in Rovergauge when it was back home and now there is a different ECU and the voltage is showing correctly. So looks like the cause was something internal of the ECU. I'm hoping this also solves the long term trims that keep disappearing.

[PabloGee]

I think it's always the fear in the back of my mind that the ECU will develop a fault.

But mostly because I'll probably be constructing the point to the wife that I now need to drop £1-2k into an invisible part of the TVR for an ECU, loom and injection system, all because one little pin inside a small metal box has burned out...