Engine stall under heavy electrical load : where to look ?

[Tony Hoffman]

Also, check the voltage going to the ECU when the fan comes on. Best with
an O-scope, but a good DMM will also work. You want to see the ECU voltage
relative to it's ground, so start with probing those two terminals. If it
drops significantly when the fan comes on, there's your problem.

HTH,
Tony

On Tue, Mar 27, 2012 at 4:40 PM, S P SHERMAN <spsherm at msn.com> wrote:

>
> I'd start by checking the alt output.  Easy with a voltmeter at the
> battery. Check voltage on the battery terminals with the engine at idle and
> no load, then add load, then up the rpm.  Should be able to maintain a
> fairly constant voltage, say around 14v. If it drops alot as you add loads
> and does not recover as you up the rpms, the alt is not producing power or
> not enough power. For an even better picture, get a high capacity amp meter
> in line to the battery while doing this test. That will let you know how
> much current your alternator is putting into the battery (if any) with the
> loads on line.
>
> For an even easier test go to one of the auto big box stores. They will
> test the electrical system with a load for free. Although it won't tell you
> a whole lot more than this simple test (other than maybe whether its your
> battery or alternator at fault).
>
>