EGI Fuse Question
 

S5 TII- First, let me say the car runs fine, but as the battery is old and drops the charge after sitting for a week or so,
thought it's time for a new one. As I was having the "normal" starter hesitation every once in a great while along with
slow power windows, thought I'd do some voltage checks before pulling the battery. Just a side note, when the car is
running there is 14.4 volts at the terminals, new 160 amp alt, don't need that much, but for the price thought I'd
pick it up.
The battery reads 12.2 but with the EGI pulled, there is only 11.6 when the spades are checked, and with the key
on, the voltage across the two spades drops to 10.8 and bat voltage still 12+. My question is why?
Thought I'd check voltage at the interlock and came up with an 11.8.

Any ideas?
TIA

Of the two fuse spades, only one receives voltage w/no key, and that would be the spade receiving voltage from the battery. The other spade should have 0 voltage w/no key. W/key to on, the spade that's connected to the battery should still have the same voltage while the other spade could have voltage from possible backfeeding in the main relay (if this were the case, the results might be different if the relay plug was unplugged). Not sure how you are checking voltage of the spades, as only one is used at a time to check voltage.

Check your grounds as a bad chassis ground can cause a significant voltage drop.

The main chassis ground for the car is on the driver side strut tower and tends to suck. It's fine when new but it is exposed to lots of grime and isn't good for the long term. You can leave the stock ground in its location and run a better ground to the fuse box bolt on the top of the strut tower, just use 8ga wire or bigger.

The engine ground sucks too, and the bolt for it tends to get loose. Check it since you are having an EGI fuse voltage issue because all of the engine sensors ground there. The S5 ECU ground is located on the upper intake manifold, on the vacuum spider (unlike the S4 ground that sucks to get to). Make sure that is tight and good. If your transmission has ever been replaced by you or a previous owner, I can garauntee you main engine ground isn't in the right place. The main engine ground connects to the passenger side firewall via spade connector and bolts to the top of the tranny. Trans shop morons snapped it off and connected it on the driver side firewall making it useless on my car. I moved it to the passenger side bolt of the slave cylinder to make it work again. Moving the main engine ground to this location works, it is just only 2 inches from where the factory ground went.

As usual, a wealth of knowledge in a couple of posts. My mistake as I was checking across the spades.
As long as I finally got up enough energy to work on the car, I'll also check the various grounds as
it certainly can' t hurt.

Once again, thanks.

Just thought I'd give an update as to the grounds. They are all in place and in good shape.
Probably because we purchased the car new and it hasn't been in the rain for 25 years,
just sits in the garage and out once in a while. Might find this interesting, but yesterday was
the first time in 27 years the under hood fuse cover was taken off.
Will get a new battery before the weekend and see how that works out, and if any additional
problems I'll reach out.
Thanks again