I'm getting about 90ma of current drain, which in a couple of days runs the battery down enough that it will not crank to start.
I have connected the positive terminal of the battery directly to the under hood fuse block without the starter and alternator tied in. With all things turned off I'm getting
90ma of current draw. The question is, with all fuses and relays pulled from the under hood fuse block, where could the drain be coming from?

 

Just the fuse's and relays from under the hood? You might look in the cab for another fuse block, I believe drivers side?

 

The best place to always start when looking for a draw is to have your DVOM hooked up and monitor what the draw is and then unplug the alternator. The diodes in there can go bad causing a draw and that is an easy place to start. Since you have done the relays under the hood then the next place is the fuse block under the dash at the firewall and I believe there is a fuse cover on the driver's side end of dash that you can search for the problem as well. When you find the culprit, make sure you check all items ran by that fuse/relay. Many times the fuse will control several items. There is also fuse block under the vehicle along the frame area near the back to look at. It is more of a power junction block but should be checked. You should also read this, especially if you are in a rust belt state:

https://www.fixmyoldride.com/Chevrol...pos=3&at_tot=4

 

I have also removed the fuses and relays in both fuse blocks in the dash area, no reduction in current drain. The same for the alternator, unplugged
and no reduction in current. I have also unplugged the connectors underneath and around the under hood fuse block, same result of no change in current draw.

 

That should not happen to a healthy battery.

In a couple of days, 0.09 A x 48h = 4 Ah
A typical battery will have 120min x 25A of reserve capacity = 50Ah
With a 90mA drain, your battery should last more than 23 days and still be able to start the vehicle.

I have read that computer modules in new cars can normally draw up to 100mA.

Either the battery is in bad shape, or you have a bad connection.

 

With everything unhooked, put the ignition switch to start, does the voltage (or current) drop?

 

After I first had this problem I made sure I wasn’t leaving any lights on and the problem of not having enough power to start the vehicle continued after setting for
10 to 12 days. My first action was to have a new battery installed thinking that a 4 year old battery was probably on its last legs. The new battery acted the same.
By the way, in looking in the repair manual, it indicates that a100ma drain would cause problems after 8.5 days. This seems to correlate with what I’m experiencing with my Tahoe.

 

90mA = 0,09 A. Are you sure that it can call as a parasitic drain? Try to find any good working car and measure its current drain. I think that a car's central processor can use 90mA in idle mode, central lock, and car alarm

 

Yes, I agree entirely

@staskus , It would be best if you thought about a new battery. If you write what cat you use, I can find a good battery for your car model.
Also, I can recommend this website to choose the right AGM battery.
There you can find battery group descriptions, battery capacity, and sizes for many cars

 

Yes, I agree entirely

@staskus , It would be best if you thought about a new battery. If you write what cat you use, I can find a good battery for your car model.
Also, I can recommend this website to choose the right AGM battery.
There you can find battery group descriptions, battery capacity, and sizes for many cars