My buddy has a 96 Bird with 83K on the clock. He has gone form 280-310 a tank to barely over 240 with the same driving.


His mods are:
1 Piece Drive Shaft
MSD Wires
SLP Loudmouth
3.23 Disk Brake Rear from 3.08
Rear O2 Sim, but cat still in place


He has replaced the timing chain 6 K ago
He replaced the O2 sensors 30K ago
Did the plugs 10K ago
Wires 30K ago
Coil Packs 20K ago


Any ideas for such a severe drop? He was considering doing the following:

Sea Foam through the brake booster
Throttle Body Cleaning
Possible Fuel Injector Cleaner (Pressurized one)
New Plugs after that

 

I've had a drop in mileage as well, after it hits the half way point of the gas gauge, which is usually 200 miles at half way but is now much less (170-180), it appears that it loses gas quickly. The gauge drops real fast after the half way point for some reason, and I don't know whether to trust it or if it's just the shape of the gas tank.

The first 2: seafoam and throttle body were the first things I thought of and will be doing myself.

 

could be O2 sensors I have seen them do that when they are bad

 

Mine were recently checked, but that is a good posibility for his buddies' car, I also recommend he gets them checked.

 

wierd... definitely not running right, I just seafoamed and did fuel filter on my car, and running the **** out of it since I seafoamed it, and I am up to like 275 at this tank, and I probably 1/5th-1/6th left...