BMW Repair: fuel usage-85bmw 535i 5spd man, fuel pressure gauge, replacing a head gasket

Question
my 535i uses gas like crazy!check engine light flashes then coolant light comes on-no overheating but when it happens my already bad gas mileage goes way worse.the condenser fan has been rigged to come on with the switch via the coolant temp switches on the radiator.power has decreased as well throttle has to be adjusted manually to keep it from spitting.i know im loading up with fuel b/c i just put a new exhaust system on it less than a month ago and the tip is as black as night already-and of course i smell gas and have an exhaust leak.help

Answer
The check engine light flashing is a BAD thing.What it means is there is a cat damaging problem,probably due to either excessive fuel or coolant.You say there is no coolant loss but you also say it is "rigged to work".So you need to put a fuel pressure gauge on and see what it is and that should be what is stamped on the fuel pressure regulator,which I believe it is around 3 bar.If the pressure is high then you need to replace the regulator.If it is fine then compression and a cylinder leak down tests need to be done.Those will tell you the condition of the motor.After all the tests are done you probably will be replacing a head gasket,make sure you resurface the head as well.