My gas gauge is stuck how do I fix it on a 1970 olds delta 88

Check the supply voltage and connectoins between the guage and tank sender.

if it bad need to replace it cleaning it not going to work

Someone will need to drop the gas tank to access the top where the pump assembly enters.

Check for power to the fuel pump. Is it possible the old pump was fine but had no power to it? If there is no power than check the fuse and the relay. If those check out good let me know and I'll get some more info for you.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

It may be the sending unit in the tank that needs replacing. Here's how you can check: Turn the key on and disconnect the sender unit at the gas tank. Ground the sender unit's wire with a jumper wire from the truck's harness to ground. Watch the gauge. If the gauge on the dash is good, grounding the sender wire will cause the gauge needle to react and should move to full. This would indicate a new sending unit is required. If the gauge doesn't move when the sender unit is grounded, the gauge is bad and needs replacing. Pull the instrument cluster out to replace the gas gauge. Likely any old ford gas gauge might work-back then, there were not so many production changes.

can i put an auto start in a 1984 olds delta 88

By wireing Im assuming you mean the wires for the fuel pump which is on top of the tank. the tank must be dropped to access them

Hard to say on a older car such as this. If running well and healthly it should receive around 16 to 18 highway miles per gallon

check to see if crank sensor got damage