Is it time to shoot her? 8 mpg is all my '90 Bonneville gets!?

Question

We have changed the spark plugs, used additive to the gas tank & recently had to replace her water pump but my poor old Bonnie still only gets about 8 mpg!  Please tell me what else I can do to improve this.  I have been reading about O2 sensors but I'm old school so fill me in.  
We live 15 miles away from the nearest town and do not have a money tree in the back yard so buying a car is not an option yet. :(

Anonymous · Accepted Answer

check the exhaust and fuel filter

oinch79 · Answer

I'm sure this is a 3.8 litre in this car should get over 25 mpg is it losing power as well have your catalytic converter checked it maybe clogging up to where the exhaust is not getting out will also cause power loss over heating poor performance and bad mpg if the check engine light is on need to have checked out go by auto zone they will scan it for free or at least they do here in Memphis could be o2 but that shouldn't kill the mpg that drastically i work on cars every day I'm tech for 27 years its hard to diagnose a car with out running some test but this is something to look into lots of luck to you

campmano · Answer

its not time to shoot it, but its the age guessing would be the answer without seeing. there are quite a few things attributing to and or the may cause to list. a plugged cat can cause many problems, o2 can cause a little mileage difference. but not what your seeing. i believe you should be looking at the fuel injection and intake manifold area. and be sure to check the vacuum lines, pvc and mapping sensor. that can cause major fuel increase usage. you have a check by check problem, good luck.

jb · Answer

02 sensors tell your vehicle to run rich or lean usually the case when your mpg is getting bad . probably running to rich

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Is it time to shoot her? 8 mpg is all my '90 Bonneville gets!?

4 Answers