hey guy been getting reallly bad mpgs in my 95 zj 4.0 latley and ive already in the last month replaced plugs, wires, cap and rotor, ccv elbow and hoses, air filter and fuel filter and shes running rich my plugs are already black. what could be the problem?

 

so i think i just found that my car has no pressure regulator on it. how is it running???

 

See if the injector cleaner will work. Any codes?. The O2 sensor will make the engine run rich. The MAP sensor will do it too.

 

On the '97 ZJ the fuel pressure regulator is an integral part of the fuel pump module and can't be replaced separately.
Dan

 

thanks guys. there was no light but i checked the codes and it was code 21 or something like that and it said that my 02 sensor was staying at 4.5 to 5 volts

 

that o2 sensor reading that voltage will cause it to run super rich

 

ok so thats my problem. ill be putting a new one in in the morning

 

Disconnect the negative before replacing and reconnect after repair.. That will reset the computer code.

 

ya was going to do that. i just find it wierd theres a code but no light