Bad gas mileage and poor performance

[Clearalbino]

I just filled up my tank and got an average of 23 miles to the gallon, all of which are freeway. The car hesitates right around 3500-4000 rpms in every gear when its cold and hot. I've done all the basic tune ups to the car. Its a 95 240sx with intake and exhaust. I did have the check engine light come on for fuel injection system but havent found the problem, its running pretty rich right now.

[S13FASTBACKSR]

make sure your spark plugs are gapped correctly make sure your timing is correct. check your mafs voltage and tps voltage. also make sure your fuel injectors are spraying correctly. also if you turn your key on you will see a l.e.d. on the back of your ecu. it comes on when the key is on. if you start your engine and it stays on you have a bad ecu. if it goes off your fine.

[Clearalbino]

Well i know for sure that the maf voltage at the maf is reading incorrectly, its only reading at 2.5 volts at 4000 rpms. Whats the spark plug gap supposed to be?

[S13FASTBACKSR]

if your maf voltage is reading incorrectly especially as bad as it is then that definately sounds like your problem. you can try cleaning it but you are probably going to have to replace it.

[D-UNIT]

Don't forget one of the most underlooked most important things that fail. Coolant Temp Switch and/or harness plug. It is the cheapest easiest thing to change.

[Pollarican]

Try swapping the relay that controls your fuel pump. If you are running rich, it could be due to your relay getting stuck and your fuel pump getting stuck pumping rich gas like it should do to prime your car when you start it. I had the same symptoms with a 91 Ford Explorer my family had. I swapped the fuel pump and everything and in the end the main cause of the problem was a 15 dollar fuse relay that jammed.

[S13FASTBACKSR]

I just filled up my tank and got an average of 23 miles to the gallon, all of which are freeway. The car hesitates right around 3500-4000 rpms in every gear when its cold and hot. I've done all the basic tune ups to the car. Its a 95 240sx with intake and exhaust. I did have the check engine light come on for fuel injection system but havent found the problem, its running pretty rich right now.

do you hear your fuel pump pumping fuel longer than it should? by the way if you arent having problems starting your engine when warm then this is probably not your problem...too much fuel means that your engine would be flooded and not be able to start back up very easily

[Clearalbino]

I'll have to check the relay and fuel pump, i had a check engine light code 76 come on saying fuel injection problem. I've changed out my CTS and that helped a little but still have bad gas mileage. I'm on half a tank with only 140 miles on it.

[S13FASTBACKSR]

sticky injector probably..that would explain bad gas mileage and richness and hesitation..never have any problems starting it? ...heres what you do...pull your spark plug wires and your fuel rail off but leave the injectors in the rail and connected to the harness..turn the key on to pump fuel into the rail..now crank the engine over..you can now see which injectors are staying open too long or if its only one you can see which one it is..another thing you can do is pull the spark plugs if 1 or more of your injectors are stuck open then the spark plug for that fuel injector is going to be blacker than the others (its not likely that all 4 are stuck open)