I have had my z for a couple weeks now and I have noticed that my car does not perform as well when I get to a 1/4 tank of gas. At first I thought it was just bad gas, now Im sure there is something going on.

I filled it up with premium and its is fine. The performance increase is not much, but enough that I notice it.

Any ideas?

 

Don't know if you put that you filled up with premium for any reason, but you should use it all the time in a Z28, not just whenever.

 

Yea.. I have always put premium

 

Our fuel gauges are famous for being wrong, so if it shows 1/4 on the gauge, it's probably less. It's a good idea to keep the fuel tank at a higher level as the fuel pump is cooled by the gas in the tank and our fuel pumps are also known for failing. I would think if you were not getting enough fuel the car (because the tank was low) it would run really crappy and you didn't state that was your issue.

 

Don't think it should make any difference if it's 1/4, 1/2, 3/4 - fuel pressure should be the same...use premium.

 

No my fuel gauge has to be right, because I got it way low from the dealer. Do you think it could be a fuel filter issue? A clogged filter would have more push behind it with a full tank right?

 

Our pumps use the fuel in the tank to cool. Less fuel = hotter pump and warmer fuel getting to the engine.

Running down under 1/4 tank can cause pump failure from overheating.

 

The reason you see the needle plummet past half and even more after quarter tank is the tank is an irregular shape. The top half is even on both sides, but the bottom is shaped like a V. The fuel level arm uses a variable resistor, so it does not know the difference in fuel tank shape. You are not losing any performance or mpg, it is just the shape of the tank. Reset your trip counter with a full tank, and see how many miles you get before the 1/2 mark and you will see what I mean.

 

I've been trying to understand this for a while now. What is the specific reason youre suppose to use premium gas? I know it enhances your performance a bit but is using regular gas bad on your engine or something?

I usually alternate between mid grade and regular just because gas isnt cheap now a days..

 

This is the cheap version of why you need premium in our cars.

Our cars have around a 10.5:1 compression, the higher the compression the higher octane required or else "detonation" or "knock retard" (If im wrong correct me), This means the fuel in the cylinder is detonateing to early. For example if you have a 8:1 compression car you only need 87octane, the higher the compression, the higher octane you need.
Also this kind of sorts out how 110 octane in lets say a geo metro will not help performance even though people claim it does.
Oh, and to anwser your question lol, yes it can damage an engine.

 

thanks for the reply, yeah i did a search and looked at alot of posts...seach does wonders

in any case yea i just bought a 94 z, i loved it from the moment i drove it, its a money pit but its just too much fun. i just wish i would have researched more as this is my daily driver right now, guess im gunna have to find a nice pos to get to and from work everyday huh

 

I always kinda noticed this as well.. I figured the computer was like "hey we're low on gas.. let's limit the usage"

 

You get less performance because the ECU pulls timing to keep the engine from detonating on the lower octane fuel. This way you can run lower octane and not hurt the engine.

 

Peoples math skills these days kill me. okay how much more a gallon is 91 compared to 87?

normally super unleaded can be found within 10 to 15 cents more a gallon then regular.

your fill completly up lets say 14 gallons of gas, at 15 cents more a gallon your out $2.10 for a full tank of gas.

if you need to save on gas buy a honda.

 

And it kills me that people insist on talking when they don't know what they are talking about.

Our fuel pumps are in a bucket and run submerged in fuel ALL THE TIME. Even if there is only a half gallon in the tak the bucket is full. It makes NO difference how much fuel is in the tank. Even in applications that don't have a bucket the pump is still cooled by fuel because it runs through the motor.

The performance of the engine is the same no matter how much fuel is in the tank. It's in your head.

Re'