1972 240z all stock . Stock 4 speed R200 rear end. The engine is getting tired and using a little oil. However around town and to work 22 MPG. Freeway driving I have got as high as 29 MPG. The faster I drive her up to a point:nervous: 75 to 80 MPH the better mileage I get. I also might add all I put into this car is Premium.:classic:

One thing I would suggest on the EFI cars, and this may only apply to California cars, is to unplug the top gear and O.D. switches from the trans since they change the spark advance in those gears, and get rid of the little round vacuum delay valve that's in the egr vacuum line. I gained nearly 2 mpg on my 810 with those changes.

Now that is an increase.

One thing I would suggest on the EFI cars, and this may only apply to California cars, is to unplug the top gear and O.D. switches from the trans since they change the spark advance in those gears, and get rid of the little round vacuum delay valve that's in the egr vacuum line. I gained nearly 2 mpg on my 810 with those changes.

Stephen,

Are there two separate switches for Top and OD on the tranny? My memory says I have one type of sensor connector on the right side of the tranny in my 79 ZX. Did you just disconnect them and leave em hanging?

Did you notice any improved driveability or difference in the way it ran?

I recall taking the vacuum delay valve off of the timing advance when I installed the Big Throat Throttle body years ago, and thought I could tell a difference then.

The 810 has three switches on the right side. Front to rear; reverse light, top detecting, and o.d. detecting. According to the FSM, those, other than the reverse light switch, are only on California cars. When I disconnected them the car ran smoother, and accelerated better in fourth and fifth gear which are the only areas effected by those switches. They are part of the 'spark timing control system' which is an emission control thing as is the vacuum delay valve.

One thing I would suggest on the EFI cars, and this may only apply to California cars, is to unplug the top gear and O.D. switches from the trans since they change the spark advance in those gears, and get rid of the little round vacuum delay valve that's in the egr vacuum line. I gained nearly 2 mpg on my 810 with those changes.

Are there 4 or 5 of these switches that get unplugged?

That all only applies to California cars. Yours shouldn't have them unless it was originally a California car. And then it would only have the vacuum delay valve mounted in the hose between the BPT valve and the thermal vacuum valve. The extra switches on the trans were only on the 79 and up California cars.

I see.

I filled up last week and only got 17.5. I got 23 on 240 mile tank with 200 miles on freeway (some in gridlock). I just plugged the egr valve and I'm replacing the old vacuum lines. I'm only on the second thousand miles of driving a Z so I have some learning to do. I've been trying to keep the shift rpm down around 2500, but it does seem I'm always 10 miles over the speed limit.

Doug, Longview WA

I'm not sure I'd plug the EGR valve on an EFI car. When mine didn't work, the gas mileage suffered until I replaced it.

I am right around 20ish mpg right now. Then again, I also have a T03/04E turbo'd L28 fed by Supra 440cc injectors. This is mixed driving with some boost runs.

Got an appontment for Thursday to get the five speed installed - would have liked to have done it myself but need a deacent lift setup - hoping to see a significant difference in MPG from the four speed.