Extremely bad MPG and gas smell

[RickJC288]

So in my 1990 non turbo I fill up my car and at the gas station it'll say 11 or 12 gallons filled. My odometer reads around 160 miles 170miles and my fuel gauge is on E but the light isn't on if that even works. So this is probably by far the worse mpg I've gotten in a vehicle.. i dont drive like a maniac either. And on top of that this morning I could smell gas so I smelled one of the top of the plugs and one plug I could smell gas like as if it were in a bottle under my nose and it was the driver side second plug.
Don't know what this could be if it needs a tune up from as in air to fuel ratio or something leaking or something simple.

[z.Leinbach]

I can say. These cars get horrid mpgs. It's part of the over engineering of the engine, but you may have some bad injectors, or the fuel regulator, and dampener my be going out. With my car, when I got it I was around 140 for a full tank and it thankfully has gotten better, I use VP racing fuels one tank supplement, every fill up, and I also run 87 (regular) and now I'm up to about 190/290 ish per intown and high way distances. Also make sure all the major and minute routine maintenance is current

[RickJC288]

Yeah I changed the oil with mobil 1 full synthetic and changed all the spark plugs to ngk platinums and now I can't notice if it's even getting better. Idk if it the injectors or Mass air flow sensor. Just is a bummer to get on E and your only at 170 even though my last car was a V8 and got 230 a full tank highway hah

[DCaff300ZX]

The gas smell can also be loose clamps on the fuel lines to/from the fuel rails, and/or all the rest of those fuel line clamps- a quick check never hurts as there are always a few loosies, and a leak definitely kills your gas mileage plus maybe even you with a car fire.
Definitely look into what zleinbach said as well as think about a new fuel filter as further necessary maintenance options, and also realize you have the old style injectors that die from ethanol in the gas and electrolysis- almost a miracle they made it this far honestly. One or more can be failing and will cause poor mileage, erratic operation and hard starting, and a bad miss when they are completely dead.
This WILL happen some day soon so be ready and when replacing, replace with new style injectors with the old style fuel rail adapters (CZP, Z1, SPZ...) for lowest job cost/best operation.
I've also had success with the Lucas upper cylinder lube in the NA as it went past 200K miles, it smoothed things out quite a bit which improved gas mileage...my NA got 20+ mpg to the day she died.
Good Luck!

[javadave]

^^^^ agreed
I started to get a slight gas smell and immediately thought injectors. Took the throttle cable cover off and looked at the front fuel lines at the fuel rail and both were a bit damp. Tightened up the clamps and viola, no more gas smell. That was nearly two years ago. I calculate my MPG every time I fill up, getting between 22 to 23+ each time. Got 24+ on the last tank ( was driving like an old lady while braking in my clutch ). Lower MPG can be a first sign that something isn't right or soon to be not right.
Things to note. If that N/A is a 2+2 you have a 19 gallon tank, not sure about the 2+0. When the needle on the gauge reaches E, you have 5 gallons left, or should if the gauge and sender are working correctly. The 'light' should come on after you driven it past E. It will go off again, after a bit more driving, then return. Odd to me, but verified.

[DCaff300ZX]

Good call on the tank size, I believe the 2+0 has the same tank but not 100% sure- I used to get 320-330 miles per tank fill if all freeway...and have noted the same pattern with "E", both with miles available (mileage, 89 miles is PUSHING it!) and the off then back on then off. If it goes off again, you better see a station in a few yards and get there.

[z.Leinbach]

I agree with dcaff, 18.9 gallons on the 2+0 BTW. Like I said, if your looking for a economy car. The fairlady series is not the car for that. Z31/32 are grand touring cars, made for power and comfort, mpgs weren't a priority, but simple mods can spare you some, stage 0, and then stage 1. Intake, exhaust.

[RickJC288]

Thanks for the help guys! I'm still new to the car K3 weeks) is there any videos or diagrams on how to tighten or check the fuel injectors or rails

[RickJC288]

It has and exhuast but the piping is the same stock size. No after market air filter, havnt checked the o2 sensor or any sensors. So far what I've done so far is mobil 1 full synthetic oil change 10w30 new ngk platinum plugs spaced .040mm and an additive to stop a leak. I did use stp fuel treatment aswell

[DCaff300ZX]

Try tt.net and RoboZ, they both have a lot of how-to's with pics to help out.
The fuel rails are located at the rear of both sides of the motor, on top and down between the intake runners of #5 and #6. Basically any small hose clamp you see in that area and above that needs to be completely tight, and checking them you most likely will find many/all are loose and some leaking. The VG30DE and DETT run a lot of fuel pressure and heat cycles cause the hose clamps to loosen, and the high pressure forces the fuel out ANY small opening. It is a well-known job each and every fall and spring to tighten the fuel hoses in our ladies, or be reminded when you smell fuel as I did this AM...I will be tightening hoses tomorrow myself.
You also can use the free online service manual available here, it will walk you through various projects and has pics/diagrams, too...and has professional advise and tests rather than word of mouth and trying to figure isht out yourself. Invaluable to have, do yourself a favor and download it after you read this!

[RickJC288]

Awesome! Thank you so much!

[RickJC288]

Which file do I download from this page for the fuel system

[DCaff300ZX]

Which file do I download from this page for the fuel system

Check the "Everything you need to know...300zx" sticky, osm is 4th down.
LOTS of good stuff there to read and know ahead of time...
Also, many/most of the build threads like mine go over the things we've done to our cars and with pictures. Many of the things we do are the same things many/most others do, or will need to do, so that is also another good way to learn about DIY-ing things.

[RickJC288]

Oh I forgot to say so when ever I fill up and remove the gas cap alpt alot of escaping air comes from the gas cap enough to where it'll hush for about 5 seconds

[z.Leinbach]

That is normal, our fuel tanks pressurize to help with fuel pressure, along with vapors from the fuel return system move does that, only time it doesn't is when the cap isn't sealed properly

[RickJC288]

Oh okay cool I knew they were pressurized I just didn't know if that much air was normal haha
Thank you!