Horrible Gas Mileage

Post by **240dreams** » Sun Jul 06, 2003 3:54 pm

I get about 12 mpg in my 90 240. I changed the o2 sensor on the exhaust manifold but that didn't help. What else should i check or do?

Post by **Nismo_Freak** » Sun Jul 06, 2003 3:54 pm

1. Check the coolant temp sensor output to see if its in spec2. Check for a stuck injector(s)

Post by **corn322** » Sun Jul 06, 2003 3:54 pm

I'm getting like 19mpg on a good week. what's the mpg for the '90 240 supposed to be?

I had horrible gas milage the first week I had my 240. I stopped driving like a maniac all the time, and that helped a lot.

Post by **WingsNThangs** » Sun Jul 06, 2003 3:54 pm

Time for an oil change? Fuel filter change? Fuel pump change?

My 91 S13 got 25-30mpg last time I was on the freeway. 108000 miles, just replaced O2 sensor, need oil change when odometer hits 109XXX mi.

Post by **240dreams** » Sun Jul 06, 2003 3:54 pm

22mpg stock

Post by **i2ice4m3** » Sun Jul 06, 2003 3:54 pm

Nismo freak, how do you check for stuck injectors? I tried the wet spark plug method but i think the gas evaporates too quickly before i can see if it's wet. I recently failed the Idle portion of the smog test. It said the carbon monoxide was too great at idle, but fine at 2.5k rpm. The guy said it is probably leaky injectors. I got the code for leaky injectors a little while ago and i replaced the o-rings. The light doesnt come on anymore.

Post by **Jookmasta** » Sun Jul 06, 2003 3:54 pm

my 93 is pullin 29 with about 115000 on the engine. yipeeeeee

Post by **240dreams** » Sun Jul 06, 2003 3:54 pm

I just got new spark plugs and cables. Waiting to see how much mileage i get.

Post by **captain nismo** » Sun Jul 06, 2003 3:54 pm

My 89 gets about 30mpg if i drive like a normal person. When i want to drive fun, the fuel milage drops drasticaly...

Post by **drift-sx** » Sun Jul 06, 2003 3:54 pm

use some carb/injector cleaner did me wonders jsut poor it in before you fill up your tank .

Post by **goshoryuken** » Sun Jul 06, 2003 3:54 pm

on regular, i get 10mpg, and on super i get 15, it's ridiculous, i think i need to restore compression. it's an 89 ka24e

-GoShoryuken

Post by **trpower7** » Sun Jul 06, 2003 3:54 pm

1) Coolant temp sensor2) Oxygen sensor3) Injector cleaner (seafoam)4) Change plugs, gap correctly5) Vacuum leaks6) Injector leaks7) Bad Fuel Pressure Regulator8) TPS9) MAFS

The only way to restore compression is with an engine rebuild, and usually bad compression doesn't show itself THAT much in fuel mileage, more in oil loss and performance loss. Check the above list, I'd bet my life if all those are in order your mileage will be almost stock.

Post by **180fan** » Sun Jul 06, 2003 3:54 pm

Try a full tune up. I was getting jacked with my mileage before I did my tuneup. It came back to stock, then got a S-AFC and had it tuned up more, found out my car was running very rich in most cases so I had it leaned out a bit. Now getting about 27mpg in the city, and about 30mpg on the highway (this figure varies not a little bit based on driving style but is pretty consistent).

I changed:1. fuel filter (300zx)2. spark plugs (NGK Ir plugs)3. ignition wires4. distributor cap (oem)5. distributor rotor (oem)6. o2 sensor (21 bucks over at pdm-racing.com)

Try those out and see if they help you out a bit. I don't think the S-AFC did too much for my mileage, but did make it a little bit better.

Post by **sammy** » Sun Jul 06, 2003 3:54 pm

i agree with 180fan.......i just did all the changes he did.....my mileage went from 17-18 to 22 in town.........except i got screwed when i bought an o2 sensor from the dealership=71$

Post by **goshoryuken** » Sun Jul 06, 2003 3:54 pm

Okay, well here's some information that might help narrow down the problems. The spark plugs and wires are both Autolite's. I know NGK is the best, but the guy who sold me the car had put in brand new Autolite plugs and wires. My mechanic said there weren't any leaks anywhere, but then again . . he is an idiot. I have no radiator over-flow coolant, because my radiator over-flow coolant bottle has a huge azz crack in it, the car has received an oil change, I bought a brand newbosch o2 sensor but that one's probably still in my old engine, I dont know about the fuel filter, and I don't know about the distributor rotor or cap but the car turns on fine every single time, I don't know about the injector cleaner, vacuum leaks, bad fuel pressure regulator, tps, or the MAFS. I think the MAFS is okay, but then again the guy who sold me the car put some busted "custom" magnaflow intake on it, with a custom extension down to the front of the car, and the filter on it seems pretty dirty to me. So basically I should....

Purchase:1 - A new coolant temp sensor2 - A new o2 sensor3 - new ngk ir plugs4 - new ngk wires5 - new fuel filter6 - a replacement over-flow tank so i can have coolant in it.

and check:

1 - for vacuum + injector leaks2 - tps and mafs carefully3 - distributor cap and rotor4 - the fuel pressure regulator5 - the injector cleaner

I will purchase what I need when I get paid, as for the rest . . I will check that in a few minutes as to the best of my knowledge. I'm somewhat of a newb at this so I might not catch it the first time. If you guys have any extra help or suggestions . .please post!!!!!

PS - Could the lack of a radiator over-flow coolant in the cracked coolant tank be causing over-heating under the hood and bad gas mileage?

PSS - If I can't solve this problem myself, what should I do or who should I go see? I'm sick of taking it to a mechanic and having him say it's okay . .because 10 - 15mpg is obviously not okay!!

-GoShoryuken

Post by **240dreams** » Sun Jul 06, 2003 3:54 pm

i feel ya goshoryuken

Post by **drifts14x** » Sun Jul 06, 2003 3:54 pm

Hey, if that fuel filter would help, how much is the one for the 300ZX, and where is a good place to buy one?

Post by **goshoryuken** » Sun Jul 06, 2003 3:54 pm

I get paid next on the 23rd so if you guys have any more suggestions or help, post!!! I spoke with one guy and he said that it could be either the catalytic converter or o2 sensor. I'm going to check the o2 sensor and see if it looks okay or not. It's like I just can't rest or sleep knowing that my car isn't running the best it can.!!!

Post by **240dreams** » Sun Jul 06, 2003 3:54 pm

how could the cat affect mpg?

Post by **sammy** » Sun Jul 06, 2003 3:54 pm

if the cat is plugged...or getting plugged....it would restrict the exhaust flow=bad mileage/ poor performance. mine was on the car for 180,000miles and never was even slightly plugged.....but now it is in the corner of the garage making a home for crickets

Post by **240dreams** » Sun Jul 06, 2003 3:54 pm

did changing it help gas mileage? My cat sounds pretty bad, it kinda hisses i think.

Post by **p00t** » Sun Jul 06, 2003 3:54 pm

also if the fluid in the mechanical fan gets funky it will run full on all the time. it is supposed to "disengage" alittle when the engine runs at higher rpm, if it doesnt your fighting alot of air....which is alot of excessive drag on the engine.

cat could be it too

Post by **goshoryuken** » Sun Jul 06, 2003 3:54 pm

Here is a picture of my current o2 sensor. Does it look okay? In my opinion it doesn't. It seems to have a bit of rust, it smells bad, and it looks burnt, not to mention the body of the o2 sensor has little dents in it as you can probably see.

Post by **gibbo80** » Sun Jul 06, 2003 3:54 pm

mine gets about 17-19 i have 89 coupe with 150k

Post by **180fan** » Sun Jul 06, 2003 3:54 pm

Well I'd replace the o2 sensor every year or so, and at 21 bucks from pdm, not such a bad idea since they do get clogged, etc. You can also try carbon cleaning your car before you do the tune up and then pour in some fuel system cleaner after you've done the tune up. I use greased lightning fuel system cleaner. I've tried NOS, and Slick50. They're both more expensive and don't work as well as the greased lightning stuff. I've yet to try the chevron's techron additive but yeah, clean out your fuel system. I've done that on my sister's altima helped raised the mileage too on her ka24de. So it couldn't help to try it out.

Post by **240dreams** » Sun Jul 06, 2003 3:54 pm

i just got a full tank of shell 89 octane gas and added STP fuel system cleaner and i feel a drastic improvement in mpg. It's not in the 29 mpg range but it went from around 12mpg to at least 17 or 18 or so.

Post by **trpower7** » Sun Jul 06, 2003 3:54 pm

I'm getting almost 34mpg now, but my car is INSANELY in tune, I passed emissions with better results than some new Honda's I've taken.

Post by **i2ice4m3** » Sun Jul 06, 2003 3:54 pm

did you just replace all the stuff you mentioned earlier? 34mpg is a number i can only DREAM of. I wanted to clean the MAF sensor, but i dont know how to do it. My AIV malfunctioned before and it routed exhaust gas through my intake. I heard it can coat your MAF with crap.

Post by **180fan** » Sun Jul 06, 2003 3:54 pm

whoa! 34mpg...that's like godly or something. Ha ha ha. What were some of the things you did trpower7?

Post by **trpower7** » Sun Jul 06, 2003 3:54 pm

It's just tuned VERY well, every little valve or sensor is clean or new, the only aftermarket items I have are a pop-charger and an electric fan in place of the mechanical one. I even think mine is running a bit rich, with an SAFC I bet I could lean it out a little more and squeeze a couple more horses out. I also ran the codes relentlessly and brought everything to within factory spec, TPS, MAFS, all that business. And that's 34 highway mpg by the way.....

Horrible Gas Mileage

Horrible Gas Mileage

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