What's wrong with my gas mileage?!?

[S13CoupeLuvr]

Hey tech guys... Wow, I am getting horrible gas mileage on my 100,xxx original miles KA24E... I know they're not all that efficient to begin with, but they're much better than the 14 MPG I've been getting... God, I didn't know that the "240" on the back of the car indicated miles per tank as well... j/k. Anyways, I think I am having a vacuum/fuel purge tank problem... I just want to be able to diagnose it before taking it to someone! When I abruptly step on the gas pedal, the engine chokes for a split second and then accelerates like normal. Also, when I shift, I hear a loud suction sound coming from the engine compartment, and, no, this is not from my Autozone cone filter. This sound I am speaking of is not always present, either. I don't get it! My friend's S13 has the same sound when shifting and she was told that her vacuum chamber was bad. Which parts of the system should I expect to have to replace? Does this sound like a vacuum problem? With gas prices the way they are, I don't want my commuter engine sucking fuel like this! Anyways, thanks to all who respond! Your help is much appreciated!!!

[IveBeenBad]

You may have a leaky injector, a clogged fuel filter, bad plugs.... many things could be wrong, but those are a start

[S13CoupeLuvr]

The injector problem could be a definite possibility, but I failed to mention that I have a new distributor, new plugs, new wires, new 02 sensor, new temperature sensor, 14.8 ohms per fuel injector (they say it should be about 12 ohms, but I don't know how big of a problem this is), all cylinders firing normally, 179 PSI compression on ALL FOUR cylinders, new catalytic converter, blah blah blah... I just can't figure out the problem! I couldn't get it to pass emissions, so they eventually waived me. HELP!

[Structure240sx]

im right there with you buddy at about 16mpg. i know my problem though...haha sorry

seriously alot of things could br your problem

[leper421]

Check the voltage between the ground wire on your airflow meter and the negative battery terminal while the engine is idling. I dont know if the E has the same air flow meter as the DE, but one of the nissan techs on this board said if its more than .02 volts, splice a wire onto it and run it to the negative battery terminal. Dont cut the wire from the air flow meter, just strip the insulation and solder another wire to it. Mine was .07 volts and doing that increase my mpg from 18 to a still crappy 21. I used to get 27-28.

[IlIkEmYz]

use seafoam http://www.nissaninfiniticlub....afoam

then replace spark plugs , o2 sensor, oil change, oil filter and that should help the engine run better.

Good Luck:ylsuper

[navysnail]

which part of the emmisions did you fail

[S13CoupeLuvr]

I failed on Hydrocarbons and Carbon monoxide, both... And it wasn't by "a little bit" either... It was way too high! It kept coming down very slowly after I replaced each part, too... but not by any large amount at all.

Also: I just realized a new condition of my car...

When I have a COMPLETELY full tank of gas, I get excellent gas mileage for about 40 miles... The car runs so much better, is significantly faster, has immediate throttle response (instead of the pause I mentioned before it begins to accelerate slowly), and is actually fast (for a KA24E, that is). Is this because there is more pressure in my fuel tank when it is full? Could this pressure be temporarily providing enough fuel pressure to the factory fuel purge tank to make the engine act close to normal? I don't know why this is happening!

[leper421]

The gas gauge is in no way linear. Mine stays a little above the full line for 30-35 miles. By 50 miles it is about half way between full and 3/4. After that it drops fast to about 1/4 then goes down slow. I read somewhere that the gas guages were designed like that on purpose.

Did you check the air flow meter ground like I suggested? Suposedly it is a common problem as 240s get older. A higher voltage on the ground line will cause the ecu to think you are getting more air than you really are, and you will run rich.

[xrenox]

I'm having the same problems as you, except now sometimes my car won't start and will idle high and then stutter when I give it gas. I ran out of gas a a couple weeks ago so I'm going to change my fuel filter etc.

[S13CoupeLuvr]

Huh... No, I have not yet checked my ground from the MAF, but I don't know how! I will have to talk to some guys in the area to see if anyone has a meter I can use, and how would I go about making a ground wire? I really think this is the problem! There's not much else it could be! Also, my car doesn't have problems starting, but it sure does idle high after startup (like sometimes 1800RPM!). I want to do this, but I need more info, if possible. Thanks so much for your suggestion.

[S13CoupeLuvr]

I re-read your reply from above, and I will try this as soon as I get time to breath (I work like CRAZY so I can make cash for my car!). Thanks again, and any other suggestions will help!

[wangless]

i have a set of 4 used (~1k miles) injectors and fuel rail for sale if you want. those might help. i wouldve used them on my car but well... i dont have one anymore. i think they need o-rings, but not sure. email me if you want them.

[navysnail]

if you failed in hc, then that means you are running way rich, which is probobly the leaky injector

[MIKEL240]

You should get a Fram Fuel Filter, it's like $10 at Walmart and it made a difference in my fuel consumption. Also try cleaning out your gas lines with some cleaner or treatment liquid. I also got a Tornado fuel saver which really helped and took out all the unecessary stuff out of my car. also use 5th gear more often and don't idle for long periods of time.

[D-UNIT]

You could also get a 300zx fuel filter from Pinnacle Nissan for 10.50.

[ray240sx]

D Unit, is that the OEM Fuel filter for the 300zx? because from PDM its like twice as much around ($24.00), or it doesnt matter if its OEM or aftermarket like bosche? reason i am asking this is because i have the same problem with gas mileage and I am looking to change my fuel filter hoping it will improve my mileage. Plus I dont want to get some brand offered by my local auto parts store ( PEP BOys, RS STruass, Autozone etc.) So should i just order my filter and new NGK plugs from PDM?

side note: I did the seafoam treatment last weekend myself, and i do notice the difference in my throttle response, I highly reccommend this product to all 240sx owners. I just hope this improvement will last awhile until my next treatment, every 2000- 5000 miles according the the recommended period. currently i have 160,000 miles and counting, and i just had my oil changed today. even better response after the oil change.

PS- I must say these NICO forums are one of the most helpful ones around the net, thanks guys for all the insights to improving my car, your fellow 240sx owner.

RL

[D-UNIT]

Hope this helps (works) LOL!!

http://www.trademotion.com/par...gid=1

I swear I bought mine from a Nissan dealership for like $12-$15.

[Silvia2b]

o.k. I have normally had great mileage compared to my old s13, but since last week something has changed drastically. I purchased gas on Monday, I had an oil change at Beaverton Nissan Tuesday morning. Since the fill up I have driven exactly 142, the gas gauge reads 1/4th of a tank remaining. I was able to get like 135 miles with half a tank previously. Do you think it had anything to with the oil change? Oil looks clean still, and is within range on the dipstick. I also checked my tire pressure because I think they sometimes change it when I bring it for an LOF service. I have 225/50ZR16 sized tires, with stock wheels, 31 PSI front, and 30 PSI rear. I don’t mean to post jack but after searching this was the only related post that fit the description of my problem. Does anybody have any suggestions? I am going to take it to Nissan back if I can’t figure it out.

[D-UNIT]

I had a similar problem I was only getting like 2-220 miles per tank. I advanced the timing ( check it first ) , checked spark plugs , filled up the tires. Now I get 360+ miles per tank. I've never seen that kind of gas mileage ever. So I can't you tell EXACTLY what I did to make it better. I think it was the timing.

[Silvia2b]

O.k. so now I'm running really rich with advanced timing? How did this happen I don't think they would have checked or changed timing for me when I was just having them do their 30 point check lube oil and filter change special. Would they, any tech out there have some input for standard operating procedures of an LOF?

[SilviaS14KA24DE]

just go to autozone for the 300zx filter.