Getting really bad MPG on my S13

[gosu22]

Hmm, so lately I realized that I was getting bad MPG when the trip was like showing 150 miles for 3/4ths of my tank.

I have a '91 S13 with 19X,xxx miles on it.

Things I've changed recently:

-Spark plugs (Bosch I think, the one with like 4 prongs I believe)
-Fuel injector (OEM)

I usually fill up on regular now, but it was never a huge difference between regular and premium I've found.

I haven't found time to change the oil in a little bit, but am planning to. I doubt that this has anything to do with it, am I wrong?

What else should I check for?

[Jgrand03]

check ur maf, o2 sensor, timing etc its been gone over 10000000 times

[blueshark123]

knock senor,fuel leak

[KiLLeR2001]

What engine? Whens the last time the O2 sensor was replaced?

[Folken]

I don't know if it has anything to do w/ your gas mileage but I heard running the stock spark plugs is the best for your car, i think the KAs used NGKs, those 4 prongs will run hot and could cause preignition causing damage... since plugs are like $6 for 4 I'd try the stock ones first and see if anything changes before you start spending money... check this out for the o2 sensor b4 you buy a new one http://www.nicoclub.com/articles.php?id=161680

[gosu22]

What engine? Whens the last time the O2 sensor was replaced?

KA24DE and dunno

[gosu22]

I don't know if it has anything to do w/ your gas mileage but I heard running the stock spark plugs is the best for your car, i think the KAs used NGKs, those 4 prongs will run hot and could cause preignition causing damage... since plugs are like $6 for 4 I'd try the stock ones first and see if anything changes before you start spending money... check this out for the o2 sensor b4 you buy a new one http://www.nicoclub.com/articles.php?id=161680

Technical Articles (http://www.nicoclub.com/subpages/articles-main.shtml) > Does my 240sx have a bad O2 sensor? All you wanted to know about 240sx O2 sensorsA bad O2 sensor can have a significant affect on gas mileage. Here's a procedure for checking the O2 sensor. The procedure may be the same for your year.
Checking the O2 sensor
The following procedure applies to all 1991 and up 240-SX models:
1 - Turn on ignition switch (do not start engine).
2 - Turn diagnostic mode selector on ECU fully clockwise.
3 - Wait a few seconds.
4 - Turn diagnostic mode selector fully counterclockwise.
5 - You are now in MODE-II.
6 - Start engine and let fully warm up (temperature up to normal).
7 - Run engine at 2000 RPM or higher for about two minutes under no load
8 - Check that the inspection lamp (red LED) on the ECU goes on and off more than 5 times during 10 seconds at 2000 RPM.




Questions about number 7: what do they mean by run engine at 2000 RPM?


And after #8, does that mean that if it does NOT go on and off more than 5 times at 5k rpm, then the o2 sensor is bad, or vice versa?

[DreamN]

Dude I'm right there with you. Getting horrible gas mileage. I keep getting code 45 Leaky injector from my ecu and when possible been trying to do all the recommended things when having that code.

Changed out my injectors. Cleaned MAF, cleaned TB, cleaned AICV (didn't know it needed a gasket so now I have a freakin' leak - gonna take care of that today), now I'm gonna see if it's my o2 sensor that's buggin'. Few other things on the list as well.

Check for vacuum leaks and definitely check for codes if your cel light is on.

[drft_n_s13]

maybe ur fuel injectors... i had a bad one on my ka24de with over 190k and i had a half tank gone in less than 30 mins of driving it was that bad... and yea i wouldnt use bosch plugs on a nissan, u should run NGK iridium plugs =)

[DreamN]

^ oh right. our engines don't like bosch plugs. friend told me too stick too densos or ngks.

[((sr)) kelly]

OMGGGGGGGGGGGGG


NEVER EVER EVER buy multiple prong spark plugs..;


the prong on the spark plug is designed to fail if the engine is running abnormal... so if you have single prong spark plugs and they fowl out, you can tell much sooner that there is a problem and what the problems is... when you have multiple prong plugs you cant.. when one prong fowls out the spark will just jump to the next. and so on... making the engine run longer under conditions that its not supposed to...


it is most likely an O2 sensor... obviously your car is running rich if its consuming that much fuel.. and since you have the oem injectors, there is no fuel over lap.. so there sould be no reason its using more fuel then its supposed to.... so replace the O2 sensor

when a O2 sensor goes bad the ecu no longer gets a reading from it... so as a deffense mechanism against running too lean, the ecu just tells the injectors to dump fuel dump fuel dump fuel, no matter what the maf is reading

[mrmephistopheles]

NGK plugs
NGK plug wires
new cap & rotor
fuel filter
change PCV valve (easy on KA24E/hard on KA24DE)
change O2 sensor (bosch is fine for this one)
clean throttle body
clean carbon out of intake mani
clean air filter

that should get you straight

[DreamN]

PCV valve! That's what Mark (drift day instructor) told me today as I was leaving from HKS. Forgot all about it till now. Good looking out meph.

[DreamN]

OMGGGGGGGGGGGGG


NEVER EVER EVER buy multiple prong spark plugs..;


the prong on the spark plug is designed to fail if the engine is running abnormal... so if you have single prong spark plugs and they fowl out, you can tell much sooner that there is a problem and what the problems is... when you have multiple prong plugs you cant.. when one prong fowls out the spark will just jump to the next. and so on... making the engine run longer under conditions that its not supposed to...


it is most likely an O2 sensor... obviously your car is running rich if its consuming that much fuel.. and since you have the oem injectors, there is no fuel over lap.. so there sould be no reason its using more fuel then its supposed to.... so replace the O2 sensor

when a O2 sensor goes bad the ecu no longer gets a reading from it... so as a deffense mechanism against running too lean, the ecu just tells the injectors to dump fuel dump fuel dump fuel, no matter what the maf is reading

so dumping all that fuel would cause the leaky fuel injector code to pop out correct? now, does the o2 sensor have to go bad for this to happen or can it be dirt or whatever?

[((sr)) kelly]

ehh idk about it throwing any injector codes...i wouldnt think so because the ecu is telling the injector to dump all of the fuel...




so dumping all that fuel would cause the leaky fuel injector code to pop out correct? now, does the o2 sensor have to go bad for this to happen or can it be dirt or whatever?

[jackjack]

NGK plugs
NGK plug wires
new cap & rotor
fuel filter
change PCV valve (easy on KA24E/hard on KA24DE)
change O2 sensor (bosch is fine for this one)
clean throttle body
clean carbon out of intake mani
clean air filter

that should get you straight

i need to do this as well.

my gas mileage SUCKS.............. and swallows.

[an_orange_s2k]

i bought a bottle of fuel system cleaner from kragen and that helped me, try doing that only $9

[SexPanda]

shit, seafoam the mother.

Seriously, i know it sounds like snake oil, but it really did help my car...

Also KA, also 190,000 miles. 7 bucks a can.

[jrocslider]

never use bosch plugs in a nissan. i swear idk why people like em... maybe in a vw or sumthing but not in a japanese car.

the o2 is cheap. i changed mine out about a month ago and it made a big difference. i went from getting about 200miles a tank to a lil over 300. from 14-16 miles a gallon to about 21-23.
like mr.meph said...

cap
rotor
wires
plugs
pcv
air and fuel filter

none of this stuff is expensive for our vehicles so just change it.

[gosu22]

Are the spark plugs so important that I need to change them immediately? Do the 4 prong vs 1 prong affect gas mileage?

Also, should I buy an o2 sensor with a new connector, or use the old one?

Does autozone have a tester for o2 sensors?

Basically, how can I test my o2 sensor with the ecu codes?

I'm going to check to see if it's my o2 sensor first, change my spark plugs into NGKs, then I guess I'll check the distributor cap and rotor.