MPG dramatically dropped...
11-07-2007, 07:29 AM
#1
MPG dramatically dropped...
Hi.
I have a 96 I30 which is 130k on it. I've been in New York in this summer. It was 2000 miles trip. At that time the MPG on the highway was over 400 miles per 16 gal. After the trip, the MPG is dramatically dropped from 330 mile(city) to 230~250miles. I used to drive the same distance and time with alway shell premium fuel (Oct 93). I have no CEL at all. Even though the car had a oil leak problem inside the spark plug wells, it made more than 400 miles per 16 gal. The problem was fixed after the trip by myself. In addition the car have the hard to start problem befor going to the trip though.
Here is list which was replaced on new spark plugs(NGK), air filter, fuel filter, new igniton coils, and cleaned T/B and IACV with new gasket. Because the car has hard to start problem when the enigine is hot.
I have a 96 I30 which is 130k on it. I've been in New York in this summer. It was 2000 miles trip. At that time the MPG on the highway was over 400 miles per 16 gal. After the trip, the MPG is dramatically dropped from 330 mile(city) to 230~250miles. I used to drive the same distance and time with alway shell premium fuel (Oct 93). I have no CEL at all. Even though the car had a oil leak problem inside the spark plug wells, it made more than 400 miles per 16 gal. The problem was fixed after the trip by myself. In addition the car have the hard to start problem befor going to the trip though.
Here is list which was replaced on new spark plugs(NGK), air filter, fuel filter, new igniton coils, and cleaned T/B and IACV with new gasket. Because the car has hard to start problem when the enigine is hot.
11-07-2007, 07:35 AM
#2
Senior Member
Join Date: Aug 2007
Location: FL
Posts: 704
I doubt this has anything to do with it. But when it gets colder outside gas stations change to a winter forumula. Some cars do better with this formula, while others are effected negatively. I do not know much of anything about cars so you best wait till someone who knows more than me comes along. 
11-07-2007, 09:44 AM
#4
11-07-2007, 10:37 AM
#6
I hate being slow
Join Date: Oct 2007
Location: Jenks, Oklahoma
Posts: 55
You might wanna try and run the grounding for your starting issues there is a thread on here about it i just don't feel like looking for it. I've got the same poopy miles though i'm getting 230-250 but it's probably because of my starting problem not really sure though who knows
11-07-2007, 05:14 PM
#11
i love it when noobs like yourself talk ****, am i wrong about the code???
it's in the sticky's
DBM ECU CODES
0304
Diagnostic Trouble Code 0304 points to a problem with the Knock Sensor. The KS is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is senses as vibrational pressure. This pressure is converted into a voltage signal and sent to the Engine Control Module (The computer).
This malfunction is detected when an excessively high or low voltage from the KS is entered to the ECM. Possible causes include...
- the harness or connector (The KS circuit is open or shorted).
- the KS
0304
Diagnostic Trouble Code 0304 points to a problem with the Knock Sensor. The KS is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is senses as vibrational pressure. This pressure is converted into a voltage signal and sent to the Engine Control Module (The computer).
This malfunction is detected when an excessively high or low voltage from the KS is entered to the ECM. Possible causes include...
- the harness or connector (The KS circuit is open or shorted).
- the KS
Last edited by jvckustumz; 11-07-2007 at 05:20 PM.
11-07-2007, 05:29 PM
#12
Originally Posted by jvckustumz
the ks throws a 0304 code and your cel will come on
11-07-2007, 05:45 PM
#13
Check for ghost codes like the KS, (which DOESNT light the CEL)
Ground that starter and tranny(we still need a sticky) *hint hint
It's possible you just got some crappy gas / crappy winter gas that had been sitting in a '91' tank for so long that it lost its octane potency.
IMO, its WAAY to early to tell if you're mileage just dropped exponentially, you're basing it on highway vs. city mileage, and on what appears to be 2 consective tanks.
not reliable results.
Ground that starter and tranny(we still need a sticky) *hint hint
It's possible you just got some crappy gas / crappy winter gas that had been sitting in a '91' tank for so long that it lost its octane potency.
IMO, its WAAY to early to tell if you're mileage just dropped exponentially, you're basing it on highway vs. city mileage, and on what appears to be 2 consective tanks.
not reliable results.
11-07-2007, 06:20 PM
#15
how long has this been going on? I got the impression from your post that this low mileage just appeared, have you been through a few tanks already to get an accurate mileage?
11-07-2007, 06:34 PM
#16
It was from the middle of August in this year. I feed the gas tank more than 10 times and I'm a full time student so the car is drivinig exactly the same distance during the semester. I'm pretty sure the low mileage.
11-07-2007, 06:39 PM
#17
well I'd pull for ghost codes,
search for all the usuals, mileage has been covered you'll find all you need to know.
basics are fuel filter, air filter, cleaning TB, IACV, etc.
a good search will yearn results man.
search for all the usuals, mileage has been covered you'll find all you need to know.
basics are fuel filter, air filter, cleaning TB, IACV, etc.
a good search will yearn results man.
11-07-2007, 07:33 PM
#18
buddy, don't get cocky. Just accept the fact tha YOU're WRONG about the CEL. Read the sticky more carefully and listen to those with EXPERIENCE.
Btw, i've been here longer than you, n00b
Thank You TunerMaxima3000 & pmohr for the constructive coments.
Last edited by heynow; 11-07-2007 at 07:36 PM.
11-07-2007, 09:37 PM
#21
Is it true that the CEL will always be lit with a CAI? When I had my codes checked it threw a o2 sensor code. Previous owner replaced the sensors about a year and a half ago. My driveability seems to be fine though. Once in a blue moon it will shut off on me. Happens about once every 2 weeks at a stop. Other than that everything seems fine except the mpg.
11-08-2007, 04:42 AM
#22
Ever since I bought the Max in May. I've ran 89 for at least 4-5 tanks, and then 91 for a whole month. Before I replaced the bad MAF and cat I've gotten about 200 per tank. Now it's slightly better...if it's all city I'll get about 210-230, but I've gotten as high as 280.
Is it true that the CEL will always be lit with a CAI? When I had my codes checked it threw a o2 sensor code. Previous owner replaced the sensors about a year and a half ago. My driveability seems to be fine though. Once in a blue moon it will shut off on me. Happens about once every 2 weeks at a stop. Other than that everything seems fine except the mpg.
Is it true that the CEL will always be lit with a CAI? When I had my codes checked it threw a o2 sensor code. Previous owner replaced the sensors about a year and a half ago. My driveability seems to be fine though. Once in a blue moon it will shut off on me. Happens about once every 2 weeks at a stop. Other than that everything seems fine except the mpg.
how mixed?
11-08-2007, 06:23 AM
#24
Ever since I bought the Max in May. I've ran 89 for at least 4-5 tanks, and then 91 for a whole month. Before I replaced the bad MAF and cat I've gotten about 200 per tank. Now it's slightly better...if it's all city I'll get about 210-230, but I've gotten as high as 280.
Is it true that the CEL will always be lit with a CAI? When I had my codes checked it threw a o2 sensor code. Previous owner replaced the sensors about a year and a half ago. My driveability seems to be fine though. Once in a blue moon it will shut off on me. Happens about once every 2 weeks at a stop. Other than that everything seems fine except the mpg.
Is it true that the CEL will always be lit with a CAI? When I had my codes checked it threw a o2 sensor code. Previous owner replaced the sensors about a year and a half ago. My driveability seems to be fine though. Once in a blue moon it will shut off on me. Happens about once every 2 weeks at a stop. Other than that everything seems fine except the mpg.
11-08-2007, 06:30 AM
#26
same as me man. i work 5 miles from where i live. there are 6 lights in those 5 miles. im gettin about 280 to a tank. but my KS is dead.
11-08-2007, 06:46 AM
#27
lol, yeah. With the heat on, the darn thing gets fully warm pretty much as i pull into my parking spot, which means that i'm running ruch for at least 80% of the trip 
.
...and that's with a clean fuel system, fixed vaccum leaks, new KS, and a new thermostat.
I can't really complain though, i only need to gas up 2X a month.
....and that's with a clean fuel system, fixed vaccum leaks, new KS, and a new thermostat.
I can't really complain though, i only need to gas up 2X a month.
Last edited by heynow; 11-08-2007 at 06:49 AM.
11-08-2007, 07:03 AM
#28
go back to kindergarden lol jk,
so is it true about the CAI throwing a code all the time??? what code does it throw, an o2 code?
and i bought a ks from courtesy nissan for 145.00 but the sell them for like 60 bucks on ebay, but i think it was well worth it, cuz when i pulled my old one out i realized it was busted into about ten peices, and the new one made alot of difference in normal driving conditions to me at least, it felt smoother
so is it true about the CAI throwing a code all the time??? what code does it throw, an o2 code?
and i bought a ks from courtesy nissan for 145.00 but the sell them for like 60 bucks on ebay, but i think it was well worth it, cuz when i pulled my old one out i realized it was busted into about ten peices, and the new one made alot of difference in normal driving conditions to me at least, it felt smoother
11-08-2007, 07:15 AM
#30
i 2nd "jvckustumz" driving experience with the new KS (totally worth it). I dunno how a CAI could throw codes all the time unless the the IATS or the MAFS were getting funky. I'd say he needs to spit out all the codes that are stored.
11-08-2007, 07:18 AM
#32
word around the campfire is that the 65 dollar ebay japanese generic one isnt that reliable - some people have good luck and some dont. and considering its a computer relay mechanism i figured it would be better to spend the extra 50 bux to get the nissan OEM one from dave b at south pointe..
11-08-2007, 09:55 AM
#34
Senior Member
Join Date: Dec 2003
Posts: 350
At 155K miles, My CEL went on and I had AutZon pull the code. It came up as the KS. I got them to reset it (though they were not "supposed" to do it). The person that did it said it would probably come back. It did in about 15 days.
I changed the KS and the CEL went out after about 2 weeks of routine driving.
Until I changed it, (used the fleabay unit for $60) my mileage was awful & I was getting about 250 miles a tank.
I'm not arguing with the info above and I'm no newbie. I'm just sharing my experience.
I changed the KS and the CEL went out after about 2 weeks of routine driving.
Until I changed it, (used the fleabay unit for $60) my mileage was awful & I was getting about 250 miles a tank.
I'm not arguing with the info above and I'm no newbie. I'm just sharing my experience.
11-08-2007, 10:20 AM
#35
Thanks for sharing your experience, Double E . In my experience though, i've had the KS code stored the computer without setting off a CEL until i asked my mech to just scan the ecu, and the code came up. Most folks on this board say that the KS code doesn't set off a CEL until there are other codes in the ECU that do.
11-08-2007, 10:29 AM
#36
Thanks for sharing your experience, Double E . In my experience though, i've had the KS code stored the computer without setting off a CEL until i asked my mech to just scan the ecu, and the code came up. Most folks on this board say that the KS code doesn't set off a CEL until there are other codes in the ECU that do.
11-08-2007, 01:07 PM
#38
Senior Member
Join Date: Dec 2003
Posts: 350
Did you also check the wire that the KS connects to for continuity to the block?
Torque the KS bolt well enough?
I would check the above & clean the area where that wire attaches to the valve cover area.
I'm surprised that the KS was bad so quick... Edit: I just realized that I didn't go through e-bay to get it. I believe it was another source but still about $60
I guess it may come down to getting another one and installing...for which you truly have my sympathies.
Torque the KS bolt well enough?
I would check the above & clean the area where that wire attaches to the valve cover area.
I'm surprised that the KS was bad so quick... Edit: I just realized that I didn't go through e-bay to get it. I believe it was another source but still about $60
I guess it may come down to getting another one and installing...for which you truly have my sympathies.