Severe gas mileage issue. Please need help
04-06-2013, 11:59 AM
#1
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Join Date: Jun 2007
Location: Lowell/Boston, MA
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Severe gas mileage issue. Please need help
okay as of late as in pretty much the past 5-6 months or so, my 98 maxi has been getting nothing but 60 to 75miles(max on fumes pretty much) for 20 bucks. Now all I use is prem gas and that is all I am able to get. Now I understand it is is a pretty old car and I am not supposed to get the projected 130miles+ for 20 bucks like it would if it is brand new but what gives? with 60-70miles per $20 bucks of prem. I am getting approx 13miles per a gallon. That is insane... Now I narrowed it down to these things...
1.I understand I do need a tuneup as I haven't done one in 3 summers.
2. I did the resistor Knock sensor mod. Got tired of constantly replace sensors plus I put in prem anyway, so I dont' have to worry about Knock AS MUCH I am sure.
3.I do have an EVAP check engine light and other than the knock sensor that is really it as well I also got a 02 sensor a while back but I need to recheck that cause that only happened once and it kinda confused me on where the banks were.
4. Bestbuy did drill into my gas tank as the morons they are to install an audio fuse switch on the back seat a few years ago, but the hole is so tiny I didn't even bother to fix the gas tank or replace it. I wish I could of sued them or did something about it but of course I had no prove "THEY did it" as the manager said. Plus the hole is very tiny and to smell the gas you got to put your nose up to the hole on the back seat. I will fix it maybe this summer but I can't see gas evaporating out of that, affecting my mileage all that much in a 3-4 day span as the holes are tiny, I know that is why I am getting my EVAP code tho.
So you think it could be any of these? I honestly think fixing the gas tank and replace an o2 sensor would be the best, but shes so old and I can't spend like $70 bucks on all 3 sensors on a "guess" it will fix it. IS it always a guarantee that if you get an o2 sensor code that if you replace it, your gas will improve?
1.I understand I do need a tuneup as I haven't done one in 3 summers.
2. I did the resistor Knock sensor mod. Got tired of constantly replace sensors plus I put in prem anyway, so I dont' have to worry about Knock AS MUCH I am sure.
3.I do have an EVAP check engine light and other than the knock sensor that is really it as well I also got a 02 sensor a while back but I need to recheck that cause that only happened once and it kinda confused me on where the banks were.
4. Bestbuy did drill into my gas tank as the morons they are to install an audio fuse switch on the back seat a few years ago, but the hole is so tiny I didn't even bother to fix the gas tank or replace it. I wish I could of sued them or did something about it but of course I had no prove "THEY did it" as the manager said. Plus the hole is very tiny and to smell the gas you got to put your nose up to the hole on the back seat. I will fix it maybe this summer but I can't see gas evaporating out of that, affecting my mileage all that much in a 3-4 day span as the holes are tiny, I know that is why I am getting my EVAP code tho.
So you think it could be any of these? I honestly think fixing the gas tank and replace an o2 sensor would be the best, but shes so old and I can't spend like $70 bucks on all 3 sensors on a "guess" it will fix it. IS it always a guarantee that if you get an o2 sensor code that if you replace it, your gas will improve?
04-06-2013, 12:11 PM
#2
Lets say you are paying $3.70 a gallon for premium. $20/$3.70=5.4Gallons.
75 Miles/5.4 Gallons= 13MPG. Pretty bad mileage there. Start with a tune up, replace your plugs and replace clean the air filter. How is your compression, engine worn out?
Don't waste money on O2s unless you have codes.
75 Miles/5.4 Gallons= 13MPG. Pretty bad mileage there. Start with a tune up, replace your plugs and replace clean the air filter. How is your compression, engine worn out?
Don't waste money on O2s unless you have codes.
04-06-2013, 12:13 PM
#3
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I will recheck the codes. I haven't done a compression test on the engine not sure where I can, without costing me a ton of money, but I will keep that idea. The engine has 225 or 230k miles on it. Yeah the gauge didn't last and I bought one off a dude on here and even that gauge is going already. He sold me a **** gauge.
Also I am using the K and N Stillen filter but It needs a cleaning for sure. I will probably get on that sometime next week
Also I am using the K and N Stillen filter but It needs a cleaning for sure. I will probably get on that sometime next week
Last edited by NmexMAX; 04-09-2013 at 10:44 AM.
04-06-2013, 05:48 PM
#4
I've got basically the exact issue. Recently replaced KS, rear 02 sensor, PCV valve, Plugs, air filter, fuel filter, etc. all that got me maybe an extra 30 miles on a full tank. Still sitting around 13mpg.
04-06-2013, 06:27 PM
#5
The evap makes a difference. Also quite a few other factors effect gas mileage, dirty oil, dirty air filter, old plugs, improper tire pressure. I have 2 leaky tires, and trust me, if your tire pressure is off a couple psi it takes quite a bit off the gas mileage. O2 sensors should be replaced every few years also because it effects the fuel trims, you may not get a code for them, but you can look at their voltage on an obd2 scanner and see if the voltage fluctuates quickly like it should.
Last edited by maxgtr2000; 04-06-2013 at 06:33 PM.
04-06-2013, 07:45 PM
#6
I am having this issue as well but I hear a leak in my pre-cats which I plan to replace with O2 sensors which are still OEM and never replaced since owning the car and have a KS code which will not go away...
04-06-2013, 08:47 PM
#7
Do you have any other codes? In the absence of other codes, a KS code guarantees a bad KS. A bad KS will kill mileage as well as hamper HP.
04-06-2013, 08:58 PM
#8
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Join Date: Oct 2003
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Something really odd must be happening. I have a 98 with 204,000 on it and I get 27+ consistently - now 29 to 30 with the TW3C 2 stroke oil. I drove 457 miles on my l last tank before I filled it.
I understand too well how throwing money at an issue does not always work - I need that with my two previous vehicles.
What is your driving style? I don't know the proper term do describe how I accelerate, but I push the gas down to a point where pushing harder does not provide a linear increase in acceleration matching the extra effort, and I don't push down too hard to cause a jump in RPM). It I need to go WOT, I will, but I usually don't.
A good question to ask, and I am sure you have asked it to yourself already is , "where is the gas going?" Could the car be losing gas somewhere between your tank and the engine?
All my cats, O2 sensors, etc., are original, except for the ignition coil on Cylinder 5 and the knock sensor.
Do you think the car is running too rich on the fuel?
I understand too well how throwing money at an issue does not always work - I need that with my two previous vehicles.
What is your driving style? I don't know the proper term do describe how I accelerate, but I push the gas down to a point where pushing harder does not provide a linear increase in acceleration matching the extra effort, and I don't push down too hard to cause a jump in RPM). It I need to go WOT, I will, but I usually don't.
A good question to ask, and I am sure you have asked it to yourself already is , "where is the gas going?" Could the car be losing gas somewhere between your tank and the engine?
All my cats, O2 sensors, etc., are original, except for the ignition coil on Cylinder 5 and the knock sensor.
Do you think the car is running too rich on the fuel?
04-06-2013, 09:54 PM
#9
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Join Date: Jun 2007
Location: Lowell/Boston, MA
Posts: 1,613
Something really odd must be happening. I have a 98 with 204,000 on it and I get 27+ consistently - now 29 to 30 with the TW3C 2 stroke oil. I drove 457 miles on my l last tank before I filled it.
I understand too well how throwing money at an issue does not always work - I need that with my two previous vehicles.
What is your driving style? I don't know the proper term do describe how I accelerate, but I push the gas down to a point where pushing harder does not provide a linear increase in acceleration matching the extra effort, and I don't push down too hard to cause a jump in RPM). It I need to go WOT, I will, but I usually don't.
A good question to ask, and I am sure you have asked it to yourself already is , "where is the gas going?" Could the car be losing gas somewhere between your tank and the engine?
All my cats, O2 sensors, etc., are original, except for the ignition coil on Cylinder 5 and the knock sensor.
Do you think the car is running too rich on the fuel?
I understand too well how throwing money at an issue does not always work - I need that with my two previous vehicles.
What is your driving style? I don't know the proper term do describe how I accelerate, but I push the gas down to a point where pushing harder does not provide a linear increase in acceleration matching the extra effort, and I don't push down too hard to cause a jump in RPM). It I need to go WOT, I will, but I usually don't.
A good question to ask, and I am sure you have asked it to yourself already is , "where is the gas going?" Could the car be losing gas somewhere between your tank and the engine?
All my cats, O2 sensors, etc., are original, except for the ignition coil on Cylinder 5 and the knock sensor.
Do you think the car is running too rich on the fuel?
I will admit. I am kindaaa a heavy foot but... I don't ever shift past 2.5k unless I am trying to pass someone or blast by someone who pissed me off and almost made me hit them or doing a nice little 6k rpm engine clean going onto the highway(that I hardly do anymore cause my inputshaft bearing is getting real bad so I don't want it to get worse) but in terms of driving I am really good at driving standard and also revsync sometimes do down shift but as of late I just get lazy and throw in neutral before a stop. On a cold drive, I will double clutch cause my synchos are really crunchy and notching on a cold tranni. So that helps a little bit, but overall. I always shift at 2.5k and always amd ALWAYS in 5th gear if I am going around 35mph and up.
oh and yes, Car is def running rich. Very potent smelling out of the tailpipe. My car has always ran rich so much you can taste it.
Last edited by NmexMAX; 04-09-2013 at 10:45 AM.
04-06-2013, 11:07 PM
#10
This is your problem, find the cause. Are you using larger injectors? Exhaust leaks close to the primary O2s? Headers that modify O2 placement?
04-07-2013, 02:11 AM
#12
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Join Date: Jan 2006
Location: Fuk 301 it's 410 Bal Md black/purple.
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Get the knock sensor fixed,because the car is running in limp-safe mode. The car is not running at it's full 190 hp rate. it's lacking in power.It's running at 150hp,because the KS is about 40-50hp itself. This will fix the MPG and the fuel filter is also a must it will increase the MPG. The other recomended service is a Tune-up if not done already and the tires inflation.
04-07-2013, 06:44 AM
#13
Also the heavy foot means the car goes into open loop a lot more often and can default to an afr of almost 10 in that loop. Those events may not be long but it all adds up, especially with the fumes leaking out of the tank since it is supposed to maintain pressure. When you remove your gas cap after running low you should hear that suction sound as the system releases negative pressure.
04-07-2013, 07:09 AM
#14
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Step 1
Fill fuel tank, FULL and write down mileage
Step 2
Drive normally until your at or very close to empty.
Step 3
Fill fuel tank again, FULL write down gallons displayed on pump.
Step 4
MATH 101 - divide miles by gallons and report back.
There is no way you can even come close to accurately obtaining your vehicles MPG on 20 bucks worth if fuel or 60-80 miles driven (about 2 hrs). That's just ridiculous.
04-07-2013, 09:59 AM
#15
you should replace the front O2. the computer uses that one to read air/fuel.
04-07-2013, 11:08 AM
#16
04-07-2013, 01:47 PM
#17
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Join Date: Jun 2007
Location: Lowell/Boston, MA
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Get the knock sensor fixed,because the car is running in limp-safe mode. The car is not running at it's full 190 hp rate. it's lacking in power.It's running at 150hp,because the KS is about 40-50hp itself. This will fix the MPG and the fuel filter is also a must it will increase the MPG. The other recomended service is a Tune-up if not done already and the tires inflation.
Step 1
Fill fuel tank, FULL and write down mileage
Step 2
Drive normally until your at or very close to empty.
Step 3
Fill fuel tank again, FULL write down gallons displayed on pump.
Step 4
MATH 101 - divide miles by gallons and report back.
There is no way you can even come close to accurately obtaining your vehicles MPG on 20 bucks worth if fuel or 60-80 miles driven (about 2 hrs). That's just ridiculous.
uhh...yes you can. first. $20 bucks is about 5 gallons for prem around here. Divide the Miles you are getting with the 20 dollar fill divided by the 5 gallons you got on that 20dollar fill until you are empty. Works out to be how many miles you are getting per a gallon.
Also with the Tiny holes I have on the top of my tank. I wouldn't fill her up the high anymore.
Last edited by NmexMAX; 04-09-2013 at 10:44 AM.
04-07-2013, 02:59 PM
#18
Are you currently throwing an 0304 DTC? Any other DTC's? Are you sure you properly installed the right value resistor?
04-08-2013, 08:02 AM
#19
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04-09-2013, 10:43 AM
#22
Step 1
Fill fuel tank, FULL and write down mileage
Step 2
Drive normally until your at or very close to empty.
Step 3
Fill fuel tank again, FULL write down gallons displayed on pump.
Step 4
MATH 101 - divide miles by gallons and report back.
There is no way you can even come close to accurately obtaining your vehicles MPG on 20 bucks worth if fuel or 60-80 miles driven (about 2 hrs). That's just ridiculous.
x 10e^10
04-09-2013, 11:13 AM
#23
Member who somehow became The President of The SE-L Club
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Join Date: Jun 2001
Posts: 16,033
uhh...yes you can. first. $20 bucks is about 5 gallons for prem around here. Divide the Miles you are getting with the 20 dollar fill divided by the 5 gallons you got on that 20dollar fill until you are empty. Works out to be how many miles you are getting per a gallon.
Also with the Tiny holes I have on the top of my tank. I wouldn't fill her up the high anymore.
04-09-2013, 01:23 PM
#24
04-09-2013, 03:12 PM
#26
04-10-2013, 06:40 AM
#30
04-10-2013, 07:41 AM
#31
Fact is a bad KS, if that's the only problem with your car, does not hurt your car as much. With a bad KS power is down to like 89% and gas mileage is barely affected. This is mostly because the KS only really comes into play when you drive your car hard, not like a granny.
04-13-2013, 06:10 PM
#34
04-13-2013, 09:47 PM
#35
The circuit is good from KS to ECU and continuity and grounds are good. There has to be a partial malfunctioning sensor that is holding this KS code which I would not mind changing O2 sensors since I never changed them since owning car..
04-13-2013, 10:59 PM
#36
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Join Date: Jan 2006
Location: Fuk 301 it's 410 Bal Md black/purple.
Posts: 1,860
if it's throwing the KS code and the voltage are good and the harness is good than just go and replace the KS. The rare case can be the ecu that's if everything checks out good.
04-14-2013, 03:16 PM
#37
Once I swap out the y-pipe and put fresh O2 sensors, it may go away since as I stated previously, it sounds like bees in a can..
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