Really Bad Gas Mileage

mattieboy87

Member
Joined
Jul 10, 2008
i never post on the forms but ive been here just reading for a while, but i really need to sove this. My gn has been struggling to even reach 13mpg and i see that most people on here with mild cars like mine get at least 17mpg Right now im a broke college student and my last tank only got me 176 miles. 200 miles is normal for me, with mostly highway miles. The car seemingly runs perfectly, and has no driviability issues. ive been driving like a grandpa trying to conserve gas but it doesnt really help. So i guess im asking if theres something i can look at or tinker with under the hood to solve my problem. I can wrench on a car but i suck at problem solving. Most of the mods on my car were done sometime in the 90s, and i think a read that having old injectors could be the cause, could that be it. I would have to save up for new ones, the plug wires are pretty old too. The car has been to some of the good shops in south florida for other things but the gas milage never seems to improve. it has been more of a nusience then a problem, but financial aid didnt help me out as much this year so i really have to solve this problem. any suggestions on what to look at would really be helpful.
 
Definatly start with a tune up, I would replace the o2 sensor and also clean the MAF with MAF cleaner. Do you have a scantool in the car? I would also say the coolant sensor for the ECU is reading cold and dumping in more fuel. Also what gears you have in the rear? Is the trans Lock-up, if so is it locking up on the highway?
 
fix all pre O2 sensor exhaust leaks. They will leak ambient air in and hurt mileage a lot.
 
Well i havent checked the plugs for differences so i might try to do that after school tomorrow. That would show if I have a bad injector correct? Fuel pressure should be good because the regulator is a newish stock one, maf is clean, ive pretty much done everything in the spring cleaning over the time ive had the car minus the gear oil, and the transmission is working good. Is there a way to check the coolant sensor, not to sound like a noob but this is the first ive heard of it. I do have a scanmaster, is there anything on there that would show what might be the problem? I cant really fix any fix any exaust leaks because im away at school so it would have to wait for winter break. Any other suggestions?
 
ok here are the idle reading after warmed up today, it was cold out

AF-05
L8-36
BAt-13.8
Int-128
BL-115
CLt-168
Ats-120
rpm-775-825
tps-.34
Iac-10-14
cc-89
Mal-00

I couldnt get the numbers while driving because there was alot of traffic this morning. Do you guys want to see the WOT as well? Im not sure on the thermostat i have, and normally im out of ft.lauderdale, but im going to school in tallahassee so ill be up here untill december.
 
At idle your tps should be around .42 Your BL should be 128, means your running rich. Coolant reading is right if the car has a 160 stat, or it wasn't fully warmed up.
Replace the wires if they are old, or Ohm them out and see if you have more resistance in some over others.
Get up to 55 mph and hit the brake for a second while still on the gas, you should feel the converter unlock for a second, then lock back in again with the rpms jumping up during unlocking, about 200 rpm - if not you have a non lock up which will hurt gas mileage.
Depends on how much your getting into the gas. Around the city, getting into it I'll have 13 mpg. Highway drive nice and easy 20's mpg.
 
I just set the tps right and the converter is a 2800 stall lock-up and it works correctly, how do i go about geting the BL correct?
 
"I couldnt get the numbers while driving because there was alot of traffic this morning".
You can recall the readings after a drive as long as you don't shut the engine off.
see post #7 for details at the Scanmaster link.
 
You have succeeded in confusing me. i thought that the recall was only for the WOT readings, the scanmaster saves all of the other stuff to??

oh and on a side note the car coolant temp is normally at like 180, i think it was just the weather making it cooler
 
As I understand, a tps value of 3.0V, will allow you to get the O2, mph, and knock.[If any]. Maybe look at O2 and see where it is...
If it's "cold outside" when you got the idle readings, I wonder why the IAT is double or more of ambient temp?? Where is the IAT sensor mtd? What was ambient?
 
Do you still have the stock Cat converter on it? If so I bet its dirty & not helping the issue. You really need to pull the plugs & take a look at them. How old are they? Gapped to what?
 
I adjusted the Tps to .42, i havent made a WOT pass yet to get the O2, knock, and mph. Theres no Cat on the car, The plugs are only a couple months old, and i dont remember what they are gapped at. Chuck i dont really understand what your saying, im still a noob at heart. I think it was around 60+ degrees outside, maybe 70, and i took the readings in a parking garage. But i dont know what you mean by IAT is doubble the temp, because the scanmaster doesnt read that, least i dont think it does?
 
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