ncfastls1

iTrader: (1)

I used to get about 250 miles a tank, now I can only get about 215. Driving route is the same, and if anything I drive less aggressive than I used to.

Here's a brief history: My engine hydrolocked early last year, but it only bent one rod. Had that entire rod/piston/bearing replaced. Had a misfire when we got it running again and thought it was the O2 sensors at first, so I replaced both of them with a pair from my work which sells Bosch (for my car at least). It wound up being a plug wire that had a tiny crack in it which was arcing to the block causing all the other cylinders to misfire too. Fixed that and it runs better than ever.

But there's my problem of getting 40 miles less per tank. My only guess is the oxygen sensors? I've heard more than a few times that GM cars don't like Bosch sensors but its not throwing a code or anything. Any guesses?

LS1121

iTrader: (17)

I have Bosch sensors and I get 26-27 mpg on the highway. I have NEVER had an issue with these sensors, they have worked great since I installed them.

LS6427

iTrader: (2)

About the Bosch sensors.......this is a fact. Some PCM's like them, some don't.

Not all PCM's like Bosch. I say the PCM because what else in the system can decide if it likes or dislikes a certain brand sensor.

If I put my front end up on ramps....unscrew my Denso 02 sensors. Then screw in Bosch 02 sensors, my engine will barely start. When it does it backfires, spits and shakes, and it will not go into Drive without stalling. Unscrew them and put my Densos back in and its perfect.

Also, PCM's will NOT throw a code until an 02 sensor is really bad. But in your case, MAYBE, your PCM simply does not like Bosch, so nothing is wrong to throw a code, but its going to run less than optimal.
Or, get a scan, maybe one or both of them are not switching properly, and thats the problem. No code will pop up until it gets really bad, in allot of cases.

All PCM's are not the same. Try switching to Denso sensors. #2344025, that part number Denso has 16" long wires, make sure that will reach your wiring harness plugs before you buy them. I use that part number Denso in both front sensor positions.

Also, of course, make sure the MAF is clean.

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LilJayV10

iTrader: (39)

Could it be the fuel? There's a difference between summer and winter blends. I noticed a loss of mpg in my blazer in the winter time. I didn't know if it was fuel related or it took the engine longer to warm up putting it in closed loop.

LS1121

iTrader: (17)

Actually running in Colder weather should help performance. The colder the air the better.

LS6427

iTrader: (2)

No way can it cause 40 miles per tank less......

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ncfastls1

iTrader: (1)

Exactly. I have had the car for 4 years and I never noticed a change in gas mileage from summer to winter.

MAF sensor is clean, that's one of the things I did when we put the engine back together. Also in case anyone asks, the fuel filter was changed early last year.

I suppose I will try Denso sensors later when I get some extra cash.

LS6427

iTrader: (2)

A sharp drop off in gas mileage is almost always failing 02 sensors....and you won't get a code in the failing stage, only when it gets really bad and the engine is hardly making power, hardly accelerating and misfiring.

You can get a scan, it will show if a sensor is on its way out or just not switching properly.

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FiredUpZ28

Put your car in the air in neutral and make sure none of the brakes are dragging. It happens, and is worth checking out. I agree with Bosch O2s. My friends dads 05 Silverado 5.3 non flex would not stop throwing B2S1 codes until we took the Bosch out and put in a Delco.

ncfastls1

iTrader: (1)

I have access to a scan tool...I'm in school for automotive so I'm in the shop every day...what should I be looking for?

Nexus9

Spark Plug color...?

LS6427

iTrader: (2)

Make sure the 02 sensors are switching properly.......I can't tell you the exact numbers to look for while idling with a cold engine, then with a hot engine. The guys in the "PCM and Diagnostics" section will tell you exactly. But the numbers will go up and down within a certain range for each sensor.

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RyanEricW

do a tune up

jam01

the epa mandated oxygenated fuel for use in winter, i dont know if your state has to use this crap or not. it is supposed to burn cleaner but it gives you less fuel mileage so you actually use more fuel so your really polluting more.

Oxygenates are fuel additives that contain oxygen, usually in the form of alcohol or ether. Oxygenates can enhance fuel combustion and thereby reduce exhaust emissions. Some oxygenates also boost gasoline octane.

The Clean Air Act requires use of oxygenated gasoline in areas where winter time carbon monoxide levels exceed federal air quality standards. Without oxygenated gasoline, carbon monoxide emissions from gasoline-fueled vehicles tend to increase in cold weather. Winter oxygenated gasoline programs are implemented by the states. The links below provide information about oxygenated gasoline, winter oxygenated gasoline areas, oxygenates (such as ethanol and MTBE), and health effects testing of oxygenates.

found this on the epa website, this is complete bs.

BOBS99SS

iTrader: (2)

good call lol

wssix99

iTrader: (5)

This is horrible mileage to begin with. (If you are talking highway travel.) Is this in heavy city driving? Do you have any modifications done to the car?

If this is not city driving, it looks like you have had a problem for a while. If it is city driving, its very hard to compare one tank to another due to the start/stop/start.


Winter gas has around 2% less energy than summer gas - so one could expect a 2% drop in highway mileage. There are lots of other variables in the winter. Shocks and tires behave differently, people "warm up" their cars, etc.

Jr.Samples

Wow This is exactly how my car is acting. Runs like a great when cold but as it warms it bucks under light throttle at low RPMS 1500 - 2700. So I end up dropping it down a gear to stop the jerking and bucking.

I do well to get somewhere around 12MPG.

Where can you get someone to scan for the O2s? I have no codes at this time. I think Autozone has the Denso O2s for around 60 each.

ncfastls1

iTrader: (1)

That's almost zero highway mileage, mods are in sig but just bolt ons. I don't live in the actual city, but I live in the suburbs with lots of hills and my usual routes don't take me on the highway much. I think the one time I was only on the highway up to Jersey, I got 400 miles to a tank and that was going 80 mph the whole time.

But like I said before, I've had the car for 4 years now and I have never seen this drop in mileage from summer to winter. I almost always got anywhere from 235-250 miles per tank depending on where and how I drove. Since I'm having trouble locating some AC Delco or Denso O2's for cheap (I work for carquest and we only sell Bosch for my car), I can try some new wires. I have MSD's right now but one of my wires has a burnt/cracked insulator on it (still sparks though), I'm not sure if that would have anything to do with it.

LS6427

iTrader: (2)

FWIW....I get about 230 per tank with my old, tired 427ci.....in the city, getting on it every now and then. Highway at 72mph, well over 300 miles. I think about 350 if I remember right from my last long trip.

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wssix99

iTrader: (5)

I've gotten 400 miles on a tank all highway on the east coast before, also. I've also gotten in to the low teens for hard core city driving with the same car. Between carbon cleanings, my mileage drops off 4-6 mpg across the board. Maybe that's all that you need? I doubt new wires will do anything but spend money better placed elsewhere. (If it were a spark issue, your car would lean you out.)