Impala Forums banner

please help MPG significantly lowered

6K views 34 replies 8 participants last post by  05_impala 
#1 ·
hey guys i been lurking the forums for a while. i own a 05 impala its a good car and does good on gas. i was getting 330 miles on a tank on average. well here is the problem, within the last 2 weeks my impala has lost 130 miles of driving range. im basically driving a truck thats how bad it is. i have to fill up every 200 miles:bang::bang::bang:below is a list of what i thought it could be.

1.a bad cat i just had it changed this week and was also having a exhaust leak. it was in the flange so i got both of those taken care off. still bad gas does run a lot better tho and i dont feel the heat of the engine anymore when i open the doors. also not as loud

2. O2 sensor i got the car scanned at o reilys . i was told it was going bad , the one closer to the manifold. if this was the problem what tools would i need to replace it and what would be a good brand ?

3. a tune up, i say this cause the car has 177,000 miles on it and i never had a tune up . i done a bit of research and figured ac delco is the most mentioned on this site . same for the wires but not sure what type of wires i would need.

4. temp sensor / thermostat when i had the car scanned it said thermostat and temp sensor. i have a thermostat just havent put it in yet. i was going to tackle the temp sensor while putting on a new thermostat since they're both close .

i cant think of anything else that could cause this . i used gas from QT by my house and i used it when the QT was brand new. on that one tank i experienced the mpg decline. i thought it was bad gas but then on the next tank it was still not doing good. i filled up using exxon and a bottle of seafoam injector cleaner not a difference. i was really hoping a changed cat would've solved this.
 
See less See more
#2 ·
I would most definitely go through your list of items and replace them all. With that kind of mileage on the car, you won't hurt anything and may fix the problem. You might also check your fuel pump and filters. Fuel, air, & spark are the 3 things you need to make sure you have enough of to get things running properly. If you eliminate those issues, then it's time to have someone dig deeper.
 
#4 ·
Get that o2 sensor swapped out. Go factory for that one as well. Stay away from Bosch. Soak the old one with pb blaster or liquid wrench the night before you go to do the work. You will want to use a crows foot socket on it, since a normal closed end wrench may not be big enough to fit the connector through over the wires. And DO NOT use an open end wrench. You will round off the sensor, and that will leave you in a world of hurt. Crows foot is the way to go. The reason you need to get that changed is because the o2 sensor going bad will nearly always cause the car to run rich, and all of the unburned fuel will plug up the cat. That may be what did your old one in, and if you don't change that sensor, it could screw up your new one as well.

Go ahead with the tune up as well. If those are factory spark plugs, they are definitely part of the problem for sure. I bet once you change those, it will feel like a brand new car power wise.

To bring a point to what csawyer said earlier about fuel filter, the fuel filter is non serviceable. It is part of the fuel pump assembly. So check your fuel pressure, and if it is low, you need a whole new pump. Stick with factory once again, and like I said before, stay away from Bosch (do you notice a trend here? Most Bosch stuff is total crap.) stay away from airtex as well. If you get one of the airtex pumps, you will be doing the job again in a year or less. Go with the oem Delphi pump.
 
#5 ·
woah i just seen the filter the other day. lol i dont own a 8th gen lol ,yea i learned bosch is crap from lurking around here. so i figured i need a socket and a extender and one of those twisty things for the spark plugs. this maybe the crows foot you speak off. me and guy at oreilys have become best friends over the past week because of this car. lol will definitly change the wires and spark plugs. ac delco for the plugs and wires right ?
 
#6 · (Edited)
Tune up might be ok and really it's due for one, but I'm curious about what would happen if you resolved all of your MIL / trouble codes before you started disrupting the ever-so-touchiness of a high mileage engine. I've learned the hard way, at this stage in the game especially with so many miles, if you don't know 100% something is bad, don't even touch it.

If you decide to do a tuneup, replace anything you have with AC Delco if you can. Call a Chevy dealer for the most recent part numbers if need be. These discount parts stores aren't always the best place to get plug part numbers, because their computers are set up to tell you basically any plug that will screw into the head will be fine for your car, which I can tell you, is basically not the case. If you use anything but AC Delco, especially with the plugs, you may end up making it run even worse. Can you get to the upstream 02 sensor with an 02 sensor socket? I know they sometimes have them for rent at the parts store. But I wonder, if you're not getting a MIL indicator from the upstream 02, why do you think it's going bad? Is it because it's not giving you the right measurements in the datastream on the scanner? Is there a pending code? I wouldn't touch any sensor unless it's either giving you a code or a pending code, or it's not giving good readings in the datastream.

I believe your last item in the list could be worth looking into, I could be wrong of course, but read on. Your engine temperature matters to the fuel injection system. The PCM must always be getting an accurate reading from the temp sensor. If the thermostat is bad, replace that, too, or you will overcool or overheat depending if it's stuck open or closed. The engine should be running at the right temp, and providing the right temp readings to the PCM. The temp sensor works with the throttle body, PCM, and fuel injection system to provide the right lean/rich mixture of fuel to the engine. Back in the day, we used to call these chokes, but those don't exist anymore, Lol. I can't be too sure, but I think the temperature sensor tells the PCM when the car is warm, and then the PCM works with the fuel injection system to back down the richness. I'd make sure you're in closed loop mode after warm up on the scanner in the datastream - if the car is at full temp, and you're in open loop mode, then your system is isn't recognizing the engine has warmed up properly - if you're not in closed loop mode after warmup, then the engine/PCM is being tricked into thinking it's in warm up mode, and will use more gas. And, of course, if the datastream isn't reporting a temperature, then that tells you the sensor is bad, and needs replaced. Could that be part of the problem?
 
#9 ·
Gotcha. If you're getting a code for it, by all means do what you gotta do to replace it. To be on the safe side, when you replace the 02 sensor, replace whatever else is giving you a bad code, since it's possible that the rich condition could destroy your new 02 sensor, or result in premature failure.
 
#10 ·
Yea got the codes just forgot to write em down. I know you guys like the codes I'll try to get them later . I did however disconnected my battery . I bought a Bosch O2 sensor , retuned it and got a refund. So I just put a full tank in it and see if the code comes back. Hopefully the reset can get it back since the cat is 3 days old . I put 10 dollars in it and it seemed the car range was back to normal for 2 gallons . I drove to the local ac delco shop and talked about my sensor . Told him bout the bosche and he said that was a good decision . He told me the denzo and ac delco are the best for GM cars. Seen all the bad stuff bought them from here so thanks again .
 
#11 ·
Sounds like you're getting it sorted out, but yes delco is the way to go on plugs and sensors, wires it doesn't really matter, I've never seen bad ones. 7th gens DO have a serviceable fuel filter, and the o2 sensor is best done with an o2 sensor socket.
 
#13 ·
The PCM may not be happy with the cat change, you didn't mention what kind you used, but these are notorious for problems with aftermarket cats. A PCM tune can have the cat code removed, but you have to be willing to drop $150 on it. Still cheaper than a $400+ factory cat...
 
#14 ·
yea its just a cat from the exhaust shop. i wanted a magnaflow hi flow but was told they didnt have good flow. i was guzzling gas with the old cat . cat was changed this week but the 14 mpg im getting has been going on for 2. had a exhaust leak in the flange and a bad converter . thought that was the reason but its still bad on gas. driven 30 miles since i unhooked the battery for reset.
 
#15 ·
Get that upstream o2 sensor changed, the fuel filter changed, and the tune-up done. See how it is after that. It is most likely the o2 sensor though, from what you've told us.
 
#17 ·
decided to quit and i was so close that last bolt was laughing at me. i lost 10 lbs of sweat today just from being outside all day. i was at least outside for 6 hrs maybe more. i was being taunted by the exhaust shield . took it off and still no luck. i figured id need some smaller tools to get the job done. i put everything back together started her up and she was running fine. well i decided to put some crc throttle body cleaner in the intake cause it was gunky. started her up and she was running a little choppy then some min later i hear this screatching noise . when i rev the engine it gets even louder im hoping this goes away in the morning. could it be a vacuum leak. i put everything back where it should be so where is this noise coming from.
 
#19 ·
Pry it out, it happens. No, its not supposed to be stuck though.
 
#20 ·
Well I changed it .I been having it forever and just now put it in. Is there a certain way you have to put it in there . I Just placed in the opening and wala. Only difficult part is just gettin to it lol. I stripped my coolant bypass bolt tho . Taking it to the shop lol. I'm afraid to drill any deeper I wish I would've drilled in straight in. Lol went to the left a bit it can be saved .
 
#21 ·
They are directional, just make sure it goes in the way the old one came out.
 
#23 ·
hey did you end up doing spark plugs? how hard was it to get to the back 3? did you use AC Delco? Autozone seems to have Iridium and Platinum versions listed in other brands like Autolite, NGK, Bosch, and Champion as well as AC Delco....I'm asking because I was thinking of doing this job sometime soon...
Any recommendations as to the part number?
Is this the plugs we should be looking at? AC Delco Iridium/Spark Plug (41-101) | 2002 Chevrolet Impala 6 Cylinders E 3.4L SFI | AutoZone.com
 
#24 ·
Stick with iridium, autolite and ngk are both good as well as delco. To get the back 3, take the bolts out of the dog bone mounts at the front of the engine, and rock it forward.
 
#27 ·
Never tried that, I just hold it with my free hand while the other is back there.
 
#28 ·
i didnt change the spark plugs myself , but i got the dealer to do it. just gave em the plugs and wires. also still getting bad gas mileage . i replaced the tps , fuel filter and did a tune up. still not getting the mileage i was a month ago. it has gotten better but its far from where it was . nothing mechanically wrong with the engine, map sensor threw a code during the last scan but hasnt came back. how can i take the map sensor out .
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top