Terrible gas mileage help!
03-30-2012, 01:59 AM
#1
Terrible gas mileage help! Well ive owned this car for about 3 days when i got back home i put 3/4 of gas into. When it got to half a tank I reset the counter and its at 1/4 now it took 31 miles to get there lol. Ive noticed too that on idle it has a small hiccup, idle sounds a bit choppy. You can tell when you put your hand on the shift ****. Any suggestions as to what i should do? or where i should start looking? Today i drove in 6th gear most of the day and shifted at 1.5-2k no way does it drive like a car that should be getting 18-20mpg.
03-30-2012, 02:08 AM
#2
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Congrats on your new purchase, my friend! I have an entire thread devoted to a similar issue on a Z28 I purchased a few months ago. It can be found here:
https://ls1tech.com/forums/general-m...e-driving.html
Things to check/replace:
-Front O2 sensors (rears have no bearing on fuel trims)
-MAF
-Fuel Filter
-Spark Plugs and Plug Wires
-Fuel Injectors
-Tire Pressure (low tire pressure can cause a .3% drop in fuel economy for every PSI the tires are low, per tire)
You may also try running a can of seafoam through a tank of gas.
I have tried all of the above with the exception of fuel injectors and improved my fuel economy on a tank of gas (95% city driving) from 160-170 miles to 200-210 miles.
Best of luck!
https://ls1tech.com/forums/general-m...e-driving.html
Things to check/replace:
-Front O2 sensors (rears have no bearing on fuel trims)
-MAF
-Fuel Filter
-Spark Plugs and Plug Wires
-Fuel Injectors
-Tire Pressure (low tire pressure can cause a .3% drop in fuel economy for every PSI the tires are low, per tire)
You may also try running a can of seafoam through a tank of gas.
I have tried all of the above with the exception of fuel injectors and improved my fuel economy on a tank of gas (95% city driving) from 160-170 miles to 200-210 miles.
Best of luck!
03-30-2012, 02:21 AM
#4
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That's a terrific question. I honestly don't believe there was one exact thing causing the problem. I think with the car being 10 years old, there were just a number of things on the car had deteriorated and needed maintenance/replacement. My tire pressure was also a good bit low. Each thing I did seemed to make a small dent in the problem and combined they all added up to about a 20-25% increase in fuel economy. For what it's worth, replacing the above items with the exception of the MAF/injectors are easy and relatively inexpensive. For the MAF, I simply unplugged mine and caused the car to shift into Speed Density mode. The problem was unchanged with the MAF unplugged, so I ruled it out as the culprit.
03-30-2012, 11:56 AM
#9
For spark plugs to cause terrible gas mileage they would have to be rotted away and corroded badly.
If I were you I'd go get it scanned while the engine is running. See how the 02 sensors are switching. You will NOT get a code or SES light while 02 sensors are failing and making you run VERY rich, which will totally kill your gas mileage.
Nothing else can really kill it like that except a fuel leak.
Now.....you say you have a stumble at idle. That could very well be the oh-so rare leaking fuel injector(s). That will take a little time to check. You have to lift the injectors and turn the key on to prime the system to see if any leak.
.
If I were you I'd go get it scanned while the engine is running. See how the 02 sensors are switching. You will NOT get a code or SES light while 02 sensors are failing and making you run VERY rich, which will totally kill your gas mileage.
Nothing else can really kill it like that except a fuel leak.
Now.....you say you have a stumble at idle. That could very well be the oh-so rare leaking fuel injector(s). That will take a little time to check. You have to lift the injectors and turn the key on to prime the system to see if any leak.
.
03-30-2012, 12:08 PM
#10
For spark plugs to cause terrible gas mileage they would have to be rotted away and corroded badly.
If I were you I'd go get it scanned while the engine is running. See how the 02 sensors are switching. You will NOT get a code or SES light while 02 sensors are failing and making you run VERY rich, which will totally kill your gas mileage.
Nothing else can really kill it like that except a fuel leak.
Now.....you say you have a stumble at idle. That could very well be the oh-so rare leaking fuel injector(s). That will take a little time to check. You have to lift the injectors and turn the key on to prime the system to see if any leak.
.
If I were you I'd go get it scanned while the engine is running. See how the 02 sensors are switching. You will NOT get a code or SES light while 02 sensors are failing and making you run VERY rich, which will totally kill your gas mileage.
Nothing else can really kill it like that except a fuel leak.
Now.....you say you have a stumble at idle. That could very well be the oh-so rare leaking fuel injector(s). That will take a little time to check. You have to lift the injectors and turn the key on to prime the system to see if any leak.
.
Would a leaky injector cause terrible gas mileage? Not sure if its an injector though, my mom had a failing injector in her 2v mustang and it misfired through out the whole rpm range, my car runs really smooth while on the throttle it just hiccups a bit on idle. Would that be signs of a leaky injector?
03-30-2012, 12:15 PM
#11
Would a leaky injector cause terrible gas mileage? Not sure if its an injector though, my mom had a failing injector in her 2v mustang and it misfired through out the whole rpm range, my car runs really smooth while on the throttle it just hiccups a bit on idle. Would that be signs of a leaky injector?
Not saying this is definitely the issue. But not many things can totally kill gas mileage. A tune up on these cars is simple.....plugs, air filter, fuel filter, clean your MAF......your done. Unless the plugs are literally rotted away its not going to change fuel mileage that much, certainly not what you're experiencing.
Could also be a failing PCM.
If you do a tune up and its still bad mileage......check the injectors.
.
03-30-2012, 12:17 PM
#12
Yes, a small leak. At idle that extra gas leaking into that cylinder(s) is not enough rpm to consume the "extra" gas, but under throttle the leak might not be bad enough and the higher rpm's consume that little extra gas easily and you don't feel any hesitation. Just like when a real dirty fuel filter causes problems at idle, but under throttle the increasing fuel pressure over-comes the dirty filter and it runs great.
Not saying this is definitely the issue. But not many things can totally kill gas mileage. A tune up on these cars is simple.....plugs, air filter, fuel filter, clean your MAF......your done. Unless the plugs are literally rotted away its not going to change fuel mileage that much, certainly not what you're experiencing.
Could also be a failing PCM.
If you do a tune up and its still bad mileage......check the injectors.
.
Not saying this is definitely the issue. But not many things can totally kill gas mileage. A tune up on these cars is simple.....plugs, air filter, fuel filter, clean your MAF......your done. Unless the plugs are literally rotted away its not going to change fuel mileage that much, certainly not what you're experiencing.
Could also be a failing PCM.
If you do a tune up and its still bad mileage......check the injectors.
.
Thanks ill give that a look over.
11-07-2013, 07:35 PM
#14
Yes, a small leak. At idle that extra gas leaking into that cylinder(s) is not enough rpm to consume the "extra" gas, but under throttle the leak might not be bad enough and the higher rpm's consume that little extra gas easily and you don't feel any hesitation. Just like when a real dirty fuel filter causes problems at idle, but under throttle the increasing fuel pressure over-comes the dirty filter and it runs great.
Not saying this is definitely the issue. But not many things can totally kill gas mileage. A tune up on these cars is simple.....plugs, air filter, fuel filter, clean your MAF......your done. Unless the plugs are literally rotted away its not going to change fuel mileage that much, certainly not what you're experiencing.
Could also be a failing PCM.
If you do a tune up and its still bad mileage......check the injectors.
.
Not saying this is definitely the issue. But not many things can totally kill gas mileage. A tune up on these cars is simple.....plugs, air filter, fuel filter, clean your MAF......your done. Unless the plugs are literally rotted away its not going to change fuel mileage that much, certainly not what you're experiencing.
Could also be a failing PCM.
If you do a tune up and its still bad mileage......check the injectors.
.
I also have really bad MPG on my car, and the high idle issue when coming to a stop and coming off the gas, I've done a full tune up on the car. I did find a leaky injector and fixed it by replacing the o rings on it.
I've checked the fuel pressure and its fine at 49 or 50psi.
I did check the spark plugs and found one that was fuel fouled, it was the same one with the leaky injector !!!
I have a basic code reader (I wish I had a hp tuners) what kinds of readings would I need to watch out for ???
thanks
11-08-2013, 02:47 PM
#15
TECH Fanatic
High idle on these cars is almost always an IAC issue - rather the IAC valve itself or a pinched wire going to the PCM. How bad is your MPG? are you doing the correct "fill up, record, drive, fill up, record, divide" method? GM (especially Camaro) fuel gauges are not exactly linear so going from 3/4 to 1/4 tank does not actually mean you are using half your fuel tanks capacity worth of fuel.
Also, what kinda plugs did you use and which cylinder is fouling plugs?
Also, what kinda plugs did you use and which cylinder is fouling plugs?
11-08-2013, 03:00 PM
#16
High idle can be bad TPS and that can hurt gas mileage a lot. I had high idle and 18mpg highway driving. I scanned it and found the tps reading too high at low throttle settings. I checked it carefully and found it was reading all over the place. I replaced it with a made in usa Delphi unit and the gas mileage went up to 23 highway.
11-08-2013, 04:49 PM
#17
Im getting about 140 miles on a full tank, I usually fill up about 13 to 14 gallons every time, I am doing the correct method to calculate (my drive is 65 miles daily, yes my wallet is bleeding right now), I've even gone as far as waiting for the same pump to make sure I get the same volume in there. I have tr 55 plugs gapped at .055, new gm performance wires.
you mention about wires being pinched to the PCM, but wouldn't that cause a SES light ??
the cylinder that is fouling is cylinder number 2, I've swapped injectors and the problem didn't follow the injector. I've also swapped the coil and wire and nothing.
you mention about wires being pinched to the PCM, but wouldn't that cause a SES light ??
the cylinder that is fouling is cylinder number 2, I've swapped injectors and the problem didn't follow the injector. I've also swapped the coil and wire and nothing.
11-08-2013, 05:08 PM
#18
High idle can be bad TPS and that can hurt gas mileage a lot. I had high idle and 18mpg highway driving. I scanned it and found the tps reading too high at low throttle settings. I checked it carefully and found it was reading all over the place. I replaced it with a made in usa Delphi unit and the gas mileage went up to 23 highway.
11-08-2013, 09:28 PM
#19
I use a simple scanner to watch the TPS as I drive. It should be 0 % at idle and move up proportional to the throttle position AND REPEAT itself. example mine was 0 at idle then 5% at idle then 30% at light cruise when it should have been 10% or less at cruise.