Horrible MPG! What Gives? :(
Thread Starter
Pro
Joined: Jun 2007
Posts: 565
Likes: 0
From: Ft. Bragg, NC
Horrible MPG! What Gives? :(
So I'm slowly nit-picking away at this car trying to get it back to running good... but I have horrible MPG right now. I estimated that I'm using about a quarter of a tank every 40 miles 
which to me seems like sh*t. There was a past history code of P0171 (Fuel system lean) don't know if that means anything. There is a service vechicle light if that might be connected to something releating to consumption of fuel but I don't know and have to take it in for that.
which to me seems like sh*t. There was a past history code of P0171 (Fuel system lean) don't know if that means anything. There is a service vechicle light if that might be connected to something releating to consumption of fuel but I don't know and have to take it in for that.
Burning Brakes
Joined: Aug 2006
Posts: 1,217
Likes: 5
From: Stark County Ohio
Wow – That is some low MPG. Are those 40 miles at the racetrack? My 2000 A4 with a 3:15 rear can reach 450 miles per tank (highway mileage at 75+MPH) with gas to spare in the tank. (19-gallon tank in 2000)
Racer
Joined: Oct 2007
Posts: 470
Likes: 0
From: Saint Cloud Florida
Dirty injectors? wal-mart fuel? heavy foot ?
maybe try to get those cleaned and adjust your driving habits
hope this helps, i can get a full tank to last me 420 miles give or take (evening commute in traffic kills me)
<1999 corvette coupe
my .02 cents!
maybe try to get those cleaned and adjust your driving habits
hope this helps, i can get a full tank to last me 420 miles give or take (evening commute in traffic kills me)
<1999 corvette coupe
my .02 cents!
Le Mans Master
Joined: Dec 2000
Posts: 9,918
Likes: 1,880
From: Hot Springs AR
If you have an exhaust leak, the O2 sensors will sense the O2 that is pulled into the system and indicate a lean condition. The PCM compensates with more fuel, but the O2 keeps sensing O2, which causes the system to start running really rich.
So, check for exhaust leaks as a starting point.
HTH, and have a Happy Thanksgiving!
Mike
So, check for exhaust leaks as a starting point.
HTH, and have a Happy Thanksgiving!
Mike
Melting Slicks
Joined: Feb 2006
Posts: 3,400
Likes: 3
From: Sarasota Florida
19.1 Gallons. Here is a link to a web site the will give you all the specs
http://www.corvetteactioncenter.com/...9/99specs.html
http://www.corvetteactioncenter.com/...9/99specs.html
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
Check your PCV valve and the connection from it to the intake. Holes can develop on the bottom side of it, out of sight. I would expect you would have problems from taking off at a light or similar such as surging. Have you checked your plugs/wires, replaced air and fuel filters? On the '99's there is a flex line that connects to a fuel return line to the tank from the fuel rail...looks like a snake type thing. Is it connected to the return line?
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Burning Brakes
Joined: Aug 2006
Posts: 1,217
Likes: 5
From: Stark County Ohio
Check your PCV valve and the connection from it to the intake. Holes can develop on the bottom side of it, out of sight. I would expect you would have problems from taking off at a light or similar such as surging. Have you checked your plugs/wires, replaced air and fuel filters? On the '99's there is a flex line that connects to a fuel return line to the tank from the fuel rail...looks like a snake type thing. Is it connected to the return line?
Thread Starter
Pro
Joined: Jun 2007
Posts: 565
Likes: 0
From: Ft. Bragg, NC
Check your PCV valve and the connection from it to the intake. Holes can develop on the bottom side of it, out of sight. I would expect you would have problems from taking off at a light or similar such as surging. Have you checked your plugs/wires, replaced air and fuel filters? On the '99's there is a flex line that connects to a fuel return line to the tank from the fuel rail...looks like a snake type thing. Is it connected to the return line?
plugs and wires seem fine... air filter is good but dunno about the fuel filter... and then could you possibly post a pic of the "flex line" showing how it's supposed to be connected?
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
Mine has that line that is contained in the picture already provided there. It will chop off some performance when its open, but not the massive loss of MPG that he's reporting. It does cost MPG though.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
So I'm slowly nit-picking away at this car trying to get it back to running good... but I have horrible MPG right now. I estimated that I'm using about a quarter of a tank every 40 miles which to me seems like sh*t. There was a past history code of P0171 (Fuel system lean) don't know if that means anything. There is a service vechicle light if that might be connected to something releating to consumption of fuel but I don't know and have to take it in for that.
which to me seems like sh*t. There was a past history code of P0171 (Fuel system lean) don't know if that means anything. There is a service vechicle light if that might be connected to something releating to consumption of fuel but I don't know and have to take it in for that.First of,, we need to know what modifications that have been done to the car. Second, yep, DTC that are present are a MUST!
Please list all the mods that have been done to the engine, last time the car was serviced/tuned up and and DTC.
This is the absolute best C5 Diagnostic Trouble Code (DTC) web site!!!
http://www.corvettedoctor.com/Code_Main.html
www.corvettedoctor.com
Go to “technical data base” and then to “Corvette ECM Computer Codes”. Then select your year car. Read the instructions and then scroll down to the "READ MORE" window to view the code definitions.\
Here is another very good site:
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
or
http://www.gearchatter.com/index.php
Look under LS1/LS6 DTC Codes for you year C5!
Make sure to include the H or C suffix!!
BC
Le Mans Master
Joined: Aug 2001
Posts: 8,145
Likes: 1
From: Bradenton FLORIDA
Save some time & frustration & visit one of the good supporting tuners in your area. A quick scan & datalog will show them whats up & I expect the fix will be extremely cheap. The way your going you are spilling $$ like crazy out the exhaust.
Even our heads/cam cars get 24-28 & a cam only MN6 will get 30-32 with the right tune (and our 1,000 RWHP twin turbo gets app 7-8
)
Even our heads/cam cars get 24-28 & a cam only MN6 will get 30-32 with the right tune (and our 1,000 RWHP twin turbo gets app 7-8
)
Thread Starter
Pro
Joined: Jun 2007
Posts: 565
Likes: 0
From: Ft. Bragg, NC
there are NO MODS besides Blackwing Air Intake.... car is 100% stock to my knowledge otherwise... done plenty of h/c swaps so I am able to identify what's aftermarket if there is anything but I haven't seen anything besides the air intake
secondly... I HAVE NO CODES! No check engine light. The car was just at GM to get rid of the code P0154 O2 Sensor CKT No Activity (Bank 2 Sensor 1) and few other things because the PCM I suppose had to be reset or something. Anyways I have no clue and am so lost. I do have a "Service Vehicle Soon Light" on that I need to get taken back in to have checked out.
If you guys don't believe me that I have no codes heres the DIC lookup:
10-PCM No Codes
28-TCS 5 Codes - C1221 H, C1222 H, C1255 H, C1282 H, C1288 H
40-BCM No Codes
58-SDM No Codes
60-IPC No Codes
80-Radio No comm.
B0-RFA 3 Codes - U1096 H, U1064 H, U1016 H
I have no clue what would be causing me to be getting 160 miles per tank The DIC reads 20~24mpg while driving but thats definetly off 
(actually wish I was getting even that)
secondly... I HAVE NO CODES! No check engine light. The car was just at GM to get rid of the code P0154 O2 Sensor CKT No Activity (Bank 2 Sensor 1) and few other things because the PCM I suppose had to be reset or something. Anyways I have no clue and am so lost. I do have a "Service Vehicle Soon Light" on that I need to get taken back in to have checked out.
If you guys don't believe me that I have no codes heres the DIC lookup:
10-PCM No Codes
28-TCS 5 Codes - C1221 H, C1222 H, C1255 H, C1282 H, C1288 H
40-BCM No Codes
58-SDM No Codes
60-IPC No Codes
80-Radio No comm.
B0-RFA 3 Codes - U1096 H, U1064 H, U1016 H
I have no clue what would be causing me to be getting 160 miles per tank
The DIC reads 20~24mpg while driving but thats definetly off (actually wish I was getting even that)
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
This is simple but most of the time effective:
Do you ever feel any cylinder misses OR do you ever see the check engine light falsh at you while your driving the car?? Cylinder misfires can be detected by observing the check engine light. If it is flashing, it is detecting a misfire.
Clean the MAF by spraying the MAF wires inside the MAF with MAF cleaner. I have used "brake parts cleaner" with good success!
If you clean your MAF and dont have any current DTC's or misfires,,,,,
Im lost ( and that is RARE).
How are you reading your DTCs??
BC
Do you ever feel any cylinder misses OR do you ever see the check engine light falsh at you while your driving the car?? Cylinder misfires can be detected by observing the check engine light. If it is flashing, it is detecting a misfire.
Clean the MAF by spraying the MAF wires inside the MAF with MAF cleaner. I have used "brake parts cleaner" with good success!
If you clean your MAF and dont have any current DTC's or misfires,,,,,
Im lost ( and that is RARE). How are you reading your DTCs??
BC
Thread Starter
Pro
Joined: Jun 2007
Posts: 565
Likes: 0
From: Ft. Bragg, NC
This is simple but most of the time effective:
Do you ever feel any cylinder misses OR do you ever see the check engine light falsh at you while your driving the car?? Cylinder misfires can be detected by observing the check engine light. If it is flashing, it is detecting a misfire.
Clean the MAF by spraying the MAF wires inside the MAF with MAF cleaner. I have used "brake parts cleaner" with good success!
If you clean your MAF and dont have any current DTC's or misfires,,,,, Im lost ( and that is RARE).
How are you reading your DTCs??
BC
Do you ever feel any cylinder misses OR do you ever see the check engine light falsh at you while your driving the car?? Cylinder misfires can be detected by observing the check engine light. If it is flashing, it is detecting a misfire.
Clean the MAF by spraying the MAF wires inside the MAF with MAF cleaner. I have used "brake parts cleaner" with good success!
If you clean your MAF and dont have any current DTC's or misfires,,,,,
Im lost ( and that is RARE). How are you reading your DTCs??
BC
...anyways I'm reading the DTC's just like everyone else... i just pulled them up for you guys in the previous post. just ran through them again to just double check and those are the same historic codes or no codes that came up
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
Hey Bill, I'm wondering if he's drawing fuel off one tank only, therefore half the available fuel supply? Could a plugged fuel filter or the feed from the right tank not getting through cause this? Just re-thinking that though...he would only be putting in half the amount of gas.
RrCox22, are you smelling any gas leaking? When you fill back up, how much is going into the tank? It holds 19.3 gallons bone dry empty to full.
RrCox22, are you smelling any gas leaking? When you fill back up, how much is going into the tank? It holds 19.3 gallons bone dry empty to full.
Last edited by dgrant3830; Nov 22, 2007 at 12:35 AM.
Thread Starter
Pro
Joined: Jun 2007
Posts: 565
Likes: 0
From: Ft. Bragg, NC
and I haven't filled her up all the way ever since I've had the car (3 months) with gas $3.80 a gallon out here in Cali... just too much on the wallet at a time
...I'm going to Vegas for the weekend and will clean the MAF and Blackwing early next week but for the meantime I'm lost as I don't think that will help much