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Help! Very low gas mileage

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
I've got a problem with gas mileage on my 03 Z06 which has steadily gone from 31 mpg hwy down to its present 16 mpg hwy and I don't know what's causing it. I've thumbed thru the archives but could find nothing with my problem. I made a service appointment at the dealership for Tues, 03/08/16 so I'm hoping someone can turn me in the right direction so I can repair this myself.

It recently threw a code 1416 which I found was a check valve located behind the intake. Rather than remove the intake to get to it I took others advice and sprayed carb cleaner into the tubing taken off of the check valve on the left side. The check engine light has not come back on since doing this. The bad gas mileage is not making this a fun car to drive. I removed the Vortex "Rammer" air box and reinstalled the OEM one. While doing so I sprayed cleaner on the MAF. Everything is back together and totally STOCK! After putting on the OEM air box, the mileage went down to 16 mpg. With the Vortex airbox I was getting about 21 mpg, also not what it was at an earlier time. So it's all stock.........what can be the problem? I've tried "tapping" on the MAF to see if it makes the engine run intermittent which it does not. I've unplugged the MAF while idling and there is a sudden shudder which smooths out when plugged back in. There are no other codes that come up.

I'm used to repairing my cars myself and don't want to take it in to be looked at. $140 for just having them look at it plus parts (if needed) plus labor. Any suggestions would be appreciated. Thank you in advance..............Brian
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
I've got a problem with gas mileage on my 03 Z06 which has steadily gone from 31 mpg hwy down to its present 16 mpg hwy and I don't know what's causing it. I've thumbed thru the archives but could find nothing with my problem.(snip)

Since you currently have no codes set, we are going to be doing some quessing, but first, do you have a scan tester? Do you have a set of Service Manuals?

The air filter...is it clean?
Have you ever replaced the oxygen sensors
How many miles are on the engine?
In the last year or so has the MIL ever been on for any reason other than the P1416?
Besides the decrease in mileage has there been any other change in the car's performance?
What prompted you to "spray" the MAF and what did you spray it with?
Did you visually inspect the MAF and, if so, were the wires clean?
 

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
Since you currently have no codes set, we are going to be doing some quessing, but first, do you have a scan tester? Do you have a set of Service Manuals?

The air filter...is it clean?
Have you ever replaced the oxygen sensors
How many miles are on the engine?
In the last year or so has the MIL ever been on for any reason other than the P1416?
Besides the decrease in mileage has there been any other change in the car's performance?
What prompted you to "spray" the MAF and what did you spray it with?
Did you visually inspect the MAF and, if so, were the wires clean?

Hi Hib,

I only have a OBD II scanner and no service manuals.

K&N filter, cleaned.
Never replaced the oxygen sensors.
43,000 miles on engine. (Original engine and mileage)
No other codes in the past year.
Seems to be no other change in performance. Still runs strong.
I cleaned the MAF using CRC Mass Airflow Cleaner. Since I was putting the OEM airbox back on I thought cleaning it would be proactive.
I inspected the MAF, although not all that familiar with them. The "horizontal" wires seemed to be not shiny as I thought they would be. Plus there are 3 thin wires connecting a couple of the thicker horizontal ones.

Also, spark plugs and plug wires have never been changed. Same for injectors and coils.
 
Last edited:

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
Hib,

My son has a bit more advanced OBDII than me. I checked it again with his and checked "ENGINE" and got a P0102 code which I looked up. There was no P0102 code on the dash. It says "Mass of Volume Air Flow Low". After searching online for possible causes I found this:
1. Faulty mass air flow sensor
2. Intake air leaks
3. Dirty mass air flow sensor
4. Dirty mass air cleaner
5. Mass air flow sensor harness is open or shorted
6. Mass air flow sensor circuit poor electrical connection

I have yet to replace the MAF. To look for "intake air leaks" I sprayed carb cleaner in areas that I thought would have air leaks and the engine did not rev higher. I had already sprayed cleaner on the MAF. Is the "mass air cleaner" the air filter that I cleaned (K&N) that is in the air box or is it something else. I have no idea what an "open harness" is but I would have to believe that everything is, electrically, working because when I remove the connection to the MAF the engine hesitates a bit. So in your expert opinion, would you agree that it is the MAF that is faulty? Or should I remove the MAF and try cleaning it again?



 

Les55

Active member
Joined
Sep 20, 2014
Messages
37
Location
Vallejo California
Hopefully you sprayed MAF sensor cleaner in the MAF sensor. Carb cleaner will destroy the MAF sensor.

Sent from my SM-G900V using Tapatalk
 

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
Hopefully you sprayed MAF sensor cleaner in the MAF sensor. Carb cleaner will destroy the MAF sensor.

Sent from my SM-G900V using Tapatalk

Yep, I used CRC Mass Airflow Cleaner. Do you know if the thicker "wires" in the MAF are supposed to be shiny or kind of dull? Mine are dull.
 

Les55

Active member
Joined
Sep 20, 2014
Messages
37
Location
Vallejo California
Yep, I used CRC Mass Airflow Cleaner. Do you know if the thicker "wires" in the MAF are supposed to be shiny or kind of dull? Mine are dull.
Yes, dull. All I can think off is something wrong with the sensor in the bellows in which controls the timing. As dadaroo said, check all codes. Keep us posted.

Sent from my SM-G900V using Tapatalk
 

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
Ok, Sunday's almost come and gone. I re-cleaned the MAF. Really sprayed the heck out of it. Hoped this would remedy the problem. Also cleaned my K&N filter again. What I noticed was that I was spraying both sides of the filter with the K&N oil. Not oversprayed by still a no-no so when it dried I only sprayed the side taking in the air. Took car for a drive. 54 miles and 2.5 gals gas = 21 mpg. Still not good. Got out the OBDII and found another code. P0001-Fuel =Volume Regulator Control Circuit/Open. Looked again at the archives and found nothing. Searched on-line for a location for this bugger and found nothing. If anyone has any idea what this code is saying and where I can locate this regulator on an 03 Z06 I would appreciate it. Car goes in on Tues a.m. and I would really like to fix it myself and cancel the app't.
 

Les55

Active member
Joined
Sep 20, 2014
Messages
37
Location
Vallejo California
Ok, Sunday's almost come and gone. I re-cleaned the MAF. Really sprayed the heck out of it. Hoped this would remedy the problem. Also cleaned my K&N filter again. What I noticed was that I was spraying both sides of the filter with the K&N oil. Not oversprayed by still a no-no so when it dried I only sprayed the side taking in the air. Took car for a drive. 54 miles and 2.5 gals gas = 21 mpg. Still not good. Got out the OBDII and found another code. P0001-Fuel =Volume Regulator Control Circuit/Open. Looked again at the archives and found nothing. Searched on-line for a location for this bugger and found nothing. If anyone has any idea what this code is saying and where I can locate this regulator on an 03 Z06 I would appreciate it. Car goes in on Tues a.m. and I would really like to fix it myself and cancel the app't.
I think you're doing the right thing by taking it in to the professionals. I would first ask them where fuel regulator is on a Z06. I have an LS1. So they may be in different places. Good luck. Keep us posted!

Sent from my SM-G900V using Tapatalk
 

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
I think you're doing the right thing by taking it in to the professionals. I would first ask them where fuel regulator is on a Z06. I have an LS1. So they may be in different places. Good luck. Keep us posted!

Sent from my SM-G900V using Tapatalk

Yep, I've thrown in the towel on this one. I'll keep you posted as to what they find is wrong. Thanks for all the help.
 

Mac

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Administrator
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Feb 13, 2003
Messages
5,476
Location
Ottawa, Canuckistan
Corvette
1973 coupe L82 (gone as casualty of divorce)
Yep, I've thrown in the towel on this one. I'll keep you posted as to what they find is wrong. Thanks for all the help.
Good luck. Let's hope they don't just start swapping parts, hoping to chase the gremlin away. :ugh

Mac
 

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
Good luck. Let's hope they don't just start swapping parts, hoping to chase the gremlin away. :ugh

Mac

That's one of the things that worries me about having someone else try to track down the problem. If I were to do it, I would know if the replacement of parts was necessary and not just a hit-and-miss operation. Hopefully the dealer service center will have someone qualified to work on Corvette's and not scam me. This is a not-so-large city in the Central Valley of CA and word of mouth is easily spread.
 

Mac

Well-known member
Administrator
Joined
Feb 13, 2003
Messages
5,476
Location
Ottawa, Canuckistan
Corvette
1973 coupe L82 (gone as casualty of divorce)
That's one of the things that worries me about having someone else try to track down the problem. If I were to do it, I would know if the replacement of parts was necessary and not just a hit-and-miss operation. Hopefully the dealer service center will have someone qualified to work on Corvette's and not scam me. This is a not-so-large city in the Central Valley of CA and word of mouth is easily spread.

The sad part is they're usually not trying to rip you off. They just don't know any better. They plug into the OBD, read a code, replace a part... rinse & repeat until gremlin is evicted. Good mechanics nowadays are the exception, not the rule.

Mac
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,526
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Check the short rubber nipple between the PCV and Throttle Body for a crack!:thumb

Mine had a small crack and my MPG went to hell in a hand basket,It didn't really effect the drive-ability much,Just the MPG!

:beer
 

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
Check the short rubber nipple between the PCV and Throttle Body for a crack!:thumb

Mine had a small crack and my MPG went to hell in a hand basket,It didn't really effect the drive-ability much,Just the MPG!

:beer

Did that and replaced the PCV while I was at it. :thumb I looked for vacuum leaks, cleaned the MAF (3 times), replaced the Vortex "Rammer" air box with the OEM one, cleaned the K&N filter (twice), check valves checked, and even looked for the Fuel Volume Regulator (couldn't find it...;LOL), and just dropped it off at the dealer this morning. I'm going to guess it's the Fuel Volume Regulator, aka Fuel Pressure Regulator, because it's throwing a code saying it's "open" so it's not regulating the amount of gas. Internet says it's a $104 dollar part and depending on where it's located will determine the labor to replace it. I think I'm going to sell it and buy a KIA. :eyerole
 

bwing

Well-known member
Joined
Oct 28, 2005
Messages
517
Location
California
Corvette
03 Z06,66 coupe(sold),99 Porsche Carrera(sold)
The service technician said "I could find nothing wrong with your car. I ran all the tests I could and everything is as good as the day it came off the assembly line". He said he drove the car on the freeway "...at 55 mph in 6th gear and the dash was reading 27.5 mpg. At 68 mph it read 31.3 mpg". He asked me if I use the computer averaged mpg and I told him I do it the old fashioned way. Divide the mileage driven by the gals. He just shook his head saying there is absolutely nothing he could find that would cause poor mpg. So I guess I'll just enjoy the car and drive it and don't worry about the mileage.
 

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