smelling gas alot, low mpg? running rich?
03-17-2015, 12:23 AM
#1
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Join Date: Mar 2015
Location: Bay Area California
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smelling gas alot, low mpg? running rich?
My 95 z28 that I just got recently, and also just got out of the shop after having water pump, and air pump replaced is running really rich. I have searched on here for "running rich" and got alot of different ideas Like 02 sensors and a charcoal canister. I'm not really sure what the culprit is. Basically I'm getting low mpg, I think. I'm not sure but let me know if this sounds low to you; On a full tank I get about 150 to 180 miles then refill it. And even tho the Guage is off (way past F when full) I know it's really empty when it's right before the E because it will take 14.5 gallons of gas. I swear I've not been driving it crazy at all. 50 to 70 MPH on free way and speed limit around town. I also posted a recent post about an intermittent reoccurring buzzing that lasts about 5 seconds near the gas tank while it's been running. There is alot of Air hissing out of the gas tank when I fill it up. It also backfires after a warm start. I just took the air box off and put a cone style filter on, I think i may be seeing a slight improvement but not totally sure.
Any ideas?
Any ideas?
Last edited by Magenta_Hearts; 03-17-2015 at 12:26 AM. Reason: typo
03-17-2015, 07:17 AM
#4
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
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Re: smelling gas alot, low mpg? running rich?
1. Scan if for codes. That will tell you if the coolant temp sensor was left unhooked. Does you SES light work? It should come on for a few seconds when you turn the key to "on" to confirm the light is working.
2. Check the fuel pressure. This will tell you if you have any leaks in the fuel system. When the fuel pump primes, then shuts off, the pressure should reach at least 40psi. After the pump shuts off, the pressure should not drop rapidly. Fast pressure drop can indicate several problems, including leaking lines and leaking injectors. Can also indicate a leaking fuel pressure regulator, which can pour fuel into the intake manifold via the vacuum compensation line.
3. Measure fuel mileage the correct way.... fill it up, record mileage. Next time you fill it up, record gallons and mileage, divide miles driven by gallons filled to get MPG. "gallons per tank" is too crude a measurement, although yours sounds pretty poor (guessing 10 to 12 MPG, which is very low). A word of caution... due to the shape of the fuel tank, when the gauge indicate 1/4 tank, you may only have one to two gallons left. You do NOT want to run out of fuel, as it may destroy the fuel pump. The gauge indicating way past "F" when full is normal.
Read this:
4th Gen LT1 F-body Tech Articles
Do not over-fill the tank. You can force fuel into the carbon canister in the driver's rear fender, and saturate the canister with wet fuel. That will cause a fuel smell.
The "hissing" when you remove the tank cap may indicate the fuel pump is on it's way out, overheating the fuel. That could also indicate a problem with the tank pressure control system, which includes the lines to the carbon canister.
I remember responding to your question about the buzzing at the rear of the car. Did you get under the car to try and find the source of the noise, as suggested?
2. Check the fuel pressure. This will tell you if you have any leaks in the fuel system. When the fuel pump primes, then shuts off, the pressure should reach at least 40psi. After the pump shuts off, the pressure should not drop rapidly. Fast pressure drop can indicate several problems, including leaking lines and leaking injectors. Can also indicate a leaking fuel pressure regulator, which can pour fuel into the intake manifold via the vacuum compensation line.
3. Measure fuel mileage the correct way.... fill it up, record mileage. Next time you fill it up, record gallons and mileage, divide miles driven by gallons filled to get MPG. "gallons per tank" is too crude a measurement, although yours sounds pretty poor (guessing 10 to 12 MPG, which is very low). A word of caution... due to the shape of the fuel tank, when the gauge indicate 1/4 tank, you may only have one to two gallons left. You do NOT want to run out of fuel, as it may destroy the fuel pump. The gauge indicating way past "F" when full is normal.
Read this:
4th Gen LT1 F-body Tech Articles
Do not over-fill the tank. You can force fuel into the carbon canister in the driver's rear fender, and saturate the canister with wet fuel. That will cause a fuel smell.
The "hissing" when you remove the tank cap may indicate the fuel pump is on it's way out, overheating the fuel. That could also indicate a problem with the tank pressure control system, which includes the lines to the carbon canister.
I remember responding to your question about the buzzing at the rear of the car. Did you get under the car to try and find the source of the noise, as suggested?
03-17-2015, 02:13 PM
#5
Registered User
Join Date: Aug 2009
Location: las vegas
Posts: 764
Re: smelling gas alot, low mpg? running rich?
1. Scan if for codes. That will tell you if the coolant temp sensor was left unhooked. Does you SES light work? It should come on for a few seconds when you turn the key to "on" to confirm the light is working.
2. Check the fuel pressure. This will tell you if you have any leaks in the fuel system. When the fuel pump primes, then shuts off, the pressure should reach at least 40psi. After the pump shuts off, the pressure should not drop rapidly. Fast pressure drop can indicate several problems, including leaking lines and leaking injectors. Can also indicate a leaking fuel pressure regulator, which can pour fuel into the intake manifold via the vacuum compensation line.
3. Measure fuel mileage the correct way.... fill it up, record mileage. Next time you fill it up, record gallons and mileage, divide miles driven by gallons filled to get MPG. "gallons per tank" is too crude a measurement, although yours sounds pretty poor (guessing 10 to 12 MPG, which is very low). A word of caution... due to the shape of the fuel tank, when the gauge indicate 1/4 tank, you may only have one to two gallons left. You do NOT want to run out of fuel, as it may destroy the fuel pump. The gauge indicating way past "F" when full is normal.
Read this:
4th Gen LT1 F-body Tech Articles
Do not over-fill the tank. You can force fuel into the carbon canister in the driver's rear fender, and saturate the canister with wet fuel. That will cause a fuel smell.
The "hissing" when you remove the tank cap may indicate the fuel pump is on it's way out, overheating the fuel. That could also indicate a problem with the tank pressure control system, which includes the lines to the carbon canister.
I remember responding to your question about the buzzing at the rear of the car. Did you get under the car to try and find the source of the noise, as suggested?
2. Check the fuel pressure. This will tell you if you have any leaks in the fuel system. When the fuel pump primes, then shuts off, the pressure should reach at least 40psi. After the pump shuts off, the pressure should not drop rapidly. Fast pressure drop can indicate several problems, including leaking lines and leaking injectors. Can also indicate a leaking fuel pressure regulator, which can pour fuel into the intake manifold via the vacuum compensation line.
3. Measure fuel mileage the correct way.... fill it up, record mileage. Next time you fill it up, record gallons and mileage, divide miles driven by gallons filled to get MPG. "gallons per tank" is too crude a measurement, although yours sounds pretty poor (guessing 10 to 12 MPG, which is very low). A word of caution... due to the shape of the fuel tank, when the gauge indicate 1/4 tank, you may only have one to two gallons left. You do NOT want to run out of fuel, as it may destroy the fuel pump. The gauge indicating way past "F" when full is normal.
Read this:
4th Gen LT1 F-body Tech Articles
Do not over-fill the tank. You can force fuel into the carbon canister in the driver's rear fender, and saturate the canister with wet fuel. That will cause a fuel smell.
The "hissing" when you remove the tank cap may indicate the fuel pump is on it's way out, overheating the fuel. That could also indicate a problem with the tank pressure control system, which includes the lines to the carbon canister.
I remember responding to your question about the buzzing at the rear of the car. Did you get under the car to try and find the source of the noise, as suggested?
03-22-2015, 12:45 PM
#6
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Thread Starter
Join Date: Mar 2015
Location: Bay Area California
Posts: 13
Re: smelling gas alot, low mpg? running rich?
Thanks for all the Ideas.
I have not been able to figure out the buzzing sound. I also have not had it up on a lift though. Im having issues with my shop trying to get them to do anything. they had the car for a week just to do the water pump and a secondary air pump. Currently this is my only vehicle. I did get the cluster replaced and the SES light does work but is not on. should I assume there may still be codes stored? My G35 used to do that. The SES light would come on then go off and the code would be stored. The buzzing sound near the gas tank is still there. I will have to get a recording of it. Since I replaced the air box with a new cone filter it has improved MPG some and it has helped with the back firing a lot. But it still runs rich I believe and backfires a little. Another mechanic suggested the coolant temp sensors also because its running so well otherwise. sigh.. Its just so hard to get anything done.
I have not been able to figure out the buzzing sound. I also have not had it up on a lift though. Im having issues with my shop trying to get them to do anything. they had the car for a week just to do the water pump and a secondary air pump. Currently this is my only vehicle. I did get the cluster replaced and the SES light does work but is not on. should I assume there may still be codes stored? My G35 used to do that. The SES light would come on then go off and the code would be stored. The buzzing sound near the gas tank is still there. I will have to get a recording of it. Since I replaced the air box with a new cone filter it has improved MPG some and it has helped with the back firing a lot. But it still runs rich I believe and backfires a little. Another mechanic suggested the coolant temp sensors also because its running so well otherwise. sigh.. Its just so hard to get anything done.
03-22-2015, 03:36 PM
#7
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,647
Re: smelling gas alot, low mpg? running rich?
Stored codes do not turn on the SES light. The codes will self-clear after the vehicle is driven a specific number of "drive cycles" without the code returning.
I've already mentioned the coolant temp sensor. You have two. The one in the driver side head is for the dash gauge, and has no effect on how the engine runs. The one in the water pump housing is what feeds the PCM. That's the one that will affect performance. Rather than replacing parts, why not test them to determine if they are OK? Lot cheaper in the long run. "Another mechanic" should be aware of this. It would take him 10 minutes to test it.
4th Gen LT1 F-body Tech Articles
As far as the noise from the gas tank.... you don't need to put it up on a lift. Pull is up on ramps, or jack the rear and place jack stands to correctly support the car. That will allow you to get under there and look for the source of the noise.
I've already mentioned the coolant temp sensor. You have two. The one in the driver side head is for the dash gauge, and has no effect on how the engine runs. The one in the water pump housing is what feeds the PCM. That's the one that will affect performance. Rather than replacing parts, why not test them to determine if they are OK? Lot cheaper in the long run. "Another mechanic" should be aware of this. It would take him 10 minutes to test it.
4th Gen LT1 F-body Tech Articles
As far as the noise from the gas tank.... you don't need to put it up on a lift. Pull is up on ramps, or jack the rear and place jack stands to correctly support the car. That will allow you to get under there and look for the source of the noise.
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