Faint whiff of gas fumes near and inside the truck

[chilerancher]

That is my primary complaint. I started noticing this a few months ago. Faint enough that I thought it was my imagination for a while. Now it's a pattern. Other observations (may or may not be correlated):

• City MPG dropped from close to 14 to the mid/upper 12's. I noticed this around the same time. -ish.
• Takes two cranks to get started. (Never done this before.)
• Fuel pressure at idle is 40-50 psi.​
• Highway MPG still solid 16+ (17+ when in the mountains for some reason.)
• Throws P0171 and P0174 at the same time whenever the weather is below 50 degrees. (This has been going on for a few years.)
• Replaced plugs, wires, and coils about two years ago.
• Replaced fuel filter one year ago.
• No obvious issues with fuel pressure regulator (pressure, vacuum leak, wet vacuum connections, etc.)
• I've done no work on the intake system (other than replace the air filter).

My strong secondary compaint is the City MPG being so low.

Thoughts?

 

[chilerancher]

• No spots under the truck.
• Fuel filter connections are dry.
• MAY BE correlated to the climate control system? I notice it when the system is on Auto, then the smell goes away. I'll do more testing with this idea.

 

[swathdiver]

That is my primary complaint. I started noticing this a few months ago. Faint enough that I thought it was my imagination for a while. Now it's a pattern. Other observations (may or may not be correlated):

• City MPG dropped from close to 14 to the mid/upper 12's. I noticed this around the same time. -ish.
• Takes two cranks to get started. (Never done this before.)
• Fuel pressure at idle is 40-50 psi.​
• Highway MPG still solid 16+ (17+ when in the mountains for some reason.)
• Throws P0171 and P0174 at the same time whenever the weather is below 50 degrees. (This has been going on for a few years.)
• Replaced plugs, wires, and coils about two years ago.
• Replaced fuel filter one year ago.
• No obvious issues with fuel pressure regulator (pressure, vacuum leak, wet vacuum connections, etc.)
• I've done no work on the intake system (other than replace the air filter).

My strong secondary compaint is the City MPG being so low.

Thoughts?

Would be nice to see your Long Term Fuel Trims, if high, probably time for new intake gaskets. It is not unusual for fuel to leak on top of tank and evaporate without hitting the ground.

This can also be a sign that the cat(s) are about to fail.

 

[Fless]

Tell us a bit more about your truck -- year, model, engine, etc. Flex fuel?

When it's been sitting for a while check the fuel pressure with the KOEO (Key On, Engine OFF) without starting it. Flex fuel pressure values are different from non-flex.

 

[chilerancher]

Tell us a bit more about your truck -- year, model, engine, etc. Flex fuel?

When it's been sitting for a while check the fuel pressure with the KOEO (Key On, Engine OFF) without starting it. Flex fuel pressure values are different from non-flex.

2002 GMC Yukon XL
5.3L Flex Fuel

Thanks for the tip, I'll try that soon and report back.

 

[chilerancher]

Would be nice to see your Long Term Fuel Trims, if high, probably time for new intake gaskets. It is not unusual for fuel to leak on top of tank and evaporate without hitting the ground.

This can also be a sign that the cat(s) are about to fail.

In cool/cold weather (<50 degrees outside temp): At idle the long term fuel trims are pegged at 25. Under load they come down to 7 to 12.
In warm weather the trims seem to behave better at idle as I recall.

 

[swathdiver]

In cool/cold weather (<50 degrees outside temp): At idle the long term fuel trims are pegged at 25. Under load they come down to 7 to 12.
In warm weather the trims seem to behave better at idle as I recall.

Ok, you've got a massive vacuum leak and it is usually the intake gaskets. If you can watch the trims or O2 sensors on a graph, you can spray water (water bottle) over the gaskets at the same time and watch the graphs. Some use propane or even Sprite, anything to detect a leak.

 

[chilerancher]

Ok, you've got a massive vacuum leak and it is usually the intake gaskets. If you can watch the trims or O2 sensors on a graph, you can spray water (water bottle) over the gaskets at the same time and watch the graphs. Some use propane or even Sprite, anything to detect a leak.

Thanks, I'll poke around here for more details on troubleshooting and replacing the intake gaskets. Are there two, one for each side? How big a job is that?

 

[swathdiver]

Thanks, I'll poke around here for more details on troubleshooting and replacing the intake gaskets. Are there two, one for each side? How big a job is that?

One on each side, not hard if you know how to turn wrenches and have a good back. Shop labor is 1.9 hours.

 

[chilerancher]

Tell us a bit more about your truck -- year, model, engine, etc. Flex fuel?

When it's been sitting for a while check the fuel pressure with the KOEO (Key On, Engine OFF) without starting it. Flex fuel pressure values are different from non-flex.

KOEO fuel pressure is around 45 psi, so I figure that's good. At this point I'm figuring it's the intake gaskets so I'm going to prep for that project over the Memorial Day weekend.

(Just now getting back to this project because it is no longer a faint whiff of gas. It's now full on fumes in the cabin and the family is complaining. Oh, and it also now has a very rough idle on cold start.)