Strong gas smell when running

[Daniel Myrick]

Hi, I have an '03 Yukon 1500 XL with the 5.3L engine. When I started it up today to go to the store, there was a strong gas odor. I checked and couldn't find any obvious leaks, thinking the truck is running really rich. Took it around the block and the smell was strong and consistant, especially when stopped at idle.

Here is some history on what I've done recently. Last November the fuel pump went out. It was a slow, painfull death, lol. I dropped the tank and replaced the fuel pump. After I got it put together, it was running really rough. Not just for a minute or two like it was clearing out the air, but missing pretty good. I got a code (dont remember which one now) that lead me to replace the the fuel pressure regulator. Funny note, the truck is an '03, but the OEM regulator didn't fit, the one that came off was for an '02. Parts guy said it was an early year model, so they were still using up 02 parts I guess.

After that it ran good. Then about a month later in December, we drove up to the mountains to get a Christmas tree and on the way back down I got the P0420 code for bank 1. Never got around to swapping out the downstream O2 sensor, due to life and several other unrelated repairs.

A couple of months ago, I checked the codes again and this time got the code on both banks. Now I'm thinking fk, by now it probably needs all 4 sensors and maybe even the cats. But I was on the fence about trading it in, selling it, or keeping it for my son. So it's been about 7 months since I got the first catalyst system code in all, and I finally decide to sell it, but before I can, i am moving so i drove it like hell for about two weeks pulling a trailer and what not. Truck ran good, no major problems except my back!

That gets me to now. Last week I was broke AF and ran it pretty low on gas. Got paid yesterday and threw 60 bucks in it right away. About half a tank so I know I didn't overfill. Ran fine yesterday, no problems. That brings me back to the start of the post so I wont repeat.

Did the cats finally burn up and that is what is causing the smell? I guess my question is, is there anything else I should check into first that may be causing the gas smell before putting out about 800 for the california approved direct fit cat and pipes along with another 320 bucks for o2 sensors so I can sell it? Would it be better to just try and find a buyer and let it go as-is? Would the issues last fall with the fuel pump and the regulator lead to a steady decline of the cats even though the problem was fixed or is it more likely that there is still an underlying problem (I haven't noticed it missing or anything else)?

I will try and run a scan on it tomorrow and update if there are any new codes, but last I checked the two codes were P0420/0430. Any suggestions are greatly appreciated and if you need anymore details, let me know.

Thanks,
Dan

 

[swathdiver]

Hi, I have an '03 Yukon 1500 XL with the 5.3L engine. When I started it up today to go to the store, there was a strong gas odor. I checked and couldn't find any obvious leaks, thinking the truck is running really rich. Took it around the block and the smell was strong and consistant, especially when stopped at idle.

Here is some history on what I've done recently. Last November the fuel pump went out. It was a slow, painfull death, lol. I dropped the tank and replaced the fuel pump. After I got it put together, it was running really rough. Not just for a minute or two like it was clearing out the air, but missing pretty good. I got a code (dont remember which one now) that lead me to replace the the fuel pressure regulator. Funny note, the truck is an '03, but the OEM regulator didn't fit, the one that came off was for an '02. Parts guy said it was an early year model, so they were still using up 02 parts I guess.

After that it ran good. Then about a month later in December, we drove up to the mountains to get a Christmas tree and on the way back down I got the P0420 code for bank 1. Never got around to swapping out the downstream O2 sensor, due to life and several other unrelated repairs.

A couple of months ago, I checked the codes again and this time got the code on both banks. Now I'm thinking fk, by now it probably needs all 4 sensors and maybe even the cats. But I was on the fence about trading it in, selling it, or keeping it for my son. So it's been about 7 months since I got the first catalyst system code in all, and I finally decide to sell it, but before I can, i am moving so i drove it like hell for about two weeks pulling a trailer and what not. Truck ran good, no major problems except my back!

That gets me to now. Last week I was broke AF and ran it pretty low on gas. Got paid yesterday and threw 60 bucks in it right away. About half a tank so I know I didn't overfill. Ran fine yesterday, no problems. That brings me back to the start of the post so I wont repeat.

Did the cats finally burn up and that is what is causing the smell? I guess my question is, is there anything else I should check into first that may be causing the gas smell before putting out about 800 for the california approved direct fit cat and pipes along with another 320 bucks for o2 sensors so I can sell it? Would it be better to just try and find a buyer and let it go as-is? Would the issues last fall with the fuel pump and the regulator lead to a steady decline of the cats even though the problem was fixed or is it more likely that there is still an underlying problem (I haven't noticed it missing or anything else)?

I will try and run a scan on it tomorrow and update if there are any new codes, but last I checked the two codes were P0420/0430. Any suggestions are greatly appreciated and if you need anymore details, let me know.

Thanks,
Dan

Hi Dan, welcome to the forum. Those P0420 and P0430 codes are for the cats, not the O2 sensors. If the O2 sensors fail, they have their own codes. A leaky injector for example could cause the smell and foul a cat. You'll want to check/test your injectors. Same for the O2 sensors to see if any are lazy. An advanced scan tool like the Tech2 can do all of this. Check your fuel lines for leaks, the top of the tank, etc.

When my cats went bad the first clue something was amiss is that the mileage steadily got worse, there was no noticeable loss in power, even ran great at the drag strip. No gas smells either but I usually run Ethanol. Then one cat started throwing a code and then another. Made sure nothing was causing them to fail other than age and put on a whole new Magnaflow Y-pipe from GotExhaust, a vendor here on the forum. The purchase of a Tech2 was instrumental in making a proper diagnosis and determined that the O2 sensors were still performing in peak form so money was not wasted on replacing them.

The catalysts are probably melted and not heating up correctly and hence the smell of fuel. Just a guess on my part. Others will chime in after breakfast.

 

[Daniel Myrick]

Hi Dan, welcome to the forum. Those P0420 and P0430 codes are for the cats, not the O2 sensors. If the O2 sensors fail, they have their own codes. A leaky injector for example could cause the smell and foul a cat. You'll want to check/test your injectors. Same for the O2 sensors to see if any are lazy. An advanced scan tool like the Tech2 can do all of this. Check your fuel lines for leaks, the top of the tank, etc.

When my cats went bad the first clue something was amiss is that the mileage steadily got worse, there was no noticeable loss in power, even ran great at the drag strip. No gas smells either but I usually run Ethanol. Then one cat started throwing a code and then another. Made sure nothing was causing them to fail other than age and put on a whole new Magnaflow Y-pipe from GotExhaust, a vendor here on the forum. The purchase of a Tech2 was instrumental in making a proper diagnosis and determined that the O2 sensors were still performing in peak form so money was not wasted on replacing them.

The catalysts are probably melted and not heating up correctly and hence the smell of fuel. Just a guess on my part. Others will chime in after breakfast.

Thanks for the reply! I guess I have a bad tendency to go to the most expensive problem straight away. Got under the hood this morning in the light to get a better look. Turned the ignitian on without cranking it and could smell gas not as strong, but it is windy today. So I think its leaking fuel somewhere. Went ahead and fired it up and sure enough the fuel pressure regulator is dumping gas out of the seal. Gonna go and get another today and swap it out and see what happens. I will let everyone know if that fixes the smell.

Maybe this needs to be in a new thread, but I wanted to ask about your comment in regards to the P0420/0430 codes above. The cats dont have a sensor so those codes are from the downstream O2 sensors correct? If I understand correctly the upstream O2s have their own code, so you know when those go bad, but the P0420/0430 is generic and just means that the difference between the front O2 and the back O2 is off and could be a number of things causing the fuel trim to be out. Does the downstream O2 sensor have it's own code when it goes bad? Is there an easy way to tell if the cat is bad? I haven't noticed any of the tale tale signs of a bad cat, sluggish performance, bad fuel economy. Actually when I was moving last week I thought it was getting pretty good economy, 360 miles to a tank pulling a trailer most of the time in 100d heat with the AC on. That's about right for this truck i think. Anyways, thanks again for the response!

 

[Daniel Myrick]

***Update***

Problem with the gas smell solved. Pulled the fuel pressure regulator and you can see the back plastic gasket is broken.



Took it to autozone and of course they dont stock that gasket, but the part was still under warranty so they just swapped the whole part out. Looking at the new gasket you can see the plastic ring has a small notch in it. Looks like a probable fail point, is this a manufacturing defect or designed this way? See below.



Any thoughts? Would there be an underlying problem that would cause this failure?

Thanks again!

Dan

 

[swathdiver]

I guess I have a bad tendency to go to the most expensive problem straight away.

Does the downstream O2 sensor have it's own code when it goes bad? Is there an easy way to tell if the cat is bad?

Me too! Still have to catch myself and quit thinking I need a new engine when a spark plug wire gets loose!

Yes, all the sensors have their own codes and symptom codes for when they fail and how/why they failed. Looking at the numbers or a graph with a scan tool, the upstream sensors will be cycling up and down rather quickly once warmed up and the downstream sensors will be fairly steady. If they are not, that is a sign of a bad cat. The computer of course is constantly checking the health of the cats and will throw a code if certain conditions are met.

Glad you the problem solved without great expense other than time! Maybe others will chime in about the sensor, I am not familiar with it.

 

[fire730]

Did you lube those orings up with some petroleum jelly or at least some oil when you installed them?
The plastic is probably just a spacer to put the oring in the correct place in the bore.

I have seen those regulators leak through the vacuum hose before. Hopefully it didn’t slowly over fuel the truck and burn out the cats.

Get the regulator back in and clear the codes. See if they come back before you buy more parts.