Gassy smell at idle

[marshallsmith27]

I have a 1993 5.7 and I have noticed that lately at idle and sitting at lights the smell of fuel has been getting stronger. We recently drove from Alabama to Montreal and Boston and back to Alabama for vacation over a week and right when we got back into Alabama my fuel pump started going out. No problem. I dont know if it was ever replaced so I replaced it. I realized what it was from the long crank over the course of the week. I bought the truck at the end of last year and it has always smelled like an older vehicle does but not as gassy and slightly oil burning. The truck does burn oil but doesnt smoke at all. What would make the smell happen? I should note I have code 43 which is knock sensor and no matter what I replace I have never been able to clear the code.

 

[2drXmobb]

Is it knocking and pinging? Is the cats fouled how many miles on the motor , did you change the fuel filter also? Check for vacuum leaks and run higher octane maybe it'll help with the detonation. It's running rich that's why it smells like that

 

[GoToGuy]

Is the wiring good. Bad, or broken wiring can simulate a bad sensor, transmitter or switch .
Code tells there's a problem not always what's broken, you have confirm what's broken, need replaced, then if it's false alarm , why is there a false alarm ? Bad ground, broken wire on power side, bad connector?

 

[GoToGuy]

Good fuel cap?

 

[Hipster]

Thinking the gas lines/fuel sender leaking after tampering with the pump. Sometimes the first place to look is the last place somebody fixed or messed with. sending unit lines corode, sending unit seal etc.

 

[Schurkey]

I have a 1993 5.7 and I have noticed that lately at idle and sitting at lights the smell of fuel has been getting stronger.

WHERE? At the tailpipe? Indicates a failed catalytic converter probably coupled to misfire. Converter may have hit the end of it's service life, or it may have been murdered by misfire, incorrect fueling, or ignition timing due to computer/sensor/wiring issues.

IF (big IF) you fix a misfire, the catalyst may or may not come back to life.

If you smell fuel under the vehicle, perhaps a leaking fuel system.

If under the hood, a leaking fuel system, or disconnected/failed hoses or charcoal canister.

I bought the truck at the end of last year and it has always smelled like an older vehicle does but not as gassy and slightly oil burning. The truck does burn oil but doesnt smoke at all.

Oil burning is hard on the catalyst. Additives in the oil--zinc, phosphorous, etc. can coat the catalyst making it ineffective.

I have code 43 which is knock sensor and no matter what I replace I have never been able to clear the code.

Download the service manual set for your vehicle from the links in the Engine "sticky" section of this web site.

Follow the Genuine GM diagnostic procedure for that code.

Knock sensor wiring harness problems are common. The sensors themselves seem to be fairly long-lived and reliable.

Connect a scan tool, verify EVERY sensor and computer output.

Make sure all the usual "tune-up" items are in good condition--cap, rotor, plug wires, spark plugs, PCV system, EGR system. Clean the throttle body and IAC passage. Assure no vacuum leaks

Wouldn't hurt to verify fuel pressure.

 

[marshallsmith27]

Is it knocking and pinging? Is the cats fouled how many miles on the motor , did you change the fuel filter also? Check for vacuum leaks and run higher octane maybe it'll help with the detonation. It's running rich that's why it smells like that

Sorry for just now responding I have started a new job and training has been all day.

I have replaced a lot. I have replaced fuel filter. I have changed the oil with synthetic 3 times since I have owned it, also the fuel filter and the knock sensor and wire and plug, also the o2 sensor also the egr valve.

It doesnt knock or ping. the engine has 273k. It has flowmasters. I have ran premium once on a full tank I think and it didnt get rid of the code I can try it again though

 

[marshallsmith27]

Is the wiring good. Bad, or broken wiring can simulate a bad sensor, transmitter or switch .
Code tells there's a problem not always what's broken, you have confirm what's broken, need replaced, then if it's false alarm , why is there a false alarm ? Bad ground, broken wire on power side, bad connector?

Brand new knock sensor and wire and connector. It wasnt a GM brand one though. It wasnt the cheapest knock sensor either but I have read non GM ones suck.

I am not sure about the fuel cap. I didnt think it would make a difference on older vehicles

 

[marshallsmith27]

WHERE? At the tailpipe? Indicates a failed catalytic converter probably coupled to misfire. Converter may have hit the end of it's service life, or it may have been murdered by misfire, incorrect fueling, or ignition timing due to computer/sensor/wiring issues.

IF (big IF) you fix a misfire, the catalyst may or may not come back to life.

If you smell fuel under the vehicle, perhaps a leaking fuel system.

If under the hood, a leaking fuel system, or disconnected/failed hoses or charcoal canister.


Oil burning is hard on the catalyst. Additives in the oil--zinc, phosphorous, etc. can coat the catalyst making it ineffective.


Download the service manual set for your vehicle from the links in the Engine "sticky" section of this web site.

Follow the Genuine GM diagnostic procedure for that code.

Knock sensor wiring harness problems are common. The sensors themselves seem to be fairly long-lived and reliable.

Connect a scan tool, verify EVERY sensor and computer output.

Make sure all the usual "tune-up" items are in good condition--cap, rotor, plug wires, spark plugs, PCV system, EGR system. Clean the throttle body and IAC passage. Assure no vacuum leaks

Wouldn't hurt to verify fuel pressure.

I am pretty certain fuel pressure is good. I had a local mechanic help with the fuel pump. He checked all the fuel lines and we replaced the fuel filter again when we replaced the fuel pump just in case.

The smell is coming from the exhaust. I never thought about the catalytic converters going bad. truck has 273k miles. I do think there is a small miss. it has a brand new distributor and wires. but I need to replace the gasket on the distributor going into the engine. it leaks oil a little

I have done all you mentioned about the tune up except clean the throttle body.


The knock sensor error is beyond me. I have done so much trying to get rid of it

 

[marshallsmith27]

We mainly drive the truck out of town and on long road trips so I would like to get it 100%.

Now that I type this I am remembering that we drove 3 to nashville at the first of the year and got 19.2 mpg and we went back again last week and got 16.5 mpg so something has clearly changed

I am not rough on the truck. I dont think I have ever floored it or even driven about 85 so its not from being rough