Help. Smell of fuel coming from exhaust

[drei4runner29]

Just like what the title states, there's a heavy smell of gas fumes coming from my exhaust when starting the vehicle up. I have about 275k miles on it. I've changed the spark plugs and wires, the MAF sensor, the 02 and air/fuel ratio sensors and the cat due to Runner running rich and basically clogged up my original cat.

Prior to me changing the plugs, apparently I was burning a lot of fuel during start up. I never noticed the smell since I usually park my vehicle outside the garage. My wife was the one that actually noticed the strong smell of gas fumes coming out of my exhaust when I parked my vehicle in the garage. Long story short, my mechanic found out that one of my plugs and wire was bad so I had it replaced a few months ago. But damage was already done when I was running rich and basically clogged up my cat. Had cat replaced and I am still noticing the heavy smell of fumes. Took it back in to my mechanic and he ran some diagnostics and he advised that my air/fuel ratio sensor is going out. Just replaced that last week but still I'm smelling heavy fumes of fuel coming out of my exhaust.

I'm afraid that I might still be running rich and I don't want to mess up and spend more money replacing my cat after just replacing it about a month or so ago. Any help would be appreciated as to what could be wrong.

 

[19963.4lsr5]

May be its as simple as a gas leak back at your gas tank. You never had your check engine light come on and start flashing?


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[drei4runner29]

Nope. Everything seems to check out fine and no codes pop up when connecting the sensor other than last week when my air/fuel ratio sensor went bad and had to replace.

Or is it just normal for the 4runners to start emitting the smell of gas fumes when it gets older. My 4R is 16 years old with almost 275k miles on it


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[thegipper]

A gas smell is not normal even on an old truck. My 97 has never smelt like gas or gas fumes.

I think you need to scan the truck while its running and see what the A/F levels are at (torque app, ultra gauge, scan gauge etc). Hopefully someone can chime in and let you know what they should be at.

And you're positive you don't have a leak anywhere? Have you tried resetting the ECU?

 

[drei4runner29]

A gas smell is not normal even on an old truck. My 97 has never smelt like gas or gas fumes.

I think you need to scan the truck while its running and see what the A/F levels are at (torque app, ultra gauge, scan gauge etc). Hopefully someone can chime in and let you know what they should be at.

And you're positive you don't have a leak anywhere? Have you tried resetting the ECU?

Haven’t tried resetting the ECU yet but I’ll take it to the mechanic again.


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[19963.4lsr5]

What is your long term fuel trim for bank 1 sensor 1 during warm up and about 10 min later after engine is up to temp and the fuel maps get updated?

Raw gas smell out the tail pipe isn't natural and to me impossible unless the raw gas smell is coming from the gas tank or lines. Between the spark plugs and the CAT that unburned fuel should not exist in a range you as a human can smell


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[TheDurk]

Just like what the title states, there's a heavy smell of gas fumes coming from my exhaust when starting the vehicle up. I have about 275k miles on it. I've changed the spark plugs and wires, the MAF sensor, the 02 and air/fuel ratio sensors and the cat due to Runner running rich and basically clogged up my original cat.

Prior to me changing the plugs, apparently I was burning a lot of fuel during start up. I never noticed the smell since I usually park my vehicle outside the garage. My wife was the one that actually noticed the strong smell of gas fumes coming out of my exhaust when I parked my vehicle in the garage. Long story short, my mechanic found out that one of my plugs and wire was bad so I had it replaced a few months ago. But damage was already done when I was running rich and basically clogged up my cat. Had cat replaced and I am still noticing the heavy smell of fumes. Took it back in to my mechanic and he ran some diagnostics and he advised that my air/fuel ratio sensor is going out. Just replaced that last week but still I'm smelling heavy fumes of fuel coming out of my exhaust.

I'm afraid that I might still be running rich and I don't want to mess up and spend more money replacing my cat after just replacing it about a month or so ago. Any help would be appreciated as to what could be wrong.

I could have told you that diagnostic was bogus for fuel smell on start-up. On start-up, the engine runs in open loop and the A/F sensor has no input. The ECM runs on a pre-set fixed fuel map until the engine warms up and it switches to closed loop and listens to the A/F sensor.

My internet WAG is a leaky injector. This could allow a cylinder to fill up (partially) with fuel overnight that would all get blown right down the exhaust on start-up. Are your injectors original? At 275K, you would be well served to send them all off to Witchhunter to be tested and cleaned. Money well spent even if it doesn't fix the issue.

Or:

https://itstillruns.com/check-leaking-fuel-injector-7760596.html

https://www.injectorrx.com/leaking-fuel-injectors/

 

[19963.4lsr5]

I could have told you that diagnostic was bogus for fuel smell on start-up. On start-up, the engine runs in open loop and the A/F sensor has no input. The ECM runs on a pre-set fixed fuel map until the engine warms up and it switches to closed loop and listens to the A/F sensor.

My internet WAG is a leaky injector. This could allow a cylinder to fill up (partially) with fuel overnight that would all get blown right down the exhaust on start-up. Are your injectors original? At 275K, you would be well served to send them all off to Witchhunter to be tested and cleaned. Money well spent even if it doesn't fix the issue.

Or:

https://itstillruns.com/check-leaking-fuel-injector-7760596.html

https://www.injectorrx.com/leaking-fuel-injectors/

That's a good call. It's far from normal. I've not watched my 4Runner but on my Saturn the time it takes to go closed loop on a 1 wire O2 sensor is seconds until it gets around 15 degrees outside. Somewhere around that outside temp I takes around 5 min to go closed loop. I really should put a ScanGauge in my Toy to watch that on my drive to and from work.

On the leaking injector thing....does your oil have a gas smell? A dripping injector or a bad O2 sensor usually gasses the oil.


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[TheDurk]

That's a good call. It's far from normal. I've not watched my 4Runner but on my Saturn the time it takes to go closed loop on a 1 wire O2 sensor is seconds until it gets around 15 degrees outside. Somewhere around that outside temp I takes around 5 min to go closed loop. I really should put a ScanGauge in my Toy to watch that on my drive to and from work.

On the leaking injector thing....does your oil have a gas smell? A dripping injector or a bad O2 sensor usually gasses the oil.


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4Runner is not seconds. Temp has to come up. It's minutes.

 

[drei4runner29]

Sorry for just replying now. Been busy with work and family.

Thanks for all the help. I’ll definitely have to check the fuel injectors to see if and/or when it was replaced.


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[ridefast]

Charcoal canister could be full of fuel. I've read a few posts of guys cleaning the canister with brake cleaner and letting it dry then reinstalling.

I've been considering doing this, just haven't finished researching as these canisters are pretty spendy.

 

[ArmArak]

Hey guys,

I'm having the same issue. On startup there is a gas smell coming, sort of like an RC car/plane running too rich. I am also getting very bad mileage. I am on 33 mud tires and am getting around 12 mpg. What do you guys think is happening?

Thanks,
Armen

 

[19963.4lsr5]

Hey guys,

I'm having the same issue. On startup there is a gas smell coming, sort of like an RC car/plane running too rich. I am also getting very bad mileage. I am on 33 mud tires and am getting around 12 mpg. What do you guys think is happening?

Thanks,
Armen

The fuel smell at startup it most likely a combination of the engine running in fuel enrichment mode and your cat is is cold and isn’t operating properly.


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[ArmArak]

The fuel smell at startup it most likely a combination of the engine running in fuel enrichment mode and your cat is is cold and isn’t operating properly.


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Ok, that's good to hear. What do you think could be causing my bad mileage?

Thanks,
Armen

 

[19963.4lsr5]

Ok, that's good to hear. What do you think could be causing my bad mileage?

Thanks,
Armen

When was the last time you did a tuneup?

How old is your front O2 sensor?

When was the last time you ran a good quality injector cleaner?

Have you ever cleaned your MAF sensor?


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[gamefreakgc]

Hey guys,

I'm having the same issue. On startup there is a gas smell coming, sort of like an RC car/plane running too rich. I am also getting very bad mileage. I am on 33 mud tires and am getting around 12 mpg. What do you guys think is happening?

Thanks,
Armen

Time to give your engine and catalytic converter some R&R. That smell is your engine telling you something's off. Even at startup it shouldn't be evident. Should smell slightly sweet with a lot of water vapor coming out if you live in a cooler climate (too hot in CA right now to see vapor).

Do the normal stuff if it's time like plugs, wires, air filter, oil, injector cleaner. Clean the Mass Air Flow sensor like mentioned above. Report back and let us know if the smell persists.

 

[ArmArak]

Time to give your engine and catalytic converter some R&R. That smell is your engine telling you something's off. Even at startup it shouldn't be evident. Should smell slightly sweet with a lot of water vapor coming out if you live in a cooler climate (too hot in CA right now to see vapor).

Do the normal stuff if it's time like plugs, wires, air filter, oil, injector cleaner. Clean the Mass Air Flow sensor like mentioned above. Report back and let us know if the smell persists.

Ok thanks for the input! I just did plugs, oil, air filter recently. I will do the wires, injector cleaner and clean the MAF sensor this weekend and report back.

I am also thinking about the O2 sensor but I'm not sure how relevant it is in this case. The car has 96000 miles.

 

[19963.4lsr5]

Ok thanks for the input! I just did plugs, oil, air filter recently. I will do the wires, injector cleaner and clean the MAF sensor this weekend and report back.

I am also thinking about the O2 sensor but I'm not sure how relevant it is in this case. The car has 96000 miles.

I’ve had them last 200,000 miles and only 50,000 miles. The 97 Limited Puppy Hauler performance picked up replacing the front sensor.


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[gamefreakgc]

Ok thanks for the input! I just did plugs, oil, air filter recently. I will do the wires, injector cleaner and clean the MAF sensor this weekend and report back.

I am also thinking about the O2 sensor but I'm not sure how relevant it is in this case. The car has 96000 miles.

They are very relevant, especially the front one. However that's $50 you don't get back if it turns out not to be the culprit so do that last.

 

[ArmArak]

So a while back I noticed that my car had a strong gas smell after a cold start. I also noted my terrible mileage (12-13 mpg). This thread helped me come to the conclusion I needed to clean my MAF.

Yesterday I cleaned my MAF sensor. WHAT A DIFFERENCE! It's a new car haha. Before I would cruise at 40 mph at a little over 2k rpm. Now I do the same at 1.5k - 1.6k rpm! Also I have to note that acceleration is a lot smoother.

IDK if its just a placebo, but I think the car starts easier too lol. Maybe takes a few cranks less.

Anyway, I didnt realize how much of a difference a dirty MAF sensor makes, especially on my 95k mile truck. I'm gonna use some injector cleaner on it soon and change the O2 sensors just for the hell of it. Ill drive a while too see how much of a difference was made in terms of mileage. It takes me about a month to drive a full tank haha.