99 3rd gen limited v6 running rich?

[Baughb]

OK, I’ve searched the forum and I have found this topic leads me to discussions regarding coolant issues rather than rich air/fuel issues.

So after driving over 200 miles I noticed that while idling, the exhaust from my truck was smelling very gasoline Rich. I am asking if this is an issue that my truck might be running with a rich fuel mixture that is causing it to get worse gas mileage. And I was hoping to find out if there is a way to check the fuel mixture in the computer so that the fuel mixture will be more optimized rather than running rich.

I did notice that on this trip I was getting approximately 4 miles per gallon less than I would have expected.

Any suggestions would be appreciated!

 

[Bad Luck]

OK, I’ve searched the forum and I have found this topic leads me to discussions regarding coolant issues rather than rich air/fuel issues.

So after driving over 200 miles I noticed that while idling, the exhaust from my truck was smelling very gasoline Rich. I am asking if this is an issue that my truck might be running with a rich fuel mixture that is causing it to get worse gas mileage. And I was hoping to find out if there is a way to check the fuel mixture in the computer so that the fuel mixture will be more optimized rather than running rich.

I did notice that on this trip I was getting approximately 4 miles per gallon less than I would have expected.

Any suggestions would be appreciated!

How many miles do you have? Has the air/fuel sensor ever been changed? IF the air/fuel sensor has never been changed then I would start there.

 

[brillo_76]

+1 on the first oxygen sensor as that's always the air fuel ratio sensor. Could be something else but I definitely check that first. They do fail from time to time.

Sent from my SM-A536V using Tapatalk

 

[Baughb]

How many miles do you have? Has the air/fuel sensor ever been changed? IF the air/fuel sensor has never been changed then I would start there.

265k miles. Was replaced a loooong time ago. I’ll give that a go as a start.

 

[phattyduck]

OK, I’ve searched the forum and I have found this topic leads me to discussions regarding coolant issues rather than rich air/fuel issues.

So after driving over 200 miles I noticed that while idling, the exhaust from my truck was smelling very gasoline Rich. I am asking if this is an issue that my truck might be running with a rich fuel mixture that is causing it to get worse gas mileage. And I was hoping to find out if there is a way to check the fuel mixture in the computer so that the fuel mixture will be more optimized rather than running rich.

I did notice that on this trip I was getting approximately 4 miles per gallon less than I would have expected.

Any suggestions would be appreciated!

What did you get and what did you expect for mileage? Modifications (lift, tires, racks, etc)? How fast were you going?

The ECU keeps what it *thinks* is stoichiometric A/F ratios for almost all running conditions. If the O2 or A/F sensor is bad, the fuel can be off somewhat.

-Charlie

 

[Bad Luck]

265k miles. Was replaced a loooong time ago. I’ll give that a go as a start.

I'd highly recommend a Denso one and to avoid ebay/amazon. I've tried aftermarket and got worse fuel economy so I ordered a Denso from eBay and it was a counterfeit.

 

[CoCoCo4Runner]

OK, I’ve searched the forum and I have found this topic leads me to discussions regarding coolant issues rather than rich air/fuel issues.

So after driving over 200 miles I noticed that while idling, the exhaust from my truck was smelling very gasoline Rich. I am asking if this is an issue that my truck might be running with a rich fuel mixture that is causing it to get worse gas mileage. And I was hoping to find out if there is a way to check the fuel mixture in the computer so that the fuel mixture will be more optimized rather than running rich.

I did notice that on this trip I was getting approximately 4 miles per gallon less than I would have expected.

Any suggestions would be appreciated!

Vacuum leak could be causing it as well, and something you can check without throwing too much money at the truck. My truck is also running rich

 

[brillo_76]

Vacuum leak is mostly easy to find. Fire it up and use brake clean, wd 40 etc and mist all the areas of possible vacuum leaks if it speeds up you found your area that's leaking..

Sent from my SM-A536V using Tapatalk

 

[Malcolm99]

Probably best to watch the fuel trims and see what the ECU is reading first, then use the service manual to test MAF, TPS and upstream O2, either of which can cause a rich condition.

 

[Bad Luck]

Vacuum leak could be causing it as well, and something you can check without throwing too much money at the truck. My truck is also running rich

Vacuum leaks cause the engine to run lean not rich.

 

[Baughb]

Been away for a while...

So I have NOT been able to change the O2 sensors but, I did change out my MAP sensor and cleaned the throttle housing.

My hwy mileage is still reasonable (17-21 conditions depending) but, after it's been running, the exhaust still smells "rich" to me. A gasoline heavy exhaust smell.

I'll try to update sooner and thanks for the suggestions.

 

[prybar]

So I have NOT been able to change the O2 sensors but, I did change out my MAP sensor and cleaned the throttle housing.

My hwy mileage is still reasonable (17-21 conditions depending) but, after it's been running, the exhaust still smells "rich" to me. A gasoline heavy exhaust smell.

I'll try to update sooner and thanks for the suggestions.

DId you ever figure out a solution? I'm running pretty rich as well.

 

[Baughb]

Running rich

DId you ever figure out a solution? I'm running pretty rich as well.

I did change out the upstream and downstream a/f sensors and it seemed to help a bit. But since my issue is un-measurable (to me anyway) this is mostly guessing. I wish I could get my scanguage2 to give me accurate a/f measurements so I could tell. I have a few different scanguage input info for the A/F but I have yet to change them around.

 

[Robb235]

I did change out the upstream and downstream a/f sensors and it seemed to help a bit. But since my issue is un-measurable (to me anyway) this is mostly guessing. I wish I could get my scanguage2 to give me accurate a/f measurements so I could tell. I have a few different scanguage input info for the A/F but I have yet to change them around.

Is your '99 federal emissions (one catalytic converter) or California style emissions (two catalytic converters)?

 

[Malcolm99]

What is the Long term and short term fuel trims, scan gauge can provide that data, it should be around zero +/- 4%.