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11 votes

What's the meaning of a "lean" vs "rich" air fuel mixture

I do not know the etymology of these words or the history of their use in the context of air-fuel ratios, although their dictionary definitions (lean [adj.], rich, too bad I don't have an OED ...
Jason C's user avatar
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7 votes

What's the meaning of a "lean" vs "rich" air fuel mixture

A lean air/fuel mixture is when there is more air than required to burn the fuel. A rich mixture is when there is too little air for the given quantity of fuel. The ideal mixture, where there is ...
Steve Oakes's user avatar
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5 votes

Can a permanently stoich or lean running engine ruin a catalytic converter?

A lean burn won't necessarily ruin your catalytic converter. What it may do long before that happens (depending on how lean you're running) is burn the exhaust valves, piston crowns and overheat your ...
Mauro's user avatar
  • 2,655
4 votes

How much leaner can you responsibly run an old engine?

I wouldn't go too far with it, for risk of pinking, which could damage your pistons - plus, as I'm sure you well know, the Triumph slant 4 isn't exactly known for it's cooling abilities! You'll ...
Nick C's user avatar
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3 votes

Strange surging and like it's going to stall, hesitant whilst idling

Just because the OBD says it's an O2 sensor, doesn't necessarily make it so. Some diagnostic codes are pretty simple & to-the-point. But, the logic baked into the computer also has rules like "...
Cognitive Hazard's user avatar
2 votes

Motorcycle V-Twin CV carbs riding poorly on 1/4-3/4 throttle after carb rebuild

The symptoms you describe (hesitant, low power, running hot) point to a lean condition. It sounds like you may have set the floats too low, I'd set the floats back to where they were and see if that ...
GdD's user avatar
  • 17k
2 votes

Spark Plug Deposits

Depending on the mileage on these plugs, I'd suggest there's absolutely nothing wrong with the way your engine is running. These plugs look to be in great shape. The small amount of deposits on the ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
2 votes

How to fix Check engine error P0171 on VW Tiguan?

As Jupiter states in the comment, vacuum leaks are the most likely cause (particularly around the PCV valve and EGR valve). Be sure to listen for a hissing sound of air throughout the engine ...
Carguy's user avatar
  • 1,992
2 votes

Fuel Trim Readings

@Fred Wilson's comment is right on the money, high, positive long term fuel trims at idle that reduce at higher engine speeds indicate the presence of higher-than-normal unmetered air. The fact that ...
Zaid's user avatar
  • 39.2k
2 votes

Can fuel dilution significantly lower oil pressure?

First, change the oil to new proper grade oil as soon as possible. See if the problem is still there. I myself prefer changing oil at 5000 km no matter what the manufacturer says about the intervals ...
EᑎOT's user avatar
  • 967
1 vote

P0171 -- System Lean Bank 1

Its limited to bank 1 because unmetered air is only going into one side (3 cylinders). So basically air that is not being registered by the MAF is getting in after the intake manifold divides. Other ...
Dont Know's user avatar
1 vote

What do you think of these spark plugs?

The end with the spark gap is primary importance . What are you burning ? I have not seen that much crud since the leaded gasoline days. This much fouling would be typical of leaded fuel , not a worst ...
blacksmith37's user avatar
  • 3,688
1 vote

How can I diagnose if my engine is running lean or rich?

If your car is running rich you should have a strong smell of gasoline from your car. Have you considered using an air/fuel ratio gauge? Personally, I prefer to see the exact number. I have the air/...
Travis's user avatar
  • 26
1 vote

Can a permanently stoich or lean running engine ruin a catalytic converter?

What damages the catalytic converter is the heat of reacting unburned fuel. So a lean or stoichiometric mixture should do no damage at all.
dlu's user avatar
  • 14.5k
1 vote

Engine lean issues

From the data we have so far (thanks for supplying the second set of traces OP!) I'm leaning towards the Mass Air Flow (MAF) sensor being the culprit. Looking at the initial traces the air flow ...
motosubatsu's user avatar
  • 10.2k
1 vote

Help on diagnosing positive Long term fuel trim

+- 5% for LTFT is ordinary. +- 15% is more concerning but still not detrimental. If you see +-30% then you should worry. That said, the smaller the problem the harder it is going to be finding it. ...
vini_i's user avatar
  • 16k
1 vote

Is there a chemical limitation to the mixture an engine can maintain?

You can't go any leaner than injecting no fuel whatsoever. This may sound dumb but actually an engine will continue to spin for a few firing cycles without fuel. Some engines are able to actually ...
Steve Matthews's user avatar
1 vote

What's the meaning of a "lean" vs "rich" air fuel mixture

Ideal air fuel mixture (ratio) is 14.7:1. That is 14.7 parts of air ignites with 1 part of fuel. This will archive the best fuel economy and lowest emissions. This figure is also known as Lambda 1. ...
Adam Cimler's user avatar

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