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Old 12-05-2003, 03:08 AM   #1
BladeRunner
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What causes a car to run rich?

I know this is like a general question with many reasons but I'll ask anyway.

What causes a car to run rich, or what are the main causes of a rich burning car?
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Old 12-05-2003, 03:12 AM   #2
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Could be any number of malfunctioning sensors. If your car's running rich is your "check engine" light comming on? BMW's generally run richer than other cars, so it's normal. That's just the way they are designed.

A car will run rich when there's more fuel in the air fuel ratio mixture than there is air. If your car's running to rich, you should notice an increase in your fuel consumption.

Bry
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Old 12-05-2003, 04:41 AM   #3
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Bry pretty much put it in a nutshell there for ya. As far as the actual parts, could start with your O2 sensor, hey guys, what are other parts that could contribute?
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Old 12-05-2003, 05:35 AM   #4
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Thank you for the replies, I simply posted this for my mother. Hey I want an avator when can I get an avatar. Hummmmm did i spell that correctly?
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Old 12-05-2003, 12:30 PM   #5
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mom is a gearhead??
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Old 12-05-2003, 02:34 PM   #6
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i know older bmw's with a caburator (2002's etc) will have a tendency to run rich for the first 5 minutes because the choke needs to warm up ,,,,,,,,not that many guys here have a carburator in there car here.
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Old 12-05-2003, 02:37 PM   #7
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Quote:
Originally posted by Autotechnica
Could be any number of malfunctioning sensors. If your car's running rich is your "check engine" light comming on? BMW's generally run richer than other cars, so it's normal. That's just the way they are designed.

A car will run rich when there's more fuel in the air fuel ratio mixture than there is air. If your car's running to rich, you should notice an increase in your fuel consumption.

Bry

Uhh...kinda close, but not quite. Good shot at it though Bry. A car is running rich if the air/fuel mixture is below a certain threshold (stoichometric air/fuel is 14.7:1, first one being air, second one being fuel).

So it's not that there is more fuel than air (also known as flooded, and generally doesn't run at all that way), but that there is more fuel than can successfully burn given normal operating parameters.

Peak power will generally occur with a car running right at 14.7:1, but it's incredibly hard to tune like this, and fuel is also used for cooling the pistons and cylinder walls. So a perfect mix is often the death of an engine. Typically in the 12-13:1 ratio is about what most tuners work towards. Anything higher than 14.7:1 (ie, 15:1 or more) will lean out an engine, and either burn pistons or toss a rod. Anything less than 12:1 is probably running too rich (again, a LOT of this depends upon engine RPM; better to be rich at high RPM than lean, due to the cooling effect of the fuel, and the stresses on the engine itself).

Things that cause an engine to run rich can be:

Too little timing advance, too large a set of injectors for the engine / software, lousy fuel map (in the DME), exhaust leak upstream of the O2 sensors, faulty O2 sensors, too high fuel pressure, etc, etc.


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Old 12-05-2003, 02:50 PM   #8
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I like Bryan's explanation. K.I.S.S. !!!!!!!!!!!!!!!!!!!!!!
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Old 12-05-2003, 04:39 PM   #9
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Quote:
Originally posted by crazyvadim
mom is a gearhead??
No she's not a gearhead, would be nice, I think, to have a gearhead as a mom would be . Then I still wouldn't be running a M10B18 (despite what many say this is a good engine, but repairs are sometime more than the engine is worth), but may be a M20B25 or M50B25/28?.

Anyway, she's no gearhead. I am instresting in becoming a DIY person, but I hate to screwup .

Last edited by BladeRunner; 12-05-2003 at 04:41 PM.
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Old 12-05-2003, 04:51 PM   #10
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Quote:
Originally posted by GR8 Ride
Uhh...kinda close, but not quite. Good shot at it though Bry. A car is running rich if the air/fuel mixture is below a certain threshold (stoichometric air/fuel is 14.7:1, first one being air, second one being fuel).

So it's not that there is more fuel than air (also known as flooded, and generally doesn't run at all that way), but that there is more fuel than can successfully burn given normal operating parameters.

Peak power will generally occur with a car running right at 14.7:1, but it's incredibly hard to tune like this, and fuel is also used for cooling the pistons and cylinder walls. So a perfect mix is often the death of an engine. Typically in the 12-13:1 ratio is about what most tuners work towards. Anything higher than 14.7:1 (ie, 15:1 or more) will lean out an engine, and either burn pistons or toss a rod. Anything less than 12:1 is probably running too rich (again, a LOT of this depends upon engine RPM; better to be rich at high RPM than lean, due to the cooling effect of the fuel, and the stresses on the engine itself).

Things that cause an engine to run rich can be:

Too little timing advance, too large a set of injectors for the engine / software, lousy fuel map (in the DME), exhaust leak upstream of the O2 sensors, faulty O2 sensors, too high fuel pressure, etc, etc.


Pat
Damm this dude definitely knows his shit.Good explanation!
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Old 12-05-2003, 07:37 PM   #11
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If your car is running rich it is very likely a dead O2 sensor. Very common among bimmers...

BTW- Every car will run a little rich on start up. Wheather you have a choke or a DME there is a system to make the car run properly when cold. Cold engines need more fuel.... ever ride a dirt bike....use an outboard engine..... use a lawn tractor, weed eater..etc, they all run on the same principle.
To combat the poor emissions on a rich running engine late model BMW's have an air injection system that adds air into the exhaust headers to help burn up any fuel not used in the combustion process.

Useless tidbit of info...

Bill
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Old 12-07-2003, 04:34 AM   #12
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A fried O2 sensor will light the CE light though, which may or may not be happening in this case.

Fuel mapping, high fuel pressure etc, can contribute to a rich condition without tossing the CE light.

If the standard OBD-I / OBD-II setup is on-board, and there is no CEL, then the only way to tell if the car is running rich is via smog check. Particularly with OBD-II, it's hard to get away with an ultra-rich condition.

For your engine to actually run properly, it needs to vary from lean, to stoich, to rich and so on. NO ENGINE will run at stoich all the time; conditions vary too much. This is part of the reason you run a DME, and O2 sensors etc. As engine temps / loads vary, you'll need more / less fuel, and none of these are instantaneous adjustments.

On the dyno, if you run a wide-band O2 sensor, the graph (assuming they don't smooth the graph automatically, which you really DON'T want them to do), will spike with peaks and valleys all over the place. Perfectly normal, and in fact, that's what you want an engine to do, especially to meet emissions testing.


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Old 12-10-2003, 05:11 PM   #13
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don't forget some chips will make your car run rich too... (especially the air flow sensor chip!)
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Old 12-16-2003, 09:20 AM   #14
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how can you tell if you're running rich? what are the symptoms?
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