Over fueling

Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
New to tuning so go easy on me. How do you know when you are over fueling to the point over hurting engine. EGT’s and black smoke??? and does a diesel generate more hp when leaning out same as a over fueled Gas engine?
 

2004LB7

Well-known member
Dec 15, 2010
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diesels are the opposite to gas when it comes to lean or rich. diesels will start to throw black smoke when over fueled. A light haze is the best compromise between max HP and safe fueling. under most conditions diesels run lean until the power is needed and even though may also continue to run lean. lean is cool and rich is hot

without a wideband O2 sensor to measure the fueling, a good rule of thumb is no smoke is lean, light haze is 1 to 1 and smoke is over fueled. you want to try and avoid over fueling except in competition where you are trying to wring out every last bit of power

then you have EGT sensors to help too. others will likely chime in to correct me, but off the top of my head I think it's something like 1400f where you want to start backing off. I think you can for short term go to 1600f
 

JoshH

Daggum farm truck
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To a certain extent, EGT is what it is. When you burn a given amount of fuel, there is a set amount of heat energy that is generated. Some of that heat is transferred into energy that forces the piston down the bore, some is absorbed by the cylinder head, block, and piston, and some is expelled out the exhaust valve. I wouldn't be too concerned overall about exhaust temperature (especially during short bursts such as drag racing). I like to watch coolant temps and oil temps to see what sort of thermal load the engine is under. When you are loaded and working hard, you will see those numbers climb even if EGTs are in check. That said, you will generally see more power, when you burn as much fuel as you have available. You can overfuel to the point of cooling the combustion chamber and "put out the fire", but that is pretty hard to do on a common rail without some massive injectors and high pressure supply. A lot of tuning has to do with what parts are in the build and what the goals and uses are for the truck. Can you give us some details about what you're working with?
 

Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
To a certain extent, EGT is what it is. When you burn a given amount of fuel, there is a set amount of heat energy that is generated. Some of that heat is transferred into energy that forces the piston down the bore, some is absorbed by the cylinder head, block, and piston, and some is expelled out the exhaust valve. I wouldn't be too concerned overall about exhaust temperature (especially during short bursts such as drag racing). I like to watch coolant temps and oil temps to see what sort of thermal load the engine is under. When you are loaded and working hard, you will see those numbers climb even if EGTs are in check. That said, you will generally see more power, when you burn as much fuel as you have available. You can overfuel to the point of cooling the combustion chamber and "put out the fire", but that is pretty hard to do on a common rail without some massive injectors and high pressure supply. A lot of tuning has to do with what parts are in the build and what the goals and uses are for the truck. Can you give us some details about what you're working with?
4000lbs 57 Chevy Station Wagon, we just do a lot of spinning tires and want to get it to drag strip. Its a street machine with race tune. No problem with driveablity. There is no load and is not much WOT , maybe only 8 seconds:eek: . Bought a short block all built to hold 1000hp. Rods, .20 over Mahle pistons flat top with releif, Wagler Alt fire cam with springs and retainers,Roller rockers, Mild ported Heads, over size up pipes and Manifolds , 480/366 turbos, 100% bosch injectors from Lincoln, Duel injection pumps, twin 4’’ pipes. Had it tuned with 60% injectors , now running 100% over injectors. Have run it this summer on 60% tune and it runs crazy good and sounds great, no knocking and runs free. Hits 4000 rpm quick. With 60’s street tires sideways at 85 third gear lockup torque convertor. It is a little smoky, blackish haze up through rpms. Of course quite Black at take off so thinking on backing things down especially idle and up to maybe 2500 RPMS. Top end it seems to be ok .IT runs smooth and quiet compared to some other tunes i have run. just do not want to blow it up. Thinking pulse width shortened and little less fuel. Other wise the tune is Sweet. If I can back it down a little and it still runs good I will take it to a dyno to see where it is at. I was told with these turbos lucky to see 900 hp. I have injector flow sheets so will see if I can figure things out. Any Input would be appreciated.
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Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
We ran it on 85 degree day and was hard on it for a while. Oil pressure stayed steady and coolant goes to 210 fan kicks on and stays cool in traffic or playing. Open exhaust 5’’ to two 4’’ pipes.
 

Dozerboy

Well-known member
Jun 23, 2009
4,428
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B0795 is the fuel limiting table and it will be key to cleaning up the way it runs. I have a love hate relationship with this table. For me it's been hard to get that table just right. Been years I been playing with it so I'm not losing performance long, but it still runs clean. If you search that table you'll find some post discussing it.

If you're happy with the way it runs I don't know if you really meant need to mess with much in the tuning aspect other than this table.
 

2004LB7

Well-known member
Dec 15, 2010
3,449
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Norcal
B0795 is the fuel limiting table and it will be key to cleaning up the way it runs. I have a love hate relationship with this table. For me it's been hard to get that table just right. Been years I been playing with it so I'm not losing performance long, but it still runs clean. If you search that table you'll find some post discussing it.

If you're happy with the way it runs I don't know if you really meant need to mess with much in the tuning aspect other than this table.
I'm in agreement here especially with the love hate relationship part. playing with it can leave one confused or frustrated. takes a lot of tweaks and testing to get it working good. that's why most will leave it alone or max it out and then adjust the PW tables but this can still create times where it's still smoky. get the B0795 right and it can be as clean as you want anywhere in the powerband
 

JoshH

Daggum farm truck
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Feb 14, 2007
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If you're going to play with the MAF limiting table, you need to do a lot of data logging to see exactly where adjustments need to be made. I do not recommend maxing that table, or you will have a smokey mess.
 

Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
If you're going to play with the MAF limiting table, you need to do a lot of data logging to see exactly where adjustments need to be made. I do not recommend maxing that table, or you will have a smokey mess.
I agree. Going to do litttle steps first, try to get idle and low rpm a little less smokey or hazey. Adding little timing and a little more FRP to see results. Let ya know what happens.
 

JoshH

Daggum farm truck
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Idle smoke is typically more fuel pressure and timing related than anything else. Sometimes pilot injection can have an affect on that as well. What sort of rail pressure are you running at idle?
 

Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
Idle smoke is typically more fuel pressure and timing related than anything else. Sometimes pilot injection can have an affect on that as well. What sort of rail pressure are you running at idle?
Im running it now and is not really smoking at idle. Just a little strong for lungs and eyes while idling. Maybe thats just 100% characteristics.. Pressure at idle around 5000psi
 

Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
Idle smoke is typically more fuel pressure and timing related than anything else. Sometimes pilot injection can have an affect on that as well. What sort of rail pressure are you running at idle?
My mAF Sensor keeps going to 0 so Im not getting fuel. Checked wires and New sensor. Think can be ECU.?
 

JoshH

Daggum farm truck
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Feb 14, 2007
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My mAF Sensor keeps going to 0 so Im not getting fuel. Checked wires and New sensor. Think can be ECU.?
Anything is possible, but I would bet it is a wiring problem unless you installed a cheap parts store sensor.
 

Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
Anything is possible, but I would bet it is a wiring problem unless you installed a cheap parts store sensor.
Found wire rubbing to fender on my frankinstein. Hopefully get video if no rain tomorrow. I guess bunch of issues at one time making things tuff. Everytime i removed Ecu to test wires it moved them enough so was not rubbing, put back to gether and take a ride it must have moved back and grounded out.Apreciate the help
 

monster50iii

Member
Dec 5, 2014
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As dozerboy said, table B0795 can help alot. I've found if you can get it kind of close with that table, it helps to further the improvements by adjusting your maf scaling a bit where it's needed. I've found that B0795 can't fix everything in regards to limiting fuel vs air. Small adjustments by lowering a the maf scaling where over fueling is occurring makes a big difference.
 

Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
On B0795 whats is g/cyl on that table. It starts at .30 to 2.40. Where is it getting that value from? Is there a way to log lambda? Mine stays at . 625 on log
 

Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
JoshH, I found my answers, found a efi live post from 2010 where it was added to efi live. . Grams/cyl & Play with air PID to get it to work. It is air to fuel ratio.
Adding fuel pressure at Idle helped Lope and cleaner burn at idle, (its a van ecu so needed 60 at idle,instead of 40.
Now as you said way back then “I have a set of 80% over injectors and my truck would have billows of smoke rolling from the exhaust if I wasn't careful. I have fine tuned it to a haze that quickly dissipates, but I can easily make it completely disappear but drivablilty suffers if I do that.”
Now I have 100% over injectors with 480/366 compounds. Is it possible to limit the bellows of smoke and make turbos light quicker on the launch without hurting performance.? Or does it just take Compounds fuel and time to get up to boost?
 
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Max1957

Wcarman 57 LBZ Badd Gass
Sep 26, 2021
27
0
1
NY
For anyone who is interested!
Mass Air Flow” (MAF, for short) is a method of measuring airflow into an engine in order to supply an appropriate amount of fuel and adequate spark timing. First, vocabulary:
  • ECM, ECU, Engine computer : used interchangeably to mean the computer operating the fuel injectors and running the engine
  • MAF : Usually used as a shorthand for Mass Air Flow Sensor / Meter
  • Vane Air Flow Meter (VAFM, “Flapper” type meter) : An early type of air meter rarely used today that relies on air pressing against a metering plate (“flapper”) to provide an airflow signal
  • Karman Vortex air meter : A type of air meter that not used very much anymore that creates and counts vortexes (air disturbances) in order to measure airflow.
  • Hot-Wire MAF : A type of MAF Meter that uses a thin wire heated by an electric current to directly measure air mass. The most common type of MAF today
  • Hot Film MAF : A type of MAF Meter that uses a metal film heated by an electric current to directly measure air mass. Another type of MAF that is found today.
  • TPS : Throttle Position Sensor
  • MAP : Manifold Absolute Pressure Sensor – a sensor that measures the pressure of air in the intake manifold
  • Displacement : the volume swept by a piston descending from the top to the bottom of the cylinder bore. More here.
  • AFR : Air Fuel Ratio – the ratio of air to fuel present in a combustible mixture. Usually stated as a ratio, i.e. 14.7:1 for the stoichiometric AFR for gasoline. Stoichiometric AFR varies from fuel to fuel.
  • Lambda : similar to AFR, except usually expressed as a number where 1.0 represents a stoichiometric mixture for all fuels. Lambda and AFR are the same concept expressed in different units.
Types of MAF Meters and General Operating Principles
Hot Wire MAFs and Hot Film MAFs are the dominant technology in use today. Earlier style meters (Vane/Flapper, Karman) required an external temperature sensor in order to provide a meaningful airflow reading. Hot Wire and Hot Film sensors are often found coupled with a dedicated air temperature sensor but they do not strictly require one because the method in which they generate a signal accounts for the temperature of the air they meter. If you want to learn more about meters, read up here.
ECMs generally have a routine (usually called the “MAF transfer function” or something similar) that converts the raw sensor readings into an airflow value. Sometimes this is a real-world unit (such as g/s or lb/hr) and sometimes it is a purely arbitrary synthetic unit that merely defines the shape of the curve. MAF transfer functions for hotwire MAFs are usually an exponential curve. The shape of the curve is usually determined by the physical characteristics of the sensor. The metering range of the sensor is usually determined by the cross-sectional area of the housing it is in. This means that an easy way to increase the amount of air a given MAF can meter is to put it in a pipe with a larger cross-sectional area. The new MAF transfer function can be approximated (usually fairly closely) by multiplying the old transfer function by the difference in cross sectional area.
Example Question: a meter in a 2″ diameter round housing can meter 1000g/s. The same meter in a 4″ diameter round housing will measure how much air?
Answer: First, find cross-sectional area of 2″ diameter pipe. Area of circle = pi * r^2. Diameter = 2 * radius. Radius = 1″, area = 1 * pi. Second, find cross-sectional area of 4″ diameter pipe. Area = 4 * pi. New area / Old area = 4 / 1 = 4. Multiply original airflow (1000g/s) by ratio of area (4) to get maximum value of 4000g/s. Note that each individual point in a MAF transfer function can be multiplied in this manner to rescale.
MAF Systems
From here on in this guide, “MAF” and “MAF Systems” will refer exclusively to systems using Hot Wire MAFs and Hot Film MAFs. The reason for this is pretty simple: these type of sensors (at least theoretically) are capable of measuring air mass without the need for significant compensation for air density (i.e. altitude changes, forced induction, changes in air temperature). In practice, many control strategies use other sensors to try to increase the accuracy of the MAF by additional adjustments but it is not strictly necessary. MAF sensors do not know what “boost” or “vacuum” are – they deal exclusively with airflow. If you are trying to make the transition from tuning mostly Speed-Density systems to MAF Systems, be very cautious with timing values as the same trends and rules do not apply to both systems.
Fueling with a MAF system is about as simple as it can get. It goes something like this:
  1. The raw sensor output is converted to an airlow value
  2. The next step after determining airflow is to figure out how much fuel is needed to achieve a “target” AFR (more on AFR targets later) which is usually achieved by multiplying by AFR expressed cleverly (see footnote)
  3. Finally, the desired fuel value is achieved by multiplying/dividing by a value (injector constant, injector slope, async BPW, …) to account for injector size. Also any battery compensation is added. (See Theory: An Injector Model for more information)
  4. Done! At this point, we have an injector pulsewidth! PulseOut = (MAF_Transfer(RawMAFSensor) * TargetLambda * injector size) + injector latency
There is no “standard” way of doing timing with a MAF system, but all variants basically calculate a value that represents how much air is entering the cylinder each time the motor turns over. It goes something like this:
  1. Start with the same airflow value from step one of fueling. (MAF signal -> MAF Transfer) This tells us the amount of airflow per unit time.
  2. Measure how fast the motor is spinning (RPM) and from this calculate how many revolutions happened during the same time frame as our MAF sample.
  3. Multiply/divide airflow by engine revolutions to get airflow / rev. Most engine management stops here (GM, Subaru, Mitsufeces, …) and spark tables are indexed in grams/rev. This is a measure of engine load (with a lowercase “l” to denote that we are talking about something different than “Load”, explained next)
  4. Ford (and others?) instead use a “Load” (with an uppercase “L” to denote that we are talking about something different than “load”) value that is calculated by multiply/dividing airflow/rev by engine displacement to get a measure of how full the cylinders are relative to their maximum capacity naturally aspirated at sea level with certain air conditions. If you’re at all familiar with Speed-Density, this should sound somewhat familiar because it is a concept VERY similar to Volumetric Efficiency.
  5. Timing tables are usually in the form RPM x calculated load. MAF timing tables will display a very different characteristic shape than RPM x MAP tables common in Speed-density systems.
Now that we have some concept of cylinder filling (“Load” or “load”), we should return to a piece of how fueling happens in a MAF system: target lambda/AFR. Usually the same measure used to determine appropriate ignition timing is used to determine an appropriate target AFR/lambda. In these cases, there is a table that dictates target lambda/AFR indexed by RPM and load. Sometimes, RPM and TPS is used to determing target AFR instead of calculated load.
Strengths of Mass Air Flow
  1. Extremely accurate fueling and spark delivery across a diverse range of engine conditions (at least while in steady-states): the holy grail for engine management. A properly set-up MAF system can adapt to changes in weather and altitude with ease.
  2. Minor changes to engine equipment (i.e. headers, minor camshaft changes, intakes that do not significantly alter the placement of the MAF) do not require recalibration of the ECM.
Weaknesses of Mass Air Flow
MAF systems are known for having these issues:
  1. MAF systems are extremely intolerant of vacuum leaks. Any leaks between MAF sensor and engine generally cause all manner of odd problems, running lean in most cases due to un-metered air making it into the engine.
  2. MAF sensors can be extremely sensitive to how they are “clocked” – merely rotating the sensor at a given spot in the intake tract can be sufficient to significantly change its output.
  3. MAF sensors require laminar flow to read 100% accurately. True laminar fluids do not exist so this introduces some degree of inaccuracy to MAF sensor readings. Placing MAF sensors near bends, size transitions or obstructions where flow is less laminar greatly magnifies this issue.
  4. A MAF sensor can be a flow restriction in cases where the MAF housing is the smallest portion of the intake system.
  5. Hot-wire MAF elements are very fragile. Debris can destroy delicate wires easily. Dirt and oil deposits can build up on the sensor element, adversely affecting readings.
  6. MAF systems have a relatively poor response to transient conditions, such as sudden throttle changes. This is explained by the time it takes air to move from the MAF sensor where it is measured to the cylinder where it can be involved in combustion.
  7. MAF sensors are not “one-way” sensors – reversion from a camshaft with large amounts of overlap can cause air to be metered on its way in to the engine and then again on its way out resulting in an artificially high MAF reading. This can almost always be fixed by placing the MAF sensor sufficiently far from the throttle body, however doing so comes at the expense of making transient response even worse.
It may seem like there are a lot of weaknesses of MAF systems, but it is truly hard to emphasize just how amazing and important the strengths are. It is no secret that the majority of OEMs today are implementing MAF systems as the primary control strategy. There is a good reason for this, namely that engines can be controlled much more precisely (with the goal of meeting stricter and stricter emissions standards) with a MAF system than any other type of control strategy.
Note: I say “Multiply/divide” multiple times because multiplication and division are very similar operations but division is generally much slower on microcontrollers and other “small” processors often found in ECUs. For this reason, most division is implemented as multiplication by carefully changing the scale of one of the operands.
 

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