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This is a "tuning 101" guide for supercharged 3800 front-wheel-drive applications. Most of this can be applied to the naturally aspirated motors, and you Aussie guys too! ;)

Enjoy!


Mass Air Flow (MAF): Detects the amount of air flowing into the motor. This should be viewed in your scan tool in "frequency", not "lbs/min". You should never see over 11,500Hz, if you are getting into the 11,000Hz area then you should think about an upgraded MAF and table or custom PCM tuning.

Injector Pulse Widths (IPW): Shown in milliseconds, 22 is the max you should to see and is considered approaching static (injectors cannot flow any more fuel). Anything over 22 milliseconds and you should consider bigger injectors.

Manifold Absolute Pressure (MAP): This should be viewed in your scan tool in "PSI". Really, the MAP is almost useless on the supercharged motors. We have a 2-bar MAP sensor and most 3.20" and smaller pulley cars max out the MAP sensor almost immediately. It’s good to watch if you think you might be having boost dumping issues (the PCM is overriding the boost bypass valve on the supercharger, causing it to open and bypass the boost before it reaches the motor). You will see a drop in this value if you are losing boost. When the sensor is maxed out it will show a value of 29psi, which obviously is wrong, but when you know what to look for with this sensor it can be a useful problem solving tool.

Oxygen sensor, bank one - sensor one (O2B1S1): You have two oxygen sensors in your front-wheel-drive 3800. Bank one - sensor one is the O2 sensor that is in the rear manifold. This is the sensor that your PCM uses for almost all of its calculations when it relates to air and fuel. You will view this sensor in your scantool in “millivolts.” This sensor is of the “narrow band” design, and consequentially, is rather inaccurate when it comes to very fine tuning. But, most light to moderately modified cars can use this sensor to gauge the basic air and fuel health of their motor. It is my opinion that a non-intercooled 3800 should be in the .940-.950 range at wide open throttle, and an intercooled 3800 should be in the .920-.930 range. This goes against what most people will tell you, because to a point the leaner a car is the more power it makes. However, I have made well over 400 front wheel horsepower with a stock 115,000 mile shortblock – and I didn’t do it by running my motor lean. I would rather be safe and lose 5 horsepower due to running my motor a little on the rich side, than to run it on the edge and take out a piston or two due to a sensor hiccup. This is the other reason for running your motor to the rich side, if you have a sensor hiccup or a small tuning error the motor will not be on the edge and will probably make it through the weak moment without damage. I don’t believe in squeezing out every possible horsepower in every possible manner, motors aren’t cheap and I don’t like constantly replacing them.

On your front-wheel-drive 3800 you have a second O2 sensor, bank one – sensor two (O2B1S2), which is directly after your catalytic converter is used only for emissions detections. That is why you can disable the bank one – sensor two oxygen sensor and have no ill performance or reliability effects. There is no need to monitor this sensor.

Knock Retard: Contrary to popular belief, knock retard is a natural occurrence in almost every non-intercooled 3800. What, you say your car never has knock retard, and you don’t have an intercooler? Sounds like you don’t scan your car enough, or you need to drop a pulley size! Knock retard is a function of pre-detonation. Pre detonation (sometimes called pre-ignition or knock – hence “knock retard”) is when the air and fuel mixture in a cylinder catches on fire before the spark plug is ready to ignite it. This can be traced to many different factors: the wrong octane fuel is used, bad fuel, too small of a pulley for the motor, too much timing advance, etc. The important thing to remember is that on a non-intercooled 3800 a few degrees of knock retard is healthy. One of the biggest questions I am asked is, when someone has 2 or 3 degrees of knock retard what in the heck should they do (like the sky is falling)? I tell them that it’s perfectly normal. Our stock blower setup is not optimized for higher boost, and you will see a little knock retard now and again. What I always is explain is that up to 4 degrees of knock retard is considered healthy, 5 to 6 is a little excessive but other factors should be considered at this level. Is it really hot outside? Have you been beating on the motor pretty heavy in the last few minutes, bringing the temperature up and heat soaking it? If you consistently see more than 6 degrees of knock retard than it’s time to consider your setup. What size pulley are you running? Keep in mind, that in temperate climates (like Ohio) you may be able to run a 3.00” pulley in the winter when it’s 30 degrees outside, but when it gets into the 80’s and 90’s in the summer you may have to back that pulley off. It’s very common to change to a larger pulley in the summertime due to the hotter climate. Do you usually see 3 to 4, but spikes of up to 8 or 9 on hotter days? Then it’s time to consider a few smaller knock fighting modifications. Colder thermostats, colder plugs, exhaust modifications (including higher ratio rockers), even up to adding an intercooler, will all help to lessen or eliminate your knock retard problem.

"Alright smartass, how do exhaust modifications help to remove knock retard?"

Good question! When you are running boost into your motor, the more air that your motor can process then a lower amount of boost has to be stored in your lower intake – this boost is also becoming superheated with every turn of the blower because a natural byproduct of compression is friction, which creates heat. Hotter air makes a hotter air and fuel mixture, and, you guessed it, makes that mixture easier to pre-ignite. This is why an intercooler works so well, it cools the heat off of the compressed air which makes the mixture much cooler. Anyway, when you add better flowing exhaust components like higher ratio rockers, headers, cams, heads, etc. then the more air your motor can process and the chances of pre-ignition lessen.

Fuel Trims:Fuel trims are the PCM’s way of adapting and changing to different fuel flow demands from one second to another. They are the reason that your car runs well in 20 degree weather, and still runs as well in 100 degree weather (or with bad gas, a small vacuum leak, etc). It’s the PCM’s way of estimating what fuel the motor will need to stay running properly. 0% is near perfect fuel delivery, the PCM is not compensating in either the rich or lean direction. If you see a negative value, it means the PCM is removing fuel (the car is rich), a positive value means the PCM is adding fuel (the car is lean). The PCM can accurately compensate up to 16% in either direction to keep the motor from running too lean or rich – however, if you are beyond 8% in either direction you really should be doing a little tuning to get your trim numbers back toward 0%.

"Okay, what is the difference in short term (STFT) and long term (LTFT) fuel trims?"

Generally, you will not concern yourself with the short term fuel trims. The short term fuel trims will bounce around and are directly affected by the real-time response of the O2B1S1. The long term fuel trims are estimations the PCM makes based on the values read from the short term fuel trims. Basically, the long term trims are the corrections the PCM estimates the motor will need in the future. Suddenly going wide open throttle will cause the PCM to engage the long term fuel trim values.

I hope this helps some of you in your tuning quests.:cool:
 

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That is by far the best and most understandable explanation for tuning basics I have ever read. I'm sure I can speak for more than a few people when I say that we can all pretty much do most of the mods to our cars ourselves, but when it comes to tuning we are lost. :confused: And with all the time and money we spend on these vehicles, it's nice to know that they're running right.

Thanks
 

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k0bun said:
That is by far the best and most understandable explanation for tuning basics I have ever read. I'm sure I can speak for more than a few people when I say that we can all pretty much do most of the mods to our cars ourselves, but when it comes to tuning we are lost. :confused: And with all the time and money we spend on these vehicles, it's nice to know that they're running right.

Thanks
No problem, I'm glad that it helps you to understand what the heck is going on!

I'll write up a few more as time progresses. :)
 

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Thanks for the lesson! I was confused about fuel trims, I understand much better now. BUT... Could you please give a better explaination as to why 2-4 degrees of knock retard is good, or normal for the 3800. I have never heard of anyone saying this... I was always told that any amount of knock is not normal, and should not be allowed to occur, be it a forced induction street machine, or a high compression racing engine. Also, how does "pinging" relate to knock? Also, do you know how many degrees of KR = audible knocking, becuase I have heard the heavy knocking sound before... but never it in my regal, even though it has had 8* of KR in the past. Thanks. :)
 

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Brian, I think what he's trying to say is that because we use a roots blower, it is much more highly susceptible to knock. Pretty much everyone here should have at one point in time seen KR if they were scanning on a regular basis. If you have never seen a blip of KR, then the pulley you're running is too small. What that means is that you can push your engine further. You should run the smallest pulley you can without knock. However, there will always be days where your engine does not perform as well as other days, usually due to weather conditions, and your engine is experiencing knock.

So bottom line is that 2-4* of KR is not good. The more power you push with these engines, the more susceptible your pistons are to breaking with even a small amount of knock over an extended period of time.
 

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Excell said:
The important thing to remember is that on a non-intercooled 3800 a few degrees of knock retard is healthy. One of the biggest questions I am asked is, when someone has 2 or 3 degrees of knock retard what in the heck should they do (like the sky is falling)? I tell them that it’s perfectly normal. Our stock blower setup is not optimized for higher boost, and you will see a little knock retard now and again. What I always is explain is that up to 4 degrees of knock retard is considered healthy, 5 to 6 is a little excessive but other factors should be considered at this level.

If you consistently see more than 6 degrees of knock retard than it’s time to consider your setup.
Normal? Yes. Healthy? No. I disagree that ANY amount of knock is 'healthy'. I DO agree that it is normal and almost impossible to run with 0 KR, 100% of the time. If you are seeing ANY KR (assuming it's real) then your engine is knocking causeing a lot of extra stress on it's parts. Extra stress equals shorter engine life. If your engine is consistantly knocking, even if it's only knocking enough to retard timing 2-4°, that's still not a good thing. That's the way I see it. I would like to hear your reasoning behind smaller amounts of knock being healthy though.
 

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Let me expand on Knock Retard...

I'm excited to see some questions! I was hoping the knock retard portion would inspire some good discussion. :D

Our knock detection system is one of the most advanced and quickest responding systems ever designed. For good reason! The reason I say that a couple degrees of knock is normal and healthy is because every car is going to get a little knock. I have seen 100% stock cars with up to 6 degrees (or spikes of more!) consistently. General Motors would not have over designed a system without a cause, and that cause is because they knew that these cars would see some detonation.

However, using the term "healthy" may have been a little misleading. What I was trying to express is that if you see a few degrees of knock retard that you should not worry about your motor exploding. I get several paranoid e-mails a week asking about a few degrees of knock retard. While it's not "healthy" in the technical sense, it is healthy in the literal sense. Any knock is undesirable; however a small amount of knock is not going to hurt anything. We have a very advanced system in place that does a damn good job of saving your motor from small amounts of pre-ignition.

"Pinging": Before the days of advanced knock retard systems (think pre-1996) your engine and/or computer had no way to battle against pre-ignition. Pre-ignition commonly causes a "ping" or a knocking sound when it is occurring. Our knock retard system listens for the specific sound frequency of this knock, and categorizes it in degrees by the amplitude (how strong) of the sound. For every "degree" of knock it detects, one degree of ignition timing is retarded ("knock retard" :) ). Retarding the ignition timing causes the spark plug to fire sooner, and earlier in the piston's compression stroke. This catches the pre-ignition before it occurs, but it also produces less horsepower since the mixture is not being compressed as much when the ignition sequence takes place. This is the reason that you do not hear pinging or knocking, but you have knock retard. The PCM hears the knock before you do, and is already compensating for it.

Now, let's take my late 1988 Mustang 5.0L (R.I.P. :( ). Those cars do not have a computer controlled ignition system like our newer vehicles have. You had to increase timing manually by turning the distributor. You found where your timing advance limit is by advancing two degrees, driving the car, and listening for pinging. You just kept adding timing until you hear pinging, and then back the timing off two degrees. Instant horsepower! :cool:

I hope that answered your question as to why you don't hear the "pinging." :)
 

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Thanks for the explaination. Its good to know that the few degrees of knock I have now is not as serious as I thought. There seams to be reports of blown pistons every few weeks on ClubGP, it really scares me away from further modding.

So, pinging is just a lesser form of knock, right? I remember hearing pinging in my old 93' Regal (series I 3800) quite often... I knew it was not good but the owners manual said that pinging was normal, but on the same page it also warned about knocking and how bad it was for the engine. I guess my 93' did not have a good knock supression system.

Another thing that GM had to compensate for with good knock supression equipment is people putting regular gas in instead of premium. We all know how cheap old people are (I have a GS :D ). The owners manual says nothing less than 91, but some people will surely put the cheapest they can find in. I think is is really due to poor education. GM should devote a page in the manual to explaining what can go wrong when you put crappy gas in, and exactly why most cars can run 87, and why we need nothing less than 91.
 

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VT Regal said:
Thanks for the explaination. Its good to know that the few degrees of knock I have now is not as serious as I thought. There seams to be reports of blown pistons every few weeks on ClubGP, it really scares me away from further modding.
That is what I was trying to express. That a few degrees of knock will not kill your engine. :)

VT Regal said:
So, pinging is just a lesser form of knock, right? I remember hearing pinging in my old 93' Regal (series I 3800) quite often... I knew it was not good but the owners manual said that pinging was normal, but on the same page it also warned about knocking and how bad it was for the engine. I guess my 93' did not have a good knock supression system.
Not exactly, pinging and knock are the same thing. Some people call it ping, some call it knock. They are referring to the sound that the pre-ignition emits in a vehicle without a knock suppression system. To some it sounds like a ping, others it sounds like a knock.

It's true; too much knock can result in severe engine damage. Any pro-longed knock in vehicles that do not have a good suppression system is also very bad. But we are lucky to have a good knock retard system. :)

VT Regal said:
Another thing that GM had to compensate for with good knock supression equipment is people putting regular gas in instead of premium. We all know how cheap old people are (I have a GS :D ). The owners manual says nothing less than 91, but some people will surely put the cheapest they can find in. I think is is really due to poor education. GM should devote a page in the manual to explaining what can go wrong when you put crappy gas in, and exactly why most cars can run 87, and why we need nothing less than 91.
Exactly. GM knew that people would run 89, get a tank of bad gas, drive in the desert, etc.
 

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:Retarding the ignition timing causes the spark plug to fire sooner, and earlier in the piston's compression stroke. This catches the pre-ignition before it occurs, but it also produces less horsepower since the mixture is not being compressed as much when the ignition sequence takes place. This is the reason that you do not hear pinging or knocking, but you have knock retard. The PCM hears the knock before you do, and is already compensating for it.
Isn't retarding the timing causing the spark plug to fire LATER (closer to TDC), not earlier? Hence Knock Retard, not knock advance? If the spark plug fires too early, then the pressure wave will cause a separate flame front to ignite. E.g the PCM calls for 15 degrees of timing (fire at 15 degrees before TDC) but then dials in 3 degrees of KR. So available timing is 12 degrees BTDC. It produces less horsepower because the flame front is not providing maximum force on the piston top as the piston moves through TDC.
 

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You are correct. If you start with timing BTDC, retarding the timing brings it closer to TDC, not further away. One of the causes of knock is the fuel being completely burned too far away from TDC. Since higher octane fuel burns slower, you can have more advance than with the quicker burning regular.
 

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Questions and comments

Questions...........

Why would you have to upgrade your MAF if the frequency gets higher than 11,000? Also, what is meant by the "table". I've heard it used a lot and never figured out what it actually is. Is it how much fuel is used for each different flow of air or something? Where do u get a table and how do u put it in?

Also, another big general question....I can read over and over what values are supposed to be for certain things, but if u scan and the values arn't the "correct" values, then how/what do u adjust to get the values right? Maybe thats just too big of a questions though...

Comments.....

Also, about pinging...pinging is actually the noise that is resultant of the 2 frame fronts hitting. One from the spark plug, the other from the pre-ignition. Just thought maybe that would add clarity to VT Regal's question about ping and I didn't see anyone post it yet.

Nick
 

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1Hot97 said:
You are correct. If you start with timing BTDC, retarding the timing brings it closer to TDC, not further away. One of the causes of knock is the fuel being completely burned too far away from TDC. Since higher octane fuel burns slower, you can have more advance than with the quicker burning regular.
Thanks for the confirmation. I guess I was trying to politely point out that Chris may want to go back and rethink his statements about how KR works.

Yenick1 said:
Questions...........

Why would you have to upgrade your MAF if the frequency gets higher than 11,000? Also, what is meant by the "table". I've heard it used a lot and never figured out what it actually is. Is it how much fuel is used for each different flow of air or something? Where do u get a table and how do u put it in?
The stock MAF converts airflow into a proportional output frequency. If you have mods that outflow the stock MAF, then you "top out" the MAF.

The "table" is the calibration table in the PCM that converts MAF frequency, intake air temp, engine coolant temp, and other parameters into a base injector pulse width. Then the PCM uses the feedback from the O2 sensor to determine if it needs to add or subtract fuel to meet the desired air/fuel ratio.

For example (numbers for illustration only with no basis in reality):
Let's say the MAFF is outputting 8000 Hz. First the PCM uses intake air temperature to correct the airflow. So let's say it corrects to 5 grams per second (39 lb per hour -- typical for a GTP under 1/2 throttle). Now, the PCM looks at the coolant temp and engine load and determines that in order to have an air/fuel ratio of 14.7:1, it needs to meter .34 gram of fuel. Now it knows the injectors flow 36 lb per hour which is approximately 4.5 grams per second. So in order to meter .34 grams of fuel, the injectors have to be open for a total of .076 seconds, split over the 6 cylinders which is .012 seconds (12 milliseconds). This is the base injector pulse width (IPW).

But during this time the engine is monitoring the O2 sensor and reading the actual A/F ratio, and it adjusts the fuel trims to compensate. So it may skew the base pulse width from -22% to +16% to remove or add fuel to maintain the desired A/F ratio.

In the above example I am ignoring acceleration enrichment or power enrichment because those are open loop modes that don't use the O2 sensor.

Also, another big general question....I can read over and over what values are supposed to be for certain things, but if u scan and the values arn't the "correct" values, then how/what do u adjust to get the values right? Maybe thats just too big of a questions though...
You can do a few things:
1) You can use a tool like AFC 2.0 to modify your MAFF calibration curve. The MAFF table in the PCM is calibrated to the factory intake. If you modify your intake design, then the MAFF will not read exactly the same. So you use an AFC 2.0 to rescale the MAFF.
2) Install a ICCU to custom tune the AFC and timing.
2) Use a custom PCM programmer to fine tune your car.
 

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So this has been a good read, but nobody has mentioned tuning LTFT's when using a cam. I have read that LTFT's should be toward the +16 number because of valve overlap. Can someone please explain why?

Thanks,
Dave
 

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From the incressed overlap in larger cams. (exh. valve closeing, int. starting to open time) Your getting more of the fresh intake charge getting around the exh. vavle in the overlap time window now. It's un-burned so its has fuel still, This gets to the 02 with reads it at rich, witch is false info of the combuistion.

So with your ICCU/mini AFCv.2/programmer/ect you bandaid the flase info. Your car warmed up, most idle between hi 2K- mid3K on the Maf Hz. depending on you idle rpm, maf..... So in thouse placments you slowing, lean out. The PCM uses the FT's to correct you. So you sneak up on it utill they max (16.4). Than lean it 2-4 more %, out of the FT's reach. It's not super accurte, but dose help. If you let your car warm up in the garage before work everyday. And anytime it idles the exhust dosn't smell so rich and stink up your clothes.
 

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John,

You got the overlap right, but you're mistaken on the rich part. The O2 sensor can only detect presense of free oxygen. It does not sense the presence of fuel, burnt or otherwise. When you get fresh uncombusted air and unburnt fuel finding it's way to the O2 sensor due to overlap, the O2 picks up the unburnt oxygen and falsely assumes that the motor is running LEANER (not richer) than it really is. And in response to that, it tries to add more fuel which hurts emissions even further.

The logic behind tuning a car with a large cam to idle close to +16 LTFT is so that it will not be able to add any more fuel to go richer yet, and stink up the exhaust even further.

John
 

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22 is the max you should to see and is considered approaching static (injectors cannot flow any more fuel). Anything over 22 milliseconds and you should consider bigger injectors.
Technically that's not correct.

IPW is a time window in which an injector is able to fire (intake cycle). I have seen in numerous reference material that its 1/2 an engine revolution. Basic unit conversion yields static = 120000/rpm.

That means at 5000 rpm you have 24 ms (6000 rpm = 20 ms) in which the injector can fire (open). Anything longer is considered static..meaning the injector is basically held open and never closing (dump all the fuel it can)). Its important to note IPW and Static are always based on time..the injector flow rate is flow/time. Also, it might be good to note that injectors are usually tested at 3 bars (43 psi), higher pressure = more flow, less pressure = less flow.
 

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The logic behind tuning a car with a large cam to idle close to +16 LTFT is so that it will not be able to add any more fuel to go richer yet, and stink up the exhaust even further.

This makes sense but why would it not be recommended?

Why is ZZP the only vendor to recommend tuning a large cam to +16 at idle?
 
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