Discussion in 'Engine & Performance Modifications' started by Mr MoPar, Jun 7, 2009.
Great write up. I appreciate all your knowledge on these platforms.
I agree this is all very good info for those wanting to build a reliable f/i motor.
I second Rubbles comment, this is great stuff!!! It's well on it's way to be one of the best threads on the big "C"
Okay, this is rather long, but lets give it a go.
As I stated early on, I do not perform CMR tuning. I have had lengthy discussions with those who do. To get an exact description of what is being manipulated in the ECU, an actual ECU tuner will need to chime in and be willing to discuss what is being performed.
I have not had much luck in that area beyond voice conversations.
It is clear that not every ECU tuner does things the same way. A lot of it is based on knowledge level primarily from trial and error. Other than advice provided by the software manufacturer, â€œtricks of the tradeâ€ is not generally shared among competitors. The reason why some lock their tune files.
I am sure this is not an all inclusive list, but some of the areas generally addressed are;
MAP voltage scaling
Volumetric Efficiency tables
Power Enrichment tables
Ignition advance and retard
Electronic Throttle Control tables
Coolant Temperature tables
Intake Air Temperature tables
BLM (Block Learn Modifiers, fuel correction factors)
Commanded AFR tables
WOT tables (both fuel and transition point from closed loop operation)
Various adaptives, transmission and torque management tables
Knock sensor sensitivity (reduced or turned off)
Barometric pressure update (normally turned off, if it takes a reading while in boost, it really screws things up)
Battery temperature and system voltage tables
I am sure this is not an all inclusive list, but it will give you a good idea of the complexity involved in manipulating the ECU data to come to a good compromise of parameters to run forced induction.
You have to keep in mind, that the vehicle operates in a three dimensional world, and when it comes to tuning, you have to look at it from a multi dimensional viewpoint as well. When you change one parameter, that is going to have a cause and effect in multiple other areas and these must be balanced to be in harmony with each other as the original ECU data interacts with the various other areas.
A good simple example can be related to MAP sensor voltage.
If I artificially lower the MAP sensor voltage, the ECU reads this as a reduced load that does not require as much fuel; therefore it will reduce the injector pulse width spraying less fuel.
Sounds like I can do this to run a larger injector!
Thatâ€™s easy, piece of cake. But wait, thatâ€™s not all. If it is under a reduced load, then more timing can be run, so the ECU will advance timing. If you are trying to run FI, you certainly donâ€™t want more timing!
Lower load indicates less need for transmission line pressures, so line pressures may be lowered depending on the vehicle (remember the actual load has not reduced, I have only reduced the MAP voltage).
It is also going to look at the throttle position versus table data related to the MAP voltage; this will be out of synch. So will the fuel tables, now the various adaptives start trying to figure out what is going on? It will start applying modifiers in various areas to see if this is an actual fault of some kind, or simply some type of aging issue. Eventually, it is going to update multiple parameters to realign the bad data with the good data.
In other words it will learn around the change.
With a MAP sensor, I only have 0 â€“ 5 volts to play with, what happens at idle when I need to reduce the voltage more to compensate for the larger injector, but I canâ€™t go any lower?
What happens when I reach a point where I now need more fuel, and it has to take a sudden increase in voltage (major step change) yet none of the other parameters the ECU monitors have changed?
This is just one very simple example of only one change. You can see where it is a very complicated endeavor. This is basically the issues observed when using MAP voltage skewing to try and run a larger injector with a typical old style piggyback. But it shows cause and effects related to manipulating data.
Here are some definitions related to some of the parameters involved.
â€¢ PE Mode: power enrichment mode; this is the ECU's modification for the car being at full or wide-open throttle (WOT). As more power is made at AFRs of less than the 14.7:1 default target AFR, this mode allows the engine to run at a richer AFR when at WOT.
â€¢ VE: volumetric efficiency, describes how well the engine can receive incoming air for combustion; so, for a given maximum of how much air could be ingested at a given point at normal atmospheric pressure (100kPa), the actual amount ingested is a percentage of that maximum. Obviously higher VE numbers mean better efficiency; 100 can be approached and even met and slightly exceeded with a naturally-aspirated engine; but numbers well over 100 are easy for forced induction setups like turbos and superchargers.
â€¢ IAT: intake air temperature, used for the respective sensor; measures incoming air temperature, used with the VE tables when in speed density mode to calculate fueling.
â€¢ ECT: engine coolant temperature, used for the respective sensor; measures engine coolant temperature, used with the VE tables when in speed density mode to calculate fueling.
â€¢ Battery temperature and system voltage, used to adjust overall system parameters, lower or higher voltages will affect the injector pulse width and fuel pump output. The ECU will adjust based on the voltage, primarily in WOT where fixed tables are used, in closed loop, the O2 sensors provide feedback and injector pulse is adjusted via the fuel trims maintaining the target AFR.
To say who does what and why, is probably a conversation that is not going to evolve, simply due to the competitiveness of ECU tuning. At least the above will give you some idea of what is involved.
Several have asked what I am doing. I will give you an explanation of how that works from a factual standpoint; I will let the reader discern the pros and cons.
The method I employ is different than anything else on the market. There is a similar unit out there, but is does not have the same capabilities nor is it configured properly in key areas to function with the Hemi ECU operation.
Basically, the unit is a stand alone engine management system that has its electronics and software modified to work with a factory ECU.
The manufacturer has been building stand alone systems for over 15 years, and the original concept of working with the factory ECU evolved around 10 years ago.
There have been several variations of the current unit, and previous versions (still produced) were configured and produced for use on well over a 1,000 supercharged and turbo charged Dodge Vipers.
My original unit was one of the viper units that was modified and updated (electronics, software, and firmware) by the manufacturer on my turbocharged 300C with the 5.7 Hemi.
Two specialists flew in from Sweden and performed all the work and modification here on the vehicle itself first hand.
It then went through two years of testing and validation before being updated in the fall of last year to add some additional functions and to expand the fuel and ignition tables from single rows to the more commonly used X/Y axis cell maps.
When I started, ECU tuning software was not out, so previous efforts used the SMT-6 (no capability for part throttle fuel correction), Split Second, and Unichip piggyback units. These are all based on MAP voltage skewing principles, and the modern ECUâ€™s such as we have just doesnâ€™t like that approach.
So that is the history of what I am running.
The current ECU tuning has evolved as many things do, from what it was a year ago. Then, there were far more issues during the learning curve. However, even today certain issues still linger simply due to the limitations of the ECU.
When adding forced induction, what do you really need to have take place?
â€¢ You need additional fuel when operating in a pressurized state.
â€¢ You need to accommodate for larger injectors to provide that fuel.
â€¢ You need to be able to retard timing to control knock and combustion chamber temperatures.
â€¢ You need to prevent over ranging the MAP signal to the ECU.
â€¢ You need a method to control these functions, and have fuel and timing occur based on the fact that the engine is in a pressurized state.
Instead of trying to rewrite a myriad of data in the ECU to attempt to create an envelope to deal with forced induction, I took a different approach.
During this time I also switched out to almost two dozen ECU tunes for testing. I always switched back.
The unit has its own high impedance injector drivers, it can actually run two banks of eight for a total of 16 injectors. You can control eight pairs in that situation.
The original ECUâ€™s injector pulse is routed into the unit and used as a reference. You set the percent of original pulse to use based on a global overall size percentage of old versus new injector.
For example, a 50% larger injector would use 50% of the original fuel pulse length (measured in milliseconds). There is also an injector offset to compensate for variations between the old/new injector, primarily related to idle.
This basic setting allows the vehicle to immediately start up and operate properly in the vacuum range on larger injectors.
There is no feedback to the ECU once the pulse is sent to the injector. Therefore there is no updating that will take place to the original tables and data written in the ECU. The ECU does look for a spike on the injector circuits, so it is connected to an electronic load board providing that spike on each circuit (a false electronic injector).
The unit has its own internal 2.5 bar MAP sensor that all calculations are based on. The original factory MAP sensor is left in place, and continues to function normally throughout the vacuum range. This signal is also fed into the unit, but it is not modified. The unit has a built in signal clamp that prevents the factory MAP voltage from exceeding the top of its normal range and causing over range issues in the ECU.
When additional fuel is required, additional milliseconds of pulse width is added to the original percent of stock pulse based on the reading from the onboard MAP sensor which correlates to the point in the fuel tables based on pressure, and rpm. These are user generated and user programmable.
This is direct injector control, just as if you are running a true stand alone unit. The only difference is that we leave all of the original programming intact in the factory ECU so the entire vacuum range of operation is unaffected and behaves like stock.
I only need to compensate for the larger injector in the vacuum range, nothing else.
Timing is controlled by signal delay, and whenever in boost, the unit applies the amount of retard specified in the ignition table, again based on pressure and rpm.
Closed loop part throttle boost fuel correction is ingenious in its simplicity. It is based on an understanding of just how the O2 system operates, and how the ECU responds to it.
Instead of trying to fight the system or try to somehow manipulate the data to create an envelope to provide fuel, I simply let the Factory ECU do it for me.
The O2 sensors operate in a 1 volt range similar to a narrow band O2 sensor. However, it actually has a 0-5 volt range and operates around the midpoint varying up and down by about a half volt depending on if the condition is rich or lean.
When the unit sees boost, it applies a programmed offset to the O2 signal being sent to the ECU. The ECU sees this as a lean condition and simply adds fuel to compensate, resulting in instantaneous fuel correction that is consistent and repeatable.
Since the unit applies an offset, (resistance wonâ€™t work, a fixed signal wonâ€™t work), the actual signal floats in itâ€™s range as it normally does, the ECU sees just another normal condition present in everyday operation, and it simply corrects the situation as it is programmed to do.
I can sit with the car at idle, and drive the AFR to 10/1 and below, and the ECU stays in closed loop operating normally up to the point I limit out the long and short term combined trims.
All of the ECU normal functions and adaptives are left in place, so there are no issues related to corrections for atmospheric conditions or aging issues of the various vehicle components. It continues to operate exactly as it was originally designed, thereby eliminating the common drivability issues found by rewriting ECU table data.
For turbochargers, it also incorporates an advanced closed loop (feedback) electronic boost control, and it can also provide progressive control of a water/methanol spray pump.
All functions are controlled in one place, all controlled based on actual manifold pressure, and completely programmable by the end user.
If interested, I have a 107 page PDF document available that I wrote discussing tuning methods on modern OBDII compliant vehicles. It also contains a lot of technical end user information on the unit I use.
It can be downloaded at http://www.iems3.com/pdf/Tune%20It%202.pdf
Hopefully this answers some of the general questions.
Thanks, much appreciated.
I like your slogan!
haha, neither have we.
I got the rest of it (wonderful! and wonderfully put!).
This part implies that the ECU does not correlate/check MAP against AFR right?
[all of this is in the context of closed loop boost]
You've clamped the stock MAP sensor so as to not over range it.
You're using the additional MAP sensor to detect boost.
With boost detected, you're modulating the 02 signal to the ECU to have it supply more fuel.
At this point we're counting on the ECU not to realize or sanity check that MAP is remaining constant while continuing to add fuel? I guess it makes sense that they are independent.
And is there any check or accomodation to reconcile throttle position with MAP? Again, MAP is clamped at some max while the throttle position might still be increasing or changing?
Thank you, I got a lot of heat for making shirts with that saying but i always love a challenge!!!
I find myself (keep in mind i am no way close to being a calibrator) reading these posts and I am finding it very usefull. We started on the Ford side (Saleen for 12 years) and a lot of us were given the opportunity to start Techco. I know a lot of the best tuners on that side and am getting to learn about the ones on the dodge and GM side. They never talk about what they do,how they do it, what causes them to do it and ofcourse, how they learned how to do it. I give them all credit for even trying to master the brain that keeps these monsters alive but I doubt any tuner will publically post any information becasue onc eit is out their trade secrets are gone.
anyways, thanks again for you taking the time to educate us.
See response below in BOLD.
Thanks, I agree with what you said, and I don't blame them, it is their livelihood.
If I can ever be of assistance, drop me a line or give me a call.
How do you determine the amount of fuel to add for boost?
Is it a percentage addition to whatever is being commanded by the ECU based primarily on the amount of boost (and maybe other inputs)?
Or do you adjust by incorporating your wideband input? A table lookup primarily based on boost and wideband?
It sounds like you're using the first. I'm assuming you considered the second approach since then you really wouldn't care if the PCM was in closed or open loop right?
I have sent Mike, from DiabloSport, a link to this thread and have asked him and possible Johan to chime in where they could.
Hopefully they will?
Doh... actually you already said that:
So I guess the question is: If you used the wideband feedback to determine (do the lookup) the offset to the 02 signal then you wouldn't care if the PCM was in closed or open loop? As soon as you're in boost the same algorithm control would work right up through WOT?
It will only stay in closed loop till you pass the throttle threshold to transition to WOT in the original ECU programming. Then it transitions over to the normal fuel table in the unit. You are always using the base percentage in the ECU maps, and then adding or subtracting in the units table.
The fuel map is easy to set up, basically I already have a base map, with a wideband hooked up for datalogging, you can go back and click a point on the datalog and it will indicate what cell it was in, and you just adjust the millisecond input up or down to adjust that point.
I appreciate all this information and truly want to understand more. My car doesn't exhibit any of the symptoms you all have been talking about, i.e. surging, touchy pedal, run on, etc. My car really just feels normal below 2,500 rpms and then when I hit the throttle it's a beast. I didn't do the meth because my tuner/shop is telling me I don't need it. I explained that it wasn't a question of money. I was told that if I run meth then the car MUST be tuned for it. The catch is if I run out of meth, then I can't run the car until I fill the meth. Now I know everyone's entitled to their opinion and I'm certainly feeling like the dunce of the class here, but what's right? Is 5 to 6 psi safe? Or are meth, guages, continuous monitoring a MUST have and not a nice to have?
So it's just the table or cells that change when the ECU goes from open loop to closed loop? I was thinking that if you used the wideband input as part of the cell selection then the piggyback wouldn't need to be aware of the ECU operating mode. Might make for a large table in which a lot of cells never get used. I guess it wouldn't make much difference either way and is more of an implementation detail.
(Dang, this was simply outstanding! You must be an excellent instructor)
I dont think it's necessarily a direct component of x lbs vs xx lbs but the fact that under boost in part throttle the ECU doesn't know what to do to keep things safe. From my experience you have two choices when it hits boost go WOT or back off. All you have to do is watch the AFR and boost gauges (providing you have them) and you will see boost at xx and the AFR hunting for 14.7 Lowering the throttle threshold to go WOT sooner just makes traffic pretty damn scary and takes the fun out of driving it pretty quick. My car is a beast when I hit it too but I don't always want to "hit it" I just want safe gradual acceleration until that wild hair kinks!
Yeah but if you punch half throttle to move over a lane or for whatever reason you'll most likly be in PT Boost with the AF gauge hunting for stoich! And if you actually hold the pedal there you will drive for miles under PT Boost and with the A/F gauge in the 14's.
This is were things get ugly, Your alot safer with a forged bottom end and custom pistons but for the stock block guys this can be a huge problem. I dont have the fix but Im hoping theres a quality solve preferably with no piggy back,
if they do not get a chance ron, i will be certainly asking johan a ton of questions regarding this topic when i head down to see him in a few weeks to continue fine tuning my tune!!! lol
I think gauges are a must. Even more so after this thread. Meth? If you had gauges you'd know if you needed meth. If you had gauges and you ran out of meth you'd know when to back off to stay in the safe zone. Is the 5 to 6 psi safe? Maybe? From this thread it sounds like pretty much everybody tunes for WOT and then some do better than others with the part throttle boost? ... if you had gauges you'd know.
(I'm guessing there's going to be a run on EGT gauges )
It sounds as if you have a decent tune going on, and you are pretty happy with it. If you really want to know where things are at, simply install an EGT bung, pop in the probe and hook up the gauge. Go out and drive it to see how hot it runs normally, and then see how hot it gets under full boost. This will tell you exactly what you need to know. Then you can make a decision based on real data. For $200 and a little time installing it, it can provide a lot of peace of mind.
Even if you just install it temporarily to get some data, it sounds like it would be worth it for you to know exactly what conditions are.
Regarding water/meth, running a 70/30 (water/meth) to a 50/50 mixture really does not need to be tuned for. Of course you could tune for it and probably extract a little more power by running a bit more timing, but it is primarily simply to remove heat from the combustion chamber simply injecting a spray that vaporizes in the air stream, and then the small amount of water vapor flashing to steam during the combustion cycle.
I don't tune to take any additional advantage other than the cooling effect.
As long as you are not in boost, you are not using the injection, so even if you ran out you could still drive the car, just stay out of boost.
you DO NOT have to tune for meth. most tuners will tell you not to do it simply because of some of the reasons you touched on. running out, pump goes bad, nozzle clogged, wire shorts, etc, etc...... anything that would cause the meth system to malfunction would leave the car vunerable to catastrophic failure. meth is simply a means by which to cool the cumbustion chamber down while in a boosted state. i have mine set up to come on at 2 - 3 lbs of boost. boost and a/f gauges are a must!!! continuous monitoring..... well isn't that what we all like to do anyway?!?!?! lol
you hit the nail on the head!!! i see mine stay in the 14.x range at times if i come into lower boost levels, ie 1 - 2 lbs. as soon the pedal position increases, albeit not wot, the a/f retreats to the neighborhood of 10.xx.
There is only one fuel map. Keep in mind that the unit is firing the injectors, not the ECU. With a 50% larger injector, it is using 50% of the pulse width provided by the ECU. The fuel map is used to add additional pulse length to the 50% base pulse when in boost. The unit does not care what mode the ECU is in. On my map, with the exception of some very slight tweaking in the idle region, the entire map is filled with zeros in the vacuum range.
All of the ECU adaptives continue to make normal changes, and the 50% larger injectors see 50% of whatever pulse width the ECU calculates and sends out. In this fashion, the 50% larger injectors mimic the original size injectors.
When you go into boost, now the unit starts adding fuel pulse length. If in Part throttle boost, the O2 offset causes the ECU to extend it's fuel pulse length to bring the O2 signal back to what it perceives to be a 14.7 condition. But what it is doing is increasing the fuel ratio to whatever you have the offset to bring the mixture to.
The wideband AFR input is only for datalogging purposes. It has no input on fuel correction.
It is very simple in it's execution.
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