PCM controlled S2 w/toys & mapclamp

[Plan B]

Howdy,

Under PCM controlled boost, is there anything to look for / quirks when 'tuning' with a mapclamp? Got the wideband and know the benefits of an actual fuel controller, so I'd like to limit the discussion to what is already wired in the car. Couple things I 'm chewing on:

- Will it have any effect on boost levels?

- PCM control consistant enough across gears/ weather conditions to keep a steady AFR with a limited voltage clamping device?

- HOM: What will happen once 'clamped' for non-HOM mode

Pretty much just want to start a discussion of possible outcomes / variations / pointers / performance results....

[Plan B]

Bump for Eric to see so we can discuss exactly what applications the MAP sensor reading plays into in an S2 PCM....

[Plan B]

Eric must of been exhausted!

[blackbird]

Started typing at work and then got side-tracked on a couple projects and things like salary negotiation. :paranoid: Then woke up today feeling pretty crappy and stayed home from work. Should finish up post tomorrow... :lol:

[Plan B]

No worries homie! I await your input and foresee a good discussion sprouting. Cruisin down to Portland this weekend, so may have to play a little and get some real world results.

[blackbird]

I said I'd eventually get around to posting but have apparently been a little busy lately.

Bump for Eric to see so we can discuss exactly what applications the MAP sensor reading plays into in an S2 PCM....The question of such importance that I had to bump the reply out of order and put it at the top. How important is the MAP sensor reading to not just the Stage 2 computer but all stock-based computers for the SRT-4? Think of it as being the number one sensor the computer uses to determine all timing and fueling changes. It's that big. On car utilizing a mass airflow (MAF) engine management system they have a sensor that can directly measure the amount of air going into the engine (usually in grams/second) and taking the temperature into account the engine controller knows the overall density and mass of the air and therefore how much oxygen is going in. It can then alter fueling accordingly.

Chrysler went the other route by utilizing a speed-density system on the SRT-4 like they have an a majority of their engines dating back to their very first electronic fuel injection setup. In the early years the MAF sensor was deemed "too expensive" and it would cost them less to implement a speed-density setup. Little did they fully take into consideration that parts costs going into a new vehicle is only one part of the expense of putting it on the road. They still have to develop the engine calibration for all there vehicles and this is where they somewhat shot themselves in the foot.

Unlike a mass air flow setup that can directly measure the amount of air going into the engine, a speed-density system has to calculate this amount. The computer does this by being programmed with the displacement and VE (volumetric efficiency) numbers for the engine and by running that again the pressure (or vacuum) of inlet charge taken from the MAP sensor combined with engine rpm's and inlet air temps it can calculate the air going in and from there determine fueling required. The problem is that any small change in the engine or powertrain, vehicle, etc. requires a ton more work to develop the PCM calibration and the logic has to be more advanced (which was an issue back when you had 8 and 16-bit engine controllers with only kilobytes of memory).

Without the MAP sensor the computer cannot calculate how much air is going into the engine. It therefore can't calculate proper fueling. And if it can't determine the load the engine is under (load coming from throttle input to MAP sensor reading) it can't determine the correct timing.

Up until recently we didn't have any easy to install stand-alone engine management systems and we could reprogram the stock computer. About the only choice for those owners trying to alter fueling was to change it mechanically (i.e. alter fuel pressure or change injector sizing) or attempt to alter or trick the PCM into changing the amount of fuel it wants to provide. The easiest way to do this and one that's been utilized on a number of speed-density cars is to alter the MAP signal.

As many people are aware there's quite a few ways you can accomplish this. One of the simplest is to install a MAP clamp. They can either be a fixed clamping voltage or adjustable, but at the core is a Zener diode that is essentially limiting or cutting off the voltage going to the computer and never allowing it to see over whatever voltage amount you set it to. If you have a MAP clamp that limits the voltage to xx volts and the computer determines xx volts equals yy psi boost the computer will max out and only see yy psi boost no matter how much higher it goes above that. Whatever fuel the computer is designed to provide at that xx volts/yy psi level is all you're going to get. An alternate method to the electronic MAP clamp based on the diode is to mechanically change the manifold reference pressure going to the MAP sensor (such as by putting a bleed or ball-and-spring pressure regulator on the MAP sensor line, which is a little more difficult on the SRT-4 since the sensor directly connects to the manifold.)

The common piggyback controllers such as the DTEC, S-AFC, eManage, etc. can all function on a similar basis to a MAP clamp but generally have a lot more adjustability. They also alter the MAP sensor's output and change what the computer will read, but instead of having on set limit they can be wired up and/or programmed to add or (more commonly) remove fuel by reducing the MAP sensor voltage and therefore the boost the computer can see. Most have different cells or ranges you can adjust when and where it makes these changes.

With either method you might be able to get and air/fuel reading that looks "okay" but it would be hard to say for certain unless you monitor things like knock, fuel trims, EGT's, and so on. If you alter the MAP signal you're altering the most important sensor the computer uses but you can probably get an A/F ratio close to what you want. Especially if you try to mechanically alter fuel delivery first and use the piggyback or MAP clamp to fine tune. The problem is the computer doesn't just use the MAP sensor for fueling, it requires it to determine load and therefore timing. You could have what appears to be a perfect air/fuel ratio but if the timing is all out of whack you could be giving up a lot of power or running on the dangerous verge of knock or the opposite extreme where EGT's skyrocket.

Howdy,

Under PCM controlled boost, is there anything to look for / quirks when 'tuning' with a mapclamp? Got the wideband and know the benefits of an actual fuel controller, so I'd like to limit the discussion to what is already wired in the car. Couple things I 'm chewing on:

- Will it have any effect on boost levels?

- PCM control consistant enough across gears/ weather conditions to keep a steady AFR with a limited voltage clamping device?

- HOM: What will happen once 'clamped' for non-HOM mode

Pretty much just want to start a discussion of possible outcomes / variations / pointers / performance results....Now back to your other questions, keep in mind that the computer, whether we're talking stock or "Stage" all operate along the same principles but with different "settings" or adjustments, so to speak. That means your S2 setup is still utilizing a torque-based model where it receives a request for a desired torque level (i.e. you pushing the accelerator pedal) and attempts to deliver the requested power using a combination of things to include boost and fueling/timing.

Let's say your S2 car is bone stock S2 and on a warm day hits about 17-19 psi in the mid-range and tapers down towards 14-16 psi on the top end as back-pressure starts to build and choke off flow in the small turbo/manifold. If you took control away from the computer and directly controlled boost via a WGA and bleed or manual boost controller (MBC), an electronic boost controller (EBC), etc. you might be able to get that same 17-19 psi up top and taper down to 14-16 as redline, for example. On the same weather conditions you should be making about the same power but if the weather got colder and therefore the air became denser with more oxygen to burn you're either going to run leaner and/or make more power (unless you go too lean and get knock that kills timing).

That's kind of off on a tangent, but it's related to how the computer works. Remember that when you have factory boost control the PCM is trying to deliver the same requested/commanded toque no matter if you are in the middle of the Arctic circle, in Death Valley heat in the middle of summer, or at the top of a mountain pass with thin air density.

Back to the MAP clamp and how it works and why it works somewhat okay for a stock turbo car you have to look at where the engine is richest and the boost response curve. Back to our example of 17-19 tapering to 14-16 lets say the car is rich in the mid-range but you don't want to lean it out up top because of the exhaust gas temperatures (EGT's) starting to skyrocket. If you installed a MAP clamp and set the voltage to the point that equals 15 psi the computer will never see over 15 psi. So with you controlling the boost when it spikes up high in the mid-range you still only get 15 psi of fuel which leans the car out some. Then when boost starts dropping off again and hits that point or drops back below it you have regular fueling.

Keep in mind that fueling changes are also accompanied by timing changes since the MAP sensor plays a key part in determining engine load from the manifold pressure compared to how much go pedal you're giving it. In general if you hide boost from the computer it will try to add more timing advance. This can sometimes be good for power and it can sometime lower EGT's by altering when the combustion burn process starts, but more timing isn't always better. I'd suggest you look up MBT or minimum timing for best torque (http://www.visteon.com/utils/whitepapers/2003_01_3266.pdf). Too much timing for the fuel octane and compression ratio can also make the engine more susceptible and prone to detonate/knock.

To the next part of your question relates to if you keep the factory boost control in place. The PCM works on sensor feedback so if determines it wants 16 psi of boost and you have a MAP clamp set to the equivalent voltage of 14 psi, what's going to happen when it adds wastegate duty cycle and reaches 14 psi and the boost stops rising. Chances are it's going to keep increasing duty cycle and which means your boost will spike higher but the computer will not see this. A couple things will more than likely result. First is your drivability will go out the window. You may run lean and/or get knock. And you may set codes depending on the S2 programming. The NGC (Next Generation Controller) performs sensor rationality checks meaning that it attempts to look for bad sensor inputs and double-check things such as using the TIP sensor and vice versa.

If factory boost control and drivability was a key selling point to you for S2 then you're probably going to say goodbye trying to install a MAP clamp and leave the factory boost control in place. Depending on how much you clamp will also affect your timing. In general the S2 computer runs about 6° more advance in high-octane mode with no changes to fueling. You might get a lot more timing just from the MAP clamp as well as running leaner and neither of these may go along well if you decide to put the car in high-octane mode. Overall no matter what path you take you'll want to monitor OBD-II parameters to include timing and fuel trims, knock retard (which will require a scan gauge or high-end scan tool), a wideband air/fuel gauge, and optimally an EGT probe mounted pre-turbine if you're still on the restrictive stock-based turbo just to keep an eye on what temps are doing since you have no direct control over fueling and timing.

[Plan B]

OMG, so worth the wait Eric! I'm leaving work now, but will pull this back up when I get home! (only read half before I have to leave).... More comments to come...

[Plan B]

Okay, so after reading all that, it appears that using the MAP clamp is less than a half assed way to go about manipulating things... I had somewhat of a handle on all that was stated, but after reading your post Eric it put it all together quite nicely, thanks again. So the best way to actually get more power out of a staged PCM would be to alter the torque destination, correct? Does the SCT make it as easy as that due to the logic of the PCM? Up the desired torque and the rest will follow?

And how does the PCM/Car assess it's torque level? Is it even an actual ft/lbs calculation or is it more of a general equation?

Just looking for possible ways to get every ounce of performance safely out of the S2 setup.... Not thinking of doing an after market WGA, for I can't stand PTB and have and will track the car (need the ability to apply maintenance throttle). Thanks again!

[Y4L]

Damn son..........

Eric you truely are a fucking G

[thepowertowin]

I lost interest and started eating funyuns.

[blackbird]

To sum it up in simple terms there's nothing "wrong" with a MAP clamp if it does what you want and what you're looking for, but if you want factory controlled boost but the computer can't read what boost is actually doing in order to control it you're going to run into issues.

Yes, you can alter all these parameters with the SCT software but be very conscious to the fact there is no instruction manual that tells you what you need to change and how to do so. You'd also need to look into the Pro Racer Package to be able to make any changes for yourself otherwise you're stuck with buying only the XCal 2 handheld flasher (which also comes with the Pro Racer Package's tuning software) and paying for tunes from the SCT dealer you purchase the XCal 2 from.

The throttle pedal is one of the inputs that the computer uses to determine demanded torque, or in other words how much power you want. The more you press the more torque the engine controller will try to produce. That means trying to provide it with the right combination of boost, fuel and timing. If you wanted to make changes to the engine calibration with the SCT tools to increase boost you wouldn't actually want to change the tables for boost. Those define the characteristics of the turbo and the WGA and are used in calculations. Instead you would alter the torque tables or other variables in order for the computer to produce the higher boost using what it knows about your engine.

I'd haven't looked at the software in a while but I'm pretty sure it calculates in N-m. In theory it might actually be able measure the torque output the engine produces by measuring engine acceleration from the crank angle sensor over time but it does not do so nor does it care. It knows what you want (from the gas pedal) and already is programmed with how to get that so there's no need to measure and ensure output. The NGC performs rationality checks of various sensors and calculations to make sure everything is working accordingly and if you're tricking the computer that's what usually sets off the codes and check engine light.

If you're looking to get every last bit of performance out of Stage 2 but want to track the car you might consider calling it good as-is. If you had a bone stock S2 car (meaning a non-modified car other than a non-modified Mopar Stage 2 kit) you could try leaning the car out and/or raising the boost. Problem is the Mopar engineers are pushing the stock turbo to the durability limits which is one of the reasons they run it pig rich. There's a ton of SRT-4 owners out there who advertise how they leaned out their cars to 12:1 AFR, cranked up the boost to S2 levels on a stock fuel system, but how many have done more than a few pulls on the highway like that? Run the car at extended WOT under high load and see how well they do when EGT's climb north of 1800°F.

Your best bet for reliable power might be to use high-octane mode if you have S2 w/toys. Since the Stage 2 computer is less picky about knock than the S3 computer you could always consider trying an alky/water injection setup to try to get it to hold high-octane mode on pump premium (probably in combination with a larger intercooler). Another option would be to clip the stock turbine wheel to reduce backpressure and lower EGT's. Spool shouldn't be affected much and you should see a nice bump in power on the top end. Recalibrating the PCM with the SCT software is an option if you think you can either a.) do better than the Mopar engineers, or b.) want to attempt to keep the same drivability/reliability the Mopar engineers provided while taking advantage of other modifications. There is a little more power to be had from tweaking the S2 code and if you're running a lot of logging and monitoring equipment you definitely could get more power out of a stock S2 setup, but you could really see more power once you start adding modifications to the mix compared to trying to get them to work with the stock or "Stage" computer and something like a MAP clamp or piggyback. Then again if for your setup the piggyback or clamp is making power and doing so safely you may not notice much if any gain from reprogramming. More than likely it won't be running optimally everywhere or will be sacrificing something like durability or drivability to get it to work.

[blackbird]

I lost interest and started eating funyuns.

So did I. I didn't even proof read the last post. :lol:


BTW you guys have any of the 3 bar MAP's in stock? Last I saw about 28 were still on back order. :furious3:

[Plan B]

Once again, all good points... I think I see water/meth injection in my future..... Or S3, whichever comes first :lol:

Thanks Eric!

[turbofrog]

What about both the S3 and Injection, Go big B........

[Plan B]

What about both the S3 and Injection, Go big B........

Never said it was one or the other :djortiz: