I was requested to start a thread discussing Part Throttle tuning for FI on the Hemi. This first post will be lengthy, but is the only way I know to layout the intent of the post and observations I have seen working on FI for the Hemi over the past 3 1/2 years. So, if you are running FI on a Hemi or even contemplating this power adder, please read on, post up your own observations and questions. First, this thread is NOT to poke fingers at any vendor, system, or tuner. It is not seeking disclosure of any CMR or SCT tuners tricks. Admins, I would ask that you help keep such statements out of this thread. It is intended for technical discussion and to lay the cards on the table. I also ask that individuals running FI post up what their observations are with their vehicle, keeping in mind we are strictly talking about what is going on in CLOSED LOOP and boost is present. What do I mean when I say "Part Throttle Boost" I am strictly speaking of the area of operation where FI is producing boost, and the ECU is still in a "CLOSED LOOP" state where the O2 sensors are still commanding a 14.7 AFR. Regardless of what the throttle or pedal position is, if it is not in CLOSED LOOP, then it is in OPEN LOOP, and the AFR is being commanded/controlled by the ECU OPEN LOOP (wide open throttle) tables. That is a different state altogether. To start it off, I quote from another post on here. "....... didn't know that (name removed) tune at 1/2 to 3/4 throttle would not adjust for the boost and was most likely seeing 3-5psi with 14.7 afr and 18-20 degrees of timing ...... I personally told (name removed) tuner within a week of having my car back about this. I have the data logs and the emails still to prove this". That pretty much sums it up. Part throttle boost, no fuel or timing correction, still in CLOSED LOOP. So why the discussion? An individual appears to have recently popped a ring land running FI. While this situation may or may not have played a part, but discussion of fuel correction in part throttle boost came up, and it was desired to expand the discussion. It is an important area of discussion for current or potential FI modifications. There could be a myriad of reasons why this happened, and the exact cause may never be known, that is not the intent of this thread. A couple of basic observations related to FI on the Hemi engine. First and foremost, the Hemi engine has a shallow ring land on the top of the piston, and has tight ring gaps. Heat is a big issue in the Hemi. They run hot to begin with. Both my 5.7's in my previous 300C and the current Grand Cherokee will see 1150 to 1200 degrees on an EGT gauge in cruise on a stock engine. Add in FI, even with adequate fuel and timing retard, and EGT's can quickly approach 1500+ degrees. Run part throttle boost with a 14.7 AFR and minimal timing retard..... well it is not a good situation to be in. This is far too hot for stock internals. Keep in mind the tight ring gap, get the cylinder temps too hot, the gap closes, the ring continues to expand, and pop goes the ring land. This is almost always the culprit, I have yet to see signs of detonation which is a whole other discussion. I will make some observations related to controlling temps later. Running 7 psi on a stock 5.7 with water/meth, I generally stay in the 1250 degree range. Even on a hot day. This is manageable, and I have never had any issues, even with over 32,000 hard miles on a stock 5.7 Hemi. Now you look at the 6.1 engine, higher compression, higher original power output, same ring land design. Heat becomes even more critical on the 6.1 Hemi, and a stock engine can not run as much boost as a 5.7 can. On 5.7's, no more than 7 psi, and on a 6.1, no more than 6 psi when running stock internals. Is this a little conservative? Yes, but anything more and you have no room for margin. I know for a fact, that at 9 psi on a stock 6.1 Hemi, the rod bolts will begin to stretch, the heads begin to lose their seal, combustion gasses escape to the water jacket, engine temps go up on the dash gauge, and you start puking coolant out of the overflow reservoir. This is regardless of anything else going on, and I have seen vehicles do this and not have any type of engine failure if everything else is in check. But it shows the limitations of the engine. I hear of people running FI, and maybe they have an AFR or a boost gauge, some have none. I will not do an install unless the owner is providing vac/boost, AFR, and EGT gauges. There is no way to know what is going on without them. Sure, the XXX brand system is supposed to run XXX lbs of boost, but if there is no gauge, how do you know? What if it is running 2 psi higher than it is supposed to? What happens then? Without an AFR gauge, how do you know one of those new injectors has not failed? Or something has gone wrong with the tune? What happens then? Without an EGT gauge how do you know that something has happened to the cooling or water/meth if you have it? What happens then? If you don't have a Dashhawk or predator or similar (and use it), how do you know what is going on with your IAT temps, or your fuel trims? Important clues that can divert bigger issues are missed. Running FI where you have no part throttle fuel correction or timing retard on these engines is over the edge in my opinion, and I have yet to see an ECU tune that truly can apply part throttle fuel correction based on the fact that the vehicle has gone into boost, and not simply from preset table data that can not take into account the myriad of variables that occur in daily operation. I hear a lot of people discuss it the background, but rarely do I see someone actually discuss it in public. I have never understood why that is, it is not their fault, it is simply limitations of the ECU and what can be done to it. That is why I do not run an ECU tune on my vehicles, I much prefer to have fuel and timing correction anytime I drop into boost. The whole point is, FI on the Hemi has always been a challenge, and I have yet to see two vehicles behave the same and not need some type of tweaking. If you are running FI, and you do not have vac/boost, AFR, and EGT gauges, get them, and learn how your vehicle behaves in normal driving and compare to how it behaves under boost. With a good setup, you should see a correlation, and you will be able to see things out of the ordinary and get off of it before something bad happens. If you don't have water/meth, and you have never looked at EGT's, do so. Once you do, I think you will be making a call to get a water/meth injection setup in short order. 1500 degrees you are at the edge, 1600 degrees, the aluminum is losing it's metallurgical properties and ring lands have probably already closed. A word on cooling; Intercooling will help lower the intake tract temp, but it can not remove the amount of heat needed to be removed from these engines. I know many view water/meth injection as a pain, having to fill the reservoir, an additional expense for the system, etc. But from my experience, even a forged modern Hemi should be running water/meth with FI, and no question it is a must on a stock engine. So, now with all that said, onto the discussion at hand. The vast majority of tuning on FI Hemi vehicles is performed by rewriting part of the information stored in the vehicle ECU. Generally, the parameters in the stock ECU are modified, rarely is the actual computer software code changed. On older vehicles, (GM and Ford primarily) the actual ECU software in some cases has been â€œleakedâ€ to the aftermarket or hacked, and either tuners or PC software is available where one can rewrite exactly how an ECU functions. An experienced tuner can make a heavily modified vehicle perform as if it was a factory power option. Around 2004, the Federal Government really started to crack down on vehicle manufacturers regarding emissions compliance, and they have instituted some highly advanced encryption methods in their software to prevent the ECU from being modified. False warranty claims have also become a concern of the manufacturer, so expanding the encryption techniques and capabilities of the control systems to detect and report tampering is the rule, not the exception today. ECU tunes are created using licensed software that is not available to the end user of the vehicle (most cases). Since the software opens up nearly all of the ECU parameters and tables, there is generally a very steep learning curve, in particular on new models coming to market. Since the original vehicle manufacturerâ€™s software that operates the actual ECU is proprietary, there is vigorous enforcement and prosecution of copyright infringements. Since the actual software programming is not being modified, the tuner is left to figure out how to manipulate the parameters and tables that can be accessed to achieve a particular goal. It is not a simple matter of just changing a single parameter (spark for example), but it has to be approached from a three dimensional aspect and all of the cause and effects must be considered and changes made in those areas as well. The manufacturers spent considerable time and money to develop the operating envelope for the vehicle, and it is not a simple task to modify those parameters and still keep all other aspects of operation in check. It is not uncommon for certain adaptives and functions to simply be â€œturnedâ€ off or desensitized to make the process simpler, however this practice can lead to unexpected results. Modern ECUâ€™s have very advanced adaptive capabilities and provisions to protect your investment from damage, it makes more sense to work with these capabilities rather than fight them. These tunes generally work well for Naturally Aspirated engines; however, Forced Induction is another challenge all together as the original ECU programming does not have the needed parameters and tables built into it. This is a very important part of this discussion. The ECU was never intended to deal with a pressurized state in the manifold! I have heard claims that boost tables are present, but the ECU architecture is not set up to be able to use them. Therefore a lot of manipulation has to take place to develop a new operating envelope and adapt what can be changed in the ECU to this. Sometimes it works out okay; many times it does not, as the ECU is being asked to do something it was never designed to perform. Almost always, there are residual drivability issues that remain as a result of modifying the parameters outside the norm for the particular ECU. Part Throttle (closed loop) boost is one of the issues. Many times, I see a Wide Open Throttle (WOT) tune session on a dyno and that is it. What about day to day street drivability? If you have things like high or low idle, surging on start up or at idle, poor gas mileage, jumpy throttle, sloppy shifting, degrading performance with either colder or warmer weather than when it was tuned, are all signs that the ECU is having a tough time dealing with FI, One of the things that must be done, is replacing the factory MAP sensor with a 2 bar or 3 bar sensor primarily to prevent over ranging of the MAP sensor voltage to the vehicles ECU when in boost. When improperly scaled, this practice creates its own set of drivability issues. Regardless of how the factory ECU is scaled for a larger MAP sensor, it can not use that input to recognize a pressurized manifold state as would a vehicle turbocharged from the factory, increasing fuel whenever boost is detected. In many instances, adding a larger MAP sensor (even when scaled for it), can have the effect of actually lowering transmission line pressures since the MAP sensor voltage is now half or less of what is normally expected. This can contribute to transmission issues and codes, and is similar to the problems caused by MAP sensor voltage skewing piggy backs that donâ€™t function correctly on an OBDII compliant vehicle due to the ECU adaptives. Generally, fuel addition is handled by lowering the Wide Open Throttle (WOT) threshold. This is a fixed state, and it is not dependent on boost being present, but by some other setting such as throttle position. This can lead to additional drivability issues such as; surging, run on, sudden acceleration, touchy pedal, etc.. I have run countless ECU tunes by many different people, and I have yet to have one where there was not an area where I could drive in boost and the AFR still remain at 14.7, indicating it is still in closed loop mode. I have heard it stated that the commanded AFR can be changed. My question is based on what? A fixed setting in some other table? The only way I see this as working, would be directly related to MAP voltage, and at precisely the voltage that relates to a boosted state, the ECU changes the AFR to a richer condition. If this is the case, why do I continue to hear of people running an FI tune with no fuel correction in a Part Throttle (closed loop) state of operation? From what I have seen and heard from others, it is not due to simply the fact that pressure is present and based on MAP voltage, but from some other parameter such as throttle position. The original programming in the ECU does not work this way. Yes it has a commanded AFR whenever in Closed Loop mode. It maintains this AFR until triggered to go into Open Loop (wide open throttle) based on a percent of throttle opening, and rate of increase in the demanded throttle position by the go pedal, and I am sure other parameters. If the commanded AFR is being changed by anything other than MAP voltage, then one should see the AFR suddenly go rich regardless if boost was present if set low enough, or there would still be an area where one could be in Part Throttle (closed loop) boost without fuel correction. If set too low, then one should see a rich condition in normal driving as well. I don't want to get into any discussion of what can be done in the ECU tables other than by using the tuning software manufacturers product as issued by them (not a modified version not available to all tuners). So there you have it, I have rambled on long enough. What are your personal observations with your FI system. Do you have an area where you can be in part throttle boost and NO fuel correction? Do you have other issues such as surging, touchy pedal, run on in boost, sudden acceleration, runs bad above or below a certain temperature? Lets hear what you have to say. Remember, keep it to your observations, don't call out a vendor or tuner by name, don't use this to try and resolve some other issue with someone or some company. Keep it on topic.