WizardBlack Posted July 31, 2007 Share Posted July 31, 2007 That's contrary to the OE's. They are normally tuned to 'fail rich'. I too share the opinion that closed loop should be pulling fuel, on a leash of course. I'm curious what issues you have run into with this method? I think it's more about the instantaneous amount of torque you get from stoich versus quite a bit leaner like we are talking about. For a constant amount of air with pulsing: stoich...16.5...stoich.. type of situation you will get the surging. At least, I have on other cars. Having it tuned for 15.5 or so without closed loop already puts it closer to the mark so it isn't constantly returning to stoich with the closed loop cycle. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 31, 2007 Share Posted July 31, 2007 If you guys really want to run lean, put a big heavy flywheel on it! That dampens out the surging quite a bit. The only reason I say this is because I would run mileage marathons in the late 70's and early 80's and we would jet so lean it wasn't funny! One of the things we would do is clearance the bellhousing and bolt on almost a double inertia ring to smooth out the engine from 'lean surge'... At that time, if you have EGT, and a vacuum gauge, you were right up with the OEM's in terms of sophisticated instrumentation! LOL I mean, we had a daily driven Karmann Ghia running a 1641cc engine that would turn in 35+mpg in the city, 45+ on the freeway, and during the competitions we would break 50mpg! Obsession with maximum mileage is nothing new, we thought 68 cents per gallon going to $1.41 in a three month period was obnoxious as well. To remember that, and look at the prices today...well I can't get excited, it took a year plus to 'double'... But I digress. More on topic, I agree that the "Failure mode" of the OEM's is rich, as it's safe. The O2 on an OEM will rarely compensate more than 10% of total fuel. With the new MAF setups it's more biased on mass-flow through the engine than the older AFM style setups, so O2 can be set up for a wider correction to fuel---but it's almost always (matter of fact I don't know any OEM that is otherwise) Rich to Lean. The O2 sensor will correct to stoich and that is PURELY a function of proper catalyst function! There has to be enough unburned HC to keep the catalyst bed hot enough to scrub the exhaust stream. You can easily lean out the mixture far more (if you aren't running catalyst) and make plenty clean emissions if you incorporate good old fashioned A.I.R. in the exhaust manifold! I piped my 73 with SU's clean to 83 Catalyzed standards with Lean-Misfire adjusted carbs half a turn out, and utilizing AIR injection... From what most ECU Manufacturer's reps say for cruise portions of the map---if you are catalyzed tune for Stoich, and for anywhere else outside the EGO parameters tune for peak torque (peak HP) which is usually 11-13:1 AFR. For fuel mileage and best power, this seems to work VERY well. If you are not catalyzed, tuning to the point just on the verge of lean-surge would be counterproductive as the O2 will correct to stoich. Really for fuel mileage you would not want the O2 to correct to stoich---you would use one of the WBO2's and shoot for a targeted switching point (unless you have target af-maps...) and then simply program for target AFR's in the incipient lean-surge area during most cruise conditions, and peak torque outside that... say anything below 40% throttle opening, and MAP from 0 to 50Kpa, rpms bins between 1700 and 3600 (or wherever you are at highway cruise depending on tire height and gearing). My wife's Frontier gets 20mpg when she drives on the interstate, I get 16... She is running along at 75mph, and is totally in closed loop at 3000 to 3200 rpms. When I'm driving, I'm right on that switchover point where Nissan goes open-loop at 3500. Frustrating as hell because the truck pulls just fine, and even if it IS coming on to the cam at 3500, putting the O2 correction to 3700 would probably make my extra 5-10mph just as thrifty as my wife's feather foot! Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted August 3, 2007 Share Posted August 3, 2007 If you guys really want to run lean, put a big heavy flywheel on it! That dampens out the surging quite a bit. The only reason I say this is because I would run mileage marathons in the late 70's and early 80's and we would jet so lean it wasn't funny! One of the things we would do is clearance the bellhousing and bolt on almost a double inertia ring to smooth out the engine from 'lean surge'... At that time, if you have EGT, and a vacuum gauge, you were right up with the OEM's in terms of sophisticated instrumentation! LOL I mean, we had a daily driven Karmann Ghia running a 1641cc engine that would turn in 35+mpg in the city, 45+ on the freeway, and during the competitions we would break 50mpg! Obsession with maximum mileage is nothing new, we thought 68 cents per gallon going to $1.41 in a three month period was obnoxious as well. To remember that, and look at the prices today...well I can't get excited, it took a year plus to 'double'... But I digress. More on topic, I agree that the "Failure mode" of the OEM's is rich, as it's safe. The O2 on an OEM will rarely compensate more than 10% of total fuel. With the new MAF setups it's more biased on mass-flow through the engine than the older AFM style setups, so O2 can be set up for a wider correction to fuel---but it's almost always (matter of fact I don't know any OEM that is otherwise) Rich to Lean. The O2 sensor will correct to stoich and that is PURELY a function of proper catalyst function! There has to be enough unburned HC to keep the catalyst bed hot enough to scrub the exhaust stream. You can easily lean out the mixture far more (if you aren't running catalyst) and make plenty clean emissions if you incorporate good old fashioned A.I.R. in the exhaust manifold! I piped my 73 with SU's clean to 83 Catalyzed standards with Lean-Misfire adjusted carbs half a turn out, and utilizing AIR injection... From what most ECU Manufacturer's reps say for cruise portions of the map---if you are catalyzed tune for Stoich, and for anywhere else outside the EGO parameters tune for peak torque (peak HP) which is usually 11-13:1 AFR. For fuel mileage and best power, this seems to work VERY well. If you are not catalyzed, tuning to the point just on the verge of lean-surge would be counterproductive as the O2 will correct to stoich. Really for fuel mileage you would not want the O2 to correct to stoich---you would use one of the WBO2's and shoot for a targeted switching point (unless you have target af-maps...) and then simply program for target AFR's in the incipient lean-surge area during most cruise conditions, and peak torque outside that... say anything below 40% throttle opening, and MAP from 0 to 50Kpa, rpms bins between 1700 and 3600 (or wherever you are at highway cruise depending on tire height and gearing). My wife's Frontier gets 20mpg when she drives on the interstate, I get 16... She is running along at 75mph, and is totally in closed loop at 3000 to 3200 rpms. When I'm driving, I'm right on that switchover point where Nissan goes open-loop at 3500. Frustrating as hell because the truck pulls just fine, and even if it IS coming on to the cam at 3500, putting the O2 correction to 3700 would probably make my extra 5-10mph just as thrifty as my wife's feather foot! Some interesting stories and I totally agree with the technical comments. I had an 03 (IIRC) Mitsu EVO running an AEM standalone before they had one running and I got quite a bit more economy due to "lean burn" settings. As for the technical side, I was ONLY discussing what I'd recommend for best drivability and whatnot. So this is purely with a standalone, NO emissions concerns (and no cat for that matter), a wideband and A/F target maps. Failing rich is safe for OE cars, but I still think you would be constantly flopping back and forth through the significantly fluctuating "best torque" A/F ratios which is IMHO a significant factor causing the surging. By failing to 15.1:1 and then having your closed loop targets a bit leaner than that (16.5:1 for example) you avoid the areas where your torque bumps up significantly with every oscillation of the closed loop system. Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 3, 2007 Share Posted August 3, 2007 That may well be, but target AFR's a wideband to the ECU would be the way to do that I suppose. Or Innovate's simulated switched output with your target set to 15, and tuned to 16's... I know that you can really knock down emissions running at those parameters, though NOx goes through the roof due to temperatures in the combustion chamber. A little tweaking on the EGR through a GPO on the ECU, and you could tame combustion chamber temperatures and lean it out some bit further. Use the EGR coolers present on some diesels nowadays, and I suspect the EGR influence on lean-running would be even more positive. But since EGR is an 'emissions component' most people tend to simply remove it without giving much thought to what it actually does: Cool the combustion chamber. Ford was famous for really laying EGR to engines to keep detonation under control with super-lean mixes in early carburetted emissions control scenarios. For someone shooting for mileage, it actuall lets you lean out slightly more, and run similar advance... Now we are crossing from the merely strange into the downright wierd: EGR as a performance enhancing device on a fuel mileage motor! LOL Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 3, 2007 Author Share Posted August 3, 2007 I saved my EGR valve and pipe. Easy bolt on mods! Quote Link to comment Share on other sites More sharing options...
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