Jim Warman Posted July 14, 2009 Share Posted July 14, 2009 Many values are computed... And they can base many of these on load, mass fuel desired and many other values that give know results. Of course, these are based on a "properly operating system".... but then any management system is bound bay that overwhelming principle. I'm not too sure of any speed density calculations (other than a small run of trucks that didn't get a MAF) but on a MAF equipped truck, devoting CPU time to speed/density calculations seems like an abject waste of time... (something that engineers are adverse to at times). In the hundred and some odd years since the creation of the Otto-cycle, infernal (sic) combustion engine (hmmm, is the modern diesel a true Otto-cycle? or will we find out it is a veriation of an Atkinson cycle or whatever?). anyway, you can pretty well bet that the boffins have analyzed (did you notice you can't spell analyzed without getting "anal"?) a lot of the cause and effect and predictability stuff.... With the constants..... cylinder dimensions - the somewhat variables... ambient temp, atmospheric pressure, engine rpm, MGP... I don't think this shit should be much of a surprise. They can write an algorithm that pretty much predicts what is going to happen (where the fuck is Cetane when you need him?) when this much of fuel in <that> cetane range is dumped in a cylinder with the other much air........ But we are starting to lose sight of the things <WE> should be worrying about? Yeah, it would be damned fine to understand EXACTLY where IAT2 falls into our world.... but it ain't a big requirement. Our job isn't to fuck around with IAT2... our job is to keep it clean - though we do need to learn "warning signs". Does the EGR test on the IDS give a rats rosy red if IAT2 is good or bad? How about if we unplug IAT2 and perform the EGR test? - consider this high on my list of goofy shit to try now I thought of it. Yes... IAT2 isn't the best measure of CAC efficiency in the world.... but suggest what other means the PCM has of determing this?????? Quote Link to comment Share on other sites More sharing options...
rlchv70 Posted July 14, 2009 Share Posted July 14, 2009 In the hundred and some odd years since the creation of the Otto-cycle, infernal (sic) combustion engine (hmmm, is the modern diesel a true Otto-cycle? or will we find out it is a veriation of an Atkinson cycle or whatever?). a Diesel cycle: http://en.wikipedia.org/wiki/Diesel_cycle Quote Link to comment Share on other sites More sharing options...
Damon Posted July 16, 2009 Share Posted July 16, 2009 Quote: Name some variables that can't be cross-checked and validated by the other sensors. Well, if your only asking about IAT2 variables- No you missed the question. Keith said: Originally Posted By: Keith Browning It still seems to me that there are too many variables that can affect manifold temperatures at the point of the IAT2/MAT... therefore using IAT2/MAT would not be a good choice as direct feedback for EGR valve operation. I asked for these variables that can't be "seen" by the other existing sensors. Quote Link to comment Share on other sites More sharing options...
Damon Posted July 16, 2009 Share Posted July 16, 2009 I actually had an experience with a non responsive iat2 sensor causing a severe over active egr valve last week. Smoked (black) on tip in consistantly when warmed up, egr cmnd shot to 100% an every tip in. Pissed around for a few hours, and noticed if i took command of egr @ 0%, concern was gone. Also found that @ 100% egr command, egr vp @4.5v, driving under load, iat2 was only 10`c warmer than iat 1. Cleaned iat 2 sensor and concern was 100% fixed. This was on a 2006 with 85000 kms. Kinda what I was expecting. Thanks! Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted July 16, 2009 Share Posted July 16, 2009 Just so I can poke at rich... wiki isn't real clear if this is a 4 stroke cycle or a two stroke cycle (a la old Detroit Diesel). Check Wiki for "Otto cycle" and it will mention a four stroke cycle suck/squeeze/bang/blow engine with either compression or spark ignition. FWIW, there are a lot of variations on the theme(s) (the Atkinson cycle is 'common' in some hybrids... its only difference from an Ottocycle engine is valve timing - since this motor is assisted by electric traction motors, it doesn't need to build much torque outside of a very narrow band. I'm still looking for an old link I used to have that described (among things like the Pogue carburettor) some unique engine designs - including a horizontally opposed twin cylinder that used a scotch yoke rather than a crank/ rod arrangement. I guess this thread has been shanghai'd Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted July 16, 2009 Share Posted July 16, 2009 Originally Posted By: Keith Browning It still seems to me that there are too many variables that can affect manifold temperatures at the point of the IAT2/MAT... therefore using IAT2/MAT would not be a good choice as direct feedback for EGR valve operation. I asked for these variables that can't be "seen" by the other existing sensors. My statement on variables includes EGR cooler flow issues, EGR valve position like slow response and sticking open, clogged IAT-2 sensor, cooling system concerns, sticking turbocharger vanes and charge air cooler concerns. OF COURSE there ARE ways of "cross checking" what the IAT-2 sensor is seeing however I think doing so would place an unnecessary load on the processor. There is a lot of stuff there I mentioned that can and does commonly go wrong. How many ways to you think the PCM is going to cross check this sensor when it uses the EGRP sensor to control the EGR valve? This is described as a closed loop function which tells us this is the direct feedback for EGR valve operation. In reading the OBD theory and operation information the only time I see IAT2, or MAT, mentioned is EGR system and comprehensive component monitors in checking efficiency of the cooler. This has NOTHING to do with closed loop operation. More reading discovered that fault detection only occurs during the following conditions as quoted from the PCED: Quote: Fault Detection The low idle engine speed is between 600 and 750 RPM . The exhaust gas recirculation ( EGR ) valve position is greater than 0.08 volt. The mass fuel desired ( MFDES ) is between 4 and 16 mg/stk, at low idle for a minimum of 30 seconds. No exhaust pressure (EP), barometric pressure ( BAP ), manifold absolute pressure ( MAP ), pressure signal, intake air temperature ( IAT ), IAT2 temperature signal, vistronic drive fan ( VDF ) fan P0480, or EGR related faults. Fault condition: IAT2 exceeds a calibrated temperature for more than 30 seconds, based on IAT temperature. DTC Description P2457 = Exhaust Gas Recirculation ( EGR) Cooler System Performance Quote Link to comment Share on other sites More sharing options...
Damon Posted July 17, 2009 Share Posted July 17, 2009 Originally Posted By: Damon Originally Posted By: Keith Browning It still seems to me that there are too many variables that can affect manifold temperatures at the point of the IAT2/MAT... therefore using IAT2/MAT would not be a good choice as direct feedback for EGR valve operation. I asked for these variables that can't be "seen" by the other existing sensors. My statement on variables includes EGR cooler flow issues, I think you're missing the point here, since you're referring to IAT2 fault detection. What we're referring to is the intended job of IAT2 in EGR control and whether IAT2 can play a part in detecting EGR flow. A perfect job for IAT2 would be detecting EGR cooler flow issues or lack thereof......when it's signal's validated by the other sensor signals. Originally Posted By: Keith Browning EGR valve position like slow response and sticking open, Slow valve response would be another good function of IAT2 when used with EGRP vs desired. Sticking open is another.....These are all variables in MAT that can be effectively "verified" by IAT2 and the other sensors. Originally Posted By: Keith Browning clogged IAT-2 sensor, Got me there. A clogged IAT2 can't be detected and validated so well by the other sensors. That's the very heart of this thread, IMHO....What happens then? Originally Posted By: Keith Browning cooling system concerns, sticking turbocharger vanes and charge air cooler concerns. OF COURSE there ARE ways of "cross checking" what the IAT-2 sensor is seeing however I think doing so would place an unnecessary load on the processor. If the role of the processor is to analyse inputs, why is this an unnecessary load? It's all part of the job. It's actually "harder" to ignore. Originally Posted By: Keith Browning How many ways to you think the PCM is going to cross check this sensor when it uses the EGRP sensor to control the EGR valve? Maybe you misunderstood me. I'm saying the PCM is using IAT2 to cross check the EGRP, not the other way around. To command EGR and see EGRP is fine, well and good, but if the desire is to determine flow, EGRP isn't enough. It needs to see EGRP and IAT2 rise (as well as the other sensors to validate the speed density calculations to comoute EGR flow)to determine if the flow is as was intended. Originally Posted By: Keith Browning This is described as a closed loop function which tells us this is the direct feedback for EGR valve operation. Valve operation, yes. SYSTEM operation, no. The sensor can only report th eposition of the valve. It's described also as a delta pressure feedback system elsewhere. You can't do this without IAT2, plain and simple. Originally Posted By: Keith Browning In reading the OBD theory and operation information the only time I see IAT2, or MAT, mentioned is EGR system and comprehensive component monitors in checking efficiency of the cooler. This has NOTHING to do with closed loop operation. More reading discovered that fault detection only occurs during the following conditions as quoted from the PCED: Quote: Fault Detection The low idle engine speed is between 600 and 750 RPM . The exhaust gas recirculation ( EGR ) valve position is greater than 0.08 volt. The mass fuel desired ( MFDES ) is between 4 and 16 mg/stk, at low idle for a minimum of 30 seconds. No exhaust pressure (EP), barometric pressure ( BAP ), manifold absolute pressure ( MAP ), pressure signal, intake air temperature ( IAT ), IAT2 temperature signal, vistronic drive fan ( VDF ) fan P0480, or EGR related faults. Fault condition: IAT2 exceeds a calibrated temperature for more than 30 seconds, based on IAT temperature. DTC Description P2457 = Exhaust Gas Recirculation ( EGR) Cooler System Performance Nothing I said disagrees with that quote. What could we expect if the sensor were fouled? IAT2 would NOT rise above the threshold, and NOT fail the monitor. So then, under those conditions with a clogged IAT2 incapable of quickly seeing a temp rise, could EGR flow be excessive and not log any faults? Yes, it can. Quote Link to comment Share on other sites More sharing options...
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