300exPat
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« on: May 29, 2013, 06:55:46 AM »
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Please don't simply state "to prevent turbo/valve damage". Why is it that so many other turbo cars do not have factory EGT sensors for tuning but the 2.7t does? I don't understand why most other cars use the air/fuel sensors to detect a lean condition, but the 2.7t needs egt sensors as well.
For comparison, my 2007 stg.2 GTI does not have nor need an EGT sensor for tuning.
Thanks for any info,
Pat
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prj
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« Reply #1 on: May 29, 2013, 07:15:57 AM »
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The EGT sensors are not used for "detecting lean conditions".
Furthermore the 2.7TT does not have a wideband O2, but that is irrelevant.
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silentbob
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« Reply #2 on: May 29, 2013, 07:39:52 AM »
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Main reason is cost.
The 2,7t has been the first turbo engine with a lambda 1 concept, which means that it wants to stay at lambda 1 even at full load until EGTs reach a certain limit all the exhaust parts can take, for fuel economy reasons.
Because of the rather massive sensor tip which causes a pretty big delay in measuring the real temperature in transient conditions, it turned out that you need some precontroled enrichment anyway to prevent temperature spikes above the set limit of 980°C.
So on later engines the sensors where dumped and (almost) every engine used wideband lambda sensors with modeled EGTs to accomplish the EGT limitation. A EGT sensor would have only been an additional fail save feature then which didn't justify the cost.
That's about it why.
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« Last Edit: May 29, 2013, 08:13:44 AM by silentbob »
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300exPat
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« Reply #3 on: May 29, 2013, 09:16:53 AM »
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Interesting, so more modern cars all use wideband sensors as a replacement? Did previous turbo cars such as the mitsubishi eclipse gst/gsx just run on the rich side to prevent excessive heat? I'm unfamiliar with the lambda 1 concept and a quick search on google didn't turn up much on it, but I'm assuming it attempts to achieve even closer to the ideal air/fuel ratio. Am I asking for trouble by tuning these sensors out? In my mind the air/fuel sensors should sense the lean condition (excessive heat) and add extra fuel to cool things down, but I'm afraid now that I am missing something.
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phila_dot
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« Reply #4 on: May 29, 2013, 09:34:03 AM »
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They run at lambda 1 basically at all times in stock configuration. IIRC The only real enrichment comes from ignition angle efficiency intervention. The enriched portions of KFDLBTS are at load ranges outside of stock operation.
Lambda sensors have no concept of exhaust gas temperature and only intervene for lean conditions on the opposite side of stoich.
Why tune them out?
They are a bonus IMO.
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ddillenger
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« Reply #5 on: May 29, 2013, 09:42:05 AM »
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Since we're into this, how does BTS work on non-EGT equipped cars? I assume it has to be calculated, but the o2's have to have some sort of involvement no?
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Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your experience!
Email/Google chat:
DDillenger84(at)gmail(dot)com
Email>PM
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AARDQ
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« Reply #6 on: May 29, 2013, 09:49:08 AM »
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Interesting, so more modern cars all use wideband sensors as a replacement? Did previous turbo cars such as the mitsubishi eclipse gst/gsx just run on the rich side to prevent excessive heat? I'm unfamiliar with the lambda 1 concept and a quick search on google didn't turn up much on it, but I'm assuming it attempts to achieve even closer to the ideal air/fuel ratio. Am I asking for trouble by tuning these sensors out? In my mind the air/fuel sensors should sense the lean condition (excessive heat) and add extra fuel to cool things down, but I'm afraid now that I am missing something.
With narrowband once you go open-loop at near WOT you've no watchdog with EGTs coded out. With wideband A/F is always accurately monitored so generally you are better protected even if no EGTs are installed. EGT, though, is the parameter of direct concern so (except for the delay noted by silentbob) almost by definition is the best way to ensure temps are not out of control. Audi's implementation is half-assed, though, because while it will attempt to dump in additional fuel to curb high EGTs, if that fuel isn't available (undersized injectors, weak fuel pump), there's no way for a narrowband set-up to know if the additional fuel is actually there and no programming to put the car into limp if EGTs continue to climb. |
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silentbob
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« Reply #7 on: May 29, 2013, 10:03:26 AM »
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.................Did previous turbo cars such as the mitsubishi eclipse gst/gsx just run on the rich side to prevent excessive heat? That's excatly what they did. I'm unfamiliar with the lambda 1 concept and a quick search on google didn't turn up much on it, but I'm assuming it attempts to achieve even closer to the ideal air/fuel ratio. Though running on the rich side on high loads is not that big of a deal in most regions of the world it can make a big difference in fuel consumption in Germany were you can go at high speeds for a longer periode of time without problems. That's why you want to stay at lambda 1 as long as you can (much better BSFC). For example the new GEN3 EA888 1,8l/2l TFSI engines use a cooled cylinder head integrated exhaust header to keep enrichment because of high temperatures to a minimum. |
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« Last Edit: May 29, 2013, 11:45:35 AM by silentbob »
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phila_dot
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« Reply #8 on: May 29, 2013, 10:06:15 AM »
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Since we're into this, how does BTS work on non-EGT equipped cars? I assume it has to be calculated, but the o2's have to have some sort of involvement no?
It's the same, except that fueling is closed loop. Target is lamsbg == lamsoni |
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silentbob
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« Reply #9 on: May 29, 2013, 10:23:41 AM »
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With narrowband once you go open-loop at near WOT you've no watchdog with EGTs coded out. With wideband A/F is always accurately monitored so generally you are better protected even if no EGTs are installed. EGT, though, is the parameter of direct concern so (except for the delay noted by silentbob) almost by definition is the best way to ensure temps are not out of control. Audi's implementation is half-assed, though, because while it will attempt to dump in additional fuel to curb high EGTs, if that fuel isn't available (undersized injectors, weak fuel pump), there's no way for a narrowband set-up to know if the additional fuel is actually there and no programming to put the car into limp if EGTs continue to climb.
BTS in early ME7 is shit. Later software can reduce load if EGTs are still too high. There are audi TFSI engines with binary sensors and no EGT sensors but because of bad experiences not any more  In the end it always comes down to what risks can be taken with minimal cost these days. The perfect technical solution is a thing of the past. |
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« Last Edit: May 29, 2013, 10:38:29 AM by silentbob »
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phila_dot
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« Reply #10 on: May 29, 2013, 10:30:18 AM »
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I always thought it was stupid that LDPBN only responds to sensor error
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silentbob
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« Reply #11 on: May 29, 2013, 10:53:28 AM »
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B_atrf also triggers LDPBN
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phila_dot
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« Reply #12 on: May 29, 2013, 11:09:37 AM »
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B_atrf also triggers LDPBN
Ahh...good catch. So, it does trigger limp if conditions are bad enough/don't improve. |
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AARDQ
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« Reply #13 on: May 29, 2013, 01:46:00 PM »
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Ahh...good catch.
So, it does trigger limp if conditions are bad enough/don't improve.
Interesting, going to have to try and figure out what 'bad enough is' Must be pretty darn bad seeing that I once hit 1,010*C. Sure made a believer in functioning EGT sensors out of me. |
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phila_dot
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« Reply #14 on: May 29, 2013, 01:49:34 PM »
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It's based on enrichment delta and time threshold.
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