Date: 27 Dec 1998 23:20:20 GMT From: "A4 quattro" <richquinlannopsamamatt.net> Subject: Why do you want to go 12.1??
I understand the 'safety factor', but 14.1 is plenty safe on a o2 equipped car, since it will (within the limits of the fuel system) maintain that ratio.... I think perhaps you are thinking back to the old days of turbo, where it could go lean, and you wanted a 'cushion' just in case... If you get your a/f down to 12.1, you will lose GET and HP due to being so rich... We have discovered this in tuning my 1.8L 5 valve turbo motor on my Audi. I'd say best bet is to get an EGT gauge (expensive I know), and watch it...if it stays below about 925-950, you're fine..... if not, THEN I'd worry about making the a/f more rich. -- Rich Quinlan '97 A4 1.8tqms in Pearl, More mods than I can shake a wastegate rod at... **** To reply, remove the 'nospam' after the **** "If it ain't broke, make it faster!!" http://home.att.net/~richquinlan <--- Quinland--my own little world.. Firestarter <NOSPAMnopsamAM.com> wrote in message news:368a7bbb.270432769nopsam.preferred.com... >This is a continuation from my earlier post entitlted "Turbocharged >engine pings under boost". > >I have a theory. I first thought that the O2 sensor would benefit my >turbo system, but now I am thinking it may actually be causing my fuel >enrichment problem. > >Here's the reason. > >The oxygen sensor's job is to keep the mixture within an acceptable >range (for emmision purposes). I came to the conclusion that the O2 >sensor's goal is to make up any deviation caused by wearing >components, changes in altitude, temperature, etc. > >The system has a set of known variables it goes by but relies on the >reading from the O2 sensor to keep these in range in case something >changes. > >That's the problem with carburators. You set them to run at a given >temperature, humidity and altitute but when you stray away from those >conditions, the mixture changes. > >On my X 1/9 which has almost 200,000 miles on it, a new oxygen sensor >made a world of difference because the engine was running way too >rich. I even got an extra 10 miles per gallon! > >But on the Spider which has a new air flow meter and half as many >miles on the componetns, a new oxygen sensor made no difference. > >Some earlier L-jetronic systems like the ones used on Datsun Z cars up >until 1979 did not use an O2 sensor but the system was otherwise the >same. Actually this system was a clone built by Nippon Denson under >licence from Bosch. > >When I hit boost, I want to mixture to be at around 12.1. As of now, >the richest it get's is 14.1. Just like it before I installed the >turbo under WOT. > >I keep cranking up the fuel regualtor but it does not have any effect >on the mixture under boost. > >It did not occur to me until now, but the oxygen sensor is doing what >it is supposed to do. My original theory was that when the turbo >started forcing air into the engine, the O2 sensor would pick up the >lean mixture and add more fuel which would keep the mixture from >leaning out. It seems to be doing this, however it also seems to be >limiting the fuel mixture to 14.1 under boost. > >Under wide open throttle, the contacts close in the throttle position >switch and bypass' the control loop. This is one of the tricks used by >Legend industries. At 1 pound, a pressure switch closed the WOT >contacts which bypassed the closed loop allowing the other two >switches to trick the coolant temperature switch into thinking the >engine was running colder which enrichened the fuel mixture. > >Without tricking the TPS, the lambda system would override the first >two switches and try to keep the mixture from getting any richer than >14.1 . > >That's why I suspect my fuel pressure regulator is not doing it's job. > >I think it's as simple as disconnecting the oxygen sensor from the >computer. > >In one of my experiments, I found that by doing this caused the engine >to run lean and not cycle. Some say by doing this causes the engine to >run rich. But if you look in the shop manual, it says to disconnect >the O2 sensor and set the mixture by turning the screw in the air flow >meter. > >Or I can rig up the same sort of switch to close the WOT throttle >contacts under boost like LI did, but I see no reason to because by >unplugging the O2 sensor will do the same. > >Or install the pressure switch to break the circuit between the >computer and O2 sensor under boost. > >So here is what I need to do, unplug the O2 sensor, set the mixture to >14.1, leave the sensor unplugged and see what the mixture is under >boost. > >As boost increases, the fuel pressure should also rise and get richer. >Then I can adjust the fuel pressure regulator to what I want the >mixture to be. > >The control loops seems to be defeating the purpose of the rising rate >fuel pressure regulator. > >However there is always the fact that the mixture may actaully go the >other way under boost. I will just have to wait and see. > > >Due to the overwhelming amount of SPAM I receive, send replies >via email to mailto:firestarternopsamcron.com > >------------------------------------------------------------ > >1980 Fiat 2000 TURBO Spider (Fuel injected) Summertime daily driver >1981 Fiat 2000 Spider (Dual 40 webbers) Growl! >1981 Fiat X 1/9 (Fuel injected) Slot car like handling >1994 Jeep Wrangler (2.5 liter) Wintertime daily driver > > >Get your own Forwarding address : http://www.netforward.com/ > >------------------------------------------------------------
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