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Adjusting CO in fuel head

Hi Guys-
My car is a 964 Turbo. Trying to get baseline CO adjustment dialed in before I do any adjustments on my BL adjustable WUR (which I don't think will require much - maybe just WOT boost - we'll see) but anyway I've been trying to get warm/hot idle at ~13.5 on my AFR meter. So I will get it there and it will be consistent for a couple days - then suddenly it will be 14.5 for a few drives. Then yesterday after things seeming to be pretty dialed in for a few days I get in the car to go home (after driving the car a few times during the day) and is idles really low at startup, AFR is 15-16+ - it gradually came down as the engine came up fully to operating temp but never back to 13.5 (more like to about 14.5 maybe 15. And exhaust popping on decel _seems_ to have increased, but that could just be me. Air pump has been disconnected for a week or so while attempting to get things dialed in.

Any thoughts appreciated-thanks

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Brandon
'91 911 Turbo
'00 Audi S4 highly mod'd DD
Denver, CO
Old 03-30-2013, 08:47 AM
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Hey, Brandon, just sent you a PM.
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Old 03-30-2013, 09:38 AM
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Just a quick update - This morning car started up perfectly normal warm idle at ~825 rpm AFR back to 13.5 while I putzed around town for the first 15 minutes - did an ~100 mile drive up the mountains - man it was nice! Got to my lunch spot after being on the road about 75 minutes, elevation likely 7000 ish - and the car was idling with AFRs at about 12.9. Came back and park her in the garage back to 14.1 idle speed ~850. Is this normal to have these fluctuations? Magical mysteries of CIS?

I think I need to lean out my cruise a little - been pretty consistent at about 13.5. Boost is 10.0 - need to address that.

One last thing - when, say in 3rd gear, accelerating from low rpm, pedal down all the way and when you get up in the revs to say 4000 or 5000 and you let off, even smoothely, but a little quickly, the engine bucks - is this a sign of richness? or? Note - the 964 Turbo uses a different BPV setup than the 930 and I have a brand new 710N BPV, FWIW.

Any thoughts appreciated - TIA!
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Denver, CO

Last edited by turbo ride; 03-30-2013 at 01:14 PM..
Old 03-30-2013, 12:41 PM
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No way of knowing if the lambda system and other emissions hardware is still on the car.
From my experience with my own car CIS is no longer consistant all the time once the lambda system is removed.

If it finally settles out to the AFR's you want to see after 30 minutes of driveing and it runs good the whole time all I can say is stop being obsessed with the stupid AFR gauge and just drive it and enjoy it.
Or remove the gauge completely and forget about it so it doesn't bother you.
Old 03-30-2013, 01:06 PM
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I can totally live with that, Jim. Just wanted to make sure this wasn't a symptom of something amiss.

Just to provide a bit more info - I've also disconnected the 02 while I set everything up. I think I read you are suppsoed to do that.

Once everything is dialed in I do plan to remove the gauge to keep the cockpit clean.....

Thanks much-
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Old 03-30-2013, 01:13 PM
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Re-install the O2 sensor and check your readings. The Lambda system cannot be simply unplugged as the frequency valve will have no reference point. Your idle AFR should be rock steady if everything is working properly and you have no vac leaks. Even tiny leaks can cause the idle AFR to fluctuate.
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Old 03-30-2013, 01:44 PM
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Quote:
Originally Posted by RarlyL8 View Post
Re-install the O2 sensor and check your readings. The Lambda system cannot be simply unplugged as the frequency valve will have no reference point.
Brian, I must be missing something but I don't understand your comment. Like many, I run without the O2 sensor plugged in. Thus, with the lambda system in open-loop, the frequency valve simple defaults to a fixed duty cycle (50%?) since the computer is no longer getting a signal from the sensor, so the fixed duty cycle becomes a constant against which to tune around. My AFR's are really fairly predictable and consistent, plus or minus a few tenths depending on ambient and engine temperature.
Could you expand a bit on what you're referring to?
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Old 03-30-2013, 07:44 PM
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I'm a little unclear myself - I do plan to run the system with the O2 sensor - so should I be setting the CO (or warm idle ~13.5 AFR) with the O2 sensor plugged in or Unplugged? Warm idle AFR goes from ~13.5 unplugged to ~14.5 when I plug it in...

Thanks much-
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Old 04-03-2013, 10:21 AM
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Mark, Brian and Jim are much smarter regarding the K-Jetronic system than I am, so I think they would have better advice, but I am currently using the O2 sensor system so set my idle AFR with it plugged in. If I set it with the O2 sensor unplugged, and then plug it in, it goes too lean and starts to miss/stumble . . .
Old 04-03-2013, 11:46 AM
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CIS became more complex through the 19 years it was used on the turbo. The 965 has layers of switches, sensors, EZ69 timing control, etc. that all must be considered when any tuning changes are made. If any subsystem is eleminated or bypassed (such as Lambda on the late 930s) they must be compesated for. If you find a situation where the idle or AFRs become unstable I would hook everything back up and see where the baseline is. You can really get things out of wack in a hurry once the baseline is lost.
If your Lambda system is bypassed you cannot overlook the still needed function of the frequency valve. It will function in open loop but you must compensate for the lack of signal during events that normally are run in closed loop. Idle mixture should be adjusted with the sensor in place if Lambda is to be left intact as that is the baseline under those conditions.
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Old 04-03-2013, 06:45 PM
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That makes sense Brian. So I was out messing around - doing my little test loop in the car a few minutes ago - I reconnected the O2 sensor and warm idle AFR went from 13.5 to basically 14.7 - stoic. So to experiment I richened it up at the fuel head to try and bring it back to 13.5 warm idle AFR as I've seen mentioned here many times - however idle AFR stayed at stoic - no change. I guess that is what the O2 sensor is trying to do, eh :-) For grins I disconnected the O2 again (after richening it up) and idle AFR was 12.2. So I had made a noticeable adjustment. So I guess my question is since I will retain the full lambda system on the car - what do (or how do I) tune the warm idle if the O2 will keep it at stoic anyway? I should have watched cruise AFR but I didn't pay attention.

For the record I adjusted the fuel head back so that warm idle with O2 DISconnected was 13.7 then REconnected the O2 sensor. If the O2 will bring it to stoic regardless should I just adjust warm idle to ~stoic with O2 disconnected then?

Thanks for the continued help guys-

P.S. - so whats going to happen when I reconnect the air pump?? Isn't air pumped in before the O2 sensor? I know it affected the readings on the AFR gauge quite a bit - about 4.0 at idle!
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Last edited by turbo ride; 04-03-2013 at 08:12 PM..
Old 04-03-2013, 08:09 PM
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unplug o2 - disconnect air injection
set afr to 13.5 at idle ...this will increase mixture (AFR)all the way up RPM -EXCEPT when o2 is
connected ...
o2 (frequency valve) will always pull back afr to 14.7 when not under boost

when afr is set to 13.5 @ idle plug o2 back in and check AFR in 3rd -4th and 5th gear under boost at higher RPM
when setting your afr to 13.5 engine needs to be @ operating temp and blip the throttle
several time during the process till it is stable.

if you reconnect air pump afrś will be off again (leave disconnected so you can monitor)

I have a1991 C2 turbo I set my afr like this , leave o2 plugged in and air pump disconnected.
Old 04-04-2013, 06:23 AM
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EDIT

set afr to 13.5 at idle ...this will increase mixture (AFR)all the way up RPM¨

I meant to say

set afr to 13.5 at idle ...this will increase mixture (gas /air ratio ) all the way up RPM

english is my second language
Old 04-04-2013, 06:39 AM
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excellent stuff - thanks again.

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'91 911 Turbo
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Denver, CO
Old 04-04-2013, 03:15 PM
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