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homey
Joined: 31 Jan 2009
Posts: 31
Location: Lynchburg VA
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 Posted: Thu Feb 17, 2011 10:50 pm Post subject: Ditch the Lambda system |
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From another thread, slam said
| Slam wrote: | Mmmm... Fresh metal...
A word about 1980 CIS - ditch the Lambda system. I found quite a bit of power lurking in Chrenan's old car when I started tweaking the mixture. |
Anyone else want to weigh in on this ? If so, how would you "ditch" the Lambda ? Disconnect stuff or replace stuff ?
Thanks |
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Grenadiers
Joined: 20 Feb 2007
Posts: 3222
Location: Nelson, WI & Prescott, AZ
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| Posted: Fri Feb 18, 2011 12:49 am Post subject: |
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Yes, curiously, my Euro 931 I found in Arizona last year has no lambda system. Was wondering how engine manages mixture throughout the power band and at idle. The PO owner grenaded the engine at some point, hence my concern, and the 'new' engine I rebuilt is actually a US version.
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Fri Feb 18, 2011 12:55 am Post subject: |
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Just unplug the 02 sensor. Then the frequency valve defaults to 50:50 operating mode, and your A:F screw setting determines the mix with no automatic tweeking from the lambda system.
Full load enrichment for the 931 is handled by the WUR.
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11733
Location: PacNW
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| Posted: Fri Feb 18, 2011 1:47 am Post subject: |
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The frequency valve is capable of only extremely small variations in control pressure. If you have emissions in your state, you are far better off with a properly functioning system. Aside from the $30 to replace O2 sensors every couple years, there is no downside, IMO.
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- WeiBe (1987 924S 2.5t) - 931 S3
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Fri Feb 18, 2011 2:27 am Post subject: |
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Just to circumvent/avoid confusions, the FV affects A:F by bleeding off fuel from the lower chambers of the FD, having no affect on control pressure. -
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"..it's made in Germany. You know the Germans always make good stuff."
'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox |
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Rocco R16V
Joined: 03 May 2009
Posts: 497
Location: PNW
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| Posted: Sat Feb 19, 2011 5:44 am Post subject: |
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| Smoothie wrote: | | Just to circumvent/avoid confusions, the FV affects A:F by bleeding off fuel from the lower chambers of the FD, having no affect on control pressure. - |
just for clarification, the fuel pressure to the injectors is deterimed by the difference between the primary pressure and control pressure. so while the lamba system doesnt change control pressure it does affect delivered pressure and that is what (i think) rasta meant.
i do not see any advantage to running a lambda system unless you have to do emmisions.
the less parts to fail the better IMO
Also the contol box and Frequency valve, can be removed and the lines to the the FV plugged, but this will require retuning before it will run correctly. the primary pressure will be higher and the control pressure will need to be raised an equal amount.
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homey
Joined: 31 Jan 2009
Posts: 31
Location: Lynchburg VA
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| Posted: Sat Feb 19, 2011 2:07 pm Post subject: |
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| Quote: |
Also the contol box and Frequency valve, can be removed and the lines to the the FV plugged, but this will require retuning before it will run correctly. the primary pressure will be higher and the control pressure will need to be raised an equal amount. |
Thanks for all the responses. So, does "slams" original premise that a few more horses be gained be getting rid of the lambda true or false ? If true , probably only a very small gain, would be my guess. And to rocco's input. How would you raise the pressures ?
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Rocco R16V
Joined: 03 May 2009
Posts: 497
Location: PNW
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| Posted: Sat Feb 19, 2011 5:05 pm Post subject: |
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HP gained by ditching the lamda system would be miniscule on a properly tuned system.
To retune, Hmmm, its been so long i cant remember the exact details, sorry  but (I think) its done by adjusting the number of shims in the fuel pressure regulator.
someone on here should know the details and post.
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Sun Feb 20, 2011 5:18 am Post subject: |
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| Rocco R16V wrote: | | just for clarification, the fuel pressure to the injectors is deterimed by the difference between the primary pressure and control pressure. |
Ok class, I'm sensing still more confusions out there... 
Fuel flow to the FD's upper chambers is regulated by the up-down position of the fuel metering rod, and pressure to
the injectors is regulated by a difference in pressures between the upper and lower chambers of the fuel distributor.
(-And the control pressure area isn't one of those chambers.) When pressure in the lower chambers is less than in the
upper chambers, the diaphragm between them drops, which opens the passages to the injectors, increasing
injector fuel flow/pressure.
Control pressure exerts backpressure on the top of the fuel metering rod which counteracts intake air pressure that's
pressing on the air metering plate.
-So, the difference between intake air pressure and control pressure determines the position of the
fuel metering rod. That in turn regulates fuel flow into the upper chambers (fuel flow to the lower chambers is primary
pressure, but delivered via a small "fixed orifice"), and as was said, flow/pressure to the injectors is determined
by the pressure difference between upper and lower chambers.
-And of course the WUR alters control pressure, and therefor the fuel metering rods' position, to provide a richer
a:f mix during warm-up. -And the 931's WUR also provides full-load enrichment by dropping control pressure based on
intake vacuum/pressure levels.
Bleeding-off of pressure from the lower chambers via the frequency valve was added in Rube Goldberg-like fashion as
a way to reasonably-quickly affect injector fuel flow for closed-loop lambda system operation. As more fuel is bled off,
the diahragms drop, increasing fuel to injectors.
If the FV were eliminated and its' lines plugged, primary (aka- "system") pressure would not be affected - only
the lower chamber pressure and the pressure differential between upper-lower chambers would be.. I'd be willing to guess
that an adjustment to the mixture screw would be all that's needed to compensate.
-Still way easier to simply unplug the o2 sensor (assuming the FV, controller, and relay are good).
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'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox |
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11733
Location: PacNW
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| Posted: Sun Feb 20, 2011 5:31 am Post subject: |
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| homey wrote: | | So, does "slams" original premise that a few more horses be gained be getting rid of the lambda true or false ? |
Buddy, he's Canadian, eh?
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- WeiBe (1987 924S 2.5t) - 931 S3
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Rocco R16V
Joined: 03 May 2009
Posts: 497
Location: PNW
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| Posted: Sun Feb 20, 2011 12:53 pm Post subject: |
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 thanks smoothie, I knew someone would have a better explaination than mine.
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FJ40Jim
Joined: 13 Feb 2011
Posts: 26
Location: Central Ohio, USA
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| Posted: Mon Feb 21, 2011 4:09 am Post subject: |
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Lambda is ditched at WOT anyway. That's the job of the full throttle switch. Lambda fine tunes mixture at part throttle cruise. At WOT, the system goes open loop and should enrich to ~12:1.
On some CIS vehicles, the system isn't calibrated perfectly, and it doesn't hit the full power enrichment target. In those instances, there are ways to tweak the mix for better WOT performance. Fiddling with the WUR or tricking temp sensor input are the common methods. |
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