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Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Shaggy is getting a digital control pressure regulator. I am wondering if I should eliminate the "lambda loop" (narrow band O2, TPS, digitally controlled frequency valve, lambda computer).

It seems like its main purposes (fine idle adjustment & WOT enrichment) won't be needed with the UTCIS. Since I am having new lines built, I am in a position to cleanly delete the frequency valve. I especially don't want a "battle of pressures" between the UT controller and lambda controller at idle.

Thoughts?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Cedric · Joined: 27 Aug 2004 Posts: 2810 Location: Sweden

The tps is needed for the ignition. Is it incorporated on in the fuel system on the us cars? If I were in your seat i would remove the lamda system and run open loop. It must be a pain to tune in the utcis while the lambda always tries to "correct" the AFR. I assume you dont have a cat anymore.
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1980 924 Turbo
www.instagram.com/garagecedric/

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

I don't believe TPS does anything for SI ignition. Got one interesting response at Pelican in the 930 section:

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

stevekat · Joined: 19 Jan 2008 Posts: 719 Location: Los Angeles, CA

My Lambda system and UTCIS seem to work well together.

Also, I have posted in the board before, my narrowband AF gauge goes rich at 3300 rpm or so, regardless of gear, load or boost, so the Lambda system may be regulating things beyond idle and WOT. I think someone has noted a tach input into the Lambda when I posted on this issue, though nothing certain has emerged as to this feature having been originally engineered into the OEM system.
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"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

Cedric · Joined: 27 Aug 2004 Posts: 2810 Location: Sweden

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Steve, sounds like your UTCIS is mapped to enrich too soon (much like factory WUR operating from boost signal only). Keep it flat 'til 4000 RPM and see what you get.

Also, SII TPS has an output signal (part throttle) that SI does not, it is likely Lambda is trying to regulate cruise emissions as well.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

stevekat · Joined: 19 Jan 2008 Posts: 719 Location: Los Angeles, CA

The enrichment does not seem to be boost dependent, so don't think it is coming from the UTCIS. Also does not seem to be throttle position dependent, as the rich condition seems to occur at a specific rpm, rather than boost pressure, or throttle position, at least from the basic driving tests I've done. If I put my foot down early in the rpm range, or run boost up earlier, this rich condition does not occur eariler. Seems to occur very reliably at about 3300 rpm +/-. Keep in mind I have a narrow band gauge so the degree of richness is hard to determine, but it does go of the scale at 3300 rpm and otherwise remains somewhere between the stops at most other times, except under extreme inputs. I am using the factory map, set up for their test 931.
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"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

FWIW, on the 941, since I've installed the PLX wideband, I've been slowly tweaking my mixture. I have it idling now at 14.0...14.8. At 75% WOT and above, it goes full rich, and I mean pegged full rich, regardless of RPM. Under light load, maybe 50% WOT it runs about 11.0 or so. I am amazed at how fat the mixture was before, and yet the car still ran. Everything I've read is that the adjustment is extremely finnicky, but not so on this particular car. I've backed out the mixture by at least a quarter turn (incrementally over several sessions) since installing the wide band. I don't know how useful the narrow band is in this situation...

...oh yeah, and I don't have the narrowband O2 plugged in, so I'm running open loop ATM.
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erstwhile owner of just about every 924 variant ever made

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Steve, you can also set control pressure on that unit by RPM, can't you?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

stevekat · Joined: 19 Jan 2008 Posts: 719 Location: Los Angeles, CA

Yes, control pressure can be set based on rpm and manifold pressure. Keep in mind less than 1 bar, is less than atmosphere in their setting I believe. So 1 bar is sea level and less is vacuum (but double check on this.) In the map I use, changes begin around around 3000 rpm +/- and stop changing about 3500 (using their 924 turbo map) however control pressure actually goes up very slightly, so that leans mixture a bit I believe. Control pressure goes down and mixture gets richer as boost gets reasonably past 1 bar. I haven't fiddled with this much as I have a narrow band gauge, and the results so far have been really good in drivability and performance from what I had before.
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"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.