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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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 Posted: Sat Sep 16, 2017 7:30 am Post subject: 931 Air/Fuel ratio at high RPM? |
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I recently connected the O2 sensor on my 80 931S (I've been running on the safe mode so far) and I have a question about A/F ratio at cruising high RPM (off boost).
Since I connected the O2, I notice that I get A/F ratio enrichment above 3500 RPM off boost.
My idle A/F is set at 14.5
Cruising below 3500 RPM is also around 14.5-14.7
Cruising above 3500 RPM is between 11.2-12
Enrichment under boost is low 10
Is this A/F ratio enrichment above 3500 RPM off boost a normal behavior?
Anybody else notice something similar?
Thanks
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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Kg1961
Joined: 09 Aug 2017
Posts: 39
Location: Calgary
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| Posted: Sat Sep 16, 2017 8:57 am Post subject: |
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Lmk I would love to know just got mine to start and run
Just need to do the fan and we are good
I'm not running my 02
1980 931 |
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morghen
Joined: 21 Jan 2005
Posts: 9095
Location: Romania
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| Posted: Sat Sep 16, 2017 10:10 am Post subject: |
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You know what? I'm going to check 
But srsly 3500 is not high rpm cruising 
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Supercharger and EFI kits
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Sat Sep 16, 2017 12:15 pm Post subject: |
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| morghen wrote: | | You know what? I'm going to check |
Thanks
| morghen wrote: | | But srsly 3500 is not high rpm cruising |
Fair enough, let's call it mid-rang RPM 
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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Carrera RSR
Joined: 08 Jan 2010
Posts: 2312
Location: Somerset, UK
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| Posted: Sat Sep 16, 2017 6:54 pm Post subject: Re: 931 Air/Fuel ratio at high RPM? |
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| 924-76 wrote: | I recently connected the O2 sensor on my 80 931S (I've been running on the safe mode so far) and I have a question about A/F ratio at cruising high RPM (off boost).
Since I connected the O2, I notice that I get A/F ratio enrichment above 3500 RPM off boost.
My idle A/F is set at 14.5
Cruising below 3500 RPM is also around 14.5-14.7
Cruising above 3500 RPM is between 11.2-12
Enrichment under boost is low 10
Is this A/F ratio enrichment above 3500 RPM off boost a normal behavior?
Anybody else notice something similar?
Thanks |
Nothing wrong with those numbers on a stock 931. All controlled by the WUR with limited adjustment. If you try to lean of at one end of the rpm/boost curve you will lean off the other end too, the same when trying to enrich. The other issue is that the WUR is boost controlled and will enrich the AFR early on in the rpms dumping more fuel too soon until it is over rich in the 10’s. This it to help protect a non IC motor from detonation and shouldn’t be messed with too much if at all. On modified turbos with IC’s and higher boost, then this is a different story.
By the way, over 3000 rpm you will likely starting to generating some boost, even on a static throttle maintaining a cruise speed on level road. Certainly from 3500 you will be on low boost and therefore the WUR will be enrichening the AFR.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Sat Sep 16, 2017 7:30 pm Post subject: Re: 931 Air/Fuel ratio at high RPM? |
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| Carrera RSR wrote: | | On modified turbos with IC’s and higher boost, then this is a different story. |
Could you elaborate on this? Because this is my case, FMIC and higher boost.
| Carrera RSR wrote: | | By the way, over 3000 rpm you will likely starting to generating some boost, even on a static throttle maintaining a cruise speed on level road. Certainly from 3500 you will be on low boost and therefore the WUR will be enrichening the AFR. |
According to my vacuum/boost gauge I'm not producing boost at steady speed/cruise at 3500 RPM, still on the vacuum side. So if my gauge doesn't see boost, my WUR should be the same and this is why I'm trying to understand why I see enrichment. Now, if I push on the accelerator at this RPM range, boost comes on quickly.
And it's not around 3500 RPM, the enrichment start exactly at 3500 RPM. Looks to me like it is control by the box.???
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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Carrera RSR
Joined: 08 Jan 2010
Posts: 2312
Location: Somerset, UK
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| Posted: Sat Sep 16, 2017 9:27 pm Post subject: |
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What box? Ditc?
Modified turbo fuel enrichment control http://www.924board.org/viewtopic.php?t=42373
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Sun Sep 17, 2017 4:36 am Post subject: |
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| Carrera RSR wrote: | | What box? Ditc? |
Bosch box under the steering, I don't have DITC, stock '80 CIS.
Thanks, I will have a read through
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Mon Sep 18, 2017 3:33 am Post subject: |
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Anyone with a 931 stock CIS, wideband O2 and A/F gauge had a chance to drive their car this week-end and see what kind of A/F they get above 3500 RPM off boost?
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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Carrera RSR
Joined: 08 Jan 2010
Posts: 2312
Location: Somerset, UK
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| Posted: Mon Sep 18, 2017 5:15 am Post subject: |
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| 924-76 wrote: | | Anyone with a 931 stock CIS, wideband O2 and A/F gauge had a chance to drive their car this week-end and see what kind of A/F they get above 3500 RPM off boost? |
Will not be the same results on differing engines. Too many variables. Get your motor on a dyno and get it tuned.
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Mon Sep 18, 2017 6:16 am Post subject: |
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| Carrera RSR wrote: | | Will not be the same results on differing engines. Too many variables. Get your motor on a dyno and get it tuned. |
If I'm not mistaking, the Bosch box under the steering adjust fueling via the frequency valve based on the O2 reading. In this case, stock 931 S1 CIS system should have similar result.
So, I'm trying to identify if enrichment over 3500 RPM is directed by the Bosch box or if something else in my system trigger this enrichment.
Please correct me if I'm wrong
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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Carrera RSR
Joined: 08 Jan 2010
Posts: 2312
Location: Somerset, UK
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| Posted: Mon Sep 18, 2017 5:34 pm Post subject: |
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| 924-76 wrote: | | Carrera RSR wrote: | | Will not be the same results on differing engines. Too many variables. Get your motor on a dyno and get it tuned. |
If I'm not mistaking, the Bosch box under the steering adjust fueling via the frequency valve based on the O2 reading. In this case, stock 931 S1 CIS system should have similar result.
So, I'm trying to identify if enrichment over 3500 RPM is directed by the Bosch box or if something else in my system trigger this enrichment.
Please correct me if I'm wrong |
Must be a US thing!?
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252 |
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Sat Sep 23, 2017 10:19 pm Post subject: |
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Am I the only one driving a 931 with stock CIS above 3500 RPM off boost? 
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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Fasteddie313
Joined: 29 Sep 2013
Posts: 2595
Location: MI
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| Posted: Mon Sep 25, 2017 6:48 am Post subject: |
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| 924-76 wrote: | | Am I the only one driving a 931 with stock CIS above 3500 RPM off boost? |
Maybe with a wideband..
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Mon Sep 25, 2017 7:29 am Post subject: |
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| Fasteddie313 wrote: | | Maybe with a wideband.. |
I guess...
My latest observation about A/F ratio enrichment on a 1980 931 with stock CIS system.
I notice 4 different enrichments:
-WUR enrichment on cold start,
-WUR enrichment under boost,
-Lambada enrichment above 3500 RPM off boost, and
-Lambada enrichment at Wide Open Throttle (WOT) off/pre boost.
Anybody else experienced similar or different enrichment situations?
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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