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9dreizig's Avatar
 
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AFR's at idle

What AFR's do your well idling 930's have ? Just setting up mine and wondered what's optimum ?

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"Todd"
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Old 05-20-2020, 03:00 PM
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I thought it was the same as any other car 14.6 at idle.
Old 05-20-2020, 03:05 PM
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Quote:
Originally Posted by mdj930 View Post
I thought it was the same as any other car 14.6 at idle.
yeah, I know that's theoretically correct. Just checking where everyone else's is happy
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"Todd"
98 Tahoe ,2007 Saturn Vue
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Old 05-20-2020, 03:47 PM
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Typical target is 13.0:1 to 13.5:1 AFR at idle for stock cams, 12.5-13.0:1 for SC/964 cams. This should result in ~14.5:1 at cruise.
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Old 05-20-2020, 07:04 PM
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Quote:
Originally Posted by RarlyL8 View Post
Typical target is 13.0:1 to 13.5:1 AFR at idle for stock cams, 12.5-13.0:1 for SC/964 cams. This should result in ~14.5:1 at cruise.
^^^"Ditto"^^^
With CIS anyway...is EFI any different?
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1981 SC Steel Widebody, DP Lid, 930/51 to 3.2l, K27 7006 Turbo, DOD, P&P Twin Plug heads, Twinfire Ignition, Ruf Intercooler, Powerhaus headers, Zork, CIS Euro FD, 009 injectors, 044 pump, BLwur, 930 4 sp LSD, Mocal 44 w/fan, LM2, Brembo, Retroair, Euromeisters
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Old 05-21-2020, 02:38 AM
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If your CIS Kjet is lambda/stock then will get to 14.7ish when warmed up and transitioned to closed loop control

From Charles Probst Bosch book

"because lambda sensor operation depends on high temperature the system operates open loop before the sensor warms up. this can cause driveability problems and increased exhaust emissions do too imprecise mixture control. To correct this many cars have a lambda thermal switch located in the coolant or on the cylinder head of air cooled Porsches to give the control unit an additional input and ensure proper fuel metering during engine warm up. When the engine is cold the thermal switch is closed the control unit send a fixed slightly rich duty cycle signal of 60 percent to the lambda control valve. When the thermal switch warm enough to open the control unit sense of fixed middle signal 50 percent duty cycle. when the lambda sensor reaches operating temperature so it signals are valid the control unit switches to closed loop operation. Remember in closed loop the duty cycle signals are constantly changing cycling back and forth between about 45 percent and 55 percent so that the air fuel ratio is maintained near stoichiometric - lambda equals 1."
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Old 05-21-2020, 04:15 AM
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Stoichiometric 14.6 for most of our cars seems too lean. When I had an AFR meter, mine idled best at around 13.5 if I recall. I ran (and still do) without the lambda circuit, i.e., O2 sensor unplugged/open loop.
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Old 05-21-2020, 05:12 AM
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Cold idle around 13, warm around 15, cruising 14.5 and full boost less than 10... happy engine
Old 05-21-2020, 06:27 AM
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^^^

I thought full boost should be between 11.0 and 12.0 afr?

Rahl
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Old 05-21-2020, 09:06 AM
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Agree Mark ...I'll start driving easy after partial warmup before CIS goes into closed loop and AFR's in 12ish range - idle is 13's --just to 2500rpm start stop, cruising and it runs stronger

not sure of CIS configuration of OP. Just adding to discussion from some past posts i was involved in.

Also your comment got me tinkin - before my rebuild 930 was my daily for a year or so and i had a lot of highway travel - kept lambda control and got decent highway mpg...... i might just unplug and run open loop with FV at default duty cycle and further improve NA operation until i figure out my WOT problem.

Sorry to hijack


Quote:
Originally Posted by mark houghton View Post
Stoichiometric 14.6 for most of our cars seems too lean. When I had an AFR meter, mine idled best at around 13.5 if I recall. I ran (and still do) without the lambda circuit, i.e., O2 sensor unplugged/open loop.
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Old 05-21-2020, 09:08 AM
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Well since my Lambda apparently pooped the bed.. it's unplugged so I'll be setting it up that way.. Thanks!!
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Old 05-21-2020, 10:47 AM
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I took the advice of the experts here when I was tuning it after a bunch of upgrades and let the car tell me when it was happy. I'm at about 13.5 at idle with no lambda and stock cams because that's where it idled best. I'm a little higher at cruise and on full boost it drops to about 11 or 11.5 or so. Below 10 on boost it was painfully rich and it wasn't happy. Point is that while we should start with a common baseline, every car runs a bit different and you should tweak it from there to make yours run its best.
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Old 05-21-2020, 02:09 PM
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Quote:
Originally Posted by mark houghton View Post
Stoichiometric 14.6 for most of our cars seems too lean. When I had an AFR meter, mine idled best at around 13.5 if I recall. I ran (and still do) without the lambda circuit, i.e., O2 sensor unplugged/open loop.
Definitely too lean for anything but NO control.

13.5 is about right for mine with stock 3.3, sc cams, longneck ic
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Old 05-22-2020, 05:54 AM
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Each engine is a bit different - depending on mods and wear in engine. Worn engines prefer a bit more fuel. I set mine where the idle is most happy - irrespective of numbers. Rather than target a number. Mine seems happiest around 12-12.5. It has very little effect on your running AFRs - except maybe a slight effect on low throttle running. 13.0 is def unhappy for me.
Alan
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Old 05-25-2020, 01:43 PM
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Mine Idles happy on about any AFR? Whitch afr should bring best emission values for MOT onE98 (93)? Last time I was on E85 and around 14.7AFR and had trouble passing the emissions test? This time I will go with E98 (US 93). I remember we had to put a rag on the other muffler exit so possibly it was too much oxygen in the tester as hc limits are high for old cars and mine does not even need cat.
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Old 06-04-2020, 09:53 AM
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Quote:
Originally Posted by Hot Euro View Post
^^^"Ditto"^^^
With CIS anyway...is EFI any different?
Mine was happiest @ 3.0% CO at idle with CIS & SC cams. It seemed to idle fine with lower, but that could cause hesitation tipping-in off-idle, and sometimes a lean surge on light cruise.

Twin-plugged with sequential injection, idles fine @ 1.0, 1.05 lambda on E10.
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Old 06-04-2020, 01:56 PM
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My car always seems good at 14.5-7 at idle 14.5 at cruise and it hits 12.5 at 1bar on the money every time. Pulls pretty clean throughout without hiccups even down low. Modified CIS system and twin plug though.
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Old 06-06-2020, 07:54 AM
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got it all ironed out!! running and starting great at about 13.5 ... Thanks!!
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"Todd"
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Old 07-21-2020, 10:09 AM
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The Service manual for my '91 states 3.0% CO.
With tolerances, this charts out to 13.7 - 14.1 afr.
My car idles fine at this setting, even with SC cams so I called it good.
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Old 07-24-2020, 04:29 AM
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interesting, I think I'm at 13.1 to 13.4, Euro 1985 W/O o2 control loop
there may be a difference between what models with o2 feedback loop like VS what those without like such as Euro models.

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Last edited by Roby466; 07-24-2020 at 09:20 AM..
Old 07-24-2020, 07:03 AM
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