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What mixture should I be looking for?
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924RACR  



Joined: 29 Jul 2001
Posts: 8088
Location: Royal Oak, MI, USA

PostPosted: Tue May 31, 2016 10:44 pm    Post subject: What mixture should I be looking for? Reply with quote

So, I finally got off my butt and installed a wide-band O2 sensor. Yay!

But like with all data... I have zero reference points for this engine on what I'm looking at, what I should be expecting if it's adjusted properly.

On my first run this AM, it was idling around 15.0 once fully warmed up. While coasting in-gear fully off-throttle, I was seeing around high 12's/13.0. Likewise, I was seeing mid-to-high 12's up to 13.0 at 3000rpm into the boost, into the throttle (at least 1/4 throttle).

One finding so far is that with the very initial tip-in of throttle, it goes quite lean (high 13's to low 14's) - so maintenance throttle to maintain speed (5th gear 70mph/3000rpm). But if I push past that, it recovers and goes richer into the 12's as noted above.

This leads me to think that my throttle switch ('82 931, BTW, stock boost and everything else) needs adjustment.

I also noticed that low rev (2000 or even less) response was quite poor (1st/2nd gear low speed), once warmed, with mixture up around 15-16! When it was cold, mixture was down in the mid-12's under these conditions, and it pulled much better.

So I've richened it up a good bit, let's say a 30 deg adjustment... will see what that does. But I'm sure there are other things to address. Gotta check my vacuum line routing, make sure the WUR is plumbed to the right port.

Any other thoughts, or general observations on running a 931 with a WBO2 readout? New ground for me...

Thanks...
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CÚdric  



Joined: 27 Aug 2004
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Location: Sweden

PostPosted: Tue May 31, 2016 11:07 pm    Post subject: Reply with quote

Mine was around 14-15 at low load, idling and 13-14 of boost at highway. Under full boost it goes down to 11 and stays there until redline. It was impossible to run at around 12,5 WOT when my WUR was broken, that would trigger the knock warning directly. But US spec might be very different with the low power/cat etc... But even then i wouldnt want to run leaner than maybe 11.5-12 at load, not without IC.
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Tue May 31, 2016 11:12 pm    Post subject: Reply with quote

Cedric's experience is very similar to mine on both the Club Sport and the 941. Club Sport is ROW S2, 941 is US S1. I have both cars set to idle at between 14 - 14.5:1 (there is always some minor fluctuation). Both cars go to about 15 or so at lean cruise, with an initial lean spike on tip-in, but then recovery to full fat (usually 11:1 or so) at WOT.
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Tue May 31, 2016 11:39 pm    Post subject: Reply with quote

Awesome, thanks guys. I neglected to mention, once I richened it up at idle it was showing around 14.5 (at idle)... so will be looking to see what that does on the return trip, hopefully it's closer on target to what you've all described.

Still suspecting some flaky connections for the K-Jet-E system, as I'm seeing some interesting jumping around of numbers when cold. Much steadier when warm. May try replacing contacts on the connector at the mix adjusting valve...
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morghen  



Joined: 21 Jan 2005
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PostPosted: Tue May 31, 2016 11:44 pm    Post subject: Reply with quote

Same with mine, starts rich 11AFR..then when it warms up it leans up to 13.7-14.2 at warm idle.
Cruising off boost is quite lean 14.X

From a cruise, if you give it the beans it will lean out for a very short amount of time(i'm guessing CIS has a responce time) but when boost kicks in it goes very rich...mine reads up to 9 AFR..but since i use a bigger than stock turbo mine actually leans out to 12.5 above 5000 RPM on full beans.
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Tue May 31, 2016 11:53 pm    Post subject: Reply with quote

My S1 lambda car idles and cruises at stoich...never goes leaner. Dips under 12 at WOT+boost, and approaches 12 from tps alone (on minimal/no boost).

WUR should be plumbed off the fat line going to the brake booster.
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Wed Jun 01, 2016 12:00 am    Post subject: Reply with quote

Rasta Monsta wrote:
WUR should be plumbed off the fat line going to the brake booster.


Thanks. I've been trying to find a definitive diagram for the S2, think it's buried in my hardcopy manuals back home (at work now). Currently mine is connected to a general vac port in the intake manifold...
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Wed Jun 01, 2016 12:31 am    Post subject: Reply with quote

Hmmm. I don't have a nipple by the brake booster vac generator, like I guess the S1 does. Mine is currently plumbed, along with the decel valve, to a port on the throttle body just downstream of the butterfly. Not actually at the throttle valve, but just inside of it, more measuring the boost level in the intake plenum.

So I think that's right... anyone can confirm?
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ideola  



Joined: 01 Oct 2004
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PostPosted: Wed Jun 01, 2016 12:46 am    Post subject: Reply with quote

I have two non-running US-spec '82 motors for reference, plus the ROW 81 Club Sport motor.

On all of these (as well as my S1 cars), there is a vac line attached to the post-throttle-plate port on the TB, which goes to a Tee. The tee is connected to the WUR and the decel valve.

On the US-spec S2 cars, there is a pre-throttle-plate port as well, and this has a single line that goes to one of those funky heat/temp sensors in the hard pipe coming off the back of the head. The ROW throttle body has the boss for this port, but there is no nipple on it.
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Wed Jun 01, 2016 12:57 am    Post subject: Reply with quote

Cool, sounds like I'm pretty much hooked up correctly, then.

The only real exception would be, the line at/before the throttle blade goes straight to my evap control valve (for the carbon canister), though it should go through the vac temp valve to be correct. But it's kinked off and closed at the evap control valve anyway, since I determined quite some time ago that the damn thing leaks vacuum anyway. Besides, who cares, just stupid emissions crap anyway...

Thanks for the confirmation, Dan...
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924RACR  



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PostPosted: Fri Feb 24, 2017 9:59 am    Post subject: Reply with quote

Update on this, with the car running better etc...

Idling, I have had it in the range from 12.5 to 14.0 or so currently.

Full boost... it still, once the revs get up, dips just below 11, to 10.7-10.9 range... no matter what I seem to do... perhaps control pressure a bit off, but... there definitely seems to be a toggle switch type of effect when I hit the last 5% or so of pedal travel, otherwise it'll be in the low 11's.

I also, as I work to lean it out, notice an ugly lean spike when I drop throttle at high revs (shift, lift-off, or the like) - it'll briefly spike up to 16 or so on the gauge, often accompanied by a brief/light backfire.

I'm wondering if the latter indicates an improperly-working decel-bypass valve...
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Fri Feb 24, 2017 11:41 am    Post subject: Reply with quote

I'd check your throttle idle and WOT switches, maybe your WOT is coming on way too early, 5%..

Then tune it to the dwell method 45%, then see what AFRs you get..

Are you running both O2 sensors with a functioning lambda?

Tuning along side a functioning lambda will be tricky because it's doing its own tuning too.
Say if you try to tune it to below stioch at idle really you will be way far rich because you have gone so far rich you are now outside of the operation range of the lambda rich plus whatever rich below stioch you are..

Tune it to the dwell 45% and see what your WOT AFRs are.. If you want your WOT richer tune it to 35% dwell or leaner 55% dwell..
But you will still be stioch at idle and cruise, unless you tuned massivly outside the range of the lambda to where you see results at idle and cruise but then you are way out there at WOT which ever direction you defeated the lambda in..
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Carrera RSR  



Joined: 08 Jan 2010
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PostPosted: Fri Feb 24, 2017 9:59 pm    Post subject: Reply with quote

Will always lean out coming off the gas pedal with a brief spike. No issue as the motor is on over run. I do miss my popping exhaust on gearchanges and over runs. It went after going electronic dizzy.

Idle AFR is controlled by the idle mixture screw. You should be able to get 14.7 AFR on idle.

For WOT mixture, this is far harder as its all in the WUR adjustment. Check out my thread on the boost enrichment mods I made. Sub 11AFR is no issue on a non IC turbo. You need to fuel to stay safe from det. Its usual to see low 10's.

I'm now mid to high 11's in the mid range at 1.2bar but at WOT I still dip into the 10's above 4800rpm when the boost switch opens the WUR enrichment. EGT;s drop as soon as more fuel goes in at higher rpm.
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Sat Feb 25, 2017 12:14 am    Post subject: Reply with quote

Well, I have an S2, so no individual switches - which complicates things, 'cause yes, that would match perfectly with the symptoms. I have verified repeatedly that the TPS (which is really all the switches in one housing, not a true sensor) is correctly adjusted.

I don't run a functioning lambda now, just the WBO2.

Thanks for confirming that the pop on lift is OK/normal, along with the rest - I'll not worry about it, and just get 'er leaned out to more normal settings. It's been pig-rich for a long time... only just now getting things right, after fixing the flaky ignition...

Will check out that other thread...

Oh, yeah - long-term intent is to be switching to Megasquirt, to ditch the CIS and more easily support putting in an IC and raising the boost. So maybe this is the point of "don't mess with it, it's as good as it usually gets stock, so leave it be and focus on other things."
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Sat Feb 25, 2017 4:55 am    Post subject: Reply with quote

924RACR wrote:

I don't run a functioning lambda now, just the WBO2.


If the lambda is completely disabled then your FV duty % = 0 zero and your differential diaphragm pressure is set max lean and you are giving up a lot of your maximum fueling capacity..

Fasteddie313 wrote:

All of these numbers are with the airplate at 100% travel and full flow, per injector..

103 psi system pressure

Frequency valve full closed/unplugged
76.5 grams in 30 sec

Frequency valve plugged in and running as default
102.53 grams in 30 sec

Frequency valve full open, +12v constant
163.97 grams in 30 sec


Frequency valve full open 163.97 grams in 30 sec = about 330HP worth of fuel..
Full closed FV 0% = only about 205 hp worth of fuel..

Completely disabling your lambda looses you a lot of fuel and makes you pretty lean/low fuel flow for any given airplate position..

If you don't want your lambda to interfere in your tuning you should still run it but leave the O2 unplugged, it will run in half flow limp mode and still give you WOT enrichment this way..
Running the FV completely off/full closed is not a great idea IMO..
I think you are running it in limp/default or you would not be worried about possible TPS WOT enrichment coming on too soon..

If you are planning to run MS anyway, you could hook up all your sensors and have the MS run your FV directly for pretty darn good tuning capability right there, with your stock WUR..
Then you could swap out to EFI injectors at a later time if you are not satisfied with that..
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