924Board.org

924-76 · Joined: 05 Jun 2006 Posts: 1489 Location: Ontario, Canada

I finally installed my AEM UEGO wide-band gauge in my 931.
At idle and cruising, the readings are all over the place between 12 and 15 and seem to be fairly steady at WOT around 12.5-13.
Is this normal?
What are you guys getting from your AEM wide-band?
Thanks
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP

924-76 · Joined: 05 Jun 2006 Posts: 1489 Location: Ontario, Canada

I was working on the car and the idle became unstable.
I unplug the frequency valve and the idle stabilized as well as my AFR gauge.
Thoughts?
Could it be a faulty O2 sensor?
_________________
1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2595 Location: MI

Try unplugging your O2 sensor instead of your frequency valve.. You're probably seeing the ARF hunt back and forth as the lambda system manipulates it based on its narrow band signal from the O2 sensor..
You want to leave your frequency valve plugged in and lambda operating to get its WOT enrichment but you can unplug the O2 sensor and it will revert back to default leaving you with its good WOT enrichment but getting rid of its AFR hunting..
You ever watch the frequency valve duty cycle with a dwell meter before?

If you're trying to tune your engine via your wideband and you still have your OEM lambda system running they are going to fight each other, your going to try to tune rich and lambda is going to try to tune you back lean, that's its job.
By time you defeat the lambda by adjusting rich so far it cant bring you back lean it will have the frequency valve pegged at full/highest (or lowest??) duty cycle fighting you and your actual tune will be whack because you just tuned rich as far as you want it rich + as far as the lambda can fight you back lean..
If you want to tune by the wideband unplug the O2 for the lambda, or you could tune by lambda with a dwell meter and see what AFR that gives you with your wideband..
Assuming you are running your wideband and the OEM lambda..

Or are you emulating narrowband with your wideband for the lambda system?
What exactly do you have set up? I read as you are running both systems therefore 2 O2 sensors..
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80 Turbo - Slightly Modified

924-76 · Joined: 05 Jun 2006 Posts: 1489 Location: Ontario, Canada

Wideband sensore for the gauge and narrowband for the frequency valve.
I will test the frequency valve and O2 next week.
Thanks
_________________
1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP

leadfoot · Posted: Fri Jul 17, 2015 11:23 am Post subject:

From a standing idle around stoic/slightly rich, slowly drops to max rich 11.5 at wot to redline, let off throttle will peak it lean the other way pretty much
This is for CIS...
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

924-76 · Joined: 05 Jun 2006 Posts: 1489 Location: Ontario, Canada

Well, almost 2 weeks of poking around and still not working.
I change the O2 sensor and moved around wire on the TPS (recently convert from S1 to S2 TB) and still not good.
I can get the car to idle steady at 14 AFR but running lean at cruse and I can feel it not running properly, almost stumbling.
When I go WOT, I get around 13 AFR.

Any ideas?.....I`m getting frustrated.
_________________
1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2595 Location: MI

Have you tried adjusting the mixture screw to where you're not so lean at cruise and WOT but rich at idle?
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80 Turbo - Slightly Modified

924-76 · Joined: 05 Jun 2006 Posts: 1489 Location: Ontario, Canada

No, I didn't
But my understand is it should be around 14 at idle and getting richer as RPM goes up.

Could this be a fuel pressure issue?
If yes, why I get around 13 at WOT?
_________________
1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP

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

13 at WOT is way too lean. On the 941 and the Club Sport, my AFR behaves exactly as Stu describes...the stock CIS system goes WAYYYY fat at WOT. On my cars, I get steady 14.5:1 at idle (941 is S1 ignition setup, CS is S2 with DITC). Both cars go to 11:1 or richer at WOT.

I'm wondering if you're having an issue at your fuel distributor or your WUR. Have you done full CIS battery of tests?
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erstwhile owner of just about every 924 variant ever made

924-76 · Joined: 05 Jun 2006 Posts: 1489 Location: Ontario, Canada

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

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2595 Location: MI

Are you running with the frequency valve operating and the o2 sensor unplugged like I said if you're trying to tune to the WB?

If your only "tuning" with the mixture screw that won't get you far, the real tuning is in changing system pressure, and temperature/boost variable control pressures to really adjust the curve.

You can move the whole fuel curve rich/lean a bit with the mixture screw but it's mostly only effective at idle where a tiny change in metering plate position is the most effective.. If your lambda o2 sensor is in play it will override your tuning at idle and cruise as much as it can..

Tune to a 45% duty cycle with a dwell meter off the OEM lambda system with the o2 plugged in and see what your WB gives you from there..

Then if you don't like the AFR you have there unplug the o2 and tune to WB from there..

That's what I would do..

Doing a proper CIS test will be fun and rule out a lot of stuff for you, I'd do one regardless..
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80 Turbo - Slightly Modified

leadfoot · Posted: Thu Jul 30, 2015 12:19 am Post subject:

also
where in the exhaust and how is the sensor placed...

have you done a spray test of each injector... you may have a blocked line or injector...
when was the last time you ran some injector cleaner through the system??
the springs in the WUR can fail...
fuel filters clogged...
etc etc etc
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

924-76 · Joined: 05 Jun 2006 Posts: 1489 Location: Ontario, Canada

I just did the control fuel pressure test and I get 5.3bar at cold-ish (34 degree Celsius outside) and warm.
Why is it so high? Is this mean that my system pressure is too high?
_________________
1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP

924-76 · Joined: 05 Jun 2006 Posts: 1489 Location: Ontario, Canada

Stop for diner, when I went back out I jump the 30 and 87 terminal on the fuel pump relay and NOTHING append; that's right the fuel pump didn't start.
I double and triple check that I had the right terminal and unplug and replug the wire few time to ensure proper contact without success.

So, How am I suppose to check system pressure? and why is the fuel pump is not running?

The funny thing is I checked the factory manual to confirm the terminal and the say "the fuel should run"....but they don't say what to do if it doesn't...

_________________
1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP