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Lau Christophersen · Joined: 17 May 2013 Posts: 123 Location: Denmark/Copenhagen

I recently finished my new exhaust including a wide band censor and a AFR gauge.

The problem I find is that it shows good values (11,2-11,3) when at idle, but as soon as i touch the pedal it goes out of scale(above 1

when hitting boost it goes down again into scale and when on full boost goes in the "green area"(good values) again.
If i drive at steady speed the value is around 17,2.

Is the problem a vacuum leak or? I was testing all vacuum connections for leaks and could not find any.

Any good ideas? I can feel it is going to lean and I dont drive any more before i find the problem.

Cedric · Joined: 27 Aug 2004 Posts: 2818 Location: Sweden

Sounds weird, should look something like this:

Ive just tried two different 931s but both of them were around these values. Cruise was around stoich, 14,7.

When I had a broken WUR the car ran 12-13 at full load (cant remember exactly), that made the knock sensor light up, until I swapped in a working one. and everything went fine ever since

_________________
1980 924 Turbo
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Carrera RSR · Joined: 08 Jan 2010 Posts: 2312 Location: Somerset, UK

I'd recommend placing a known accurate AFR sensor in the tail pipe and running both gauges in tandem so you know they are both working with similar values. Don't assume your gauge and sensor are good until verified.
_________________
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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Lau Christophersen · Joined: 17 May 2013 Posts: 123 Location: Denmark/Copenhagen

Thank you for answers

I just dont understand that it goes fine with heavy boost and at idle but too lean between these to situations.

Any idea of how many hp a stock euro 931 with FMIC makes with 1,4 bars boost?

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

Perhaps you forgot to calibrate it ?
Or you messed up the calibration.
Read the instructions, you have to power it and leave it in open air for a while if I remember correctly.

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

Lau Christophersen · Joined: 17 May 2013 Posts: 123 Location: Denmark/Copenhagen

Just Asking because it was at that level when I bought the car now it is back at stock boost at 0,7 bar.

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

If its an euro car I would be a bit more optimistic about the HP figures.
The 924 Carrera GTS made 245hp at 1.1 bar and if i'm not mistaken 285hp in the CS version at 1.2bar. From 1.0bar upwards gains are more substantial with 0.1increments of boost than under 1.0bar.
For example, it looks like 1.2bar over 1.1bar will give you 40hp on the 924 turbo engine. While 0.8bar over 0.7bar will not give you 40hp.

I remember when the wastegate boot failed on mine, clouds of black smoke and such torque that it would squat the rear suspension completely.
It will not hold for long at those power levels, headgasket fails, but with some investments it will hold.
_________________
Supercharger and EFI kits
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Carrera RSR · Joined: 08 Jan 2010 Posts: 2312 Location: Somerset, UK

Stock turbo CIS will not support 250bhp+, nor will the stock turbo at 1.0bar+. But we all knew that already!!

_________________
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
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Lau Christophersen · Joined: 17 May 2013 Posts: 123 Location: Denmark/Copenhagen

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Turbo =/= CIS

The turbo can be overspun to produce a bunch of boost, but the fuel system won't support it and you'll risk seriously damaging the motor (the 931's seem prone to cracking rings anyway).
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

Unless someone shows me that the cis afr screw is turned all the way to the max, boost gauge showing 1.4bar and wideband gauge showing lean conditions i wont believe the cis is limited to 250hp.
I'm running more mixture than stock 931 with a k27, reading afr of 10 at 1.1bar. When i installed a wideband i saw i was drenching the engine with 8 and 9afr at the same boost levels. I really think that cis can deliver serious amouns of fuel.
_________________
Supercharger and EFI kits
https://www.the924.com

Carrera RSR · Joined: 08 Jan 2010 Posts: 2312 Location: Somerset, UK

When I fit my new head I'll test this theory of screwing in for super rich mixture and crank the boost North of 1.2 bar and I'll see what happens. I'll be sure to run the video as well so we can all giggle at the results

_________________
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

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania