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Car runs great, but some odd issues
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Nein37  



Joined: 29 Dec 2009
Posts: 513
Location: New London, CT

PostPosted: Tue Feb 26, 2013 6:39 am    Post subject: Reply with quote

The missing cap on the mixture screw is quite a large vacuum leak. You should plug it with something and see if that helps. When proper mixture is set with the car fully warm, the idle will stumble when the plug to the mixture screw is out. Once you put the screw in to seal up the hole the car should run perfect... if you're mixture is correct.

If you plug up the hole and the car still stumbles at warm idle, the mixture is still off. If it gets a little better but still not quite there, your mixture is probably a bit lean. Give it a tiny turn clockwise and try again.

You need to unplug the oxygen sensor to do this or your FV will just fight the changes you make.
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1992
Location: Redmond, Oregon

PostPosted: Tue Feb 26, 2013 6:52 am    Post subject: Reply with quote

Nein37 wrote:
The missing cap on the mixture screw is quite a large vacuum leak. You should plug it with something and see if that helps. When proper mixture is set with the car fully warm, the idle will stumble when the plug to the mixture screw is out. Once you put the screw in to seal up the hole the car should run perfect... if you're mixture is correct.

If you plug up the hole and the car still stumbles at warm idle, the mixture is still off. If it gets a little better but still not quite there, your mixture is probably a bit lean. Give it a tiny turn clockwise and try again.

You need to unplug the oxygen sensor to do this or your FV will just fight the changes you make.


Wait... the cap on the fuel distributor that covers the allenhead adjuster can cause a vacuum leak? I thought it was nothing more than an adjuster screw (think carbs).
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
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- 1999 Ducati 900SS
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Nein37  



Joined: 29 Dec 2009
Posts: 513
Location: New London, CT

PostPosted: Tue Feb 26, 2013 6:54 am    Post subject: Reply with quote

Yes it is a vacuum leak. It is air entering the system after the metering.
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1992
Location: Redmond, Oregon

PostPosted: Tue Feb 26, 2013 6:55 am    Post subject: Reply with quote

Interesting. I'll try plugging it this afternoon and see if that helps.
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1992
Location: Redmond, Oregon

PostPosted: Thu Feb 28, 2013 10:18 am    Post subject: Reply with quote

Nein37 wrote:
Yes it is a vacuum leak. It is air entering the system after the metering.


Removed the boot to take a look and sure enough I see what you're saying. I first put a screw cap on it (8mm bolt) with a paper gasket ring I made and it seemed much better. It fluttered a tad still at idle under warm. I turned it ever so slightly clockwise and it mostly went away.

I took it for 5 mile increments at operating temp and then would make fine adjustments. The hesitation is almost entirely gone at this point, idle is fantastic, runs great, doesn't die on me anymore. I think a few tiny adjustments and then a tailpipe sniffer and I may be able to get it accurately tuned.

I called up all the good shops around here I know and none of them have a CIS tester.
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1992
Location: Redmond, Oregon

PostPosted: Thu Feb 28, 2013 10:18 am    Post subject: Reply with quote

Another issue I forgot to mention... the windshield wipers randomly turn on. Sometimes when I turn on the turn signal, other times when I turn. Not always... sometimes. So something is loose or I have a short somewhere.
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ideola  



Joined: 01 Oct 2004
Posts: 15503
Location: Woodstock IL

PostPosted: Thu Feb 28, 2013 10:31 am    Post subject: Reply with quote

In my experience, the only way to get the CIS system properly tuned is with a wideband AFR. All of the other half-ass methods I've tried are only good for rough tuning, including the Gunson gas tester I have, the stumble lean / stumble rich method, and dwell meter. So if you don't plan to add an AFR, I would suggest finding a shop with a quality tailpipe sniffer...however, even this may not work because of the cat. There is a test port on the 931 exhaust prior to the cat, which is the proper place to tap in for sampling the air. Either that or replace the stock narrow band O2 sensor (which is probably shot at this point anyway) with a wideband sensor. Most wideband setups have a narrow band emulation mode / wiring setup that you can use to tie in to the stock Lambda system (for proper operation of the frequency valve and the related WOT enrichment...very important!), and you can use the wide band feature for proper tuning of the CIS fuel mixture.

As for the wiper problem, joecitizen did a writeup, I think it's in the how-to section. You should look that over, because it sounds like you're having a short in the steering wheel / steering column / wiper-turn-signal assembly. You don't want to take a chance with this because some of those circuits are (amazingly) unfused, and if they short out, you can melt wires and wreak all kinds of havoc in the big messy bundle of wires behind the instrument cluster. Get after it quick or unplug the wiper harness until you have time to properly diagnose it.
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11378
Location: PacNW

PostPosted: Thu Feb 28, 2013 10:40 am    Post subject: Reply with quote

Dwell meter method has worked very well for me (it is what factory techs used) but AFR is good insurance to verify boost enrichment and warmup cycle.
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ideola  



Joined: 01 Oct 2004
Posts: 15503
Location: Woodstock IL

PostPosted: Thu Feb 28, 2013 10:56 am    Post subject: Reply with quote

Dwell left me significantly rich, AFR revealed that there was a lot that could be dialed in. Out of curiosity, Rasta, have you verified your dwell-adjusted setup with an AFR? I have not gone back to check using dwell since installing the AFR, but now that I think of it, this would be a very interesting set of data to examine...
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Joes924Racer  



Joined: 03 Nov 2002
Posts: 11964
Location: Oregon, Denver Colorado native!

PostPosted: Thu Feb 28, 2013 5:11 pm    Post subject: Reply with quote

You need a wide band afr guage.B-)
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Nein37  



Joined: 29 Dec 2009
Posts: 513
Location: New London, CT

PostPosted: Fri Mar 01, 2013 1:47 am    Post subject: Reply with quote

ideola wrote:
Most wideband setups have a narrow band emulation mode / wiring setup that you can use to tie in to the stock Lambda system (for proper operation of the frequency valve and the related WOT enrichment...very important!)


I thought the FV went to WOT enrichment regardless of whether the oxygen sensor is connected? Isn't it controlled be the TPS?
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11378
Location: PacNW

PostPosted: Fri Mar 01, 2013 4:29 am    Post subject: Reply with quote

ideola wrote:
Dwell left me significantly rich. . .Rasta, have you verified your dwell-adjusted setup with an AFR?


Something else was wrong if this was the case. If you have a 50% FV duty cycle at idle (45 dwell on the 4 cylinder scale), you should be sitting at stoich. Cruising under zero or light boost, you should also be at stoich. In my case, both of these parameters are verified through wide band O2 sensor.

Nein37 wrote:
I thought the FV went to WOT enrichment regardless of whether the oxygen sensor is connected? Isn't it controlled be the TPS?


This is correct. Enrichment is a combination of mechanical action by the control pressure regulator (triggered by manifold pressure) and electrical triggering of the lambda system by the TPS WOT switch.

Derek, bring me your car! We can smoke test the intake, and test the fuel system, getting it over with and getting that thing running like it should.
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1992
Location: Redmond, Oregon

PostPosted: Fri Mar 01, 2013 6:56 am    Post subject: Reply with quote

I hate driving to portland. Mostly in portland. It's a significant reason I rarely go there because the traffic makes me want to punch kittens.
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
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- 1999 Ducati 900SS
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1992
Location: Redmond, Oregon

PostPosted: Fri Mar 01, 2013 6:59 am    Post subject: Reply with quote

ideola wrote:
As for the wiper problem, joecitizen did a writeup, I think it's in the how-to section. You should look that over, because it sounds like you're having a short in the steering wheel / steering column / wiper-turn-signal assembly. You don't want to take a chance with this because some of those circuits are (amazingly) unfused, and if they short out, you can melt wires and wreak all kinds of havoc in the big messy bundle of wires behind the instrument cluster. Get after it quick or unplug the wiper harness until you have time to properly diagnose it.


Is this what you're talking about?
http://www.924board.org/viewtopic.php?t=24984
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11378
Location: PacNW

PostPosted: Fri Mar 01, 2013 2:18 pm    Post subject: Reply with quote

CorsePerVita wrote:
I hate driving to portland. Mostly in portland. It's a significant reason I rarely go there because the traffic makes me want to punch kittens.



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