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Cynical Misanthrope
 
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Acceleration Enrichment Issue : SOLVED (?)

I've posted this twice on RL, so pardon me if you've already seen this.

I bought this '92 C2T w/ 86k and noticed this low-rpm stumble. Initial inspection revealed very loose intake manifold, so I tore out, cleaned up and reinstalled all the intake and fueling from the heads up. I still have a part-throttle acceleration stumble and lethargic throttle response at low rpms. And the wideband confirms, when I crack open the throttle it pegs the O2 at 16 for half a second.
Here's my first post for more info http://forums.rennlist.com/rennforums/showthread.php?t=383859
For perspective, it idles on lambda, steady throttles on lambda, and WOTs at ~12.5 to redline so though I have not checked fuel pressures yet I'm not suspicious of them. I also cleaned, flow-tested and matched the injectors, so I'm satisfied with fuel supply.
I've narrowed down two possible sources;
-The WUR is not getting manifold pressure signal: so last night I ripped out the WUR and rebuilt it, doublechecked the throttlebody tap, and replaced all the vacuum plumbing. Started it up, still stumbles
-OR, the O2 Control Unit is not getting Throttle Switch part-throttle signals. While I had the manifold off last week I cleaned all the contact surfaces on the TPS. This does not confirm that the ECU/O2 Unit are actually receiving these signals though. I'm still favoring this suspicion b/c if I FLOOR it it enrichens fine, it's just the part throttle opening that it starves. The Control Unit is supposed to up the frequency valve whenever the throttle is opened, and again at 7d. The more I prod the accelerator from idle the more it stumbles, unless I floor it.
I don't have the Bentleys yet, so I don't have pin-out on the Controller Unit. How can you test/monitor the frequency valve activity? If anybody can offer TPS troubleshooting advice, or other input I'm all ears!
Thanks!!!
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.

Last edited by AFM744; 10-26-2007 at 02:23 PM..
Old 10-25-2007, 12:52 PM
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I would ck. the A.A.valve to see if it has stuck open .It is suppost to be open when engine is cool . It has a heating element just like the W.U.R. that is suppost to close it off as engine warms up. You can take the hose going to intercooler and clamp it off with a pair of vicegrip pliers and a couple small peices of wood and see if your problem gets better. Good Luck.
Old 10-25-2007, 07:42 PM
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Crotchety Old Bastard
 
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Unfortunately many things can cause those symptoms.
Did you inspect your injector blocks carefully for spiderweb cracks when you had it apart? Those phenolic blocks can cause all sorts of subtle problems with age.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 10-25-2007, 08:34 PM
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Cynical Misanthrope
 
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I checked the AAR, was fine.
I also carefully scrubbed down and inspected the injector blocks. They had obviously shrank with age so I reinstalled them with new gaskets (old ones were shagged with carbon from leaking). I then retorqued them after a few drives, they're still snug.

Thank you both for your thoughts!
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 10-25-2007, 09:06 PM
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What frequency valve are you referring to? Also, the throttle position sensor(TPS) on the CIS cars is only for WOT. It is basically a switch, not a potentiometer.
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Dave
'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 10-26-2007, 07:41 AM
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Cynical Misanthrope
 
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Werk, the C2T has a throttle switch that opens right off idle, then another closes at 7d, then another closes at 66%. Not a contemporary potentiometer, but does measure more than WOT.
The frequency valve modulates fuel flow to the return line, modulating control pressure in parallel with the WUR.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.

Last edited by AFM744; 10-26-2007 at 09:58 AM..
Old 10-26-2007, 07:49 AM
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Cynical Misanthrope
 
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Keeping the info posted as I go...
Last night I intensively inspected the TPS and tested with an ohmmeter. I then pulled the driver seat and verified the same signals to the O2 module. So I put it all back together, unplugged the O2 sensor then drove it to work this morning.
After 15min driving I pulled off, it was idling at 10:1 afr (and I smell like it), but it sure was more happy to rev!!! I adjusted the 3mm until I saw 13.4:1 and went to work. So in my understanding, if the CIS was trying to idle at 10:1 then the O2 and frequency valve were working very hard to compensate to get to lambda. Lunchtime drive with the idle CO set may reveal more, but I'm most curious to see what happens when I go closed-loop again (and my eyes stop watering).
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 10-26-2007, 09:25 AM
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Crotchety Old Bastard
 
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It is not uncommon for the Lambda loop to deteriorate in function. Many folks unplug the O2, adjust the CO and never look back.
You seem pretty hands on and might want to fix it. Have you installed a new O2 sensor?
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 10-26-2007, 09:41 AM
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Cynical Misanthrope
 
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I have two new O2s from my Audi, which carry almost as heavy a tarriff as The Porsche Tax ($180). They are 4-wire and I'm currently searching for how to rewire and use it. The sensor has definitely moved to the center of my radar screen.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 10-26-2007, 09:49 AM
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Cynical Misanthrope
 
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So my next question, and this may be different between 930 and 965; does the frequency valve adjust fueling for part throttle accel if you're running open-loop? My understanding of the system is that the part-throttle accel enrichment is commanded by the O2 Unit briefly pulsing the frequency valve at 75%. Does anything else control or modulate the frequency valve if you're "unplugged"?
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.

Last edited by AFM744; 10-26-2007 at 10:02 AM..
Old 10-26-2007, 09:56 AM
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It's nice to read your messages because you know what you're talking about and are correct with your words.

I don't know the answer to your last question..

On the older CIS systems as I understand it and listen to it, unplugging the O2 sensor leaves the frequency valve (inline injector) just buzzing away returning fuel to the tank at one frequency all the time accept maybe at full throttle.

I have it disconnected on my '87 930 and it idles smoother/better that way, but have thought about reconnecting it and tapping into the lambda harness under the seat and wiring in a switch to disconnect it there.
That way I could enable it during highway driving and maybe get 1 or 2 more miles to the gallon of gas.

Too many more important things though and may never bother doing that.
Old 10-26-2007, 10:26 AM
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Cynical Misanthrope
 
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Cheers JFairman.
I've been through enough cars and their enthusiast forums to tell the difference between knowledgible and generous contributors and keyboard-brave narcissists. I'm combing through these forums and learn as much as I can. I will keep adding to my threads to document however this gets resolved for future searchers.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 10-26-2007, 12:07 PM
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Cynical Misanthrope
 
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I think I fixed it!
I assumed since the car smogged well that the base CO was good. I also speculated that fixing the air leak would affect that, but I didn't actually CHECK IT on open-loop. So this morning I drive it with the air leak fixed but the O2 unplugged and saw AFRs at 10:1 at idle and cruising (that's how bad the air leak was). So I just got back from a lunch drive where I started with a 10mi warm-up, set the idle AFR at 13.4, drove 10mi, car ran great. Then I plugged the O2 back in, car ran great AND on cruise and idle I have lambda. But the best part? No stumble!!!
Synopsis Theory: Car was tuned while it had an air leak (lots of compensating fuel), I fixed the air leak, now engine runs rich as hell, except the O2 system compensates with frequency valve. This control pressure imbalance screws up the accel enrichment. I unplugged O2, now engine runs open-loop, rich as hell, but the frequency valve was not pulling on the control pressure so the enrichment works properly and the stumble disappeared. Reset base AFR, plug in O2, engine runs great and I don't smell like a Shell station.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 10-26-2007, 02:08 PM
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Excellent! Congrats!
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'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 10-27-2007, 06:57 AM
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Crotchety Old Bastard
 
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Good for you!
You have to wonder how many CIS engines are running less than optimally due to loose intake nuts and/or cracked injector blocks.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 10-27-2007, 08:03 AM
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Great news!
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WTB: 964/965 Turbo stuff...carbon fibre bits, Techart wheel parts, RS/lightweight flywheel, 993 EVO uprights, G50 gears or 6 sp., 964 RSR swaybars, custom droplinks and any other cool stuff, pm me! Also a nice medium build 327 Chevy engine.

Coming SOME DAY...1991 3.3 turbo, Tahoe Blue Metallic with some mods
Old 10-27-2007, 04:52 PM
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