CIS Misture "Leaning" Out - Calling on the CIS Gurus
11-02-2006, 12:49 AM
#31
Rennlist Member
Well, it "feels" smooth, but it "sounds" a bit lumpy. I seem to have run into a funky exhaust resonance when I set the idle near the top of the spec(~840RPM) to get the alternator to put out enough current at idle. When turned down to 750RPM it has a deep, even growl and idles smooth as glass, especially with new MMs and new MM shocks. I liked it better at the low idle -- maybe I can get back to that when I improve on my alternator situation.
Here's a clip -- I think the mic needs to be further from the exhaust(plus it was the crappiest mic I own, all I could find when I wanted the clip) and it would help if the fan wasn't running.
Here's a clip -- I think the mic needs to be further from the exhaust(plus it was the crappiest mic I own, all I could find when I wanted the clip) and it would help if the fan wasn't running.
11-02-2006, 09:38 AM
#32
Burning Brakes
Thread Starter
Dave,
It's no suprise that our exhausts sound very similar - the Borla set-up is nice. I would not consider my idle smooth. Some small/minor vibration with an occasional small "bump" or "shimmy". Maybe this is a result of my idle being set at the top of the spec. Could be the same exhaust resonance. After some driving around town the idle is more smooth. I should say that I have only put about 300 mi on the shark in the last year so it may need to be run in too.
It's no suprise that our exhausts sound very similar - the Borla set-up is nice. I would not consider my idle smooth. Some small/minor vibration with an occasional small "bump" or "shimmy". Maybe this is a result of my idle being set at the top of the spec. Could be the same exhaust resonance. After some driving around town the idle is more smooth. I should say that I have only put about 300 mi on the shark in the last year so it may need to be run in too.
11-02-2006, 12:47 PM
#33
Rennlist Member
Yeah, I'm pretty happy with the Borla exhaust. I can't hear it much inside the car, unless I'm in a parking garage with the window down -- then it makes a good bass riff to accompany the music of all the car alarms going off. 
CIS likes to be driven. You might try putting about a cup of Berryman's B-12 in 1/4 tank of gas, then flog it till the low fuel light comes on & refill the tank. That will clear out most of the gum/varnish buildup so you can tell how it's really running.
CIS likes to be driven. You might try putting about a cup of Berryman's B-12 in 1/4 tank of gas, then flog it till the low fuel light comes on & refill the tank. That will clear out most of the gum/varnish buildup so you can tell how it's really running.
11-02-2006, 03:20 PM
#34
Dave that sounds amazing! I need a borla catback.
Hupp that small shimmy or bump at idle is what I have been trying to battle for two years now. It's so small you can hardly feel it, but it's there. I just can't seem to get rid of it, and it's is now starting to really grate on me.
Hupp that small shimmy or bump at idle is what I have been trying to battle for two years now. It's so small you can hardly feel it, but it's there. I just can't seem to get rid of it, and it's is now starting to really grate on me.
11-02-2006, 03:58 PM
#35
Burning Brakes
Thread Starter
BC,
That's why I consider my shark to idle "with character". Very smooth acceleration and good pull, but just a little rough around the edges at idle.
That's why I consider my shark to idle "with character". Very smooth acceleration and good pull, but just a little rough around the edges at idle.
11-02-2006, 04:29 PM
#36
Rennlist Member
Thanks Robbie... I don't know if the "bump" you're talking about is the same kind of lumpy sound that you can hear in my .wav file, but if it is, and you can put your hand on the plenum while it's idling and it doesn't shake around, it's probably just exhaust resonance.
11-02-2006, 04:34 PM
#37
That's the same thing that my shark is doing. Great performance, very smooth at all conditions except at idle very small bump or shimmy. I think it still smells fishy. there has got to be something we are missing. I was thinking maybe due to the fact my cats are removed, are yours removed? From prior posts I see you have changed your fuel distributor, so I'm chalking that one off my list. I've got new eng shocks, maybe I need to change the eng. and tranyy mounts. Do you have new shocks, and mounts installed?
11-02-2006, 04:49 PM
#38
Rennlist Member
New shocks & mounts up front only. Stock cat(single) still in place. Try running the idle down to 750 - 700 RPM and see if it smooths out. Remember, we have adjacent cylinders firing one after the other, which is a good excuse for it to sound lumpier than other V8s or even compared to sharks with header/X-pipe.
11-02-2006, 05:08 PM
#39
Burning Brakes
Thread Starter
BC,
Just about everything is new/rebuilt on my CIS. Only old thing is the decel valve. My engine mounts and shocks are new. I have a '84 cat installed. I'm beginning to thing its the nature of the beast. In general, I can put my hand on the spider and it wont shake continuously. The shark will idle along and about every 20 seconds a small bump. You can just feel it, this is not something I can hear in the exhaust like a misfire or something.
Just about everything is new/rebuilt on my CIS. Only old thing is the decel valve. My engine mounts and shocks are new. I have a '84 cat installed. I'm beginning to thing its the nature of the beast. In general, I can put my hand on the spider and it wont shake continuously. The shark will idle along and about every 20 seconds a small bump. You can just feel it, this is not something I can hear in the exhaust like a misfire or something.
11-02-2006, 05:10 PM
#40
The lumpy idle sounds similar, but your tone is different. My plenum shutters @ the same time the idle bumps or shimmies. I was wondering if due to the fact my cat being removed excess fuel was igniting in the exaust causing the shimmy, but if hupp has his cat installed still I'm chalking that one of the list. I have had the idle adjusted all over the place, and I bet Hupp has tried the samething.
I've set and reset my control pressure and nothing seems to cure the vey small bump or shimmy.
I've set and reset my control pressure and nothing seems to cure the vey small bump or shimmy.
11-02-2006, 05:39 PM
#41
Most of my cis is reconditioned as well as many new ignition components. I can not hear the bump ether i can only lightly feel it about once every four seconds. I'm chalking the cats out of the picture.
My decel valve is removed. I do have a small amount of play in my distributor shaft. I think I'm just going to rip all of the cis system out again this winter and be VERY particular to all air leak locations and try again in the spring.
My decel valve is removed. I do have a small amount of play in my distributor shaft. I think I'm just going to rip all of the cis system out again this winter and be VERY particular to all air leak locations and try again in the spring.
11-02-2006, 05:48 PM
#42
Addict
Rennlist Member
Rennlist Member
Scott,
Are you talking about almost a quick little "miss" every once in a while at idle? Mine is pretty lopey at idle, you can hear the miss or blip that you say every once and a while, but the idle feels smoothe.
I have no cats on mine. I have been driving it alot the last 2 weeks after a shot of (B44 I think it was) in the fuel tank. I got it from the Porsche House and they said to use it about once a year. The stuff is supposed to be like all the other fuel injector/fuel system cleaners x 10!!! I've had good results with it after the car has sat long term before. (over 10 months).
Are you talking about almost a quick little "miss" every once in a while at idle? Mine is pretty lopey at idle, you can hear the miss or blip that you say every once and a while, but the idle feels smoothe.
I have no cats on mine. I have been driving it alot the last 2 weeks after a shot of (B44 I think it was) in the fuel tank. I got it from the Porsche House and they said to use it about once a year. The stuff is supposed to be like all the other fuel injector/fuel system cleaners x 10!!! I've had good results with it after the car has sat long term before. (over 10 months).
11-02-2006, 05:58 PM
#43
It sure sounds like there are a couple of us with this condition. What the hell is causing it? I just can't belive that it is the nature of the beast because i doubt that porsche would have released this car for sale with this inherent problem.
Well I'm off to work I'll be checking this thread tonight.
Well I'm off to work I'll be checking this thread tonight.
11-02-2006, 09:42 PM
#44
May want to check the spark plugs and heat ranges for the lumpy idle. May also want to check the voltage at the 15 post of the coil. 3 volts is acceptable but on the low end and could cause the unburnt fuel miss (i.e. lumpy idle).
Dennis
Dennis
11-02-2006, 11:37 PM
#45
Burning Brakes
Thread Starter
I would not go as far as describing the idle as lopey. Lopey reminds me of that Harley-like "potato-potato" type idle.
Chuck,
Sounds very similar if not the same. My idle is a deep " bwwaahwwaahwwaahwwaahhh" with a very small bump/miss every 10 to 20 seconds. BUT, I can only feel this miss and it is not evident in the exhaust tone. Don't get me wrong, I would also consider my idle smooth, well... it does not shake the car continuously. Most of the vibration I feel is from my borla and the occasional bump.
BC,
You are also correct -- I have chased this for two years now. In fact, I keep my CIS adjustment tool and a flat head screwdriver in my driver's door map pocket. I do not always use them but they are there and I think I would feel naked without them in the shark.
Installing the CAT did nothing for the idle. Made the exhaust tone a bit "tighter". I really think I need to drive the shark more, but I've been too hard at work restoring. That's almost done now.
Chuck,
Sounds very similar if not the same. My idle is a deep " bwwaahwwaahwwaahwwaahhh" with a very small bump/miss every 10 to 20 seconds. BUT, I can only feel this miss and it is not evident in the exhaust tone. Don't get me wrong, I would also consider my idle smooth, well... it does not shake the car continuously. Most of the vibration I feel is from my borla and the occasional bump.
BC,
You are also correct -- I have chased this for two years now. In fact, I keep my CIS adjustment tool and a flat head screwdriver in my driver's door map pocket. I do not always use them but they are there and I think I would feel naked without them in the shark.
Installing the CAT did nothing for the idle. Made the exhaust tone a bit "tighter". I really think I need to drive the shark more, but I've been too hard at work restoring. That's almost done now.