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Porsche-Poor
 
bcoats's Avatar
 
Join Date: Feb 2005
Location: Seattle, WA
Posts: 463
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CDI question

Just wondering if a faulty CDI could cause a car to run rich, foul plugs and/or cause some jerking when starting out in first gear? Having some issues, just replaced plugs, wires and ignition coil, new o-ring on intake manifold, running better but still have some jerking and heavy gas smell? Also, gas analyzer didn't detect any gas leaks, at a loss??? Any help greatly appreciated as always. . .
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1979 911 RS clone hotrod
1983 930 turbo-sold, will be missed
1992 964 C2 Coupe-regrettably sold
1980 911 SC Weissach-regrettably sold
1975 911S-sold but not forgotten
Old 10-12-2007, 10:48 AM
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what was your CO or AFR at idle?
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

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Old 10-13-2007, 02:50 AM
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I had a similiar problem and it turns out that my oil filler spout was missing the rubber seal around the oil cap and this was actually causing a vacuum leak that made my car hesitate at low rpms. Right where you pour the oil in the engine, the cap you remove should have a rubber seal on it or else air leaks thru and gets into your intake manifold thru the oil recirculating hose.

Sounds silly, I know, but my mechanic told me that nobody believes that can be a problem until it happens to them. Fixed my issue.

Probably not the probelm you are having, but worth checking whenever you feel a hesitation.

Anyway, the real problem you are having sounds more like your Air to fuel ratio is too rich in your CIS. You will feel 'surging' when under part throttle when it is too rich, as in your car will not stay at a steady speed and will want to lunge forward more than you expect when you are just trying to drive at a steady speed.

Your CD has nothing at all to do with your car running rich. If it was your CD, your car would be stalling out or misfiring pretty badly, I would think.

Just so you know, if you lean your CIS out too much then that will end up causing a 'bucking' feeling, sort of a hesitation. So when tuning CIS, you need to get it right in the middle between too rich and too lean.
Old 10-13-2007, 06:28 AM
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Porsche-Poor
 
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Thanks guys, CO at idle is 3%, after a couple days of driving problem for whatever reason not doing it that much, but do need to give more gas however to get rolling than I did before???
__________________
1979 911 RS clone hotrod
1983 930 turbo-sold, will be missed
1992 964 C2 Coupe-regrettably sold
1980 911 SC Weissach-regrettably sold
1975 911S-sold but not forgotten
Old 10-13-2007, 03:43 PM
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If you are sure you don't have any air leaks then you will have to get an AFR gauge like the Innovate XD-16 or LM-1. You can then see what happens while you drive.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 10-13-2007, 04:03 PM
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Quote:
Originally Posted by bcoats View Post
Thanks guys, CO at idle is 3%, after a couple days of driving problem for whatever reason not doing it that much, but do need to give more gas however to get rolling than I did before???
If something is not leaking air into your intake like we have mentioned, and your car is tuned right, then you would think that it is a clogged fuel filter or anything keeping gas from getting to the manifold if you need MORE gas to get it going. That is the opposite of being too rich, of course.

Some of those CIS style valve cleaner treatments will clean out your CIS system of carbon deposits. The Sauber valve cleaning bottle is good.

Keep in mind that these cars don't drive right until they are warmed up when it is cold out. My car takes ten minutes before I can get on the gas when the temperature is below about 60. It feels really sluggish before getting warmed up, hesitant. The problem goes away when the car is 180 degrees.
Old 10-14-2007, 06:53 AM
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