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Injectors, Alternator, Fuel Pump Or Something Else?
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#1
06-20-2022, 08:00 AM
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Injectors, Alternator, Fuel Pump Or Something Else?
I have a somewhat still new to me 83 911sc targa (155k miles) and I am hoping you all can troubleshoot an issue I am starting to see more frequently. It isn't a daily, but I try and get it out at least once or twice a week. Lately I have noted that on cold start ups, its starts right up but the RPMs stay under 1k until things warm up and then it idles at 1k. My biggest concern though is that by the time I get it backed out of the driveway and into 1st gear, I will give it more gas and it seems really laggy for a few seconds and then it either gets enough fuel or whatever the issue is corrects itself and off I go.
I have also noticed the tach bump on random occasion, which I believe is a sign the alternator is on its way out but not sure if the two are related So the big question is, is the lagging on the cold starts related to the injectors, the alternator, fuel pump, or something else? Any info would be appreciated. Thanks. 
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#2
06-20-2022, 11:46 AM
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CIS injectors are mechanical and easy enough to test if you are inclined. Pull them out one at a time, put them in a small container and with ignition on trigger fuel. Keep in mind the seals and cups are likely brittle and due for replacement if not done already. You can see spray pattern and measure volume of fuel with this test. Not scientific but generally close enough to ID a significant issue.
Dont underestimate the impact of a vacuum leak, worth spending time with a simple smoke machine or a flashlight and some carb cleaner. Also, I might suggest testing o2 sensor output and mixture to get a better idea of current state. Battery issue. Confirm battery connections and ground strap are in good shape. test battery, charge if required, before jumping to an alternator.
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78 SC, the 'Red Car'
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#3
06-20-2022, 08:57 PM
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Dont underestimate the impact of a vacuum leak, worth spending time with a simple smoke machine or a flashlight and some carb cleaner. Also, I might suggest testing o2 sensor output and mixture to get a better idea of current state.
Sounds like a vacuum leak to me, but Cmartin is correct, could be all of those issues. Do you have any service history on the engine? Do you notice a difference in vacuum when you remove the oil cap while the car is running? If you think it's a fuel related issue with the CIS, this video has a ton of info:
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“When I was born I was so ugly the doctor slapped my mother.” – Rodney Dangerfield Bill C "aka" Catdaddy - The Catfather - Current: 1980 911sc 2019 Ford Raptor  1987 Mercedes 560sl ------------ Sold: 2011 BMW M3 2000 996 C2-IMS 2 Row, RMS Update 1986.5 928s 1987 944 16v 1973 911t 1969 911t "My first car"!! 1969 Westfalia Bus 1973 Volks Superbeetle Last edited by catron1; 06-20-2022 at 09:44 PM.
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#4
06-21-2022, 07:51 AM
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Thank you both for this great info. I will get into this once I finish up with a move I am in the process of going through right now. It kills me to have my small 1 car garage stacked with moving boxes around the car, but thankfully I am upgrading to a 2.5 car garage so it will be worth it.
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#6
06-22-2022, 07:13 PM
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Quote:
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Steve 996 GT3 996 C2 (gone) 911SC (gone)
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#7
06-24-2022, 08:40 AM
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Quote:
https://bringatrailer.com/listing/356-sculpture/
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#8
06-25-2022, 04:25 PM
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Quote:
 wow
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