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Registered
Join Date: Jan 2000
Location: Placerville, CA, USA
Posts: 34
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CIS troubleshooting question...
Hi all,
In regards to my 1974 911, 2.7 liter, stock. I’ve been troubleshooting some problems with the CIS and I’ve run into a big one – I think. The System Pressure is low by about 1 bar. I put a few shims in the pressure regulator – in the fuel distributor – but that did not seem to make any difference. I would add that fuel flow – as measured at the fuel return line – is low. While not a test procedure in the book, I measure fuel flow out of the fuel accumulator and it is considerably more than I get from the return line. I have replaced the fuel filter – that did not have any impact. I’m thinking weak fuel pump, but before I go out and spend $350 on a new one I thought I’d ask for some advice. Thanks in advance!! Mike |
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04-28-2003, 08:50 AM
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Heck, I’m only 5 not 71!
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Are you using a CIS pressure guage and test rig to verify the fuel pressure. If you are not I would suggest blowing the $100 bucks and use it to check the fuel system before spending money on parts you might not need.
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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04-28-2003, 09:59 AM
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Registered
Join Date: Jan 2000
Location: Placerville, CA, USA
Posts: 34
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Hi Pat, I am using the CIS Pressure Gauge - that's how I know my system pressure is low by 1 bar.
Thanks! Mike |
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04-28-2003, 10:42 AM
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Heck, I’m only 5 not 71!
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The K basic fuel pressure should be 5 BAR/ 73 PSI as per the Bosch CIS fuel injection management book.
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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04-28-2003, 01:56 PM
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Registered
Join Date: Jan 2000
Location: Placerville, CA, USA
Posts: 34
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I'm getting about 3.5 bar. Question is - what components might cause low system pressure? What should I be looking at?
Thanks! Mike |
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04-29-2003, 06:57 AM
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Registered
Join Date: May 2002
Location: Chews Landing, New Jersey
Posts: 272
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This may or may not help!
I have CIS on a non P car. From the manual, the flow of the pump at the return should be 750 ccs in 30 seconds minimum. For comparison the system pressure on this car is 5.1 +/-.4 Bar Jeff
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'72 911T gone '85 TVR |
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04-29-2003, 11:06 AM
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Registered
Join Date: Jul 2001
Location: Wilmington, NC USA
Posts: 635
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Are you sure that you are hooked to the high pressure side. The first time I tested a CIS I was measuring the control pressure side which could be as much as 1 bar lower on cold starts. The line to the cold start valve is a good place to get system pressure. If it is still 1 bar low and there is no blockage in filter, accumulater, line etc then you need a new pump. This is how these roller pumps fail. They start losing pressure. And on a CIS low system pressure causes all kinds of problems from starting to running. Good Luck.
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69 911 2.3Ez 85 928S |
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04-29-2003, 12:53 PM
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Registered
Join Date: Jan 2000
Location: Placerville, CA, USA
Posts: 34
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I am measuring the system pressure from the line that goes to the warm-up regulator - but I don't remember which side I had the valve on to test for system pressure - I'll check that again tonight. I'm not getting 750 cc's in 30 seconds - it's more like 600. And I don't think there are any blockages - I get good flow out of the fuel filter.
Question - Is there an alternative to getting a replacement Bosch fuel pump – they are sort of pricy? Is there another model/manufacturer? It looks to me like a simple inline fuel pump would work – as long as it could make the pressure/flow required. Thanks! Mike |
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04-29-2003, 01:52 PM
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