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Old 08-19-2002, 04:39 PM
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Fuel Pressure Accumulator Problem?

I've tried everyting I can think of to solve my rough idle hesitation problem on my 450Sl:fuel distributor, plugs, wires, dist. cap & rotor, fuel injector seals, cold start valve, fast idle air valve, coil, fuel filter, vaccum lines, thermovacuum valve. Hey, before long I'll have a new car at this rate. The rough idle beagn when the weather warmed up. The car starts and idles ok in P or N. in D the rpms fall to ~600 and it shakes. It also hesitates until I get it up to 35mph or so. then its runs ok. It is also gettin harder to start when warm. Is it my warm-up governor? Fuel accumulator?
Could someone help please?
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Old 08-19-2002, 09:04 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Most likely it is the warm up regulator. I have seen them faulty out of the box.
Donnie Drummonds
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Old 08-19-2002, 10:17 PM
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Join Date: Jun 2001
Location: Kansas City
Posts: 12
Not sure it this will help, but I had a similar problem with my Audi. It ended up that it was the fuel pressure regulator. see
I usually had the problem after the car warmed up.
'98 E320 90k
'91 Miata Turbo 280hp
'90 Miata Turbo 230hp
'90 Audi 200 turbo 170k
'93 Caravan
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Old 08-20-2002, 07:39 AM
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fuel pressure problem

I have a Porsche 928 with CIS, and had the same symptoms for a long time. I didnt do anything until it got worse and lost all power and response. I got a CIS gauge set from JCWhitney (~$60), and a book from Amazon - How to tune and Modify Bosch EFI by Ben Watson - ~$15. This covers CIS, and will tell how to test everything, gives all pressure settings for CIS on all models it was used on. My problem was a blocking Warm up Regulator, producing high control pressure, giving lean mixture. Watson doesnt tell you how to fix WUR or fuel distributor, but the WUR is not hard to work on at all (easy to say now, I was a bit wary before though). As soon as I got pressure right, idle came up beautiful, response is superb.
Get the book and gauge set, get the system and control pressures documented, then you know where to go. If your control is more than say 60% of system pressure, you will be running lean is my guess.
Email me if you need more.
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Old 09-24-2002, 09:21 AM
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I got the fuel pressure guage and a new fuel distributor and warm-up/pressure regulator. Would you be kind enough to give me the pressures from your book for a 1977 450Sl CIS system so I can set them?

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