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gax gax is offline
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79 930 CIS Low System Pressure

Hi All,

Just after some advise on diagnosing low system pressure on CIS. Car developed a slight hesitation around 2-3k rpm a couple of weeks back so I purchased a CIS guage to check pressures as a first resort suspecting a possible fuel pump issue. What I discovered is that the system pressure is 4.8bar and should be 6.0 bar going by the manual.

Cold control pressure is 1.5bar and should be around 2 to 2.5 bar based on the current temp here which is around 25 degrees celsius. Tested fuel flow from the fuel return line and flow was fine. Filed 1300ml container in 30sec. Ran fuel pump pressure test by running the CIS gauge in between the fromt and rear pump and pressure was good at 3.2 bar.

Also checked the Fuel distributer pressure releif valve and it has the 2 shims and o rings look fine.

Any ideas as to what could cause the low system pressure if the pumps seem o.k?

Cheers Greg.
Old 01-03-2018, 12:36 AM
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Crotchety Old Bastard
 
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Could be a blockage somewhere. Replace the fuel filter first, make sure the pumps are getting 12V minimum each while running and verify flow and pressure at the fuel distributor.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-03-2018, 03:42 AM
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If your battery is down a bit you will have low pressures when testing static engine - as Brian says - need to verify you are getting proper 12V. The pumps suck a lot of power. You can do those tests with engine running (which should provide solid 12v for pumps). You may like to try again if you did those statically. You can do system pressure that way - briefly before engine wants to shut down - do your CP then flick the valve to close and see system pressure (takes about 1 sec) then open valve. If they seem in spec, let it run to warm WUR up and get WP (about 5 min idle should do it). That way you can eliminate that part of the scenario (or not).
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 01-03-2018, 03:58 PM
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Quote:
Originally Posted by RarlyL8 View Post
Could be a blockage somewhere. Replace the fuel filter first, make sure the pumps are getting 12V minimum each while running and verify flow and pressure at the fuel distributor.
i paid for an adjustable WUR. my boost CP and WCP are not separately adjustable.
when are you going to make this right?
not answering my PM's is not a solution for me.
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Old 01-04-2018, 08:52 AM
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Crotchety Old Bastard
 
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I have asked you repeatedly to EMAIL me with your contact info so we can get this cleared up. Confused as to why you will not do that, I can’t help you if I don’t know who you are.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-04-2018, 09:28 AM
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