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CIS frustration

Attempting to get my head around the CIS.

Seems I'm going round in circles. I think it's teasing me.

I'm at a point now where at idle, the air meter is so close to home that it cuts the fuel pumps. The idle has a fluctuation that can be cured by disconnecting the plug at the air meter plate. The fluctuation is the fuel pumps cutting in and out.

One could assume the engine is getting air from somewhere else? hence the meter is not detecting all the air the engine is consuming? I have searched high and low looking for air leaks and there are none that I can find.

Next assumption could be that the pressure on top of the plunger is so high it is pushing the air meter home?

Any thoughts? I'ts a 3L 930. WCP is about 3bar.

Old 10-11-2014, 05:43 PM
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Do you know what your AFR is when disconnecting the plug at the air meter plate?
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Old 10-11-2014, 06:08 PM
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Sorry still waiting on an AFR monitor.

I can settle it in between rich and lean on the mixture screw at idle.

Then when I connect the plug for the fuel pumps back up it starts surging, that is actually the fuel pumps turning on and off around once a second?
Old 10-11-2014, 06:25 PM
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Air meter plate flutter is often caused by it being out of adjustment.
Check zero position with plug pulled then switch on ignition briefly to set piston.
Tolerance is 0.5mm above zero point. If out of adjustment you have to knock in the guide pin with a punch. It is delicate work but reversible if you go too far. You may want a tech to check this and do it for you if unfamiliar. A workshop manual is helpful.
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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 10-11-2014, 08:54 PM
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Cheers Rarely.


I'm reading everything I can, seems to be something I'm missing? The car has run well in the past so I see no reason for the switch to be out of adjustment.

I cant seem to find much info on the 3 hose Accumulator in order to test it or at least understand it.

After talking to other 76 owners it, sounds like it was a year of much change. Detailed info is not easy to find. When I do it seems at odds with my car.
Old 10-11-2014, 10:01 PM
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Only 2 of the 3 hoses are active on the accumulator, the 3rd is a drain in case the diaphragm fails. When that happens the residual pressure upon shut down will rapidly drop causing hot start and re-start issues.
No do not re-set the air meter plate, simply check the height to see if that is the problem.
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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 10-12-2014, 03:47 AM
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So I could remove the bottom accumulator hose and plug it. Then expect there to be no fuel emitted from the bottom of the accumulator? Providing that works.

My fuel pressure is dropping off straight after shut down. Not my primary issue at the moment.

Thanks for your help, I'm away for several days for work but will be back at it late next week.

I've got a week to do some more reading.
Old 10-12-2014, 11:37 AM
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The bottom fitting on the accumulator recycles back into the fuel system. I would not uncap it as you would have to cap the line and risk fuel dumping into the engine bay right above the left bank exhaust system.
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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 10-12-2014, 07:39 PM
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Just as a test. To see if the accumulator leaks.

Old 10-14-2014, 03:56 AM
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