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CIS query.
I have posted this before, but will try again.
My issue is on a 930, but I think the problem is more a CIS issue than a 930 issue. This problem has been on the car from the day I got it. I have had the fuel system apart completely, several times, incl the fuel head. I cannot find the cause of it. Every now and then the airplate develops a violent vibration at idle, and the CPs go crazy. It upsets the fuel system badly. If you put your finger on the airplate, it stabilises and sits rock steady, and everything becomes normal again - CPs etc. While it is doing this vibrating, it is sending the fuel relays crazy too. I know there is a restrictor in the WUR/fuel head line, to minimise surges. Maybe this is a design issue? But I have not had the problem with any other CIS system. I really need to track the source down if I can. I have changed my WUR to a digi WUR, but the problem is still there, intermittently. Any ideas where this originates from, or how to cure it? Thanks 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:-) |
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06-29-2009, 05:59 PM
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Join Date: Jan 2009
Location: maryland
Posts: 271
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It is not an unusual problem. It seems to be a hydraulic oscillation of the primary feed pressure circuit. I had replaced the accumulator and eliminated most of it. But my problem seemed to occur during the hot summer when temps exceeded 90f and the car had been idling for about 30 minutes. I had thought it had been related to a fuel boiling issue.
Anyway there is a rebuilder in Ca that specializes in rebuilding the turbo fuel distributor heads. I believe there is a internal port that he enlarges to eliminate the oscillation. |
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06-30-2009, 07:46 AM
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OK, thanks. I can swap my accumulator over and see if it improves. I'm trying to avoid having the head rebuilt on the basis it 'might' fix it, without knowing for sure what the cause is. The WUR has a very small orifice in the line between WUR and fuel head, to provide some damping I think. So, it sounds like an inherent design issue, with a few remedies built in. I'm just trying to find which remedy is not operating.
I'll try swapping the accumulator over, and see if my SC inherits the problem. Regards 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:-) |
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06-30-2009, 11:57 AM
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Join Date: Oct 2006
Location: MYR S.C.
Posts: 17,321
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what is the primary pressure doing when this happes?
are you talking about the fuel pump relays going crazy? if so, the relays would cause the FP's to go crazy thus messing with the pressures. i am trying to remeber the power and ground ciruit for the FP relays. i think the ground side goes thru a speed "relay" that cuts the FP's off as a rev limiter, then goes to something for the boost. i have not looked at a diagram in quite a while. i am trying to say the relays or what controls them is the source of the problem and not a result, like the air plate fluctuating or the cp's changing.
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86 930 94kmiles [_  _] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD88 BMW 325is 200K+ SOLD 03 BMW 330CI 220K:: [_ _] RUNNING: [__] NOT RUNNING:01 suburban 330K:: [_ _] RUNNING: [__] NOT RUNNING:RACE CAR:: sold |
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07-02-2009, 06:45 AM
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The relays are going crazy because the airplate safety switch is on/off/on with the vibrating plate.
I dont think I can measure the primary (system) pressure while this is happening. I think the switch over in thetest line interrupts/blocks the system pressure off, and therefore cuts the fuel supply to the head. I am thinking of making something up that would allow me to tap into the system pressure without doing this - if I get no definitive answers. Regards 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:-) |
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07-02-2009, 11:44 AM
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Matt,
I think I owe you a beer. I swapped accumulators over, and in my short test to date, I cant make the 930 airplate bounce. Normally it did not take much effort to do it. Oddly, it checked out by the book in terms of holding rest pressure - which is about the only test you can do for it. But my problem seems to have gone. This is a great relief - I have spent hours on the fuel system trying to find it, and it has seriously p***d me off. Great to nail these irksome things. Now I better buy my SC a new accumulator before I forget and go round this loop all over again. 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:-) |
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07-04-2009, 06:26 PM
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