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Helmsy's Avatar
 
Join Date: May 2008
Location: South Australia
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My WUR is from BL and he rebuilt it recently (at his cost) due to the seal leaked and wasn't holding pressure. I think at the time I also tried my original wur and it still did the same thing. I can't actually remember if I did tho so I might try the original WUR again and see if it has the same effect.

Sorry to hijack. Could the enrichment problem cause some cylinders to run richer than others (fuel dump) under boost?
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Ben
'85 930 - Black on Black
'95 993 Turbo - Silver
Old 11-17-2011, 10:40 PM
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Crotchety Old Bastard
 
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Internet diagnosis is like shooting fish in a barrel.
One other thing I can think of that could cause these symptoms is a damaged metal diaphragm in the fuel head. This happens due to spikes in fuel pressure and can affect specific cylinders. Typicaly the affect severe enough that the engine does not run well, however I can imagine that a slightly damaged diaphragm could play havock with WUR function. Going back to the fuel volume test does not bear this out however.
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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 11-18-2011, 03:41 AM
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Yes, I would have thought the fuel volume test would rule this out.
However, you raise an interesting point which does raise a small niggle in my mind.
My DWUR has been having a few problems - due to the fact my fuel head has very low leakage - according to UT. The injector system they now work on is struggling to cope - not responding in correct manner as my system holds the CP for longer than most heads. I put this down to the new metering piston - ie I eliminated the scores and wear.
One result of this was CPs intermittently spiking to system pressure - ie 6 bar+ - the injector is not responding/opening quick enough.
I wonder if this has screwed something in the head. Of course mine has the rubber diaphragm - but these are very sharp/violent spikes.
Tried to post a copy of the data trace - but beyond me.
This may be getting close to the issue.
Thanks Brian. I suspect you mean 'boxing at shadows'?. Shooting fish in a barrel is usually considered easy peasy.
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 11-18-2011, 10:16 AM
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Crotchety Old Bastard
 
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You ever tried to shoot a fish? All I get is a leaky barrel, ha!
Yes if you have experienced pressure spikes they will wreak havoc on the fuel head diaphragm. Typicaly you see 1/2 the cylinders go rich. Puzzling that your fuel flow test shows no significant difference which points towards an air balance issue instead of a fuel balance issue.
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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 11-18-2011, 12:14 PM
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Well, I throw this out in case it lights any bulbs.
There seems a progression in richness from 1 to 6.
The pics won't show it in enough detail, but in the sunlight you can see the shades of dark much better.
#1 is sooty and blacker than 2 which is darker than 3 (has a slight tan colour) which is darker than 4 which is darker than 5 - which is not quite darker than 6. ie with the exception of 5 looking sl leaner than 6 , they progress from 1-6. Given it is CIS and the fuel head really has not much idea what goes where, I am trying to figure what would do this. Alternatively there is less air getting to 1 etc. Or the fuel head is capable of behaving differently to the fuel test conditions in real life. But the fuel test conditions are precisely how these heads are set up, AFAIK.
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 11-18-2011, 01:34 PM
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i think i'd try another fuel head, a good one
Old 11-18-2011, 04:42 PM
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One is on the way.
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:-)
Old 11-18-2011, 05:56 PM
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