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Fuel Distributer from hell!

My '86 930 has been in the shop for almost 4 months now. We have sent the fuel distributer to a company in California twice now ( they failed) and once up to another company in Alabama to re-build it. It is an older cast euro distributer.

When it was rebuilt they found one of the orifices had fallen out, which is apparently a known problem with the older fuel heads. We got it back and it appeared to work.

Now the car has a surge in the idle and it feels like you are "lugging" the engine when you are cruising along with an occasional backfire. It kind if surges slightly when you are driving at any steady RPM.

Has anyone had a similar problem? My mechanic is pulling his hair out.
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1986 930 Ultra-Smith RUF Slant Nose conversion, RUF VB, K-27 HF-S, B&B Headers and Exhaust, RUF Short Shifter, RUF Interior
Old 10-31-2011, 09:23 AM
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An obvious question. Have you checked for vacuum leaks? or leaks in the intake line including the pressure side. Sometimes if significant enough the air plate can get confused and flutter.
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Old 10-31-2011, 09:47 AM
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That was the first question I had. My mechanic assures me that it is plugged in the way it should be with no leaks. I keep wondering if i should ditch the cast iron FD and go with a newer aluminum one.
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1986 930 Ultra-Smith RUF Slant Nose conversion, RUF VB, K-27 HF-S, B&B Headers and Exhaust, RUF Short Shifter, RUF Interior
Old 10-31-2011, 10:25 AM
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I would go the aluminum route.
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Old 10-31-2011, 10:26 AM
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What boost level are you running?
The Euro head has a metal diaphragm that is unforgiving of boost spikes. If this has happened your AFR's will be off and not able to stabilize. It will dump fuel in some cylinders.
The cause must be determined before another head is possibly damaged. Gunk in the fuel can also clog things up fast. The system should be cleaned if this problem is possibility.
To use the late model aluminum head it should be modified to eliminate the lambda system.
I have both types of heads in stock if it found you need one.
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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
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Old 10-31-2011, 12:39 PM
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The boost is max .9 Bar with the boost dialed in. I never saw anything over .7 today when I was testing it. It ran great on boost. It is putting around off boost that it runs poorly.

It was tuned by Flotech in Alabama off of the engine. My mech sent the whole fuel injection system up there to fix it the third time. I am not sure who tried in California. I think Flotech tested it on an engine. The system was basked in calibration fluid when we got it back.

I think that the fuel is OK. I was driving it pretty regularly when it blew up. The original problem was split fuel injection blocks. I think that it cascaded from there while I was trying to get it into the shop. It sounds like the Euro Head may be the bain of my existence on this thing.

Thanks for the input. I will let you know which way we go.
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1986 930 Ultra-Smith RUF Slant Nose conversion, RUF VB, K-27 HF-S, B&B Headers and Exhaust, RUF Short Shifter, RUF Interior
Old 10-31-2011, 01:26 PM
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I am sorry, I said boost spikes and was thinking about the WUR. For the fuel head it is pressure spikes, from the fuel system. You should verify that your system pressure is steady and has no spikes.
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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 10-31-2011, 01:45 PM
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Interesting read as I have had slight surging at cruise for as long as I have had the car. Many tweaks and mods and smog removal, etc. has not remedied the problem. I believe it is the fuel distributor.

What causes the fuel pressure to 'spike'? Faulty pumps or accumulator/filter or the return line or the distributor itself?
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Old 10-31-2011, 02:53 PM
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Many things can cause the fuel pumps to surge but one major thing dampens the spike and that is the fuel accumulator. Indicators of accumulator failing is having hot start problems or pressure is bleeding down too fast.
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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 10-31-2011, 08:06 PM
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Well, finally the little beast is running fairly well. It still wants to hunt at idle every so often and it still has a very slight pressure surge but only occasionally. I know that the temp changes from mid 30's in the morning to nice upper 60's plays a bit with the CIS.

I got an aluminum head from a guy on ebay that came off of a '88 and the frequency valve. That seems to have solved most of the problems.

It is really nice to drive it again. Now I have to establish the reliability before I take it out of town. I still have the nightmarish electrical system to work through. The guys that did all of the mods at Ultra-Smith hacked up the electrical system pretty good. The alarm/locks do some pretty funny things and you never want to leave the keys in the car because it will lock you out all on its own!

Ahhhhh! The joys of restoring antiques!!
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1986 930 Ultra-Smith RUF Slant Nose conversion, RUF VB, K-27 HF-S, B&B Headers and Exhaust, RUF Short Shifter, RUF Interior
Old 11-11-2011, 03:14 PM
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Quote:
Originally Posted by sundevil64 View Post
An obvious question. Have you checked for vacuum leaks? or leaks in the intake line including the pressure side. Sometimes if significant enough the air plate can get confused and flutter.
when I was running CIS a possible future vacuum leak that I couldn't find spooked me enough for me and go spend $100 for one of those electronic vacuum leak detectors that listen for vacuum frequencies.
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Old 11-15-2011, 12:07 AM
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