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Registered
Join Date: Aug 2006
Location: Australia
Posts: 130
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New build running lean
Help! I've just had my 1981 3.3 engine rebuilt and we cant get enough fuel into it so its running lean. The mechanics are stumped so I need some ideas.
Here's what we changed: 964 cams 3.4l pistons and sleeves long neck intercooler cold air intake ported heads It has a K27 and we are running a 0.8 spring at the moment. Here's what we have checked: replaced the fuel pumps rebuilt the WUR checked the injectors apparently the fuel pressures are all ok What are we missing??????
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1981 930 headers, K27, 1 bar spring 1988 951S work in progress |
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Registered
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Which wur are you running? What are your fuel pressures? Youre probably close to the limit for cis.
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'86 930 Guards Red - EFI MS3Pro, 80lb inj, 3.4, GT35R, Tial 46, Bosch 044, B&B Headers, 3.2 carrera manifold, Turbokraft Full bay IC '12 Gallardo LP-570-4 Performante Ducati 748R |
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Registered
Join Date: Aug 2006
Location: Australia
Posts: 130
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Just running the standard WUR.
The fuel pressures have been checked and apparently they are what the manual says they should be.
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1981 930 headers, K27, 1 bar spring 1988 951S work in progress |
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Registered
Join Date: Jul 2006
Location: S. Florida
Posts: 7,249
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There's one incredibly easy way to get a lot more fuel from CIS... just unplug the 12 volt bimetallic heater element supply plug on the WUR... takes about 2 seconds to do that
![]() Only downside is it richens up the mixture across the range everywhere including idle so it will oscillate at idle and may almost stall after blipping the throttle. What you could do is install a wire wound potentiometer in the 12 volt supply wire to the plug on the WUR and after experimenting with it you might find a resisitance setting that gives more fuel where you need it and then after adjusting the idle CO screw and warm control pressure you might find something that works well at all speeds and engine loads. The WUR might end up getting around 8 or 10 volts or less then instead of the full 12-13.5 volts it usually gets. Anyway, it's a thought. I havn't tried installing the potentiometer but I have stopped and unplugged the 12 volt plug on the WUR after the motor was fully warmed up from driving a half hour or longer and after 10-15 minutes control pressure dropped down from 60 psi to 40 psi and my steady cruise AFR went from around 15:1 down to 12:1 I have an onboard control pressure gauge and wide band AFR gauge in the car so I can see them while driving. Also have a CIS flowtech modified fuel head on the car so I don't need any more fuel but I wanted to try that and it definately worked. |
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Registered
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Quote:
![]() Factory pressures are great for factory horsepower, but you're probably 100+ over that. Gotta get that extra fuel dialed in.
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'86 930 Guards Red - EFI MS3Pro, 80lb inj, 3.4, GT35R, Tial 46, Bosch 044, B&B Headers, 3.2 carrera manifold, Turbokraft Full bay IC '12 Gallardo LP-570-4 Performante Ducati 748R |
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Banned
Join Date: Nov 2007
Location: Rockwall, Texas
Posts: 8,559
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As dos noted, the pressures in the factory manual apply to a stock engine - you have to now alter the pressures to suit the new fuel demands of your highly modified engine (an adjustable WUR being a good way to do that).
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Registered
Join Date: Aug 2006
Location: Australia
Posts: 130
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How about additional injectors? When do people start adding those?
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Metal Guru
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Quote:
Procure a Leask adjustable WUR (mail him your WUR and he will mod it for you). Use an Innovate LM-1 or LM-2 to monitor your afr. Adjust warm and boost control pressures until you are in the box. I just went through this when I went to a larger turbo and SC cams. I'm running .2 bar lower on both warm and boost control pressures and my afr's are right back to what they were when my engine was stock.
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Paul B. '91 964 3.3 Turbo Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, H&R Coilovers, ESB spring plates- 210 lb |
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