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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,274
It sounds like your fuel head in it's current state is running out of fuel at high rpms.
You need the pressure gauge to see what your system pressure and control pressure is now.
I don't know what fuel head you have on your car. Is it cast iron and painted black or is it cast aluminum and silver colored with the lambda system installed and working?

You may be able to get more fuel by raising the system pressure if it's below 96-98psi. You do that by adding a shim or putting in a thicker shim under the little spring in the fuel head's fuel pressure regulator. The shims are like real small washers and that would take experimentation because i don't think you can buy the shims anywhere.

You can turn the individual injector flow adjuster allen head screws under the 4mm allen head covers clockwise a small amount but I'm not recommending that unles you are doing a fuel injector flow test with the injectors placed into 6 individual 12 oz plastic water bottles.
Also if you have a black non lambda fuel head turning those adjuster screws too far will increase spring pressure around the fuel orifices and will dent the stainless steel diaphram valves/gasket that seperates and seals the top and bottom halves of the fuel head and if that happens it's permenantly damaged and won't meter fuel correctly anymore.
The aluminum '86 and later USA Lambda fuel heads use a synthetic diaphram that is more flexable and it won't permanently dent downwards from the increased spring pressure.
This is why the aluminum USA lambda fuel heads can be adjusted and modified to flow more fuel than the heavier black cast iron euro fuel heads.

Best solution would be to call or email Larry at CIS Flowtech and talk to him.
You can send your fuel head and somewhere around $550 to CISFLOWTECH and he can modify your fuel head to flow anywhere up to 25% more fuel. He does some secret proprietary machine work in the bottom half of the fuel head, changes other adjustments and rebuilds the whole thing with new orings..
You'll also probably need the rpm switch and vacuum solenoid in the boost signal hose going to the control pressure regulator. If you don't install that the engine will be really rich in the midrange when boost comes on.

Others have kept the stock fuel head and replaced both fuel pumps with Bosch 044 motorsports fuel pumps and an inline injector or frequency pulse valve in parallel with the control pressure regulator to trim the control pressure at lower rpms for a flatter fuel curve and lower control pressure further at high rpms and get more fuel from the injectors to keep AFR's around 12:1 at at 6500rpms.

Keith/911st and another person here (I can't think of their name other than Stup) can help you with the controller that runs the frequency valve if you decide on that. I think the controller is made by AEM.

Anyway... for the next step I think you need the CIS pressure gauge to see where your fuel system and control pressures are if keeping CIS.
Old 06-10-2010, 10:43 AM
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