[Diy_efi] Donegan ECU

[Tom Visel]

It's trading mechanical complication for electronic complication.  
Mechanical fuel pressure regulators are a mature technology, and the 
math for injectors that have manifold-referenced fuel pressure is 
simpler than that for injectors with static pressure, or for 
computer-controlled feedback-requiring variable pressure systems.  Also, 
anything with the pressure control at/near the tank is going to have 
hysteresis problems which will tend to minimize the gains that might 
have been found by the increased complexity.

My vote is no, but it's not my baby to call ugly or not.

TomV


Steven P. Donegan wrote:

>I can't quite read this as a yes or a no to fuel pump pressure control -
>can you give me a binary response :-)
>
>I.E. does fuel pressure sensing/fuel pump control make sense for an EFI
>system or not.
>
>Thanks!
>
>On Fri, 2007-01-05 at 08:00 +0900, Bernd Felsche wrote:
>  
>
>>On Friday 05 January 2007 00:57, Steven P. Donegan wrote:
>>    
>>
>>>I had not thought of fuel temp at all - every vehicle I drive
>>>would consume the gas in the rails well before it got warm :-)
>>>However this does raise a point - perhaps my ECM/PCM/EFI computer
>>>needs a way to open a fuel return line and to sense fuel temp in
>>>the rails? Any ideas on how useful that would be in the 'real
>>>world' anyone?
>>>      
>>>
>>Superflous if you're running in closed-loop; which you would be if
>>the fuel rail was warm enough to make a difference.
>>
>>If the temperature in the fuel rail is a problem, then a
>>recirculating fuel pressure control system is IMNHSO a better
>>solution. In such a system, there's always "fresh" fuel that's in
>>excess to the amount required for injection from the tank flushing
>>the rail(s). The fuel tank is the cooling environment for the fuel.
>>
>>Pressure regulation also happens at the rail(s), whereas in
>>"dead-end" systems it's at the fuel pump, perhaps a several metres
>>from the rail and therefore the injectors. That increases the
>>difficulty in controlling the pressure (time delays that depend on
>>fuel pressure and temperature); especially if it's to vary
>>dynamically wrt manifold pressure.
>>
>>The ability to vary the fuel rail pressure is at least desirable to
>>get consistent injected quantities due to a fairly constant pressure
>>difference across the injector; between the fuel rail and the
>>manifold where it's injecting.  Makes for simpler calculations on
>>injected quantity.
>>
>>If you're stuck with a "dead-end" fuel delivery system, then you
>>need to add a return line and a valve that vents the rail(s) back to
>>the tank in the interval between the fuel pump running and the
>>engine actually being started. The time delay will depend largely on
>>the free-delivery rate of the fuel pump and the volume of the fuel
>>rail(s). That ensures that there's "cold" fuel in the rail(s) before
>>you start injecting it.
>>
>>    
>>
>
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