[Diy_efi] Hesitation

Mike niche
Wed Jun 28 12:22:46 UTC 2006


At 11:07 AM 6/28/06, you wrote:
>Thanks for the reply.  So the EFI system creates its
>own virtual accelerator pump of sorts? Makes sense, a
>little extra fuel to compensate for the higher demand.

The EFI for the Hitachi/Bosch ECU with AFM (VL Commodore) uses a throttle
position sensor which has a simple square wave type etching
in a circuit board with a wiper, so each time the throttle sensor
is used it traverses this and produces a pulse, so the faster you
press it the more intermediate pulses you get interspersed with
the normal injection pulses. This is necessary because the AFM
is often some distance upstream from the throttle valve and therefore
the inlet gets more flow a fraction of a second before the AFM "knows" about
it and the consequent delay through the ECU processing cycle...

iirc the pulses go to the CPU's interrupt line so the firmware can
decide to accept or reject the pulses or simply to extend the
existing pulses if the injector opening happens to coincide
with a throttle position 'change request' or map them some other way etc.

>What do I do to diagnose this and correct it?

As suggested in another post, for a MAP system the line to the
sensor can affect operation. However on further reflection, many earlier
carburetor's had an extra accelerator pump, I recall the Ford Escort 1972
had a sizable pump with a surprising amount of squirt even though the
distance from the carby to the inlet was short and it was a progressive
dual butterfly design, so I am wondering that if a MAP based EFI system with the
implication it would automatically provide means for ECU to inject fuel on sudden increase
of pressure is going to be sufficient as a carby based system would operate
similarly to MAP (yes/no ?).  If it was me and I had a MAP based unit then if I had
a hesitation on sudden throttle opening then I would use either an extra
injector driving of a differential off a throttle position sensor - assuming of course
the MAP position is correct and there are no orifice issues in its sensing,

Rgds

Mike



>Thanks
>
>
>--- Mike <niche at iinet.net.au> wrote:
>
>> Any transient mixture enrichment on rate of change
>> of throttle position ?
>> 
>> Even the oldie hitachi/bosch ecu reads rate of
>> change of throttle
>> position and intersperses extra injection pulses to
>> act like the
>> old accelerator pump of the carbie days, seems like
>> you have
>> that issue from your description as you report its
>> more than
>> noticable when on load - that is when its most
>> apparent...
>> 
>> rgds
>> 
>> Mike
>> 
>> 
>> 
>> At 01:33 AM 6/28/06, you wrote:
>> >I just put a TBI setup from a 1991 Silverado onto a
>> >1969 Mustang with a 302 (2bbl).  It runs well,
>> idles
>> >smoothly, but I have a couple of issues.  
>> >
>> >1?It has some hesitation on acceleration.  Not when
>> I
>> >rev it in the garage, but when its in gear.  Timing
>> is
>> >currently set at 10 degrees BTDC (base timing), I?m
>> >thinking of adding a little more advance to it. 
>> Any
>> >other ideas?  It actually stalls out sometimes when
>> I
>> >try to make a fast getaway.  
>> >
>> >2?I put the ECU under the dash.  I reached in and
>> put
>> >my hand on the box  after I had been driving a
>> while,
>> >and it was VERY hot to the touch.  I almost
>> couldn?t
>> >hold on to it.  Is this a normal operating
>> condition
>> >of the GM ECU?   
>> >
>> >Any tips are appreciated! 
>> >
>> >
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>> 
>> Regards from
>> 
>> 
>> Mike
>> Perth, Western Australia
>> VL Commodore Fuse Rail that wont warp or melt !
>> Twin tyres for most sedans, trikes and motorcycle
>> sidecars
>> http://niche.iinet.net.au
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>
>
>
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Regards from


Mike
Perth, Western Australia
VL Commodore Fuse Rail that wont warp or melt !
Twin tyres for most sedans, trikes and motorcycle sidecars
http://niche.iinet.net.au




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