[Diy_efi] Hesitation

Wed Jun 28 13:23:29 UTC 2006

Just a few quick thoughts...  what fuel pressure are you regulated at and
what are you using for a pump.   I notice you say the ECM gets hot, but that
the car runs... i'm wondering if TBI is a low pressure system (i thought it
was lower than PFI)  and thinking that maybe part of the problem is
overenrichment, being that when you add more throttle (lose vaccum) the fuel
pressure rises (function of the FPR) and you overenrich because of the
height of the fuel curve.   Just a thought... that maybe excessive
backpressure on the TPI injector may cause the injector drives to get hot.

not familiar with TBI, just a thought though.  and this is a place for
exchanging thoughts ;)

best regards!

-- Lee

On 6/28/06, Mike <niche at iinet.net.au> wrote:
>
> 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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-- 
Sincerely,
Lee M. Lemoine
KB1NQI  - Amateur Radio
http://www.turbochargedsoul.com/
'06 Subaru Legacy GT Limited - 250/250 AWD 5EAT
'93 Chevy Cavalier Z24 Convertible - 300/330 FWD 5MT (Mclaren Turbo!)