[Diy_efi] Hesitation

[dgilbert78 at juno.com]

Hello: If you have a MAP system make absolutely sure that the vacuum to
the MAP is on time, not delayed. Lots of times on GM TBI units (possibly
others) the vacuum port to the MAP becomes plugged with carbon to the
point that the orface is so small that the vacuum is delayed to the MAP,
this will without a doubt cause hessitation on quick throttle opening. On
slow no load throttle opening the vacuum is fast enough to run the MAP
and the problem is not present. There is no test for this unless the MAP
port is completely plugged, then it is obvious, because you will get no
MAP change. I had to pull the TPI and rod the port and choke cleaner it.
After that no more hesitation, Probably any problem with the vacuum hose
to the MAP would cause a similiar problem,
good luck
Darryl...
On Tue, 27 Jun 2006 20:07:53 -0700 (PDT) Scott Scott
<scott_o_matic at yahoo.com> writes:
> 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.
>  
> 
> What do I do to diagnose this and correct it?
> 
> 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
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> 
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