problems with EFI car idle and pressure sensors

[Eric Bryant]

> From: Craig Dotson [mailto:crdotson at vt.edu]
> Subject: Re: problems with EFI car idle and pressure sensors
> 
> > Why would I need TPS? (Except for overrun cutoff, etc)
> >
> 
> Our FormulaSAE car runs a 600cc motorcycle engine with DOHC 
> of an aggressive
> profile.  As with any agressive, long-duration camshaft, the 
> engine has very
> little manifold vacuum at idle.  If you're running purely MAP 
> control, your
> idle will be over-rich and may even choke out the engine due to the
> poor/erratic vacuum signal your MAP will see.

Yep, this is a problem with many small engines.  The EFI system on my Suzuki
TL1000R uses alpha-N (TPS vs. RPM) fuel mapping at low revs, and then
switches to speed-density (MAP vs. RPM) at higher speeds, when the MAP
signal is more usable.  Considering that this bike has some of the most
agressive cam timing of any production bike out there, it works OK.  If the
TPS is just a bit out of adjustment, though, the bike runs horribly (and for
some reason, the TPS doesn't hold its adjustment very well, and the ECU
doesn't seem to be very "smart" when it comes to learning the TPS signal).

Given a more-mild engine, though, I'd much rather run speed-density
throughout the rev range, and just use the TPS for acceleration enrichment
(as Bruce mentioned earlier).

Eric Bryant
mailto:bryante at ghsp.com
http://www.bryantperformance.com 
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