TPS and RPM only?

[Mike Olsson]

     I'm glad this came up. I'v been looking for a first step to adapt an 
     older engine to EFI and TBI is something to consider although it's not 
     discussed to often on this list...
     
     I've been doing some research on the Holley ProJection, mainly in the 
     mail archives and at Holleys Website. Holley has a BBS which mainly 
     seems to work as a department for complaints for more or less 
     frustrated ProJection users. 
     
     I have a 225 slant 6 and thus the 501-2 kit for 258" Jeep is the 
     obvious choice. This unit can (according to Holley) be adjusted (via 
     control knobs?) for:       Idle
                                Accelerator pump
                                Mid.range
                                Power
                                Choke
     
     The fuel pump pressure can also be adjusted. As I understand, it uses 
     only TPS and RPM sensors.
     
     Is this the same set-up you use? I'm asking because according to all 
     the complaints on the mentioned BBS, there are a lot of users that are 
     extremely unhappy with the system, being unable to adjust it properly 
     and getting no help from Holley as it seems. I was even offered to buy 
     a hardly used set-up from a furious user...
     
     Have you (or any one else on the list) had any problems to adjust this 
     system? Can the problems likely be explained by the fact that there is 
     no MAP sensor (i.e. "load sensor") on the ProJection.
     
     Any tips on this are interesting for me and highly appreciated.
     
     mike.olsson at eu.pnu.com


______________________________ Reply Separator _________________________________
Subject: Re: TPS and RPM only?
Author:  diy_efi at coulomb.eng.ohio-state.edu at Internet-Europe
Date:    1997-03-21 15:02


>It seems to me that if you just use TPS and RPM, you wouldn't be able to 
>compensate for load at various speeds.  Unless you feed back O2 readings, 
>wouldn't the engine tend to run rich at low loads?
     
The ProJection seems to work fine for me, and it only uses TPS 
and RPM.  In some ways it's more quirky than a carb, but I've 
run it for over a year, and through two winters.  The winter is
when it's quirkiest ... namely the choke enrichment doesn't always 
seem to work right, but once it's warmed up and/or at speed, it has 
always worked okay.
     
The way I imagine the TPS/RPM only thing is, I visualize a straight 
line on a graph.  Independent var (x-axis) is RPM, dependent var
is fuel.  Higher speed = more fuel.  Do the same for TPS.  More 
throttle = more fuel.  Now, add those two.  If you're under load, 
you'll have lower RPM, but higher TPS, so you still get more 
fuel.  The ProJection has a delta-TPS (throttle pump) function 
that injects more fuel when the throttle is rapidly pushed to 
avoid stalling.
     
I have monitored this setup with an EGO and DPM since it was 
first installed.  It has always worked fine.  It doesn't work 
at stoich.  Rather, it's lean for cruise or decell and rich
for accel, which is what I want.  An EGO feedback can be added, 
and I may do that some day so I'll have some automatic adjustment 
when I go to the mountains and altitude changes.
     
Tom Cloud <cloud at peaches.ph.utexas.edu>