[Diy_efi] Holley projection questions

Tom Visel five10man
Fri Mar 10 14:36:41 UTC 2006

IDK about Pro-jection, but if they want .63V at closed throttle, that 
sounds like a typical fool rejection setup, which would most likely 
follow these general rules of behavior:
1. It wants about .5 volts at closed throttle, 4.5V at WOT.
2. If it sees close to the WOT value during cranking, it will go into 
"clear-flood" mode, and cut the fuel way back, if not cease injection 
3. It looks at a change in TPS value (not necessarily a certain value) 
to trigger the accelerator pump function or its equivalent.
4. Some systems (Including yours, I believe) ramp up fuel dramatically 
as the TPS value nears WOT.
5. If the TPS value is too high with closed throttle, the ECM may not be 
aware of the closed throttle and cause dying at idle or closed throttle 
surging problems.

I would find out what Holley expects you to have for a TPS signal.  If 
it is as described above, then the TPS wires (back probed at the TPS 
with the connector plugged in) should have ground, signal, and 5V on 
them.  The ground should be less then .050V.  If it is higher, fix your 
grounds.  Check the ECM ground first; it most likely provides the ground 
to the sensors.

With a known-good ground and 5V source, the TPS should read on your DVOM 
or (better yet) graphing multimeter a clean sweep from about .5V at 
closed throttle to about 4.5V at wide open throttle, with no dropouts or 
spots where the signal is nonlinear.  If you have signal problems, 
change the TPS.

If the TPS on your system is wonky and you cannot get another one 
easily, you may wish to substitute a resistor (1/8 watt will do) which 
tells the ECM that you are at 1/4 throttle.  That way, you can get most 
of your driveability tuning done without the TPS interfering.


Simon Juncal wrote:

> Hello new to the list here. I found some of this lists posts googling 
> my pro-jection problems and thought maybe I could find some help and 
> opinions.
> I got the digital 1d system used for next to nothing, open loop for 
> now, So I've got a bunch of ideas and questions... like has anyone 
> hacked the ECU so that the fuel maps can be programmed via laptop?
> I notice the closed loop "system" they sell for 200 dollars is just an 
> o2 sensor, 3 wire harness and a proprietary connector... has anyone 
> patched in their own o2 sensor? Does anyone know which post in the 
> input connector accepts signal from the sensor?
> I've asked holley tech sup a few basic questions and gotten canned 
> replys and multiple copies of the instructions sent to me in PDF :)
> The PO of the system had it on a Sazuki Samurai, on which it ran super 
> rich... it's now on my Jeep 4.2, (with 4.0 head conversion, original 
> intake and 4.0 header) which is the target aplication of the 1d 
> system. The PO along with the help of someone at Holley had the TPS 
> wiring turned around and spliced in the harness ground, the voltage 
> range is 3.7 to 4.7 nowhere near the 0.63 holley's instructions 
> recomend. I can't explain why, because as near as I can determine this 
> range ENRICHES the overall fuel mix (making it harder to lean out via 
> the ECU knobs) and makes the fuel curve more drastic.
> That said this TPS setting get's me a running, smoothly idling (for a 
> jeep) engine but it runs constantly rich, doesn't start easy, gets 10 
> MPG (16 to 18 is normal)... SLOWLY leaning it out in the tuning 
> process gets me JUST to the Stoich on my autometer gauge, better MPG, 
> hessitant acceleration, and inconsistant dropout's where it leans 
> totally out if I _barely_ touch the throttle, but riches back up when 
> I get further into the pedal. Crusing with foot resting on pedal leads 
> to long off the scale lean conditions, and occasionally it leans out 
> at idle, and will stall if left alone without pedal.
> Problem is just reversing the wiring back to what the instructions 
> show doesn't get me any fuel, the ground as I said is spliced in or 
> Y'd to the Grey TPS wire both then going to the black harness wire 
> back to the ECU... Seems strange to me but I can't find anywhere else 
> in the harness that the ground wire might actually have been attached to.
> There's only one black wire at the ECU input connector, the TPS has a 
> black wire, and this ring terminal ground. are they really supposed to 
> be Y's together like that?
> Sorry for the long assed post, but I've never been too worried about 
> being in over my head. I'm too used to the feeling :)
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://lists.diy-efi.org/mailman/listinfo/diy_efi

More information about the Diy_efi mailing list