TPS and scanner readings

[iTurbo]

Recently I got an 0TC 4000E scanner with '93 Patherfinder II cartridge. I have had it hooked up to my Shelby Lancer ('87 Turbo II electronics) and Omni GLH Turbo ('89 Turbo I electronics). There is a big difference in the TPS readings I'm getting.

Omni:
.98 throttle closed
4.02 WOT

Lancer
.82 closed
2.78 WOT (!)

I'm wondering if the low TPS voltage at WOT on my Lancer is preventing the computer from seeing WOT and therefore not getting the WOT fuel enrichment (open loop). Should I try another TPS?

Despite all the fuel system mods on my Lancer, O2 sensor voltage is only .80 at WOT, which is alarmingly low. I'm only running 15 psi boost....wondering if the low WOT TPS values have something to do with it.

[86Shelby]

I'm certain it does have a lot to do with your fueling issues. Swap the TPS sensor with your Omni and redo the test. if you still get the 2.X V at WOT I would look into either high resistance in the signal or ground wires or you're not getting the full 5V to the sensor.

[shadow88]

I'd try a voltmeter reading to see the voltage value on the return wire, and like mentioned above, check the 5v reference voltage while you're at it. May as well check the ground resistance too.

[iTurbo]

I just changed out the TPS with an extra one I had laying around.

1.16 throttle closed
4.00 WOT

I'll check the 5v reference and sensor ground circuits later as well but I think I found the problem. I haven't even driven it yet; gotta go to work.

Another cool thing I noticed is that my battery temp, charge temp, and coolant temp are all reporting 59-60F', with the car completely cooled off this morning. Ambient temp right now is 60'F so it looks like all my temp sensors are agreeing with each other.

[iTurbo]

Just did one WOT run in the Lancer and O2 was reading .90. My Omni is .96 at WOT.

Both cars have Walbro 255 ltr/hr fuel pumps, MP +20s, Accufab AFPR, and fresh filters, lines and clamps. The Lancer also has the FWDP fuel rail. Lancer has 3-wire O2; Omni has 4-wire.

[iTurbo]

Drove my car all day today and the O2 volts were consistently higher by .10-.12v at WOT since I changed the TPS. Autometer is showing 18 lights. 15 psi boost and no knock retard (unchanged).