Hello,

I've put together my DIYPNP and it bench-tests OK, flashes firmware, loads base map without issue.

But when I plug it into the car (1994) and I try to calibrate the TPS, I just get a static value of about 1023 regardless of the throttle position.

I have 5v between ground and the TPS point on the main board, and 0v
between TPS and VREF. That is irrespective of throttle position. I know the TPS itself to be functional.

What have I done wrong?

 

I'd start by double checking your jumpers. Verify that each jumper goes to the correct pin on the adapter board.

 

how exactly did you wire the v5ref and TPS sig wires? where on the jumper board did you put them?

 

VREF to 4K. TPS to 4M.

 

the voltage on 4M should be zero (going to ground).

as you open the throttle, it should go towards 5v, the resistance to 5v is lessened....is this not happening?

 

Not when I measured it at the mainboard pads, no.

 

bad tps?

 

It runs fine with the stock ECU.

 

if you're seeing 1032 raw regardless of throttle, then you're putting 5v into 4M...that makes me think the TPS is bad.

 

I suppose it's possible. I'm definitely getting 5V off the harness regardless of the position of the throttle.

Is there a good test procedure for the sensor? I get continuity between the bottom two pins with the throttle closed, and lose it with the throttle cracked slightly open. The top two pins have a variable resistance that depends on the throttle position. That seems pretty normal, right?

Also, I didn't have any drivability issues with the stock ECU. Wouldn't I have noticed something if the TPS was bad? I am not exactly sure what the stock ECU does with that information.

Incidentally, both fans also turn on with the key. I'm not sure why that is. Doesn't seem likely that it would be related, though.

 

Looking at the wiring diagram, the TPS seems to be OK. The switch switches, and the rheostat, uh, rheostats. So I have two places to go from here: there's some problem with the wiring between the TPS and the ECU, or there's something with the MS that is shorting the TPS to 5V.

The logical next step seems to be replacing the stock ECU and seeing if I get the same 5V on TPS regardless of throttle position.

 

OK, with the stock ECU in place I get the expected readings from the TPS pin. The culprit is definitely the MS. Maybe I have a short. Should there be continuity or resistance between the TPS pin and the VREF? Is there a circuit diagram somewhere that I can use to trace the signals?

 

Curiouser and curiouser. Testing the MS on the 9v transformer gives me 0v on the TPS pad.

 

Here's what happens with the MS powered up on the bench and TunerStudio running. The reading just keeps climbing.


But when I try to measure the voltage difference between ground and the TPS pad, the signal drops to zero and stays there until I remove the probe.


How is that possible? How can it tell? Aren't multimeters supposed to have virtually infinite resistance in volt mode?

 

the voltage rises like that when nothing isconnected tothe input.

 

So if that behavior is normal, and the TPS is fine, what am I left with? A short on the MS board somewhere?

 

Or a ground issue, right? Where should the TPS be getting its ground? Right now I don't have anything jumpered to the SG hole on the MS, but that's correct per the 1994 instructions on the DIYPNP site.

 

youre positive TPS is going to 4M? and vref 4K?

 

Got it. Bad connection on the sensor ground pin. (4C, I think.)

 

yeah SG should go to 4D and 4C. Not sure why the instructions dont say that. but I could see a bad 4C solder preventing the TPS to ground.