PAdutch

I'm am nearing the end of my VVT swap into my 1993 and am having a strange TPS issue. It does start but the TPS issue makes it nearly undrivable.

1993 Miata
MSlabs MS3 - bought used
VVT engine swap - using VVT mega thread method
LC2 Wideband
2001 TPS, Throttle and intake manifold

Symptoms:
1. Sitting at steady state the throttle position will slowly climb in tuner studio without touching the throttle. Meaning I calibrate it to 0% and slowly it climbs to 10% or more. This happens running or not running.
2. With a very slight movement of the pedal it will drop to nearly -30% throttle position before traveling to 100%.
3. Once the throttle is depressed it rarely settles back to 0%, sometimes sits as high as 30% in tunerstudio.
4. With the megasquirt unplugged resistance between ground and the 5v supply is 4400 ohms. With the ECU plugged in resistance drops to 770 ohms when measured at the TPS connector.

Things worth noting:
1. I first though it was a grounding issue so I have put a ground on the driver side from the exhaust manifold stud to the chassis and a ground from the intake mainifold to the chassis. Neither made a difference.
2. I have bought two cheap autozone TPS as well as the one that came with the engine. All have the same symptoms.
3. I did turn the key to the on position a couple of times with the ST sign fuse in before I realized what I was doing.
4. Was a good running car perivously with a NA 1.8 engine swapped and

Did I damage the megasquirt when I didn't pull the fuse? How do I verify this?
Could it be my wiring harness? Could I have spliced something in wrong?
Should I ground it a different way?

I have attached my tune and a couple of logs if anyone wants to take a look.

I would really appreciate any advise.
Thanks ahead of time.

Savington

iTrader: (31)

Highly likely that it's a wiring issue. I had a similar issue with Rover (wandering TPS) years ago that ended up being crossed wires in the harness.

PAdutch

Thanks. I will be doing some more diagnosis in the next few days. I was hoping some one could point me to a specific place to look maybe. Something typical to a vvt swap, or even the na8 swap, or megasquirt.

SpartanSV

With a meter set to DV voltage measure the TPS input wire to the ECU. Voltage should change linearly with the rotation of the throttle. It should also return to the same voltage every time the throttle is opened and closed.

Ted75zcar

iTrader: (2)

Sounds like you may either have series capacitance or a high impedance somewhere. Measure the DC resistance from the tps end harness and the pins inside the ecu for both vref and the wiper. You can also ground the wiper pin in the tps connector to the sgnd pin through a ~2.5kohm resistor. This should give you a solid 0 in TS. Connecting that same resistor to vref from the wiper should be a sllid 100. Make sure the contacs are clean, and have good wipe lengths.

PAdutch

Thanks for the help.

Turns out I had it wired wrong per some advice I found elsewhere. For future reference people wiring in a 2001 tps in a na6 should follow this:

Wires get connected as follows
Car NB TPS
Red -------> Light green / red stripe
Light Green/ White stripe -------> Green/Black Stripe
Black/ Light green Stripe --------> Black/ Red Stripe