Link Fury - AN 5v falling steadily on some sensors - Solved

[Dean]

Hi everyone. 
Link Fury, 1.5JZ. I wired it in over 2 years ago and it’s been faultless.

I have an issue that only started recently. First with a trim pot switch (the AEM one), and has now appeared in my TPS sub signal. 
 

- ECU is showing a steady 5v output. 
- with the trim pot and now TPS sub, once the voltage gets to around 2.5v it just starts to drop gradually. 
- this causes an error in the TPS. 

All other sensors using 5v reference are fine. Oil press, fuel press, ethanol, pedal position etc. 

here’s a video of the trim switch.

 

[Adamw]

Connect a multimeter to the AN input pin at the same time so you have something to reference.

[Dean]

Hi Adam. 
Do I just try to ram the multimeter into the back of the ECU plug?

My main issue is with the TPS sub doing the same thing. Because it constantly reverts to limp mode. 

[Adamw]

Push a pin or straightened out paper clip into the ecu plug beside the wire until it touches the terminal, then put your probe on that.  

https://youtu.be/Spy8AXlxVT0

 

[Dean]

it’s giving me the same result. 
that’s the trim pot switch rotating as in the earlier video. 

This is how the TPS is reacting. (Full throttle, letting off slowly)

TP main/sub and AP main/sub all share the same 5v and GND, so i'm leaning towards a fault in the TP Sub AN wire.

 

[Adamw]

Now probe the 5V wire on the rotary pot and see what that is doing.

[Dean]

5v is constant over the whole range of the switch. 

[Adamw]

So if its got a constant 5V going into that switch, but the voltage fades away when it is biased more towards ground that would suggest the ground connection is weak/has high resistance/bad connection. 

You could try measuring resistance from the ground pin at the pot to the ECU sensor ground pin, it should be very close to 0ohms. 

[Dean]

If I’m doing it right. It starts at 1.5Mohm and slowly increases.....

[Adamw]

That would suggest you a break somewhere along that sensor ground wire, or a bad crimp at one end, or a bad splice.  Since both the pot and TPS are affected that would suggest the bad connection is somewhere before it splits out to those two devices. 

Sometimes you can find it by wiggling different areas along the wire while watching the omhmeter.

[Dean]

Thanks so much for your help. I look forward to chasing my grounds tomorrow!

[Dean]

I chased every sensor ground, and removed almost the entire loom from the car and they all came up good (except for 3ohm resistance on one wire from the original Link loom sensor ground splice. Replaced that to be safe).

 

- I finally tried another E throttle body and that fixed the issue up the front. (original TB was damaged in a crash about 5 events ago, so it must've finally given up)
- I also tried another trim pot switch and that also fixed that issue too! (I'll do some tests on the switch and probably try to get a refund)

 

So everything seems to be good, and I have confidence that at least the sensor grounds are good because they've now all been checked!

 

Thanks again or your help. I've learnt some new things from this experience!