Rb25det neo issue tps voltage

[Gram]

Hi all I have a rb25det neo that's causing some sputtering issue. I nailed it down to the tps voltage currently reference output is 1.5v, when it should be 5v.

 

Funny thing is since he boost solenoid is on the same circuit, I disconnect the boost solenoid and it gave me 5v back to tps, plugged it in and it only gives me 1.5v.

 

So I replaced a new boost sensor and new ecu it still only give me 1.5v on the complete circuit with tps and boost sensor connected. I even tried disconnect the tps and only hook up the boost solenoid to isolate if tps is actually draining it down. Still gives me 1.5v with boost solenoid attached and 5v unattached

 

Can anyone give me some pointers what I should look for now.

 

 

Thanks

[GTSBoy]

Where you say "boost solenoid" in the 2nd paragraph, did you mean "boost sensor" as in the 3rd paragraph?

You then go on to call it a boost solenoid again. Just need to know if you're talking about all 3 things or only 2 things and mixing terms for one of them.

Edited June 13, 2024 by GTSBoy

[Gram]

Ah yes the boost sensor* sorry that is what I meant

 

[GTSBoy]

OK, so, assuming that there is nothing wrong with either the original or new boost sensor, then it would seem that there might be something wrong in the loom wiring to that sensor. This is troublesome, because if that were true, then you might expect the problem to persist when the sensor was unplugged. But seeing as the voltage comes good when it is unplugged, it would suggest that the fault might (and I stress might) be right at the loom plug.

Either that, or the fault might be at the ECU, on the line in from the boost sensor. When you unplug the boost sensor, that input at the ECU is isolated from the TPS sensor and can't affect it. This would be semi-bad, as an ECU problem is never welcome, but at least you'd know where the problem is and it might be fixable, or at least replaceable.

Do you have Nistune, or any other way of looking at ECU data? I'd want to drive the car around with the boost sensor unplugged and see the TPS working properly, then not working properly with the sensor plugged back in.

You're not trying to run more than ~18 psi either? Right? Because even with Nistune that can be difficult with the boost sensor connected. Just checking, in case it might have some bearing on the issue. It shouldn't cause the voltage situation you're seeing though.

[Gram]

hey GTSboy thanks for the quick reply. im on stock ECU 

Surprisngly enough i unplug everything and replug everything, readings are still off but the car drove...ok haha

So far this is what i have done.
- Replaced ECU (still 1.5v)
- Replaced Boost sensor (still 1.5v)

Now the next thing i tried is to unplug the TPS and only plug in the Boost sensor to see if it reads 5v. No it still only read 1.5v. 

Its a new boost sensor and i know i have 5v if i dont plug the sensor back in, so that means the power wire is good. So now im thinking that it might be a bad ground on the boost sensor plug. 

on the FSM says the ground to the boost sensor is  a sensor ground, can i add a ground wire from the boost sensor ground wire to the the engine itself to ground it? or chassis?

Edited June 13, 2024 by Gram

[Gram]

Hi all quick update, so i checked the wiring circuit on TPS / Boost sensor, everything checks out fine.
So at this point im really leaning towards 2nd fried boost sensor due to bad ecu maybe?

Is there a way or value to check for when ohm testing the boost sensor?

Also is there a way to bypass the boost sensor?

Thankyou

[GTSBoy]

18 hours ago, Gram said:

on the FSM says the ground to the boost sensor is  a sensor ground, can i add a ground wire from the boost sensor ground wire to the the engine itself to ground it? or chassis?

Post up the manual extract and the wiring diagram (seeing as we've got no idea what type of car we're talking about here) to help with decision making. (Also, I'm nowhere near home and my wiring diagrams and manuals).

I wouldn't suggest you do what you mentioned above on such a vague description, for a start! Depends on whether the power is from the ECU or the ground is at the ECU.

[MBS206]

56 minutes ago, Gram said:

Hi all quick update, so i checked the wiring circuit on TPS / Boost sensor, everything checks out fine.
So at this point im really leaning towards 2nd fried boost sensor due to bad ecu maybe?

Is there a way or value to check for when ohm testing the boost sensor?

Also is there a way to bypass the boost sensor?

Thankyou

Unplug ECU.

Unplug TPS.

Unplug boost pressure sensor.

Now, all the wires, placing your ground (black) multimeter lead at the ECU end, measure resistance of the 5V line at the boost sensor plug.

Then do the same to the TPS plug.

Then do the same for all the other wires that relate to the TPS, or boost sensor.

 

All of your measurements should be very very low. You're looking to see if wiring is out of wack here.

 

Secondly, from memory on the R33 (not a neo motor, so I'm assuming an r34) the ground wire for the TPS and boost sensor are NOT equal to ground of the car/battery. IE, DO NOT connect ground of the sensor to the engine/body of car. You'll get a ground loop, and/or potentially screw shit up. In electronics, ground for a circuit, is not necessarily equal to ground of another circuit.

 

So this leads me to ask, when measuring your 5V, how are you getting 1.5V? Where are your multimeter leads touching for both the red and black lead on the multimeter?

 

If you're measuring power on the sensor wire, and putting ground on the car chassis or negative battery terminal, that could be all of your issues in "getting 1.5v".

Electronics engineers can do some funky stuff with circuits, and when both sensors are on, it's enough laid to alter how the ECU is functioning.

[Gram]

ah gotcha ill go remeasure again, thanks for all the tips.

when i measured the TPS 5v reference voltage, i put my multimeter leads on 5v power and strut tower bolt, it gave me 5v with boost sensor disconnected and with boost sensor connected it gave me 1.4v.

ill try remeasure again this time with volt meter both on the 5v reference and TPS signal ground wire.