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Eduardo Zibetti

Probationary Member
4
0
Jul 12, 2020
Passo Fundo, South_America
Hey guys, i'm new on the forum and brazilian, so my english isn't perfect LOL.
I have a problem with coolant temp sensor, as u can see in the image below:

(i've tried to upload but doesn't work, so i post the links)

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They are working perfectly, but sometimes (more than i've expected) the sensor oscillate and the CLT goes to 230ºf in 0.1s, then back to normal (192ºf).

I change the CLT sensor and the problem persists.
I have an aftermarket ECU in the original wire (plug n play megasquirt MS2), but with original ECU (with ecmlink) I already had the problem.

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There are images of my original wiring. Three white wires going into green sheeths. These wires go to pins 75, 76, and 78 (Front O2, Rear O2, and Knock Sensor).
There are also 5 black wires (one of which is pin 92 [Sensor Ground]) that are coming from the wiring harness, through the green sheeths, and then the all of the black wires are soldered back to the sheilding inside the sheeths.

My problem is these wiring? Anyone can help me?
Thank you and sorry for the gramatical errors LOL
 
Electrical problems are pain in the... have you measured resistance in that coolantwire between the ecu connector and sensor? You have new sensor and ecu so problem is likely in wiring? If you shake wires while logging can you get any spikes?

I will measure the resistance, dont meansured yet.
If i shake wires while logging nothing happens...
So I suspect ground wires...
 
Important note: On a 2g (but not 1g) ECU pin 92 (note: this pin is incorrectly labeled Ignition switch on some 2g ECU pinout diagrams) goes to the signal grounds of the following engine sensors: manifold diff pressure, engine coolant temp, front O2, rear O2, TPS, volume air flow (MAF), and on the 98 & 99 fuel tank diff pressure. Pin 92 is grounded inside the ECU but all these sensors signal grounds must NOT be grounded anywhere but through pin 92 to avoid electrical noise and ground loops from affecting the sensors differential signals and to guarantee that the sensor's ground is at the exact same voltage potential as the ECU ground (which it might not be with large current flowing through any other ground). Some people and even some mechanics, don't know/realize this and they mistakenly connect signal ground to the engine (as in a 1g). A typical example is when replacing the front O2 sensor and the harness connector/wires are damaged and need replacing. Connecting the O2 signal ground to the engine/chassis (or even battery negative) can cause misleading and noisy signals to the ECU causing the ECU to run the engine poorly. And if it is still also connected to the original harness signal ground wire, then all of the above engine sensors will also have that problem.
 
Important note: On a 2g (but not 1g) ECU pin 92 (note: this pin is incorrectly labeled Ignition switch on some 2g ECU pinout diagrams) goes to the signal grounds of the following engine sensors: manifold diff pressure, engine coolant temp, front O2, rear O2, TPS, volume air flow (MAF), and on the 98 & 99 fuel tank diff pressure. Pin 92 is grounded inside the ECU but all these sensors signal grounds must NOT be grounded anywhere but through pin 92 to avoid electrical noise and ground loops from affecting the sensors differential signals and to guarantee that the sensor's ground is at the exact same voltage potential as the ECU ground (which it might not be with large current flowing through any other ground). Some people and even some mechanics, don't know/realize this and they mistakenly connect signal ground to the engine (as in a 1g). A typical example is when replacing the front O2 sensor and the harness connector/wires are damaged and need replacing. Connecting the O2 signal ground to the engine/chassis (or even battery negative) can cause misleading and noisy signals to the ECU causing the ECU to run the engine poorly. And if it is still also connected to the original harness signal ground wire, then all of the above engine sensors will also have that problem.

In my case, only the CLT sensor have problem.
I use an ECU with internal MAP sensor and wideband, so I dont use front/rear O2, manifold dif pressure and MAF wires/plugs.
I use CLT and TPS connected to ECU, but the TPS is fine, the problem is only in CLT.
I will remake the ground wire of these sensors and test, so I come back here and give a feedback.
 
Important note: On a 2g (but not 1g) ECU pin 92 (note: this pin is incorrectly labeled Ignition switch on some 2g ECU pinout diagrams) goes to the signal grounds of the following engine sensors: manifold diff pressure, engine coolant temp, front O2, rear O2, TPS, volume air flow (MAF), and on the 98 & 99 fuel tank diff pressure. Pin 92 is grounded inside the ECU but all these sensors signal grounds must NOT be grounded anywhere but through pin 92 to avoid electrical noise and ground loops from affecting the sensors differential signals and to guarantee that the sensor's ground is at the exact same voltage potential as the ECU ground (which it might not be with large current flowing through any other ground). Some people and even some mechanics, don't know/realize this and they mistakenly connect signal ground to the engine (as in a 1g). A typical example is when replacing the front O2 sensor and the harness connector/wires are damaged and need replacing. Connecting the O2 signal ground to the engine/chassis (or even battery negative) can cause misleading and noisy signals to the ECU causing the ECU to run the engine poorly. And if it is still also connected to the original harness signal ground wire, then all of the above engine sensors will also have that problem.
That's a great answer!. I've been having random spikes in my logs (ie-coolant temp spikes, maf hz spikes, then the fuel trims go way rich). I'm thinking this may be cause by switching to speed density utilizing the ecmlink maf break out cable, unplugging the maf sensor, while the iat and mdp map sensor are logging sd.

I notice all of the harness is tied into the main wiring harness going across the top of the engine and my first thought was a bad ground connection as ecmlinks revised breakout cable wiring has you add a chassis grounded ring terminal to ground the 3in gm maf sensor. I'm guessing due to running speed density now that the ground path is compromised due to the chassis ground being connected through their maf breakout cable without the sensor running anymore.

Hope that makes sense.
 
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