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Alex3000

Wiring: What constitutes a "separate circuit"

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Trying to get my car running on it's new Megasquirt.  I have gotten it to start but not really run well. I looked at the sensor logs and the wideband O2 sensor seems to be getting jerky readings. 

 

So I read in the manual and it says the wideband sensor should be on it's own circuit to avoid not only sending out noise but also noise from ign coils etc. OK that's fine... but at the end of the day what constitutes a separate circuit?

 

What I mean is, if power flows Alternator/Battery > Kill Switch > Relay > Fuse Block > Whatever the powered item is > Ground is it just a matter where it grounds? or else how far back in the chain does it have to be in order to be separate?

 

Does this question make sense.  It just seems to me, ultimately all the circuits are not too many degrees of separation from each other?

 

I made this bad illustration as to how it is wired up now.

899267023_widebandwiring.jpg.150b5fb3d12ef340deb0d0ded8952c0f.jpg

 

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I'm still at the wiring diagram phase so can't confirm the correct approach. My understanding is what is important is that the wideband and the ECU share the same ground.  

1313691421_2019-3-3MSUdderChaosWiringDiagram.thumb.jpg.0954b6316a6360b39fc6752a539596ab.jpg

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Separate circuit being nothing else on that fuse or relay. It would have it's own relay and it's own dedicated fuse.

 

Just looked at your diagram. You should have 1 relay for your ignition feed , 1 for your A/F sensor, and I like to use a relay for the starter as well. Each relay should have its own fuse. The power to the relays can come from your kill switch or just to Ign, then the sign power can feed the other 2.

 

Edited by djsteviec

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For a separate circuit imagine one battery, if you have two separate wires that never touch each other except at the positive and negative terminals then you have two separate circuits.  I can't see your diagram as it gets fuzzy if I zoom in but I am surprised the grounds for the computer and O2 are together if that is what is shown.  If they are grounded together and away from the battery it can cause a noisy signal, if they are grounded together at the battery then it should be a pretty clean signal.

 

For the computer and sensors Ford has an all sensor ground wire to the battery, and ECU ground at the computer, then a dedicated ground from the O2 sensors to the battery.  Three separate circuits.

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Ah yes, that's right. The megasquirt instructions say to ground the O2 sensor through the ECU sensor grounds, which I did.  But the O2 sensor instructions say it should have it's own circuit.  I think I'm going to move the wideband sensor ground to go directly to the battery then and see if that changes anything.

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Grounding through the ECU ground means to use one of the ECU ground triggers, not the ground for the ECU itself.  However yes a ground straight to the battery will be the cleanest circuit.

Edited by Ron_e

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16 hours ago, Alex3000 said:

Trying to get my car running on it's new Megasquirt.  I have gotten it to start but not really run well. I looked at the sensor logs and the wideband O2 sensor seems to be getting jerky readings. 

 

So I read in the manual and it says the wideband sensor should be on it's own circuit to avoid not only sending out noise but also noise from ign coils etc. OK that's fine... but at the end of the day what constitutes a separate circuit?

 

What I mean is, if power flows Alternator/Battery > Kill Switch > Relay > Fuse Block > Whatever the powered item is > Ground is it just a matter where it grounds? or else how far back in the chain does it have to be in order to be separate?

 

Does this question make sense.  It just seems to me, ultimately all the circuits are not too many degrees of separation from each other?

 

I made this bad illustration as to how it is wired up now.

899267023_widebandwiring.jpg.150b5fb3d12ef340deb0d0ded8952c0f.jpg

 

 

 

What wideband?

 

The following applies if you have LC-2:

- If it's the LC-2 they don't have a signal ground.

- If you connect the LC-2 ground to MS signal ground you will get bad readings because the LC-2 ground is "dirty" (large currents from sensor warming create a voltage drop and that will mess up the readings from the sensors)

- The correct way with LC-2 is to connect the LC-2 ground as close as possible to the it to MS-2 ground. 

 

If you ground MS-2 to  the battery and the MS-2 to the battery then there the combined length of those cables will account for a voltage drop and sensor reading error. The MS-2 ground is also pretty messy with the injector current. 

 

At least the above is true for microsquirt, don't see how it can differ for any ECU.

 

Read this for more:

http://www.msextra.com/forums/viewtopic.php?f=101&t=65931

 

 

 

 

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51 minutes ago, turbogrill said:

 

 

What wideband?

 

The following applies if you have LC-2:

- If it's the LC-2 they don't have a signal ground.

- If you connect the LC-2 ground to MS signal ground you will get bad readings because the LC-2 ground is "dirty" (large currents from sensor warming create a voltage drop and that will mess up the readings from the sensors)

- The correct way with LC-2 is to connect the LC-2 ground as close as possible to the it to MS-2 ground. 

 

If you ground MS-2 to  the battery and the MS-2 to the battery then there the combined length of those cables will account for a voltage drop and sensor reading error. The MS-2 ground is also pretty messy with the injector current. 

 

At least the above is true for microsquirt, don't see how it can differ for any ECU.

 

Read this for more:

http://www.msextra.com/forums/viewtopic.php?f=101&t=65931

 

 

 

 

 

Bingo, this is my exact scenario with an LC-2.  My MS sensor grounds go to the engine block though.  So maybe ground the LC-2 the block as well, just not in the wiring loom with the other sensor grounds.

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4 minutes ago, Alex3000 said:

 

Bingo, this is my exact scenario with an LC-2.  My MS sensor grounds go to the engine block though.  So maybe ground the LC-2 the block as well, just not in the wiring loom with the other sensor grounds.

 

Yes you can try that. The thicker your ground cable the less voltage drop, so if the LC-2 ground is like a 28 AWG that is no good. But no need to go crazy with a 6 AWG. Something reasonable like 18-20 AWG is probably enough. Try with what you have.

 

If you still get strange readings it something else. Do you get strange readings in Tunerstudio or on the LC-2 Display? 

Note that the two outputs have different calibration. And also have you calibrated megasquirt for the AFR?

 

From the LC-2:

Analog output one (yellow) is 0V = 7.35 AFR and 5V = 22.39 AFR.

Analog output two (brown) is 1.1V = 14 AFR and .1V = 15 AFR. 

 

So if you have connected your megasquirt AFR to yellow you need to tell Megasqurt that 0v is 0.735 AFR and 5v = 22.39 AFR

(You can also change this range in LC-2 software to something closer (say 0v=10AFR and 5v=17AFR), this gives you a slight more accuracy.)

 

 

 

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When I installed my MS3Pro I mounted everything to an aluminum panel and installed a ground stud. From that stud I ran one 10 gage wire to the chassis, which is where the battery was grounded, and another 10 gage wire to the engine block. Then I grounded everything else except sensors, which use the MS sensor ground wire, to this stud.IMG_20160418_195318.thumb.jpg.791180271d5b371ac23c35bdceaa361f.jpg

 

Here is a wiring diagram of my car with the MS3Pro and 4 LS coils. The only thing different is that I installed a second LC-2, an electric actuator for the S5 variable intake, and no fan. I always had very good and stable readings from the wideband sensors, they were sensitive enough that they allowed me to find and diagnose a problem I had with my setup that was causing the leading plug on the rear rotor never to fire.

 

ms_wiring.thumb.png.9fe7b5294b1b044a9fb8752813fc28cc.png

 

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6 hours ago, Ron_e said:

Grounding through the ECU ground means to use one of the ECU ground triggers, not the ground for the ECU itself.  However yes a ground straight to the battery will be the cleanest circuit.

This is correct.

The cleanest circuit doesn't matter.  What matter is the ground of the O2 sensor is at the same potential as the ground of the circuit that reads the voltage.

Any voltage drops and noise on the sensing circuit don't matter because that is what it measuring against.

 

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8 hours ago, mhr650 said:

When I installed my MS3Pro I mounted everything to an aluminum panel and installed a ground stud. From that stud I ran one 10 gage wire to the chassis, which is where the battery was grounded, and another 10 gage wire to the engine block. Then I grounded everything else except sensors, which use the MS sensor ground wire, to this stud.IMG_20160418_195318.thumb.jpg.791180271d5b371ac23c35bdceaa361f.jpg

 

Here is a wiring diagram of my car with the MS3Pro and 4 LS coils. The only thing different is that I installed a second LC-2, an electric actuator for the S5 variable intake, and no fan. I always had very good and stable readings from the wideband sensors, they were sensitive enough that they allowed me to find and diagnose a problem I had with my setup that was causing the leading plug on the rear rotor never to fire.

 

ms_wiring.thumb.png.9fe7b5294b1b044a9fb8752813fc28cc.png

 

Nice!

 

1. Why pro vs ms2/ms3?

 

2. What condition do you have to turn on fan? Temp threshold? Or speed/threshold?

 

3. With your crank trigger, how did you do the shield? And where did you put the pullup?(if needed?)

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1 hour ago, turbogrill said:

Nice!

 

1. Why pro vs ms2/ms3?

 

2. What condition do you have to turn on fan? Temp threshold? Or speed/threshold?

 

3. With your crank trigger, how did you do the shield? And where did you put the pullup?(if needed?)

 

1. MS3Pro elements the vast majority of problems people have with MS2/3. It has a far superior trigger circuit and doesn't have all the trigger and synch problems that users of other MS systems have. 

 

2. I didn't install a fan in my car. If I had I would have used a spare injector output to trigger a relay and programmed it to come on based on temperature. 

 

3. See1. The MS3Pro comes with 2 good VR sensor circuits that already have shielded cables in the harness. I used an FC crank angle sensor that plugs into the distributor hole from early rotaries. It has 2 VR sensors and 2 wheels, one has 24 teeth I think and the other has 2 teeth. That is all you need to do full sequential ignition and coil on plug with 4 LS coils. 

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Ground loops a integral part of cars. Generally the battery will have a ground to the body next to it. Some cars then add EXTRA grounds to electronic systems. Why? The body serves as the common wire for the entire system. The positive voltage then is distributed via insulated wire to the loads. Most loads use the body to complete the circuit. Then the alternator connects though the engine and its grounding strap to the body. (Did you remember to reattach it?) Classic ignition coils are grounded through the points in the distributor. Modern motor with multiple coils seem to get the ground from the ECM. Funny? Why? GROUND LOOPS!

 

How are ground loops created? Let's look at just two systems ECU and Blower Fan.

The AC blower fan is connected to the body at one point and the ECU at another. The currents to complete the circuit follow different paths. If the paths cross or run next to each other you get interference or noise or cross noise between the (here) two circuits! Please refer to the drawing.

car-top-view_outline_2.png.c5ac43b676df060664da6147367ffbab.png

 

Note on Ground Loops
When two or more devices are connected to a common ground through different paths, ground path noise, or a ground loop can occur. Thus, a system grounded at two different points, with a potential difference between the two grounds can cause unwanted noise voltage in the circuit paths. Currents flow through these multiple paths and develop voltages which can cause damage, noise or hum in audio, video equipment or ECUs. The ground loop can be eliminated in one of two ways:
  1. Remove one of the ground paths, thus converting the system to a single point ground.
  2. Isolate one of the ground paths with an isolation transformer, common mode choke, optical-coupler, balanced circuitry, or frequency selective grounding.

More info:

https://www.lifewire.com/whining-noise-when-i-use-aux-input-534592

 

Shielding of Signal Wires

Remember when you add a shield to signal wires, connect the shield only at ONE end of the cable and make sure that the outside insulation prevents contact with the chassis at any point along the path. If it does, you get a NEW ground loop! 

 

 

Edited by SafeCarWire_Guy
Added more info about shielding
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