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Power question

Old 04-20-2015, 06:21 PM
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Default Power question

Hey guys need some help on one of my cars,

I've decided to switch to Maxima COP's and completely re-wire my engine harness in a final attempt to eliminate my high rpm CAS signal break down. Now I have some choices...

I'm debating what is the best way to power everything, particularly the MS, CAS, and coils. I can't wrap my head around using different power "sources" since they all eventually make it back to the battery. Does it even matter?

Previously I was powering the MS and CAS from the ECCS relay (B/W wire), and everything else (inj, WB, coil etc) from the ignition key (B/R wire). I was using the key ign signal to close a relay to ground which closed the ECCS relay. Attached is an illustration of what I had ("MS Power ver1.png") When I first set this up, I didn't realize that the current draw of the main B/R power wire all goes through the ign key!

Revisiting this, that method seems silly to me. My thought was to eliminate the ECCS relay and power the MS, injectors, and CAS from the key (B/R wire) and the coils separately with a relay. See "MS Power ver2.png"

Then I could use the OEM O2 circuit for the the WB o2 - Although this seems to draw through the key as well. OR possibly add a third relay, OR add it to the coil power relay that I just added?

Suggestions? Does any of this really matter or am I wasting time worrying about it?

Thanks
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Old 04-21-2015, 08:41 AM
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Default Re: Power question

Here are the diagrams I was referring too;

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Old 04-21-2015, 02:09 PM
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Default Re: Power question

What are we talking about here? What is MS?

What you have changed that is causing the CPS to drop out, for example why is one of the signal wires crossed out on both schematics? I'm not sure what kind of sensor that is, is it a dual Hall effect sensor in the same sensor package or is it a single sensor with differential outputs? It's not a variable reluctance sensor because of the power and ground. How do you know that the sensor signal is breaking down?

I'll just say this: If you want to rework something because you're having signal problems, I would pay more attention to the grounding than the power.

Last edited by Fabrik8; 04-21-2015 at 02:13 PM.
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Old 04-22-2015, 10:01 AM
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Default Re: Power question

By MS I mean MegaSquirt.

Also, The CAS signal has been having issues since day 1 of my MS intall. The ka24 CAS is an optical sensor with a 24-2 disk from diyautotune ( http://www.diyautotune.com/tech_arti...gger_discs.htm) . The stock sensor used 360 "teeth" with a second ring with 4 "teeth".
The second rind used a seperate optical sensor to tell the ECM where cyl1 was TDC. The sensor generates a 12v square wave.

I did not need the second "ring" because the new trigger disk has 2 missing teeth on the main ring to locate cyl1. MS1 v3.0 also only has provisions for one CAS input. (by default). The reason I say my CAS signal is breaking down is because my RPM signal is changing erratically.
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Old 04-22-2015, 06:32 PM
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Default Re: Power question

Oh, ok. So now we know what engine you're talking about, which is a start.

So you've got a cam sensor and a crank sensor, correct? Have you verified the hardware and software settings on the page you listed, and are you using a shielded signal cable like the schematic says you should have? You absolutely need the 1k pullup resistor (mentioned on the trigger wheel page) to 12V either in the ECU or in the wiring (you must have implemented it inside the ECU, because your schematic doesn't show it anywhere), else the CAS won't work correctly. The sensor doesn't output a 12V square wave, it actually pulls the 12V signal line to ground. Without the pullup resistor, or with a pullup resistor that isn't a proper value, the signal line won't maintain the 12V state and the sensor signal won't work.

If you're using the 24-2 wheel, thats a symmetrical wheel and tbe ecu doesn't know where cyl1 is, only where cyl1 and the opposite cylinder are. That's why you can only run in wasted spark mode. The second trigger input is the angle reference that tells the ecu which is Cyl1 and allows sequential ignition.

I don't know much about MS but this is all general engine management concepts.

So answer me this: If your RPM signal is fluctuating, where are you measuring this; are you looking at your tach? I'm trying to get a complete picture of what's happening. This is difficult because there are a lot of things that can be done wrong when dealing with a homebrew DIY ECU.

Last edited by Fabrik8; 04-22-2015 at 07:21 PM.
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Old 04-23-2015, 05:45 AM
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Default Re: Power question

So you've got a cam sensor and a crank sensor, correct? Have you verified the hardware and software settings on the page you listed, and are you using a shielded signal cable like the schematic says you should have?
OEM has Cam and crank (for 96+ I think), I am using Cam sensor only. Hardware/software is correct. Using shielded twisted pair – what’s you opinion on where to ground the shield? At the ECU ground plane, at the head, not at all, or it doesn’t matter?

You absolutely need the 1k pullup resistor (mentioned on the trigger wheel page) to 12V either in the ECU or in the wiring (you must have implemented it inside the ECU, because your schematic doesn't show it anywhere), else the CAS won't work correctly. The sensor doesn't output a 12V square wave, it actually pulls the 12V signal line to ground. Without the pullup resistor, or with a pullup resistor that isn't a proper value, the signal line won't maintain the 12V state and the sensor signal won't work.
I have a 1k pullup that is internal. But now that you mention it, the CAS has a 12v power source itself, does it really need 12v AND a pull up? I think that it does, but just want to make sure.

If you're using the 24-2 wheel, thats a symmetrical wheel and tbe ecu doesn't know where cyl1 is, only where cyl1 and the opposite cylinder are. That's why you can only run in wasted spark mode.
My mistake, thanks for clarifying. Point is, I’m only using 1 trigger input right now.

So answer me this: If your RPM signal is fluctuating, where are you measuring this; are you looking at your tach? I'm trying to get a complete picture of what's happening. This is difficult because there are a lot of things that can be done wrong when dealing with a homebrew DIY ECU.
I can see it in the digital “tach” in the tuning software, my actual tach (driven from the MS), in data logs in the rpm signal, and I can feel it/hear it as the engine misfires due to wildly off timing. The noise I’m referring to shows up as huge tach drops (typically from ~6000 down to ~2000, but sometimes the signal spikes up to like 10,000). The problem almost only happens in an rpm range of 5800-6200, if I push through (not really a good idea in know) sometimes it feels like it clears up for the last few rpm before my rev limit (6500).

Here is the list of things I’ve tried:

- Switched to the vr input circuit (it has some threshold adjustments that I was told might help)
- added caps to clean up the board voltage
- replaced the battery
- grounded the ecu to one point on the head
- ran my own shielded CAS wires (grounded at ms)
- replaced distributor and coil (using DIYAutoTune trigger disc in both orientations)
- eliminated injector pwm noise by adding injector resistors
- swapped ms boards and processors

I am trying to add “build a completely new harness with COP’s” to that list to eliminate any issues from old wires or the fact that the CAS is in the distributor, but I need suggestions on best practices for my power/ground wiring.

1. I have read/decided that I should run several (4-6 20awg wires from the MS to one common ground point on the head). But will it be a problem to also ground my coils at the same spot?
2. As you can see from the diagram, the OEM setup ran power for the coil, injectors, *o2 sensors and even the *fuel pump are all powered through the actual key cyl. (*not shown as wired this way, but it is) The ECM and CAS were powered from a fairly small (22awg) wire when the ECCS relay was closed (by the ecm). I don’t really like this. I plan on:
a. adding a relay for power to the COP’s – power being taken from as close to the battery as practical to isolate it from the MS power. I am also considering adding the WB O2 and injector 12v to this circuit, but both are grounded at the MS, so I’m not sure if that is wise or not…
b. Increasing the wire sizing to the MS/CAS by running it off the “key” circuit since the coil will no longer be powered from this circuit. (again I’m not completely convinced this is a good idea either since there are many other loads on the same circuit (ie fuel pump), although it’s pretty far “upstream”. I mean technically EVRYTHING is on the same 12v circuit in the end..
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Old 04-23-2015, 10:41 AM
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Default Re: Power question

The 12V is for the sensor power supply, and the pullup resistor is for the sensor signal. Double check the resistor value, because a value that is grossly too low or grossly too high will cause problems (for different reasons). The exact 1k value is not really important, you just need something around that range, somewhere between 1k and 2k is close enough.
The CAS shield ground should be connected to the ECU case or signal ground for that sensor, depending on the ECU. It really depends on their grounding scheme, because some grounds may be decoupled from each other with a capacitor for DC voltage blocking, etc.

I'll think about the rest of the stuff and be back later.
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Old 04-27-2015, 04:40 AM
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Default Re: Power question

Originally Posted by Fabrik8 View Post
The 12V is for the sensor power supply, and the pullup resistor is for the sensor signal. Double check the resistor value, because a value that is grossly too low or grossly too high will cause problems (for different reasons). The exact 1k value is not really important, you just need something around that range, somewhere between 1k and 2k is close enough.
The CAS shield ground should be connected to the ECU case or signal ground for that sensor, depending on the ECU. It really depends on their grounding scheme, because some grounds may be decoupled from each other with a capacitor for DC voltage blocking, etc.

I'll think about the rest of the stuff and be back later.
Thanks for the input.
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