HALP! Calling all wiring experts!! - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


General Miata Chat A place to talk about anything Miata

Reply
 
 
 
LinkBack Thread Tools
Old 03-23-2013, 10:29 PM   #1
Junior Member
Thread Starter
iTrader: (2)
 
Join Date: Jan 2012
Location: Norcal
Posts: 128
Total Cats: 0
Default HALP! Calling all wiring experts!!

Okay I'm stumped. I've been battling grounding issues for the past 2 weeks in my 1995 Miata. I have a AEM EMS4 and AEM smart coils all wired up. Now I have a few issues:

1: I think I've found a short somewhere in my METER fuse circuit. O2 sensor Black/Yellow and Black wire do not show open circuit, instead it shows a low resistance value. I don't believe this is normal but I'm not entirely sure. Logic would say that power and ground should have infinite resistance/open circuit. Any ideas?

2: Something is feeding voltage to my sensor ground. I BELIEVE that I have completely isolated my sensor ground from chassis ground. For sensor grounds I'm using the Black/Blue and Black/Light Green wires. These are pins 2C and 2D on the ECU. B/LG runs from ECU to front of engine, serves as a ground for CAS. This wire used to be linked with a clasp terminal to two Black wires. I unlinked this wire to isolate it from chassis ground. Black/Blue runs from ECU to TPS, EGR (map wired in), Coolant temp, MAF, O2 sensor. This wire never touches ground so it's also isolated. I also have the coil pack sensor ground wire grounded to the sensor ground.

Now, when I turn on the car I get .5V through the sensor ground, and all of my sensors read high. When I ground the sensor grounds to chassis my sensors go back to normal. This would be great except that the sensor grounds can't be grounded to chassis. When the car was running this way I was getting a bunch of noise in my sensors causing the car to misfire. I'm not sure if problem 1 and problem 2 are related, and I have no idea where to look now. When I start unplugging things, coil packs, fps, map sensor, the voltage drops. It kind of makes sense, if there is a set amount of current backflowing somewhere, then as I decrease resistance, voltage decreases. Connecting everything back would increase resistance and increase voltage?

Anyway maybe I'm chasing down the wrong hole right now, if someone can point me in the right direction that would be great! I'm about out of ideas...

Also my AEM EMS4 is grounded using the chassis 2A and 2B. I was considering grounding the EMS directly to the battery instead.
reddragon128 is offline   Reply With Quote
Old 03-24-2013, 12:59 PM   #2
Senior Member
iTrader: (4)
 
mr_hyde's Avatar
 
Join Date: Jul 2009
Location: Seattle
Posts: 799
Total Cats: 25
Default

Is this a new install or was it working fine and then crapped out all of a sudden? I had something similar happen with a pinched O2 wire but it's possible a sensor could have failed too. Try disconnecting each sensor one at a time and see if that .5v goes away with one of them. My problem was a dead short so the engine fuse popped immediately. I haven't messed with an NA8 harness but the same principles apply.
mr_hyde is offline   Reply With Quote
Old 03-24-2013, 08:49 PM   #3
I'm Miserable!
iTrader: (1)
 
Join Date: Jan 2008
Posts: 203
Total Cats: 8
Default

Sensors being the crank and cam sensors? I have a similar car (1994) and I'm having all sorts of timing errors.

EMS-4 Series 2, as well.
GAMO is offline   Reply With Quote
Old 03-24-2013, 09:58 PM   #4
Senior Member
iTrader: (4)
 
mr_hyde's Avatar
 
Join Date: Jul 2009
Location: Seattle
Posts: 799
Total Cats: 25
Default

Every sensor on that bus.
mr_hyde is offline   Reply With Quote
Old 03-24-2013, 11:06 PM   #5
I'm Miserable!
iTrader: (1)
 
Join Date: Jan 2008
Posts: 203
Total Cats: 8
Default

What are the sensors on that bus?
GAMO is offline   Reply With Quote
Old 03-25-2013, 02:21 AM   #6
Senior Member
iTrader: (4)
 
mr_hyde's Avatar
 
Join Date: Jul 2009
Location: Seattle
Posts: 799
Total Cats: 25
Default

I don't know. I don't have a wiring diagram for that year. On my car, every sensor under the hood (IIRC) is on the same ground bus.
mr_hyde is offline   Reply With Quote
Old 03-25-2013, 06:58 AM   #7
Junior Member
Thread Starter
iTrader: (2)
 
Join Date: Jan 2012
Location: Norcal
Posts: 128
Total Cats: 0
Default

Quote:
Originally Posted by mr_hyde View Post
Is this a new install or was it working fine and then crapped out all of a sudden? I had something similar happen with a pinched O2 wire but it's possible a sensor could have failed too. Try disconnecting each sensor one at a time and see if that .5v goes away with one of them. My problem was a dead short so the engine fuse popped immediately. I haven't messed with an NA8 harness but the same principles apply.
This is a new install. I'm also wondering if I have a short as well. I pulled every single fuse in the fuse boxes except for MAIN, disconnected ECU, dash and then i checked resistance between power cable and ground. It wasn't an open circuit, but it was reading some super high resistance value in the Mega Ohm range... Then when I pull the main fuse the power cable to ground became open circuit as i thought it should be...I'm not sure what to make of it. Shorts usually don't read giant mega ohms??

Quote:
Originally Posted by GAMO View Post
Sensors being the crank and cam sensors? I have a similar car (1994) and I'm having all sorts of timing errors.

EMS-4 Series 2, as well.
That's exactly what I'm getting. I'm thinking it's a power surging through the sensor ground. That can happen if you have your sensor ground grounded to chassis. Although, stock cars seem to all have their sensor grounds grounded to chassis or block...

Quote:
Originally Posted by mr_hyde View Post
I don't know. I don't have a wiring diagram for that year. On my car, every sensor under the hood (IIRC) is on the same ground bus.
All sensors are grounded through the Black/Blue or Black/light green i believe...
reddragon128 is offline   Reply With Quote
Old 03-25-2013, 09:42 AM   #8
I'm Miserable!
iTrader: (1)
 
Join Date: Jan 2008
Posts: 203
Total Cats: 8
Default

Alright, sounds like we're having the same issue... or something extremely similar. Are you doing a VVT swap as well or are you just moving to the NB sensors?

What type of wiring are you using for the crank and cam sensors? Straight? Twisted pair? Shielded?

Last edited by GAMO; 03-25-2013 at 03:43 PM.
GAMO is offline   Reply With Quote
Old 03-25-2013, 04:54 PM   #9
Junior Member
iTrader: (1)
 
Join Date: Apr 2010
Location: Saint Marys GA.
Posts: 136
Total Cats: 3
Default

Check that you have all of the sensors wired correctly, look for ground and Vref being swapped at the connector. Also with the ignition on but the engine off open EMS tuner and unplug sensors one by one while watch the sensor read outs.
Lee04vr is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Need help - Stock Balancer and Fastforward overlay pulleys Frank_and_Beans Supercharger Discussion 13 09-12-2016 09:17 PM
LucaCarMods's Boosted Dutch Miata Build! LucaCarMods Build Threads 11 02-14-2016 07:13 AM
My solution for Oiltemp and Oilpressure input into Megasuirt (MS3) Zaphod MEGAsquirt 41 01-24-2016 01:25 PM
MSPNPPro-MM0105: Coolant Temperature Output slomiata MEGAsquirt 5 10-07-2015 02:11 PM
wiring wideband ground to battery terminal btabor ECUs and Tuning 10 09-28-2015 06:33 PM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 05:53 PM.