Sponsored by:
Sponsored by:

Odd power on ECU ground issue...

Old 03-16-2012, 09:45 PM
Junior Member
Thread Starter
iTrader: (2)
Join Date: Apr 2011
Posts: 360
Total Cats: 10
Default Odd power on ECU ground issue...

I finally got my car together (after working for 17 hours straight on the supercharger setup yesterday/too early this morning) and went to the dyno today. Everything was going well, and we were a good bit into fuel tuning the of boost region of the base map right until the car had a small backfire, turned off, and everything got weird.

The AEM suddenly couldn't cam sync (I'm on a 99 motor with the factory 99 cam/crank angle sensors) to start again, no matter what we did. I tried changing the sync settings to falling edge instead of rising edge, at which point it synced but would never pretend to combust anything. I tried futzing with the positions of the crank and cam angle sensors for a while (tried shimming the cam sensor and tried changing the distance between the crank sensor and the tooth wheel) to absolutely no effect.

Finally, we wanted to check that I hadn't slipped a timing belt tooth or something, so I started to take off the valve cover when I noticed that when I removed the ECU grounds (I had them bolted to the spare M6 hole on the valve cover for now -- it had 0.0 ohm resistance to the chassis so I wan't worried), they actually visibly and audibly sparked to the valve cover. That didn't seem right, so I checked voltage on them and they were showing 10.8 V when disconnected (with key to on). That doesn't seem right. I could see some floating voltage on them from live sides of sensors (like the TPS for example) but not enough to actually spark/arc to a ground when brought near it.

We had to tow the car home and I just spent a bit of time unplugging every sensor/connector/fuse in the engine bay and the only things that changed anything were that if I either removed the fuel inj fuse or unplugged the blk/ltgrn-containing plug from the AEM, the voltage float disappeared, so it definitely seems to be coming directly from the AEM unit. Is it likely that the AEM unit fried itself?
codingparadox is offline  
Old 03-16-2012, 09:55 PM
Junior Member
Thread Starter
iTrader: (2)
Join Date: Apr 2011
Posts: 360
Total Cats: 10

To add some more interesting context, all morning messing with the ECU, we'd noticed issues with the connection to the laptop dropping, requiring restarting the car and AEMPro before the serial connection would work again...
codingparadox is offline  
Old 03-20-2012, 11:55 PM
Elite Member
Join Date: Feb 2008
Location: Victoria, BC
Posts: 2,318
Total Cats: 12

I'm thinking your ECU is potentially fried. You probably want to get in contact with AEM to get a replacement.
dustinb is offline  
Related Topics
Thread Starter
Last Post
Build Threads
03-16-2019 08:07 PM
Miata parts for sale/trade
03-03-2019 03:41 PM
Suspension, Brakes, Drivetrain
09-29-2015 01:42 PM
General Miata Chat
09-28-2015 07:39 PM
ECUs and Tuning
09-28-2015 05:33 PM

Thread Tools
Search this Thread
Quick Reply: Odd power on ECU ground issue...

Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.