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Floating Ground Situation
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FusionHHO Offline
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Post: #1
Sad Floating Ground Situation
Here's my ordeal:
I have a 2008 Ford Fusion 2.4L I4, and have tried 4 different designs of EFIE's with NO luck. Finally the other night I had a spark of light twinkle in my head somewhere amongst all the cobwebs! "Perhaps the ECU has it's own floating ground?!?" I recall many instances from my old Navy electronics days troubleshooting and can't get anywhere because of a stupid floating ground!!!

So I checked for continuity between the ground wire from the ECU to chassis/battery grounds - NO CONTINUITY! It has it's own floating ground so any EFIE I attempt will not work due to the voltage being supplied is in reference to a different ground. It's like powering a light bulb with one battery and hooking up another battery's positive lead only to that light bulb and expecting the bulb to get brighter... IT DOESN'T!

So, last night, I pondered this for awhile: "How do I utilize the ECU's ground and power my EFIE at the same time on the same floating ground?" - then it hit me, use a separate battery and extend the ECU's ground by connecting the ECU's ground to the negative terminal of the separate battery. So I dug up one of many 12V lead-acid batteries I have laying around (these are of the security system, UPS, or model engine starter type batteries) and tested this and viola! it worked!

If this is posted somewhere else, I apologize, but if you Google "EFIE floating ground" you get very little info, so I hope this helps someone else too.

Later,
Scott
07-21-2008 10:14 PM
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fordsohc46 Offline
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Post: #2
RE: Floating Ground Situation
what were the efies doing before you tried this? im wandering if this could be my problem. when i chk voltage across signal wires it fluctuates rapidly and will never level out.
07-22-2008 05:17 AM
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FusionHHO Offline
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Post: #3
RE: Floating Ground Situation
fordsohc46 Wrote:what were the efies doing before you tried this? im wandering if this could be my problem. when i chk voltage across signal wires it fluctuates rapidly and will never level out.

Well, the signal is not supposed to level out. However, what it's supposed to do is essentially add a small amount of voltage to the signal to fool the ECU into thinking that you're running rich, so it'll pump less gas in.

What my EFIE's were doing before the discovery of the floating ground was:

Two EFIE's would just output about 220mv, with no fluctuations - NO GOOD!
One EFIE did absolutely nothing. NO GOOD!
The fourth fluctuated between 80mv to 300mv, on the bench and in the car - NO GOOD!

Now I tested all four of my EFIE's using this idea of powering my EFIE with the same floating ground on another battery, and all four of them work now!
07-22-2008 07:26 AM
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Pinhead Offline
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Post: #4
RE: Floating Ground Situation
Could you do me a favor and see how high the ECU is floating above ground? Simply place the negative lead of your DVM to the negative terminal of your original battery, and the positive lead to the floating ground. I'm having trouble making my O2ptimizer work with my '99 F150, and I'm thinking that it may be a floating ground problem...
(This post was last modified: 07-22-2008 12:30 PM by Pinhead.)
07-22-2008 12:30 PM
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fordsohc46 Offline
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Post: #5
RE: Floating Ground Situation
fusion my efie is jumping from about 55mv to 350mv do you think i have this same problem. do you have to add a battery or can you just ground the efie with the pcm ground or does it not work that away. thanks for the posts.
07-24-2008 05:27 AM
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Pinhead Offline
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Post: #6
RE: Floating Ground Situation
Any updates??
07-24-2008 09:56 PM
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