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Old 07-13-2015, 12:59 PM   #1
ryderx
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Default Bad ground to ECU help me wire this please

Long story short an O2 sensor CEL led me to find out that i have a bad ground on a7 and a15 on the ecu. When i tap into that wire and ground to the body the CEL goes away but gives me a very odd hesitation that causes the car to die in lower RPMs. So thats not a fix.
I checked the ground on the "data link connector" that is on the same circuit and it is poor as well.

Without tracking down ever single wire, is there a way i can provide a solid ground to that circuit without getting the interference that im getting by just grounding to the body.
Or any tips and tricks to finding out why there is a poor ground to this circuit would be great as well.



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Last edited by ryderx; 07-14-2015 at 10:25 PM. Reason: more pics
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Old 07-13-2015, 01:10 PM   #2
Mulder
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Please complete your profile with your car info so we know exactly what year/model Subaru you have, and your location as well.
There could be a problem with the ground junction where those tie together, or one of the main grounds. Important grounds for engine/sensors are on the top of the manifold and firewall above the transmission, at least on older EJ's/.
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Old 07-13-2015, 03:34 PM   #3
ryderx
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Sorry. It is a 2000 2.5rs with a 2003 ej205 swap.

Firewall\back of the engine is solid. I will check the manifold one. Would you not expect to see more issues if it was one of the bigger grounds? Alternator to battery has good continuity as well...
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Old 07-13-2015, 08:59 PM   #4
Cougar4
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The drawing shows that those pins you mentioned tie to connector E3 on a blk/red wire. Have you checked to see if the ground connection is good at that point? You may have a connection problem between those points. I think the GE-1 main ground ties to a point at the rear of the engine.

Since you are having trouble with the engine idle when you ground those pins I suggest you disable the alternator by removing the rear plug connection to it. Then start the engine and see if that makes any change to the idle. If so then you most likely have some bad diodes inside the alternator which is creating excessive AC ripple voltage on the DC power bus.
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Old 07-14-2015, 10:03 AM   #5
ryderx
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I will test both of those thank you.

To describe the issue a little better. Its when taking off from a stop. When you apply just the right amount of throttle and let out the clutch at just the right time it feels like the injectors turn off for just a moment. so right RPM, Throttle, and load.

Or if i just tap the throttle to open maybe 1% the car will actually bog and not rev for just a second.
When i remove my ground the car runs normal.(minus the CEL)

I will check E3.
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Old 07-14-2015, 11:00 AM   #6
Cougar4
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You may also want to confirm that all the grounding bonds tying to the negative battery terminal are making good low resistance connections.
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Old 07-14-2015, 09:46 PM   #7
ryderx
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GE1 is solid as well as both negative terminal wires. Cleaned them up any how.

-Plugs disconnected-
E3 BR to battery =.04ohms
F60 BR to battery = - 15.5ohms
F60 BR to both data link and ecu BR =0ohms
--

-Plugs connected-
A7 A15 and data link BR to battery =-6.0
What does the negative mean?
--

Last edited by ryderx; 07-14-2015 at 11:37 PM.
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Old 07-14-2015, 11:02 PM   #8
Cougar4
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Okay, good testing there. The resistance of connection F60 to the battery is high. It should be less than 2 ohms I would think and I would really like to see less than 1 ohm of resistance. So you need to track that line down and find the faulty connection.

I assume you were reading resistance when you got the -6.0 reading. The reading was indicating that there was voltage on the line. You never want any power connected to the circuit you are trying to take a resistance reading on. The meter supplies its' own power to make the reading. Having external power applied to the circuit will change the real reading and can damage the meter if it isn't protected against that kind of thing.

EDIT: If the reading you took at F60 was while the connector was separated from the connection to ground (that would make the make the path ground for the ECU through the meter...bad idea) then you need to retest. Connect the connector together and then read the resistance between Main ground GE-3 and pins A7 and A15 of the ECU connector while it is disconnected from the ECU. You should have less than 2 ohms if the wire connection is good.

Last edited by Cougar4; 07-14-2015 at 11:15 PM.
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Old 07-06-2019, 09:39 PM   #9
RallyBlueSubaru
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Hey RyderX,

Did you or anyone ever figure this one out? I just got the same readings at F60. The resistance from ECU to GND reads 15 ohms however. Iíve redone just about every ground in my Ď02 wrx swap. Any information would be greatly appreciated. Thanks
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Old 07-06-2019, 09:43 PM   #10
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His last login was over 3 years ago, don't expect a response.
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