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ELECTRICAL ISSUE (Parasitic Draw)

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LNS_325

Freelancer
32
7
Jul 31, 2011
Sycamore, Ohio
Hello im new to the forum, but not to dsm's at all. I just picked up a 95 gst and I've got a wiring issue possibly...to start off it is 100% bone stock, all for the exception of a new alternator that was put on before I got it. With the key off I am drawing 2.25-2.5 amps, so I narrowed it down to the ecu relay which I read up that controls the fuel pump and the mpi, I also narrowed it to the mpi half of the relay...I don't know if it is the actual relay itself or I should keep looking for a short. I checked the wires comming out of the ecu and going to the relay to see if there were any shorts and there weren't any, so I pulled the ecu to check if I had any capacitor leakage and there wasn't any, so I am wondering if that new alternator isn't junk and backfeeding juice into the ecu somehow...also both the a/c and cooling fan both run all the time when the key is on...im just kinda stuck at what to do next. thank you
 
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The MPI relay should never be activated with the key off. It's blue-green wire should not be near 0V.

Do you have the doors shut or door switches disabled when measuring draw (the floor lights would draw about that much)? If so, unhook all your alt wires and see if you still have the draw (disconnect the battery before you unhook the alt and tape up the big + alt wire so it can't touch metal).

Someone may have re-wired your fans to be on with key on.
 
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Ya I will have to pull the alt wires and check that way, but that is another thing the interior lights and the power locks don't work either, I also forgot to mention that the stock radio is gone... im not sure if that affects the interior lights or not...so I dont think that my interior lights would be pulling any current during my test...the reason I found out that it was the ecu relay was that it clicks really fast when the key is off and will until it drains the battery or until I turn the key on...but I will try to unhook the alt n see if that gives me any different results, but maybe some of those other things will help a little as well
 
I pulled the alt and I had no difference in my results...so I did some more testing and I narrowed it to the mpi half of the ecu relay...I did a resistance check across the coil on the fuel pump half and it reads 88 ohms and the mpi half reads 8 mega ohms to OL . So I am pretty sure that the relay is bad and I need to get one, but it is hard locating one I have come to find out...but this is my current status on this problem
 
You do have the doors closed when testing so as not to trigger the interior lights correct?


Sent from my iPhone using Tapatalk
 
Yes the doors are closed...and I tried calling the mitsu graveyard and he said he isn't sure if he has one so I guess im going junkyard hopping or looking online, but I am pretty sure that that relay is done
 
i have a draw kinda like this one, its weird i tried to follow every wire but cant come up with a solution. i have a 90 gsx and what i ended up doing is on one of my wires to the mpi replay (i forget which one) i spliced in a switch for ground. so to start my car i turn the key to on, flip my switch which grounds? my mpi relay and my fuel pump starts running and i can turn over my engine.... BUT when i turn my car off i pull my key out, wait for my turbo timer to kill my car, then wait like 5sec and flip my switch back, if i forget to flip my switch and come back to my car a couple hours later my battery is completely dead! i still cant figure it out but maybe its something related to your problem idk but just a thought. good luck!
 
i have a 90 gsx and what i ended up doing is on one of my wires to the mpi replay (i forget which one) i spliced in a switch for ground.
If your switch allows the mpi relay to operate then obviously your drain is in the circuitry that the relay provides power to. Did you unplug everything that the relay powers to eliminate them as the source? If so then yep it's in the harness somewhere although quite often it's right near the connector to one of those items OR it's in something someone added but used mpi power to operate.
 
i have not tried that, im going to try to trace back everything today hopefully i can find it. for now that hidden switch works kinda like a kill switch but i dont like that it kills my battery, so hopefully i fix it! thanks for your help!
 
I did find out that the mpi relay coil is getting power all the time when the key is off...so I have a set problem before the relay, I wonder if I have a short, or possibly something inside of my ignition is messed up...I will dig in deeper and try to get to the bottom of this
 
Well I thought that it was the ecu before the mpi relay, so I pulled it out and it looked pretty mint...and it would suck if it was junk because its an eprom. Im gonna have to look up how to test my ignition, and see how to test that driver for the relay possibly
 
well this is a very old thread but i am planning on starting a new build thread soon so i figured i would touch back on this thread since i never did post the resolution to this problem. i did end up finding out what it was causing the drain. there were a few diodes inside of the ecu that were fried because of the old alternator that went haywire...so if you have an alt that goes bad and you put a new one on and you have a draw coming from your mpi relay its most likely because those diodes in the ecu...ecmlink fixed it for like $45 bucks.:cool:
 
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