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Old 12-10-2008, 04:42 PM   #1
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Angry Need help with Electrical Gremlin

I have a brand new electrical gremlin I need some help killing. For some reason, my car keeps blowing the 30A INJ fuse under the hood. It happened the first time last Friday while driving. I wasn't doing anything crazy and we had been driving for about 20 minutes, when it just quit. I still had power and the engine would crank, but the fuel pump wasn't running. Replaced the fuse this weekend and drove it to/from work on Monday just fine. Went to drive it this morning and the fuse was blown again.

The only thing I can think of is I recently (last month) replaced my fuel pump with the walbro 255. The car has run great since that installation with the exception of this new problem.

Called FM support today and they suggested I run the power to the fuel pump off a switch directly from the battery to see if it keeps popping the fuse. I am looking for something a bit more analytical. I have the wiring diagrams for the car, but I was wondering if any of you have some ideas on where I should start.
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Old 12-10-2008, 04:58 PM   #2
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Unless you happen to own a DC ammeter with logging capabilities, moving one device at a time off of the circuit in question is a pretty good troubleshooting strategy.
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Old 12-10-2008, 05:10 PM   #3
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Start by pulling out the back carpet and FP cover to see if an animal was in there chewing on the wires. Or that you left them in a position where they could rub raw.
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Old 12-10-2008, 10:56 PM   #4
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No, the wires are fine and there is no shorting that I could see. I have an ok multimeter, but it doesn't have an ammeter built in. Perhaps this is time for an upgrade
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Old 12-12-2008, 12:24 PM   #5
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Looks like I need to do some more work on this. I tried a brand new fuse today and it blew as soon as I turned it over. Is there any chance the pump died? It is only a month old...
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Old 12-12-2008, 06:59 PM   #6
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Looks like I need to do some more work on this. I tried a brand new fuse today and it blew as soon as I turned it over. Is there any chance the pump died? It is only a month old...
awesome, someone knows less about electrical stuff than me.

You have a short somewhere. Time to start chasing wires.
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Old 12-12-2008, 08:36 PM   #7
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I had the exact same problem. Do you have a rollbar? Make sure the sheetmetal beneath the carpet hasn't worn through the wiring harness and into that wire, because that's where I finally found my problem.
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Old 12-12-2008, 09:49 PM   #8
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hrm. I do have a rollbar, and yes, it is time to start chasing wires. Man, I hate diagnosing wiring issues...
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Old 12-12-2008, 11:39 PM   #9
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Look in the area behind the driver's seat.

Meanwhile, save some money by not using new 30A links, get a fuse holder and a couple female spade connectors and pop blade fuses instead. Then, once you're sure the problem's gone you can put the link back in.

miataunderhood003.jpg
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Old 12-13-2008, 03:02 AM   #10
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That is an excellent idea. I will try that tomorrow when I am diagnosing the car.
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Old 12-13-2008, 09:54 PM   #11
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Look in the area behind the driver's seat.

Meanwhile, save some money by not using new 30A links, get a fuse holder and a couple female spade connectors and pop blade fuses instead. Then, once you're sure the problem's gone you can put the link back in.

Your The man! Cheap easy, I didn't think about that.
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Old 12-13-2008, 10:33 PM   #12
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Yeah, 5 pack of blade style was $3. The normal ones are $4.15 and I have already gone through two of those :( I just had some of my neighbors help me push the car into the garage so I can work on it tonight. I really hope it is something simple.
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Old 12-14-2008, 08:11 PM   #13
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Solved my problem and it turns out I was the failure point... again. Not sure how it happened, but I failed to follow the first rule of soldering. Never have two joints at the same place in the loom. Apparently the heatshrink I used was not solvent safe and swelled. When this happened, the solder joints rubbed on each other until they shorted inside my tank Took them off, resoldered them to different positions, and the car jumped to life! Anyway, maybe someone else will learn from my mistake
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Old 12-14-2008, 08:16 PM   #14
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Glad you worked it out man!

Todd - when I was sorting out my problem, I must've burned up 30 something fuses. That would've added up quick if it wasn't blades. Glad I could help!
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Old 12-14-2008, 10:16 PM   #15
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Quote:
Originally Posted by posidon42 View Post
Solved my problem and it turns out I was the failure point... again. Not sure how it happened, but I failed to follow the first rule of soldering. Never have two joints at the same place in the loom. Apparently the heatshrink I used was not solvent safe and swelled. When this happened, the solder joints rubbed on each other until they shorted inside my tank Took them off, resoldered them to different positions, and the car jumped to life! Anyway, maybe someone else will learn from my mistake
One reason why the emissions system pulls fumes out of the tank is to keep all the air (oxygen) out of the tank to reduce the chance of an explosion.
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Old 12-15-2008, 12:47 AM   #16
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Good to see this fixed.

That blade fuse idea is great.
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Old 12-15-2008, 02:01 AM   #17
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Good to see this fixed.

That blade fuse idea is great.
Agreed. I think this should go somewhere in the FAQ. Maybe under fuel system or general maintenance. Really saved me some bucks.
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