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ECM Failure; Are ECM's really bomb proof?
Topic Started: Mar 1 2015, 08:48 PM (1,886 Views)
randjw
New Member
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I replaced the 5spd transmission in my 1995 Geo Metro this weekend, while the trans was out I noticed that there was some rust on the frame and thought I would repair it prior to reinstalling the trans. So I welded two small 1/2 dollar size patches on and finished reinstalling the trans. Once everything was reinstalled I reconnected the negative battery cable and attempted to start the car. The engine just cranks, no start. I then started trouble shooting, found that the 15amp fuse for the taillights under the dash and the 15amp in the main fuse panel under the hood was blown. replaced fuses and reattempted with no luck, just kept blowing fuses. I traced the short back to the ECM so I disconnected it and reattempted to start, engine cranked over without blowing the fuses but obviously would not start without the ECM. Just wondering if everyone agrees that I need to replace the ECM?
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Good bye


We use a surge protector when we weld at work and leave the batteries hooked up. I have had two bad ecms on Metros out of fifteen or so that I have owned. I learned the hard way, don't buy a junk yard ecm if the car it came from isn't wrecked.
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evmetro


Your ECM may indeed be the problem, but it would not replace it until you have done some more troubleshooting. Start by checking for spark and fuel. Let us know on this thread, and we can walk you through more troubleshooting if you need it. My guess is that it is not your ECM, but I don't have enough info.
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don_dowdy
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Pull the ECM, pop the lid and see if anything is burned or leaking. Only takes a few minutes and doesn't cost anything. Maybe another forum member is close enough to swap ECMs with you and see what happens.
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Stubby79
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don_dowdy
Mar 2 2015, 12:51 AM
Pull the ECM, pop the lid and see if anything is burned or leaking. Only takes a few minutes and doesn't cost anything. Maybe another forum member is close enough to swap ECMs with you and see what happens.
Someone with a spare, good ECM, maybe...I don't think you want to kill someone else's ECM and leave them high and dry too.
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geogonfa
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Just my $.02...follow the FSM and double check everything before replacing...might be the backup light switch, if it's bad or shorted it will cause the same problems... :type
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sphenicie


Not only would I recommend that nobody trust a "surge protector", but I would strongly tell you to unplug the ECU and TCM (for a/T), in addition to disconnecting the battery. It might take you an extra 5 minutes. But it will take much longer than that to fix.

when I worked at the fab shop, we did a lot of factory new work for CAT, JD, and Timbco. It was a fire-able offence to not REMOVE the battery(s), disconnect any control units, and use proper grounding methods.

Improper grounding can damage much more than just control units, you risk doing damage to bearings, slip joints, distributors, and sensors.

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evmetro


I have a career as a collision tech behind me and have welded on thousands of cars. The industry standard is to simply disconnect the battery, but I have indeed seen manufacturer warnings to disconnect the ECM as well for some cars. I just disconnected the batteries, and have never damaged an ECM or any other component using this method, but I have heard of rare cases where it has happened. A buddy of mine runs a muffler shop, and just uses a surge protector, and no problems.

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Hanuman
"The Almighty Grounds Cleaner"

randjw
Mar 1 2015, 08:48 PM
I replaced the 5spd transmission in my 1995 Geo Metro this weekend, while the trans was out I noticed that there was some rust on the frame and thought I would repair it prior to reinstalling the trans. So I welded two small 1/2 dollar size patches on and finished reinstalling the trans. Once everything was reinstalled I reconnected the negative battery cable and attempted to start the car. The engine just cranks, no start. I then started trouble shooting, found that the 15amp fuse for the taillights under the dash and the 15amp in the main fuse panel under the hood was blown. replaced fuses and reattempted with no luck, just kept blowing fuses. I traced the short back to the ECM so I disconnected it and reattempted to start, engine cranked over without blowing the fuses but obviously would not start without the ECM. Just wondering if everyone agrees that I need to replace the ECM?
a common mistake is to plug the cam position sensor harness into the harness on the tranny that indicates when your in reverse. the harness will plug into each other, and are near by.

no signal from the cam sensor (pick up coil) no spark or fuel.
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idmetro
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Hanuman
Mar 2 2015, 02:26 PM
randjw
Mar 1 2015, 08:48 PM
I replaced the 5spd transmission in my 1995 Geo Metro this weekend, while the trans was out I noticed that there was some rust on the frame and thought I would repair it prior to reinstalling the trans. So I welded two small 1/2 dollar size patches on and finished reinstalling the trans. Once everything was reinstalled I reconnected the negative battery cable and attempted to start the car. The engine just cranks, no start. I then started trouble shooting, found that the 15amp fuse for the taillights under the dash and the 15amp in the main fuse panel under the hood was blown. replaced fuses and reattempted with no luck, just kept blowing fuses. I traced the short back to the ECM so I disconnected it and reattempted to start, engine cranked over without blowing the fuses but obviously would not start without the ECM. Just wondering if everyone agrees that I need to replace the ECM?
a common mistake is to plug the cam position sensor harness into the harness on the tranny that indicates when your in reverse. the harness will plug into each other, and are near by.

no signal from the cam sensor (pick up coil) no spark or fuel.
This happened to me (young son was "helping"). Your clue will be to look down by the transmission if you see a pigtail that is stretched taut then this is probably your condition. Simply unplug the taut one, look for another nearby with the same connector, unplug/swap ends and away you go!
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randjw
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Up-date, I reconnected the ECM and tested the engine for fuel and spark and no signs of either. I also disconnected the reverse switch and reinstalled the 2 15amp fuses and still no signs of fuel or spark, but it did blow the fuses again. I then also removed the ECM and removed the cover and inspected the interior for signs of shorts or burnt marks and no signs of anything, the ECM looks like new inside. The 15amp fuse in the main box under the hood appears to be the main that runs most of the engine bay coil, fuel sensors and so on the other 15amp fuse is under the dash and is labeled taillights, I believe so long as the 15amp main under the hood keeps blowing I will not get fuel or fire.

Just like to thank everyone that has commented in efforts to help me figure this out.

Thanks
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Stubby79
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Did you try replacing the fuse with the ECM disconnected? That will tell you if the short is in the ECM or not.
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Metromightymouse
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Powdercoat Wizard

I second trying it with the ECM disconnected to see if the fuse still blows.
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randjw
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Yes, I already tried to crank the engine with fresh fuses installed and the ECM unplugged and the engine cranks without blowing the fuses.
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idmetro
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I am going to go out on a limb here - while I have not seen this on a Metro I have seen strange issues on other vehicles when the taillight sockets get corroded. It can't hurt to open up the lights and see if you've got a bunch of corrosion is there... Good Luck!
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