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Electric problem

Tiny
FRANXUA1
  • MEMBER
  • 1998 BMW 740
  • 130,000 MILES
I have a 98 BMW 740i, Recently my wife left her lights on and her card Died, I jump started her car using my BMW I hooked both batteries with my car running and told her to start her car, he car started but then mine started to smell like burnt cable, and after a few seconds I saw smoke coming from the engine I checked and I saw that the thermostat sensor had melted, after that the car stopped working and would start but die right away, I changed the thermostat, and the car started, so I thought the problem was solved, but after turning it off and trying to start it again, the car its still dying right after it starts, I don't know what it could be, any suggestions?
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Saturday, August 18th, 2012 AT 4:45 AM

25 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Check for blown fuses. Have the alternator and charging tested.
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Saturday, August 18th, 2012 AT 6:44 AM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
Ok I will try this tomorrow and I'll let you know thanks.
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Saturday, August 18th, 2012 AT 10:34 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Any update on this?
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Tuesday, August 21st, 2012 AT 11:19 AM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
Not yet, I have been really busy at work seems like I'll be off on Friday that's when I'll check the car and let you know. Thanks.
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Tuesday, August 21st, 2012 AT 6:29 PM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
So I checked the car and the fuses are all ok. Also the alternator it's fine. Any other suggestions on what it could be one thing I noticed its that once the car starts if I step on the gas it will die instantly.(Once I start it it will stay running for a couple of seconds)
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Friday, August 24th, 2012 AT 8:39 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Get a scan to check for trouble codes.

Yu mentioned the thermostat sensor melting and that can mean a poor ground circuit between engine and body.
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Friday, August 24th, 2012 AT 8:55 PM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
I did, before changing the thermostat there was like 7 different codes, but after changing it, all codes went away.
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Friday, August 24th, 2012 AT 9:41 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
You should have a look at the engine computer. The smoking when jump starting might have caused damage to it.
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Friday, August 24th, 2012 AT 9:53 PM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
Ok so I unplugged the sensor cable from the thermostat and started the car and it started and was actually running nicely, but after I plugged back the car shut off again, what could that mean!
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Friday, August 24th, 2012 AT 11:53 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
You could have replaced the component with a faulty one or of the wrong specifications.
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Saturday, August 25th, 2012 AT 1:45 AM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
I had an older thermostat from the car,
I changed it to that one and same thing as soon as I plug it back it dies.
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Saturday, August 25th, 2012 AT 2:18 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
I believe you are talking about the engine coolant sensor because thermostat is inside the housing and non electrical. Are you sure the replacement unit is good?

Looks like you need to put the vehicle on diagnostic equipments.
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Saturday, August 25th, 2012 AT 2:37 AM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
Yea im talking about the sensor, it comes together with the thermostat housing.I had 2 other thermostats they both have the sensor included, I tried changing both and once I plug in the sensor the car shuts off.
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Saturday, August 25th, 2012 AT 5:25 AM
Tiny
KHLOW2008
  • MECHANIC
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The computer is sensing something wrong with the circuit and it could be the sensor itself or the wiring is shorted. Check the sire carefully and ensure it is not fused together or to ground.
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Saturday, August 25th, 2012 AT 5:32 AM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
I checked the cables and up to where I can follow the cables the dont seem to be fused.I will get another thermostat and replace it, the old thermostats might have gone bad too. If that doesn't work I don't know what else it could be.
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Saturday, August 25th, 2012 AT 6:12 AM
Tiny
KHLOW2008
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If it does not work, you would need more than what you have done. The first thing is to plug in a scan tool to monitor the ECT circuit and check for faults codes.
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Saturday, August 25th, 2012 AT 7:19 AM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
Ok I got something, I plugged the scanner and Camshaft sensor came up.I belive its code P0340.
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Saturday, August 25th, 2012 AT 7:07 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Yes, that is the camshaft position sensor. Check the sensor and its wiring.

The unplugging of the ECT could be that when the PCM senses it is not working therefore it reverts to backup circuit and allow you to start sowe forget it for the time being.
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Saturday, August 25th, 2012 AT 10:03 PM
Tiny
FRANXUA1
  • MEMBER
  • 38 POSTS
It seems good, but I remember replacing that sensor about two years ago. And from what I remember it was doing the same thing it's doing now, so for now I'll just replace the sensor and hope that takes care of it.
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Saturday, August 25th, 2012 AT 10:17 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
It is possible the smoking had something to do with it and electrical components damages due to power surge/spikes can have far reaching results. Don't be surprised if other components had failed as well.

Lets hope ths cam sensor solves the problem.
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Sunday, August 26th, 2012 AT 6:14 AM

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