how smart are you? no spark, repeatedly blowing DIS fuse. (Update: SOLVED!)

[ddckec]

ok
thanks for the add......let me see if i can summarize this. 18 yr old Daughters 2007 Chevy Aveo 1.6 L manual......car started sputtering....... shes head to collage in 1.5 months. this is a must fix..ASAP

1. she limped it to Autozone, code P0300 misfire.
2. calls dad, I said start with the plugs.
2. Boyfriend Removed and replaced plugs. two plug ports, full of oil. not good.
3. calls dad, dad says if its running better drive it home slowly. 20 miles, Oil leak is a concern..
4. daughter calls.... its running better, but still stumbling not as bad, drive home slowly, dad says.
5. daughter calls says it dyed and she is stuck
6. What happened dad says?
7 Dont know, Daughter says; lost power steering and brakes, coasted to the side of the road and turned it off.
8.Dad Arrives and is confused about the relationship between stumbling / misfire and loss of Power steering and brakes.

9. Daughter defends her experiences.dad backs off. lol
10.replaced plug wires, coil pack,value cover, crank and cam sensors on side of road.
11. no spark from any plug or plug wire. confirmed with spark tester.
12. pushed car home.
13. by luck, i determined the DIS Fuse was blowing, started it at dusk and seen the spark from the fuse box.
14. determined that ever time i turn the key to start ( not on ) DIS fuse blows.
15. disconnected the Front Harness to Engine Harness isolation the engine components from the fuse box
16. dis fuse stopped blowing. OK good news...., Whats on this circuit?
17. determined components on this fuses circuit (via chiltons wire sch) are: both O2 sensors, evap canister purge Solenoid, ECM, Ac Cmprsr relay and Ignition coil module.

18. started unplugging components one at a time, reconnected harness each time and retesting the fuse. fuse still blows. So this rules out a bad component, on to the wiring.

19. NOW...all circuit components on this circuit are unplugged except for ECM and DIS fuse still blows.
20. Unplugged the ECM, Reconnected the front harness to engine and no blown fuse.
21. I have continuity along all the components wires back to the fuse box


is it safe to say that my ecm has shorted out internally? and if so why would this happen? the ECM will shut down fuel and spark to cylinders if it detects severe misfires, so how do i tell it that the misfires are fixed? maybe the stumbling was a bigger warning than just a fowled plug? is there anything else i can check before i running out and buy a new ecm? maybe a short to ground? and if so where would i start?

[avguy]

....
17. determined components on this fuses circuit (via chiltons wire sch) are: both O2 sensors, evap canister purge Solenoid, ECM, Ac Cmprsr relay and Ignition coil module....

The wiring diagram source that I use has a different collection of feeds from the DIS fuse, all of which are bundled inside of splicer SP201. The ones I have in addition to your list are the 4 injectors, cam position sensor, alternator, EGR, intake runner control, and evap canister vent. And my diagram does not have the A/C compressor on that fuse. The diagram also shows the lamp driver module protected by this fuse, but not passing through SP201.

However, I can't confirm if my diagram is correct because I don't have an '07, and the wiring for my '05 is not exactly the same. I'm sure you can run diagnostics to confirm if the list I posted is correct.

[ddckec]

this is the Power dist sch.. for a 2007- 1.6 L hatchback dis fuse. the items you listed are on a completely different fuse/circuit that is not my issue. but thanks anyway. i believe i have determine that the short to ground is somewhere between the harness (C103 PIN 3) and the splice (s126). how? well i installed my multi meter to the battery ground,removed the dis fuse, installed the red MM lead to pin B of the ign mod, and got a positive continuity result. and another positive continuity result at pin 4 of the O2 #1.

[JB_Fraser]

Did you do your continuity test with C102 disconnected as well as the components connected to the branch/splice ?
if not, you may have some ambiguous readings.

Cheers

[ddckec]

the day after my last post i found the problem... i had to get under the car to continue my electrical testing on the 2nd o2 sensor (pin 4) and the ac relay (pin 85).. and as i was inspecting the harness ..... HELLO.... The wire harness that runs along the bottom of the radiator was melted right in the area when its closest to the exhaust. in pic 4 below you can see the exhaust. im guessing the since its a manual trans and she was limping it home, that the heat from the exhaust melted the wire harness. if you look close at pic 1,2 & 4 below, you will see that alot of other items in this location have heat shield wrapping. i wonder why they did not add head shield wrap to this portion of the wire harness.... Cars running fine now.

[ddckec]

[ddckec]

[ddckec]

[ddckec]

[MetroMPG]

Nice detective work.

Thanks for letting us know how it turned out.