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'07 TBSS
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Discussion Starter #1 (Edited)
2007, MP112, New underhood fuse box Feb 2015, New Ign module when this started, Fuel pressure 60lb with key on, and doesn't fall off when cranking, all of the underhood fuses tested good, however there is no power on fuse 17 (CRNK) in any key position (not real sure on that one), Jcase fuses also ohm low, I'm open for suggestions.

No Codes present.

Spark is the only thing I haven't checked.

This started by engine cutting off at a stop sign, started back up right away. Stopped in a parking lot on the way to work, it shut off before I switched it off. Started back up when I returned out of store,and upon turning into the driveway at work it shut off, and hasn't started back since, it acts just like its out of fuel.
 

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'08 TrailblazerSS
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The crank fuse is only hot when the IGN is in the Start position. Definitely check spark as soon as you can. It honestly sounds like the typical IGN switch or underhood fuse block. Getting any codes?
 

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'07 TBSS
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Discussion Starter #3
Thanks Brandon, I'll pick up a spark tester in the morning, I also have a spare IGN switch, I'll try that one also, the one in it is New, it has never started the truck. I really hope its not another fuse box. There are no codes present according to the aeroforce gauge.
 

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'07 TBSS
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Discussion Starter #4
Update; put the spare IGN module in...No Go.....there is No Spark on either side of the engine.
 

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'07 TBSS
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Discussion Starter #5
Another update; Took my old fuse box, soldered all upper and lower connections, because I saw no traces broken, I have continuity between all trace connections upper and lower, put that one back in the truck...Same Condition...I'll start searching the electrical schematics for the coil pack signal, feel free to post up, or put me in the right direction if I'm astray.
 

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'08 TrailblazerSS
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You may have a crank sensor issue. Do you have any type of scan tool that you can scan your tach signal with? See if you are getting a tach signal when the engine is cranking.
 

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'08 TrailblazerSS
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I would think the Aeroforce would show your tach?
 

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'07 TBSS
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Discussion Starter #9 (Edited)
The damn thing fired up. I put the fuse box back in that I bought in Feb, I sparyed the blocks with contact cleaner before I bolted it back in, then set to view RPM on the gauge, and she fired up, first time all week. But I'm still leary of this damn thing. Would it help to take it back out and use dielectric grease on all of those pins?
 

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'07 TBSS
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Discussion Starter #10
Brandon, thank you for your efforts, I hope I don't have to revisit this thread anytime soon.
 

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'08 TrailblazerSS
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No problem.
 

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'07 TBSS
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Discussion Starter #12
Happened again, had to get a trailer and go get it. I pulled the fuse box, and sprayed all of the connectors with contact cleaner, and it ran for 30-45 seconds, long enough for me to get it halfway on the trailer anyway. resprayed the contacts, no luck. brought it home went to roll it off the trailer, hit the key, it cranked, got it off of the trailer and into the garage, cut off, hasn't cranked since. same as before, no spark...It is seeing the tach signal while cranking. I need a schematic of the ignition wires to and from the fusebox for the coil circuits, I'm losing power to the coils somewhere, all the fuses still show good with the test light, and ohm meter. any insight is appreciated.
 

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'07 TBSS
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Discussion Starter #13 (Edited)
Found the schematics in an older thread. Would the 2006 schematics be different than the 2007 ign, coil packs, odd and even?
 

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'08 TrailblazerSS
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2,987 Posts
Yes the control wires will be in different pins. Use these.

Ignition Coils (Even)


Ignition Coils (Odd)
 

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TrailblazerSS
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You get it fixed?
 

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'07 TBSS
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Discussion Starter #17
Yes, I took the Fuse box out, and used OX Gard on all of the pins, and in all of the receptacles of all connectors, and pried the receptacles for a tighter connection to the pins, I also removed and cleaned all of the ground points under the hood, and used the compound on those as well...

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I also discovered that previous owner had an alarm system on the truck, whomever installed it did a shitty job, because this is what I found coming through the firewall...


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I have a similar vehicle and had the same problem. After changing numerous items, I replaced to a new fuse box and the problem was solved. Double check your "NEW FUSE BOX".
 
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