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03 TB not starting, bunch done already

10-01-2009, 01:59 PM
We have an 03 Trailblazer LTZ with the 4.2L 4X4 and apx. 140k miles.
My wife went to start one morning (apx 60 degrees or so), it would crank but not start. Had it towed to Uncle's shop where he scanned it and found no codes. Gave it complete tune-up (air filter, fuel filter, oil filter, oil, plugs, etc) to no avail. The next step was the fuel pump. Changed it out but did not fix it so we thought is was a rare new but bad pump. So we exchanged it for another new one (both having new modules included) and still no change. Checked the wiring and didn't find anything bad so we thought it was the computer. Hooked the pump directly to the battery bypassing all the 'puters and relays and it would start but run horrible. He put a psi gauge on the fuel and said the old pump "was all over the place, up, down". Hooked the pump back the way its supposed to be and still nothing. The wife said the Emergency brake light and the ABS light came on and dinged a bunch of times when she was trying to start it. The uncle thinks its the BCM going bad, thinking somebody is trying to steal it and shutting the pump or whatever down. Anyway I'm ordering a used BCM off eBay for 60 bucks and hoping we can just plug in and go w/o having a dealership (which is an hour away to the closest) having to reprogram it.

What do you think? Tomorrow is a week in the shop and desperately needing a vehicle. :banghead:

10-01-2009, 06:55 PM
How about quitting the guess work and finding the root problem, the BCM most likely is not the issue, a trouble tree for the problem can be found in a factory based shop manual.

10-02-2009, 08:11 AM
Both the uncle and I have spent hours on the web and flipping through manuals from different brands including an expensive one he found. We've talked to other shop's we're close with and they are puzzled, too. That's why I posted on here, hoping somebody would give me a tip or idea, instead of "stop guessing, read the instructions."

10-02-2009, 12:10 PM
No one here can possibly have an answer without going thru the required diagnostics just like anyone or a shop must do, no? When it won't start is the spark strong enough, is there proper fuel pressure at the rail, are the injecors pulsing, will it start by spraying carb cleaner into the intake, this would at least narrow it down, I assume this has all been done, though.

10-02-2009, 12:39 PM
Yes, all that has been done and all that checks out normal. I don't know about the ignition switch. How would one check that w/o tearing half the column apart?
What has me stumped is the part about him bypassing the electronics and wiring the new pump directly to the battery. It will start then but run like crap. Is that because the BCM is no longer a factor and not being able to tell the system what the pump is doing or something else?

10-02-2009, 06:40 PM
The bcm does not control spark or fuel pump operation, the pcm does. What he did bypassed the fp relay that the pcm would power up. Is the fp relay powered up, can you hear the pump run key on, is the ign switch/pcm powering the fp relay?

10-05-2009, 07:06 PM
Haven't gone back by his shop yet to check it out. I though about buying the ignition switch and installing it just for the hell of it and see what happens. Is it difficult? Anything I need to know first?

10-06-2009, 07:36 AM
Yes, you need a tamper proof torx to get the switch out, do a site or google search or get a shop manual.

10-06-2009, 07:47 AM
I'll have to borrow a set. He has a bunch different manuals now. It'll be a couple of days before I can check it again. I'll let you know.

10-15-2009, 11:29 AM
Well, dropped off the trailblazer Monday am at the Chevy dealership and got a call a little while ago. It was the ignition switch thingy like you said (I told them to check it out, they said "it threw a leg"?). That being replaced turned on the computers but then it wasn't talking to the fuel pump. They found a bad ground between the two and fixed it. Now they say everything is good but Number 2 is not firing. I told him the first thing we did after it wouldn't start is give it a complete tune-up (spark plugs, wires, all filters, etc). He said they would check the plugs and wires first then call me. Before that, I'm up to 350 bucks (just the Chevy dealership's cost, not the previous mechanic's parts and labor bill)!!

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