Stall issue

[TBlazerD]

Hello all,
Just moved over from Trailvoy by recommendation. I am hoping for a "seasoned" Trailblazer expert on this one. This may be long but, I want you to have all info possible.
2005 Chevy Trailblazer LS sport 4.2 4X4 172000 miles The issue is after being driven 10-20 miles it will just shut off at a light. No warning, no shaking, no shuttering just shut off. It will restart immediately and I will smell a rich exhaust smell. It will only do it after being driven, not when cold or short trips.
It runs so smooth that you don't feel it running and when the idle sets at 650 ish, it is ultra smooth then it's like the key gets turned off. ABSOLUTELY NO CODES in either active or pending. None in permanent. Both PCM and BCM are code free.

Whats been done: All parts are Delco, Delphi whenever possible.
Throttle body cleaned, then replaced with a new one - no change
New fuel pump assembly
New Coils (6) and A/C plugs
New Crank sensor, new cam sensor, new VVT solenoid, new MAP sensor, new oil pressure switch, new ignition switch, new battery, Upstream and downstream O2 sensors, new thermostat, temp sensor, cooling fan clutch, IAT sensor, air filter, emisions test.
This model does not have a fuel filter or external fuel pressure regulator.
I have had the PCM and BCM updated from the GM dealer.
I also had my local shop (ex GM tech of 23 years) with both Tech 2 and Snap-on diagnostic computers spend over 4 hours trying to find it which included him checking wiring harnesses and grounds. He's stumped too....

Anyone?????

 

[Mooseman]

The plugs were 41-103? Anything else is no bueno.

When the throttle body was cleaned and/or replaced, the battery was disconnected for at least 30 minutes?

How's the exhaust? Tried a backpressure test?

I would imagine you or your mechanic tried jiggling the wiring while it's running? Checked the fuses and relays for bad connections?

One thing I'm thinking is that the PCM itself has an issue where once it's warm, it dies. If you have a pick-n-pull nearby, grab one cheap from a same year truck and swap it out. Just need to do the 30 minute security relean.

 

[TBlazerD]

The plugs are correct. Confirmed
Yes the battery was disconnected and I let sit for 30-45 minutes after done just to be sure.
I did mean to put I had the exhaust pressure checked with the emission test just to be sure of a clear Catalytic converter.
The mechanic said he put his hands on every wire in the truck...lol even did the tapping test on all connectors.
He only found one fuse that was bad and it was for the "cigarette lighter". All others and relays were good. No corrosion either.
He suggested the same thing about the PCM. He said with all the issues Trailblazers have he has never seen a bad one but, he was at a loss for anything else.
I will give the PCM a try. I just wanted to see if someone knew of a QUIRK that we were missing.
I will follow up after I try that.
I just ordered one from Highway71autoparts.com. Only $83.00 and comes Pre-programmed to my VIN#
Thank you for the quick response. Hope that this is it.
Will keep you informed.

 

[Mooseman]

With the years that these trucks are starting to accumulate, PCM's are starting to also show their age. There have been a few reported bad ones but none with such an intermittent issue.

 

[TBlazerD]

I hope it is th PCM. If not....I am done and it is gone. Too much time and money chasing the ghost in the machine.

 

[TequilaWarrior]

Check the FIT of the fuses in the underhood fusebox. My car would die suddenly with no symptoms but the fact that it died... the exciting part being that it would do it at any time: driving, parked, stopped at a light, whenever.
I racked my brain for months. I threw parts at it for months. Every time I'd think I made something resembling progress it would happen again a day or two later.
UNTIL.... I took it to a dealership (that's not what I'm recommending).... the tech really didn't want to touch it since it was shutting off while driving - something he didn't want to experience firsthand.
Serendipity stepped in... while just doing general checks the tech decided to start the car, remove the underhood fusebox cover, and gently "wiggle" fuses with his fingertip. Boom, car dies. I had 1 single solitary fuse socket - the PCM fuse socket - that didn't "grip" the fuse well any longer. A quick, slight turning of the fuse's blades with a pair of pliers and it was snug in the socket again. I've been running like that for years now.
Give your fuses a wiggle. Might be worth your time.... but don't get zapped.

 

[TBlazerD]

Check the FIT of the fuses in the underhood fusebox. My car would die suddenly with no symptoms but the fact that it died... the exciting part being that it would do it at any time: driving, parked, stopped at a light, whenever.
I racked my brain for months. I threw parts at it for months. Every time I'd think I made something resembling progress it would happen again a day or two later.
UNTIL.... I took it to a dealership (that's not what I'm recommending).... the tech really didn't want to touch it since it was shutting off while driving - something he didn't want to experience firsthand.
Serendipity stepped in... while just doing general checks the tech decided to start the car, remove the underhood fusebox cover, and gently "wiggle" fuses with his fingertip. Boom, car dies. I had 1 single solitary fuse socket - the PCM fuse socket - that didn't "grip" the fuse well any longer. A quick, slight turning of the fuse's blades with a pair of pliers and it was snug in the socket again. I've been running like that for years now.
Give your fuses a wiggle. Might be worth your time.... but don't get zapped.

Good idea. Gives me something to do while waiting for the PCM to come in.

 

[TBlazerD]

Well...good idea but, no dice. Now the wait for the PCM.

 

[TBlazerD]

OK. Here it is....may be a bit long but, if it helps one other person its worth it.
PCM came in and it had no difference. After driving for a few days things started to get more SPOOKY. The Tach would start acting like it had a seizure, the turn indicators would stop working and the Cruise control would stop at the same time randomly but would run fine until it stalled as it had before. If it stalled out while the new "spasm" it would not restart. The passlock light and battery light would light up but no gauges. I would let it sit for 10 minutes and it would restart.
I picked up my wife on Monday morning and it did it again. This time with my wife watching the dash i started pressing down on the fuses and relays and she said the gauges moved slightly. I then lifted up on the wire coming from the battery to the under hood fuse box and everything lit up and it started. I tool he home and went to work. I thought it may be a loose connection but it was not. SOOOO. thinking a circuit board may have a bad solder on it i pulled the fuse box out and pulled it apart. (There are y0outube videos to help you.) What I found was a surprise to say the least. GM in it well known wisdom decided to not use a circuit board or reguler insulated wires but exposed 20 gauge copper wire just pushed into a type of splicing clip. Holy crap. SMDH. So, I took my phone camera and zoomed in and followed every "wire". I found a few areas of discolor and one with an almost non existant break. I then looked online and found this to be an extremely common problem with videos and pictures galore. I could have just went to Lowes and got some replacement wire but I felt there were too many "suspect spots" to fool with so....I dropped $50.00 at the boneyard and got one from a low mileage wrecked one, pluged it in and Praise Jesus the problems went away and no issues.
I suggest watching a few of the videos for education and I will include a pic of what the board looks like and one of the offending area. Pay close attention to the s-curved areas of the "wiring".
I hope this helps you guys and thanks for your help.

 

[Mooseman]

Nice job figuring this out. At those discoloured spots, I can almost see breaks in there. I wonder what causes that? Heat or just corrosion?

 

[TBlazerD]

Nice job figuring this out. At those discoloured spots, I can almost see breaks in there. I wonder what causes that? Heat or just corrosion?

Apparently, according to a friend that is a master electrician, the idea of using exposed copper wire to the elements borders on stupidity. Passing a current through a exposed wire will cause it to attract moisture, make it more sensitive to temperature variances and make the possibility of shorting amazingly high. Although they are ground wires, if they come loose from the push in channel they are in (literally no glue or clips) it increases the possibility of failure.
He looked it over and stated without insulation to regulate temperature variances, the vibration has a larger effect. The insulation would slow the cooling process. When you add moisture and contaminates it was bound to happen. Also, any arc of any kind would find a perfect ground.

 

[TequilaWarrior]

Bear in mind that this lasted.... 16? years... and it doesn't happen to EVERY GMT.... this design methodolgy is very normal for automotive and is actually a dramatic improvement from the 70's when they'd mount the firewall/bulkhead connector "below the water line" - low enough on the firewall that it literally got sprayed when you went through puddles (ask me how I know).

Liberties are taken in automotive that would be inconceivable in residential/industrial/robotic applications. For instance, in robotics application we use a type of wire that has an extremely high copper strand count and is rated for repeated bends without compromising the insulation - something that can't be done with solid copper runs in a home, period.

I would posit that the clamshell for the fusebox wasn't snug / had loosened from spec and contributed to this failure with years of vibration.
The way this is constructed and assembled should keep moisture and contaminants out of the space altogether. It should NEVER get wet between the clamshell. CAN it? Maybe...
As for the lack of insulation.... realize that insulation's primary purpose is to inhibit arcing... "air" for all intents and purposes is an insulator... not a great one, though. The gaps between those bus runs is plenty when you consider that they are almost completely encapsulated when the clamshell is put together - i.e. they have plastic all around them in addition to the space between them.

I give you huge KUDOS for solving this problem as I'm sure this will creep up for others (if not myself). This was not an obvious cause based on symptoms. Good job.

The electrical system on these is far more complex and extensive than ANYTHING that came out 20+ years prior. I would not want to replace the wiring in one of these. I HAVE done a complete rewire on a '75 K10... 18 (EIGHTEEN!) circuits, only 10 were actually used if I remember correctly. These things have DOZENS of circuits.... no thank you.

 

[c good]

OK. Here it is....may be a bit long but, if it helps one other person its worth it.
PCM came in and it had no difference. After driving for a few days things started to get more SPOOKY. The Tach would start acting like it had a seizure, the turn indicators would stop working and the Cruise control would stop at the same time randomly but would run fine until it stalled as it had before. If it stalled out while the new "spasm" it would not restart. The passlock light and battery light would light up but no gauges. I would let it sit for 10 minutes and it would restart.
I picked up my wife on Monday morning and it did it again. This time with my wife watching the dash i started pressing down on the fuses and relays and she said the gauges moved slightly. I then lifted up on the wire coming from the battery to the under hood fuse box and everything lit up and it started. I tool he home and went to work. I thought it may be a loose connection but it was not. SOOOO. thinking a circuit board may have a bad solder on it i pulled the fuse box out and pulled it apart. (There are y0outube videos to help you.) What I found was a surprise to say the least. GM in it well known wisdom decided to not use a circuit board or reguler insulated wires but exposed 20 gauge copper wire just pushed into a type of splicing clip. Holy crap. SMDH. So, I took my phone camera and zoomed in and followed every "wire". I found a few areas of discolor and one with an almost non existant break. I then looked online and found this to be an extremely common problem with videos and pictures galore. I could have just went to Lowes and got some replacement wire but I felt there were too many "suspect spots" to fool with so....I dropped $50.00 at the boneyard and got one from a low mileage wrecked one, pluged it in and Praise Jesus the problems went away and no issues.
I suggest watching a few of the videos for education and I will include a pic of what the board looks like and one of the offending area. Pay close attention to the s-curved areas of the "wiring".
I hope this helps you guys and thanks for your help.

So this is the underside of the underhood fuse/relay box by the battery?

 

[TollKeeper]

A little late to the party, but just some info for the OP @TBlazerD

@Mooseman (or someone else) can correct me here, as my knowledge of the 4.2 is limited.. But if I am remembering correctly, the fuel filter on the 2005, and newer (I6 and V8), models, was moved into the fuel tank, and is part of the fuel pump in tank? And the fuel system was changed over to a returnless fuel system, so a regulator was no longer needed.

Finding that break, wow. I know I wouldnt have found it. But I also hate electronics, like with a passion. But since your dealer wasnt able to find anything either, you pretty much had to rely on yourself... So good job on ya. That took some patience I know some, including myself, dont have.

 

[Mooseman]

So this is the underside of the underhood fuse/relay box by the battery?

Yes

 

[gmcman]

Wow, very cool you found the issue. While just reading through this, my first thought was a bad brake booster causing a large vacuum leak. Would have been a head scratcher not knowing about the copper leads.....good find for sure.