NEED HELP Chasing Gremlins?

Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
Hello all -

long time lurker, first time poster.

I live in North Texas, where heat destroys all things. despite that, I've been able to keep my 2002 Trailblazer LS running (and with ice cold A/C[ironically not one of my issues]) for a good 5 years since I bought it. when I first bought the truck, I drove it home from Oklahoma without an issue. the next few days of driving I started having weird electrical...ignition would cut out randomly while driving, completely shut off, etc. Shortly came to just shut off one day in a parking lot and towed to the magic mechanic. he immediately says ignition switch - I come back with the part and he's got it running and scratching his head. few days of poking around says some under dash wiring was the culprit, bam, ok. good to go.

so minus that Chuck (the truck) has been pretty dependable except for a starter here, hoses there etc. however...just like I've read dozens of times over the net I've been chasing one problem after another ever since. I'm at a point where I'm exhausted of pulling the thread so looking for any useful input. I'm sure I won't catch them all in one go around but I'll give it a shot:

All the lights flicker, all the time. It's less noticable in the headlights and running lights (EG license plate & rear markers) but it's there. Interior dome, dash, manual AC control indicator lights, all of them. frequency does not seem to be affected by engine speed.
- I have checked and cleaned any ground location listed in the service manual. I reinforced the shock tower-engine block-front driver side fender ground with double run 8guage electrical cable. wire brushed and reseated bolts.

fan clutch was replaced by previous owner. seems to engage and disengage more "normally" than not according to the wait 2 mins for device to fully engage or disengage held at 2100 RPM and blah blah blah and it will be engaged if it was turned off while engaged and turn into an Airbus 320 and take off into the night sky. ahem.
-my issue with the fan clutch seems to be more related to the heart of the electrical which I'll get to - however - I don't feel like it should be matching engine speed 100%. at times under acceleration it acts as if it's stuck in the engaged position, matching engine RPM speed up to 4-5k before finally disengaging. I believe it also might be the cause of an incredibly rough idle at times when the AC compressor is engaged while parked.

Chuck also eats alternators. I got the lifetime warranty alternator from O'reilleys auto parts and about every 2 years I replace it. this last time the coils had gone almost black inside. previous one failed to regulate voltage, swinging pretty much randomly between 13-14.8 all the time. it doesn't seem to reliably charge or output voltage over 13.5-13.6 with a brand new alternator and brand new Duralast battery. I have an external voltage monitor wired in, in conjunction with OBD monitoring and just watching the in dash voltage gauge. when turning the headlights on there are times when it will swing up in the 14's for a bit and then dip down to 13.5. I know what you're going to say - yes this can be a normal operating condition, but the standing battery voltage with ignition off at this time is 12.3v. with a brand new battery and alternator less than 2 months old it should be charging strong.

in addition to rough idling, I get near-stalls, dimming headlights, reduced performance at times...and it all seems to be intermittent and unable to reproduce. sometimes I'll get in the truck and it runs like a top. other times I have crazy short term fuel trims and timing advance at idle (can post video and log ScanXL Pro dashboard/logs later), dash lights dim to the point of almost cutting out, poor AC blower performance.

Ive replaced the MAP sensor, checked continuity of fan relay circuit, cleaned the throttle body, checked EVAP purge valve, traced vacuum lines connectors, fuses, pulled up carpet, pulled off panels, jacked it up, taken off tires over the years and I'm pretty much lost since I've had little to no luck. I do have an aftermarket amp and single 12" sub in the back which I've fully disconnected, completely removed from the vehicle, rewired, regrounded, replaced the whole system and it made zero diffference.

being partial disabled makes it hard to get out in the friggin heat to wrench on this thing during the summer but if I dont want a car payment I feel like I gotta solve this issue sooner than later. any takers?
 

Mooseman

Moderator
Dec 4, 2011
25,260
Ottawa, ON
The flickering and dimming lights might be related to your alternator problems. With the crappy ones you're getting from O'Reilly's, it wouldn't surprise me. Might be time to get a good one instead. Also check all your grounds. Download the manuals (link in my signature) for the locations of those grounds.

It's somewhat normal for the fan clutch to be engaged for a while until the silicone redistributes itself inside the clutch. Mine does the same thing, albeit it's a thermal clutch on the Saab. On my TB, it's still the original EV clutch and it doesn't do it. May depend on the brand or quality for how long it takes to loosen up. If it takes a really long time, it may be failing and eventually may lock up for good.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
To me, it sounds like something is not right with the wiring going in and out of the alternator. Even with the crappier alternators from the parts chain stores, he should have had a good enough one to at least get rid of the flickering, even if just for a short time. I personally would start with a good ground strap running from the alternator to the frame. From there, I will also admit I suck when it comes to diagnosing electronic components, and usually hand it off to the dealer.

You mentioned above that you went to the store and came back with the ignition switch, and the mechanic had the engine running and scratching his head. You didnt indicate on whether or not the ignition switch actually got replaced. If not, start there. If you did, did you replace it with a quality brand? or some Dorman part?
 

Mektek

Member
May 2, 2017
656
FL
On the car I had flickering light at idle which disappeared at higher rpms. I found it to be a burned out rectifier in the alternator. Just one was black and the others were beige. Replaced the alternator with a rebuilt one from the PYP and flickering was gone.
An alternator should last much more than 2 years. Something might be causing to to be overloaded - maybe an intermittent short somewhere?
 

Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
thank you all for the replies. Moose, I have checked all underhood grounds, unbolted, wire brushed the location and reattached. I have reinforced ground strap location G108 from engine block to shock tower to left rear panel along the negative ground battery harness connectors with a doubled up 8 gauge electrical wire that I crimped, soldered and bolted along with the original cabling.

generator signal connector is pretty solid although I'd like to do the same as I did with the ground and reinforce along generator battery positive connection through harness to positive battery post.

mouse - yeah for sure but like Toll said you'd think that somewhere along the line of alternators Ive burned through that I'd get a good diode/regulator combo and at least change if not temporarily resolve the flickering and voltage drop or limited field duty setting is getting kicked.

Mektek - I've been searching for a short but having a real tough time getting the issue to reproduce manually so I'm just going on process of elimination at this point. this morning I checked the MAP sensor voltage and the fan clutch PCM duty/voltage constants from the front connector. after obsessively pouring through OBD log data I did see some vacuum system discrepancy alongside the fuel trim and timing advance weirdness:
happ.JPGis.JPG

so heres the next bit that gets a little wonky. so keep in mind that the pressure readings are in PSI and not mmhg

psi.JPG

all readings taken at idle. orange is vacuum reading/value indicated on secondary axis(scale on the right). so at idle my absolute manifold pressure reads ~4.5-5psi / 9-10inhg and vacuum reads -9 to -10psi / -18 to -20inhg.

wonk: in another thread I was coming I saw this connector on the left side of the intake manifold open. apparently it's for the XL temp regulator something-something. they go on to say that there might or might not be a cap on it and if there isn't it should be internally closed.

what.JPG

well, mine isn't. there is considerable vacuum pulling through this port. I covered it temporarily and started the vehicle and it ran like complete cabbage. if yo notice the biggest drop in timing advance on the above chart that is the point where I engaged the AC compressor and the engine stalled and recovered before I removed the cap from the connector and the idle RPM returned.

I took a spray bottle as well to check for leaking intake manifold gasket but I couldn't really tell if it there was any noticable drop in performance.
 

Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
thank you all for the replies. Moose, I have checked all underhood grounds, unbolted, wire brushed the location and reattached. I have reinforced ground strap location G108 from engine block to shock tower to left rear panel along the negative ground battery harness connectors with a doubled up 8 gauge electrical wire that I crimped, soldered and bolted along with the original cabling.

generator signal connector is pretty solid although I'd like to do the same as I did with the ground and reinforce along generator battery positive connection through harness to positive battery post.

mouse - yeah for sure but like Toll said you'd think that somewhere along the line of alternators Ive burned through that I'd get a good diode/regulator combo and at least change if not temporarily resolve the flickering and voltage drop or limited field duty setting is getting kicked.

Mektek - I've been searching for a short but having a real tough time getting the issue to reproduce manually so I'm just going on process of elimination at this point. this morning I checked the MAP sensor voltage and the fan clutch PCM duty/voltage constants from the front connector. after obsessively pouring through OBD log data I did see some vacuum system discrepancy alongside the fuel trim and timing advance weirdness:
View attachment 90587View attachment 90588

so heres the next bit that gets a little wonky. so keep in mind that the pressure readings are in PSI and not mmhg

View attachment 90589

all readings taken at idle. orange is vacuum reading/value indicated on secondary axis(scale on the right). so at idle my absolute manifold pressure reads ~4.5-5psi / 9-10inhg and vacuum reads -9 to -10psi / -18 to -20inhg.

wonk: in another thread I was coming I saw this connector on the left side of the intake manifold open. apparently it's for the XL temp regulator something-something. they go on to say that there might or might not be a cap on it and if there isn't it should be internally closed.

View attachment 90590

well, mine isn't. there is considerable vacuum pulling through this port. I covered it temporarily and started the vehicle and it ran like complete cabbage. if yo notice the biggest drop in timing advance on the above chart that is the point where I engaged the AC compressor and the engine stalled and recovered before I removed the cap from the connector and the idle RPM returned.

I took a spray bottle as well to check for leaking intake manifold gasket but I couldn't really tell if it there was any noticable drop in performance.

I want to also state I've never had a code for any of these issues. my coolant level upon checking it, however, is extremely low in the reservoir after running it up to temp and letting the thermostat open. there are no freeze frame, pending or stored DTCs in the PCM.
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,641
Tampa Bay Area
If you check out these Images ...there is information here on How to Diagnose the Electro-Viscous Fan Clutch Circuitry. Please note that the Fan Clutch is on the same circuit as the PCM and shorting problems with the Class 2 Network 0-5 VDC Reference Voltage and interrupted Pulse Width Modulation Commands to and from the PCM will affect them BOTH:

EVFANCLUTCHWIRINGDIAGRAM1.jpgEVFANCLUTCHWIRINGDIAGRAM.jpgFANCLUTCHGMDIAGNOSTICSCHART.jpegTRAILBLAZERPDC.jpg

If you ultimately have to PULL THE FUSE BLOCK to Remove, Clean (Spray Out the Connectors with CRC Electric Circuit Solvent) and do likewise with the PCM and then Re-Attach all of the Three Colored Connectors attached to the PCM after examining them for Broken Wires or Contact Points... these additional Pin-Out Diagrams will assist you with 'Pinning' Down any Broken Wires or Connections for specific component locations on the system:

PCMC1.jpegPCMC2A.jpegPCMC2B.jpegPCMC3ACCPEDL.jpeg



CRCQDCCIRCUITSOLVENT.jpg


"Scope On A Rope" Lighted Circuit Probe:


ASTROLCD03-48VDCCIRCUITPROBE.jpg
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
You didnt mention whether or not that technician actually replaced the ignition switch?
 
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Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
MRRSM - thanks for the info and the leads. I think it may come down to doing just that. I appreciate the direction and literature.

Toll - sorry, yes he did install the ignition switch. I can't remember the brand except that it was a 3 letter acronym and a slogan about Nascar level performance on the box. it's been a few years
 
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Eric04

Member
Dec 3, 2014
392
West Michigan
Most of what you describe points to poor charging. Flickering lights, low fan speed, assorted gremlins, even poor idle *can* result from insufficient juice. Many late model vehicles will simply shut down if inadequate voltage is detected, and not always leave a clue as to why. I'm with Toll as to a starting point, examine all the wiring to and from the alternator. Sometimes a weak spot can be hidden by the casing so do a little wiggling and see if there's anything shady along the way. You're not wrong, 12.3 resting voltage with new components is really messed up. Either the charging current pathways are being interrupted or there's a component putting one hell of a draw on the system forcing it to sacrifice elsewhere. Since you're not popping fuses at all I lean toward the former. Failing that, MRRSM's plan of attack, however daunting, looks best to me. I'll also admit to having no love(patience) for lengthy electrical diagnostics.
 

Mooseman

Moderator
Dec 4, 2011
25,260
Ottawa, ON
So the switch was replaced 'years' ago. If it's anything but an ACDelco,it may have already failed again. From.your description, I doubt it is an ACDelco. If after checking everything else you're still having issue, you should consider replacing it again with an ACDelco. Aftermarket ones don't seem to last in our experience.
 

Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
approximately 5 years ago? Ive no objection at part cost of $23. I'll keep hitting on all avenues until I hit pay dirt for sure.

Im pretty sure my current switch also has a lifetime warranty =D
 
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2001ZR2

Member
Jul 16, 2019
93
Kansas
Can I ask a question? Who did the wiring for sub woofer and amp initially? You seem savvy on the electrical area but if someone clipped a wire or connected where they shouldn't it can cause chaos.

I haven't learned as I have two blazers with that type of wiring and have had the wires arc.
 

gmcman

Member
Dec 12, 2011
4,656
Have you replaced the positive cable from the alternator to the battery? Those little metal fingers on the side terminal can get worn. The bolt will be tight but may not make good contact with the lead post.
 
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gmcman

Member
Dec 12, 2011
4,656
After some thought....I feel more strongly about this option.

I had something similar happen a few years back, lights would dim and my voltmeter would dip as well.

Turned out to be the signal wire going to the alternator, basically telling the alternator to "go online"

You can try to test this theory by loading up your alternator by turning on your rear defroster, seat heat if you have it, and the high beams.

Wiggle this wire that has a repair and listen for the engine to change pitch, ie, load up.

Screenshot_20190822-045337_Gallery.jpg

Mine was loose at the internal connection of that plastic harness.
 
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Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
Can I ask a question? Who did the wiring for sub woofer and amp initially? You seem savvy on the electrical area but if someone clipped a wire or connected where they shouldn't it can cause chaos.

I haven't learned as I have two blazers with that type of wiring and have had the wires arc.

good question, I did the install from the ground up for the audio since my stock head unit died and I'm always leery about using speaker to line out converters into power amps. I did the install twice since I'm somewhat neurotic and wanted to make sure it was done right.

I did find something of interest though in the radio wiring diagram pinout for the base audio without rear audio which is what I have. on both the general radio diagram and the specific radio without rear seat entertainment which applies to me, it has both the left and right rear speaker leads coming from the back of the stock head unit into either the HVAC auxilliary control unit or the BCM as low level inputs, and then fed back out of each module as LR/RR outputs.
lowlevel.JPG

I have no idea if they just did this for standardization and if it only serves as a PCM pass-through if there is no factory amplifier installed - but I decided to just bypass the factory harness altogether and ran my own speaker, switched/constant 12v and grounds for the aftermarket head unit. just seems weird to me to pump speaker-level amplified outputs into an on board computer module. I didn't see any negative or positve effects from running either config by the way it's just something I did to avoid causing more potential issues
 

Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
After some thought....I feel more strongly about this option.

I had something similar happen a few years back, lights would dim and my voltmeter would dip as well.

Turned out to be the signal wire going to the alternator, basically telling the alternator to "go online"

You can try to test this theory by loading up your alternator by turning on your rear defroster, seat heat if you have it, and the high beams.

Wiggle this wire that has a repair and listen for the engine to change pitch, ie, load up.

View attachment 90605

Mine was loose at the internal connection of that plastic harness.

good call, I'm sure it couldn't hurt for me to just replace the connector altogether anyway. I'll check it out and report any improvement. in answer to your previous question though yes I do have new cable between the alternator positive post and the battery positive

poking around with a flashlight I can already see the coil winding on my new alternator getting that weird black patina on it
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,641
Tampa Bay Area
Just so it is clear... The Class 2 Network Splice Pack (SP-201) AND Other Common Grounds for whole Rat's Nest of other Modules (using G-201) are situated on the Passenger Side Transmission Hump, just under the Center Console Cowling sharing One Single 10mm Bolt into the Chassis Metal. There are "BOO-KOO" Things getting serviced by that One Single Ground Point.

The Minimum-Maximum Voltage fore the Single Wire Network in the GMT-360s is (0-7) Volts DC. As long as nothing has been connected to any of those wires that involves any (12) Volts DC risking a Shorting of the Network to (+) Positive Voltage ... the Modules interacting with the PCM should not be affected by your After-Market arrangements. However... if that Ground Bolt has gotten loose... Very Weird "Electrical Gremlins" can raise their Ugly Little Heads as..described by @MAY03LT in this attached Video:


If nothing else... examining that locale will allow you to know from the Schematics in the Video about all of the things that enjoy using that One Ground... and you can Check it Off of your Diagnostics List. :>)
 
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Mektek

Member
May 2, 2017
656
FL
I'll guess your ignition switch was a BWD. I have one of those that's OK after 2 years.....
Since you noticed a problem with a vacuum fitting, I'll suggest going over all of the vacuum fittings. I had both the one you noticed and the crankcase ventilation fittings start to crack.
 

Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
Just so it is clear... The Class 2 Network Splice Pack (SP-201) AND Other Common Grounds for whole Rat's Nest of other Modules (using G-201) are situated on the Passenger Side Transmission Hump, just under the Center Console Cowling sharing One Single 10mm Bolt into the Chassis Metal. There are "BOO-KOO" Things getting serviced by that One Single Ground Point.

The Minimum-Maximum Voltage fore the Single Wire Network in the GMT-360s is (0-7) Volts DC. As long as nothing has been connected to any of those wires that involves any (12) Volts DC risking a Shorting of the Network to (+) Positive Voltage ... the Modules interacting with the PCM should not be affected by your After-Market arrangements. However... if that Ground Bolt has gotten loose... Very Weird "Electrical Gremlins" can raise their Ugly Little Heads as..described by @MAY03LT in this attached Video:


If nothing else... examining that locale will allow you to know from the Schematics in the Video about all of the things that enjoy using that One Ground... and you can Check it Off of your Diagnostics List. :>)

the bolt seems secure, nothing seems to be interfering with it...however...the tab securing the SP seems to be pretty flimsy maybe? it was hard to tell with sweat river pouring down my oculars but I plan to re check and make any adjustments needed this evening
 

Dosselhaf

Original poster
Member
Jul 31, 2019
10
Plano, TX
I just wanted to update this for all who took the time to respond and try to lend their help. so after replacing most of the under hood ground cables, redoing the reinforcement from alternator post to battery post, idler pulley, belt tensioner and belt, resecuring 2 splice packs and who knows what else...

turns out it was a very slowly failing coil pack. it finally failed a few days ago and misfired like crazy on cylinder 1. turns out there was a short in the pack itself but it was still functioning? but that totally explains all the loss in power and weird electrical stuff as well. so I did a full tune up with new plugs, replaced the pack and tested the rest and now I have full electrical function again and power is back to normal.
 

Mektek

Member
May 2, 2017
656
FL
I used to think that a coil pack is electronically controlled solid state and should either work or not.
The symptoms were certainly not typical of a coil failure.
Good thing you discovered it
 

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