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2002 gmc envoy_slt
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14 Posts
Discussion Starter #1
Hello everyone, and thanks in advance!
'02' Envoy SLT 4.2L I-6 90,000 (bought it from my sister 2 yrs ago it's been babied) And I Love it!
I've had some common problems. Battery went dead shortly after I got it. It set the "service 4WD" light Installed new Battery, tried all the tricks had to go to the dealer for a re-flash that's when I learned all about the crappy "02" TCCM (more to come). Last year Strange noise when running figured out the water pump was bad. wobbly shaft but never leaked a drop. Changed the water pump.
I've done a lot of reading and taking in all the advice from you guys you're all great! especially "Roadie".
I had a problem with (As Roadie put it) unwanted 4WD functionality. Scary! Transfer case changed functions by itself several times at low speeds and at 70 MPH I'm glad it wasn't 4LO at 70. Then it started idling rough out of the blue. I call it a hard mis (not consistent) worse when the A/C kicked on but never stalled (close a couple of times). I'm unsure of exact idle speed seems slow and only shows 100 RPM on the tach at warm idle. I know the tachs not right. Also seemed to mis at highway speeds while on cruise control I could notice it on flat smooth sections just cruising. Used OBD-II scanner No DTC codes. I/M reads everything else ready/OK! So I decided enough! I'm going to fix it all! Couldn't find a used TCCM (ebay or junk yard). So I bit the bullet. Dealer wanted $275 I told him I could get it at Gm parts direct delivered for about $200 but I would prefer to support local companies and he came down to $215 + tax. I also decided to replace the selector sw. another $30.
So here we go!
1.) The week before Seafoam through the Brake booster line (carefully) a bit of white smoke after sitting 10 min. (not bad) Checked for vacuum leaks seems Ok it set the check engine light but it cleared itself after a couple of run cycles. Added a can of Pro-Gard injector cleaner and filled her up.
2.) Next weekend Disconnected the Battery
3.) Removed and carefully cleaned the throttle body (with the help of CRC throttle body cleaner $6 at Napa) It was dirty now it shines. gasket was fine bolted back up at 89 in lbs.
4.) Carefully removed the coil packs (Luckily no broken bolts)
5.) Replaced the Spark plugs with AC/Delco 41-103 regapped them to .043" added some high temp anti-seize and torqued to 15 Ft-Lbs.. Why do they give a range like 13-16 Ft-Lbs anyway? There was about a teaspoon of oil around #1 plug but all others were clean and dry. Cleaned the engine the week before at the carwash and used compress air around the plugs before removing.
6.) Carefully replaced Coil Packs seated properly with a little high temp anti-seize on the plug cap (its conductive and anti corrosive) anti-seize on the hold down bolt torqued to 89 in-lbs.
7.) Replaced Air Filter and reattached everything else
8.) Replaced TCCM module and 4WD selector switch.
9.) Removed rear brake calipers (as one unit)(just unbolted bracket and swung up and hung by a metal clothes hanger) removed rear disk to adjust the parking brake that has never worked! (about 1 & 3/4 revolutions on the adjuster) reassembled and now parking brake starts grabbing on about 3 clicks and locks by 5. It's nice!
10.) Hooked up Battery!
Tah-Da! runs great drove it through about 6 drive cycles over the weekend at all different speeds and throttle positions everything seemed wonderful.
Had an appointment Monday morning at the dealer to have the new TCCM programmed (yes I Knew the new one had to be programmed "no choice"). I also told them to check for any rough idle / idle speed updates and asked if there was possibly a calibration update for the tach?
They did the programming and said there was an update for the ECM but nothing involving the idle or tach.
Again everything ran great for about a day then the rough idle showed back up (just the same as before). I had to drive it this Labor day weekend on about a 400 mile round trip. Got just over 20 miles to the gallon (loaded down and twice over the mountain pass). but the rough idle is still there. I really don't think it's a compression issue. So I'm thinking coil but it's not throwing any codes and it's not consistent enough to start swapping coils! Is there any way to read the coils on the vehicle? I've read about checking exhaust manifold temps but seems like it would be tough to do? I thought about buying 1 coil and swap 1 then drive a few days then swap to another until I located the bad one but that seems like a pain but so does buying 6 coils but if there going to continue to fail over the next few years maybe biting that bullet again would be best? I'm already in about $500 Any suggestions would be appreciated (any ideas about the tach? or is there an easy way to check RPM with my old style equipment?) Could it possibly be an injector issue? Sorry for the long story but I thought better to be through instead of a lot of back and forth! Thanks Again!
 

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2004 chevy trailblazer_lt_ext
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119 Posts
If the computer is not throwing a trouble code after running for a while, it could be a motor mount causing the vibration.
 

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2005 gmc envoy_sle_xuv
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419 Posts
even still without a hard code, i was still seeing misfires from coil pack 2 at idle. 2-4. I havent gotten to replace it yet, but I hope that will clear up my idle shakiness too.
 

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2002 gmc envoy_slt
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14 Posts
Discussion Starter #6
Without a code how did you determine it was the #2 coil pack?

I ordered a new coil from autoparts123.com yesterday (Wells #C1395)
Under $60.00 I did a bit of research and it appears they make quality parts (The Chev. dealer wanted $211.00 *CRAZY*)
When I receive it I guess I'll Just start by swapping one drive awhile swap to another location until I find it.
Unless someone can suggest a better plan? I'm looking for options!

Note: I found a 10% discount code on Google (24558) for first time users at autoparts123.com
 

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2002 gmc envoy_slt
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22 Posts
checking coils

I may be barking up the wrong tree here but can't you meter the coil with a multi-meter and check ohms? I'm sure the coils have spec's and if it's out of spec then that could be the problem. I know the resistance changes when the coil pack heats up so it also might not do you any good if there all in spec at cold temps?

I just got my 2002 4.2 envoy 2 weeks ago and facing simular issues with rough idle. I cleaned the "new tb" the previous owners had just got installed.... just wiped it down....and also cleaned the cpas. Filters were dirty. Didn't change my hard take off issue (at a stop if you gas it...the rpms drop like it want's to stall, then takes off with a jolt when the rpms suddenly climbs)
Also had my first stall coming to a stop in traffic on the hwy yesterday.

Needless to say it's intermittent and if I have the AC wide open....it never does it??
 
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