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2003 gmc envoy_slt
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Discussion Starter · #1 ·
Hi all,

First, great site and great people, hope you can help.

I DONT want to give up!

Ok, I have been a lurker for the past two weeks and decided to attempt a tune on my wifes 03 Envoy. Its running better just not perfect :) In the beginning it had a "chug, chug" at a stop light or with the brake applied easing into the garage. I saw the "engine light on" (my wifes light is on and blinking) commercial from Auto zone and went and got it tested.

The first diagnostic showed a misfire on cylinder 3. So I decided to replace all the plugs and boots. Gapped plugs approximately .40 to .43, and I sprayed a whole can of cleaner into the TB while the engine was running plus some injector cleaner in the gas tank. The darn thing ran worse, so I took it back for one last diagnostic and it said #3 was still misfiring. I bought a new ignition pack for #3 and it ran a bit better but not perfect :{ Back to AutoZone and another diagnostic and it said #1 was misfiring, so I spent more money I don't have and replaced the #1 ignition pack. It ran somewhat better but not what I'm looking for so back to Autozone and the computer diagnotic read multiple misfires....grrr. The guy at AutoZone said it was a mistake to gap. WTH NOW??? :) Should I give up and go to a mechanic?

The engine runs great above 2500rpm but between shifts its got a rumble. At a stop light the whole vehicle shakes (not fast just a CHUG CHUG one second apart from each shake) then you accelerate it boggs a bit but then takes off after 2500 rpm?

Would replacing only two coil packs freak out the old timing and old packs?

Should I replace all the packs?

Or is it time to pay a mechanic?

Would moving the old coil packs to different cylinders make a difference?

Should I try a different plugs?

As many have said we put 87 octane in it since we got it in 2003, the price for 93 ouch!

Parts I used OEM Delco plugs, and the packs were from Duralast.

I'm old and use to spark plug wires and carburetors. :drool

I've rebuilt 2stroke and 4 stroke motorcycles but I may be over my head with this computer engine ACK.

Thanks!
 

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2004 gmc
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Are you certain that all the codes you have are for misfires at this point? The Owner's Manual is pretty clear to point out that the Check Engine Light is OK to drive on with, UNLESS it's flashing. That means stop soon and fix it, not continue driving. Misfires can dump unburned fuel into the exhaust, where it will burn in the cat. Could do lasting damage to the cat. Good news is that a clogged cat would give you worse symptoms at high RPM, not idle.

Your idle problems could be a dirty throttle body. Spraying cleaner isn't enough. You have to take it apart and clean it by hand. Remove the battery negative cable while you do this. After you put it back together, the computer will have to relearn the throttle body response, but within an hour of driving around it should get better.

http://forums.trailvoy.com/articles.php?do=viewarticle&artid=91

How many miles? Above 30K and it's defninitely due for a manual TB cleaning. Other problems may still be present, but start with that, and then look for more codes besides misfires if the engine light doesn't go off. Did you ever get the Reduced Engine Power light on?
 

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2003 gmc envoy_slt
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Discussion Starter · #3 · (Edited)
The vehicle has 85000 miles and by reduced EL, do you mean did it reduce the brightness. Yes the light did dim slightly.

The ELO seems to stick and then blink after I work on it. Since its cold this morning maybe I will clean the TB. What cleaners do you recomend?

Thank you Roadie.

I'm reading the linked post right now.

Deep Creep Seafoam, would be the cleaner?
 

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Not that it would make a big difference but I thought the spark plug gap should be .50
 

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Discussion Starter · #5 ·
Not that it would make a big difference but I thought the spark plug gap should be .50
Dang I hope not, I read in all these post that .40 to .43 was the ticket.

Off to buy some seafoam. Any other suggestions? I'll check back after I go and get the seafoam. After I clean the TB and drive around for an hour or two, I'll post results.

Thanks again. :)
 

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Thats the spec I got out of my haynes manual on alot of the gm plugs I heard you should not adjust the gap you will scrap the coating off
 

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2005 chevy trailblazer_ls_ext
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Dang I hope not, I read in all these post that .40 to .43 was the ticket.

Off to buy some seafoam. Any other suggestions? I'll check back after I go and get the seafoam. After I clean the TB and drive around for an hour or two, I'll post results.

Thanks again. :)
Which plugs did you use? A/C Delco?
I ruined a 6.00 plug when I tried to gap the Autolite plugs I put into mine. Very easy to do.
 

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2002 gmc envoy_slt
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The AC-Delco, like most Iridium plugs, come PRE-GAPPED and should generally not be adjusted. The correct gap for our engines was originally .43 (1.07mm), however I recall reading that one of the replacement plugs used a larger gap and that plug supercedes the original plug. (Not sure if they've changed it again, but this could explain why they did not appear to have the correct gap). - If you use the replacement plug number, you need to keep it at the supplied gap.

If you're now getting multiple mis-fires, I would suggest pulling the plugs and taking a good look at them. One or more may have broken electrodes due to having been re-gapped. Other possibilities could be that the coils are not fully engaged onto the plug lead, causing the mis-fires. (They're sometimes difficult to align and press on completely. If you need to replace them again, be sure to use AC Delco plugs, the I6 doesn't like many other brands at all.
 

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2002 chevy trailblazer_ltz
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.....If you need to replace them again, be sure to use AC Delco plugs, the I6 doesn't like many other brands at all.
I replaced my original plugs at 100K with NGK's, and now have 57K of smooth, trouble-free miles on them. :m2:
 

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I've installed the NGK Iridium IX, do not gap them use as is.
Make sure the coils packs are seated properly. Your problem may have been only the # 3 coil pack, when you regap the plugs they may have been damaged. # 1 is a little tricky to seat properly because of that wire harness track. Make sure that one is not angled on the plug.

Make sure you to disconnect the Neg cable when cleaning the Throttle body, careful very sharp behind the butterfly.
 

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Discussion Starter · #11 ·
Still cleaning the TB with Sea Foam. Should I worry about the big black housing behind the TB? I mean should I physically rub inside or just use spray? The link roadie provided was extremely helpful, thank you for that, but it really says to take a toilet brush to the back black housing? :eek: Is that humor lol?
 

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Still cleaning the TB with Sea Foam. Should I worry about the big black housing behind the TB? I mean should I physically rub inside or just use spray? The link roadie provided was extremely helpful, thank you for that, but it really says to take a toilet brush to the back black housing? :eek: Is that humor lol?
Dirty Humor, Ha! I soak a rag and wipe it out.
 

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Discussion Starter · #14 ·
thanks Barron and Menthol...still in process...LOL.

Thanks
again, turning out to be a nice sunday in teh garage and the net, who knew?

:)
 

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Discussion Starter · #15 ·
Well it runs about 75% better and my mileage is up some. Still very early to tell but all in all it was worth the effort. I still have the "chug chug" shake to the engine at the stop light and entering our garage but other than that its way faster and responsive.

Any suggestions on the low rpm "chug chug," when I put the Envoy in neutral it allows the engine to idle easier and no "chug chug" shake.

In the old days I'd just up the idle a bit and sometimes that would help at stop lights, oh the old days.

Again thanks for all the help today.:tiphat
 

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What spark plugs did you buy? It is not that the engine calls for a certain gap, rather it is that for a certain spark plug to work in said engine, it is gapped for it to work. Don't change it. I would suggest going and buying new AC Delco iridiums, don't even look at the gap, and put them in. That is where your problem lies.
 

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There's been a couple pcm calibration updates to address idle stability. Do you know if your pcm has the latest updates?
Enter your VIN at this site: http://tis2web.service.gm.com/tis2web
you can browse thru and see the various updates however it will not tell you if your pcm has them. You'll need a scan tool/software that can read the cal id number of your pcm... I'm not versed on all the features of the various scanners but do know the dealer can tell you if the pcm has been updated.
 

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Discussion Starter · #19 ·
There's been a couple pcm calibration updates to address idle stability. Do you know if your pcm has the latest updates?
Enter your VIN at this site: http://tis2web.service.gm.com/tis2web
you can browse thru and see the various updates however it will not tell you if your pcm has them. You'll need a scan tool/software that can read the cal id number of your pcm... I'm not versed on all the features of the various scanners but do know the dealer can tell you if the pcm has been updated.
Thank you Absolute Zero.

And Double D I will try that next weekend. If things don't work out it looks like mechanic time. Sure wish I had one of those nice diagnostic machines. :)

I've seen you guys and gals speaking of a certain firmware upgrade, whats the best bang for the buck. I'm a cheap date!

What about superchips? I've seen a few cheepies on Ebay?
 

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Discussion Starter · #20 · (Edited)
What spark plugs did you buy? It is not that the engine calls for a certain gap, rather it is that for a certain spark plug to work in said engine, it is gapped for it to work. Don't change it. I would suggest going and buying new AC Delco iridiums, don't even look at the gap, and put them in. That is where your problem lies.
Did it, and it seemed to improve the "chug chug" about 25% but its still there (my wife says its still there :( ), am I being to much of a perfectionist? Engine light is on (blinks then stays on), gas milege is improving, and responsiveness has improved 50%. Can an "average joe" get an 85,000 mile engine to purr like a cat w/o computers?

It seems like it either needs some air or gas but how do I adjust that..LOL?

Wish it was as simple as adjusting the main jets and a few needles :crazy:

Is there a DIY intake mod? The exhaust has pressure, but with erratic puffs?

One more question, I noticed the cruise control doesn't work, could that cause the engine light to come on?

Lots of ?s

Thanks
 
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