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2003 chevy trailblazer_ls
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Discussion Starter · #1 ·
Hey guys, I've been lurking around here for awhile, so thought I'd say Hi and pick your brains, since mine is about fried now.

I have an 03 trail I6,120,000miles , has had a slight hesitation, soooo I

Changed the oil..(it was just time)
new air filter
new plugs...delco..checked gap
new thermostat....had a code
new fuel filter....figured that was the problem
Cleaned the throttlebody....off engine, battery disconnected for 1 hour

Now its worse :weird:
I've looked and looked at threads on here, but now i'm just confused. It idles about 600? sometimes 1200? will not rev past 1900 in park,(it will when driving this may be normal?) hesitates at takeoff, misses at around 1500-2000 (also misses slightly at idle) no gas smell, no codes...I'm thinking fuel pressure regulator, or a coil pack,(shouldn't that throw a code?) but why would the miss get worse..I need help, what should i check and how?

Thanks
 

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take off air intake... unbolt all the coil pack bolts (or do it one at a time, your choice) start the engine..let it idle for a bit and then one by one pull up the coil packs..

once and if you find one that does NOT change the idle then that coil is faulty
 

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2003 chevy trailblazer_ls
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Discussion Starter · #6 ·
Thanks again Majestic:thumbsup: I did that with no real noticable difference, but #6? (against firewall) was hard to pull while runnning..So I tightened all back up and removed the plug-ins and #6 made no change at all...I could actually hear it popping when I pulled the entire coil loose, but also while tightening the bolt back while hlding it down in place, I could still hear it, I thought that was odd.....So off to the parts store...Hopefull:thx
 

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2009 chevy
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A bad coil should throw a code.

The reason the problem is worse, is because the PCM reverted to the factory settings while the battery was disconnected.

Sounds like you did the normal things, fuel, spark and air and the problem is still there.

You need to look at the next level, exhaust, injectors or compression.

I'd try cleaning the injectors and then changing the front CO2 sensor (I change the CO2 sensor every time I change plugs).
 

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2003 chevy trailblazer_ls
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Discussion Starter · #8 ·
on the way to the parts store it threw a code, bad spark and all that stuff on #6, replaced the coil in the parking lot and it was fixed....for about an hour. Its runs alot better, no hesitation, can tell a big improvement in power, now it just has a miss at driving speed, but its sparatic..but overall, a really big difference..defenitely needed the pack replaced. Now i wonder if another is slowly going bad

I'm going to clean the injectors when I find some cleaner. I use the method where the fuel pump is disconnected and the engine runs off the cleaner alone....Can't think off what its called at the moment
 

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2005 chevy trailblazer_ls
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251 Posts
For cleaner use Chevron Injector Cleaner with Techron. It's GM approved and works wonders. Any miss in the engine should eventually throw a code. The computer just needs to catch up to it. A slightly dirty injector or a degraded coil may just not be bad enough yet to zero in on a cylinder.

The Chevron cleaner is really amazing stuff if you have a blockage there it should be enough to clean it without the pressurized cleaning. I ran my last truck 200K and that was the only cleaner I used for maintenance or when things felt just a bit sluggish.

Some of the higher end scan tools can actually count cylinder missfires as well
 

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Discussion Starter · #11 ·
I did look at that, but actually prefer lucas, so I just dumped in bottle. As far as the pressurized, I don't think there is anything on the market that can do a better job :m2: Generally the cleaner is only about $7 and takes about 20 min to complete but I used my last can on another truck, so the TB hasn't had it yet. The other stuff is ok, I just think that any cleaner that is diluted by 20-30 gallons of gas can't do a whole lot. I'm sure it helps some overtime, but I like the fast shot..instant improvement :D
 

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Discussion Starter · #13 ·
I'll do it, as soon as i run this tank out in a couple days, It did look like a pretty good product and you seem to be really impressed with it, so I will try it :thumbsup:
 

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Im a few miles short of 145,000.
and I also just passed the 10,500 miles since my last oil change (on reg dino oil). Im expecting my change oil light to come on very soon.
so I poured in a bottle of techron fuel system cleaner 4 days ago- I try to do this right before my oil changes...
 

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2002 gmc envoy_slt
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Im a few miles short of 145,000.
and I also just passed the 10,500 miles since my last oil change (on reg dino oil).
:eek:

Have you added any topoff oil in between?

Man, I sent my oil in for an used oil analysis, and at 5,000 the oil was just about shot (less than 2TBN left), I'd never go 10,500 on dino after reading that report, and that was Motorcraft's semi-syn 5w-30 (have since changed to Valvoline full syn and have OCI's of 7,000 miles).
 

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Discussion Starter · #17 ·
Ive always used Vavoline in everything myself, been using the full synthetic for a while now...well exept my bike, and I use Amsoil....Its a Roadie, but not the Mod :D
 

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Discussion Starter · #18 ·
Well crap....I've now run the Chevron Injector Cleaner with Techron, and my issues are back again....Not because of the cleaner....All issues went away and are now back, maybe a little different, its worse with the ac on, tb is clean, could it be the tb sensor.....I haven't went in depth yet, I've been baling hay all day and don't really feel like it right now...maybe later, any thoughts on what to check :bonk:
 

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on the way to the parts store it threw a code, bad spark and all that stuff on #6, replaced the coil in the parking lot and it was fixed....for about an hour. Its runs alot better, no hesitation, can tell a big improvement in power, now it just has a miss at driving speed, but its sparatic..but overall, a really big difference..defenitely needed the pack replaced. Now i wonder if another is slowly going bad

I'm going to clean the injectors when I find some cleaner. I use the method where the fuel pump is disconnected and the engine runs off the cleaner alone....Can't think off what its called at the moment
That is the correct way to clean the injectors, start, turn off, let soak and restart until the cleaner is used up. Disconnect the cleaner and put the relay back and restart. Should take of the injectors. If the PCM is relearning then it might take 50-100 miles to re-cal.
 
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