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Discussion Starter · #1 ·
I have a 2003 TB with 277700miles. I’ve had 3 different coils and spark plugs replaced in the last 17months and now the mechanic is telling me a 4th coil and plug replacement is needed….misfiring and hard starts are the problem. Is this due to hi mileage or possibly symptoms of another problem? Maybe burning oil and fouling plugs or coils?
 

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2004 chevy trailblazer_lt
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Welcome to the Forum!

The first thing you need to do is to find out what the OBDII diagnostic codes were or are. Without those, we would be shooting from the hip blindly.

However, speaking (or should I say writing) in generalities, if the coils replaced were the original factory installed coils, then they were over 15 years old, likely had somewhere between 200,000 - 250,000 miles on them, and have gone through umpteen zillion thermal cycles, so yes, it is plausible for three or four ignition coils to go bad.

Regarding the spark plugs, well, the factory recommended replacement schedule is 100,000 miles when using the factory recommended ACDelco 41-103 iridium spark plugs, so they could have been worn down. Additionally, old worn down spark plugs can contribute to the demise of ignition coils because the worn down spark plugs (actually the contact surfaces where the spark happens) need a higher voltage to fire (or spark) and that can put a strain on similarly aged ignition coils.

Without knowing anything about oil consumption between oil changes, oil that leaks out of seals or gaskets and onto road or driveway surfaces, and without having any information about individual cylinder compression readings, we cannot really speculate if the spark plugs are getting fouled by burning oil. Hence, for the moment let's just stick with the parts wearing out due to age/mileage as the explanation why the coils and/or spark plugs went bad.

From the way you described how your mechanic repaired your TrailBlazer over the last 17 months, I would have to say that he is not trying to sell you unnecessary work or parts. Now if he had approached you saying that you need to replace all the spark plugs or all the ignition coils at once, and recommended changing the blinker fluid and installing muffler bearings, then I would be suspicious, especially if it happened 4 times in 18 months or so.

Now comes the really tough question for you. Are you considering performing your own maintenance and repairs on your TrailBlazer, or are you going to continue to use a trust worthy professional? Doing one's own maintenance and repairs can be very satisfying and rewarding, but it can also lead to frustrations, the spontaneous vocal emission of multiple profane words or expressions, kicking the dog/cat, and the yelling at one's offspring or siblings - not to mention the spending of a significant amount of $$$ that will ultimately save you more $$$$$$ in the long run, which can then be used for the purchase of shiny baubles and other goodies for one's significant other.

I hope this helps.
 

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Discussion Starter · #3 ·
Thanks chem_man, and yes, your comments are a big help!

A couple more questions…. Since I’ve had 3, and now likely 4, of the coils changed should I go ahead and replace the rest of them and save on labor??? Also, it’s been recommended to change all the spark plugs each time. Does that seem excessive??? Should I have them all changed again with this new coil?

I’ll likely have this work done by a mechanic…..but I am open to doing a few things myself.

thanks again!
 

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There are 2 schools of thought on replacing ignition coils. One school says to replace them as they go bad. The other says if more than one goes bad in a relatively short period of time, then replace them all. If I were in your shoes, I would go ahead and ask that the remaining old ignition coils be replaced.

As far as the spark plugs go, I would go ahead and replace those spark plugs that have not been replaced. Just as an FYI, these engines are very finicky about what spark plugs go into them. They LOVE the ACDelco 41-103 iridium plugs. If your mechanic did not use the 41-103 plugs when he replaced the other plugs, either have him throw in a complete set of ACDelco 41-103s, or if he used the ACDelco 41-103s, then just have him replace the remaining plugs. I would not have them all changed again if he used the 41-103s and you have less than say 20,000 miles on the replaced plugs.

Good Luck!

Also, when you are ready to take the plunge into doing your own work, feel free to start a new thread and ask for recommendations, guidance, etc. on what brands of parts to use, what brands to avoid, special tools that will be needed besides a decent OBDII code reader scanner, and a decent digital multi-meter (DMM) if you do not already have one.

For OBDII stuff, a number of us use with android devices use a specific Bluetooth OBDII Dongle and the Torque Pro android app. You'll spend between $20 - $25 on the combination. Here is the link to the Bluetooth Dongle:


That dongle and Torque Pro is a powerful combination!

Good Luck!
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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I'd like to see a picture of the plugs and wonder if you have an oil leak from the valve cover gasket. Request to see the old parts from your mechanic.
 

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I have a 2004 tb... been the worst nightmare just fyi. I have had to replace my coil boots to many times to count and it's 308000 miles. Sparkplug not so much. But I glanced at someone saying check your plugs and boots. It's very possible it is a gasket leak. Mine has one. But the longer you drive on a misfire it will clog your cat and that's more of a headache you will have to deal with. If you order plugs and boots on Amazon it's extremely easy to replace them yourself. With the exception of the 6th boot that's basically up against your firewall. I would say order all new boots and plugs and you should be good to go. But if a misfire pops up after replacing all 6 then you may need to go from there.
There is a wide range of things that these trailblazers are notorious for breaking down from. But just a great start is to remember they run from air/gas/electric. When one is unbalanced it will cause more strain on your engine. I have probably experienced just about every way possible. O2 sensors could be a factor as well.
 

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2005 buick rainier
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Our shop will generally replace only the one failed coil. If the vehicle has high mileage or the plugs were excessively worn we may opt to "current ramp" the ignition coils. Current ramping (using an oscilloscope) measures the coils current draw & amperage waveform. I will add we almost always try and use OE parts.
 

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2006 Chevrolet Trailblazer LS
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If you suspect your leaking gasket and/or oil burning is due to excess crankcase pressure, be certain to clean your CV system - notice, I did not say PCV valve as there is none on a 4.2L.

You may have to pull the valve cover and clean the orifice on the inside.
Also, here is an excellent video from Rivalli Surfer on how to clean the bottom portion of the crankcase ventilation system.
 
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