TrailBlazer 4.2 I-6 Spark Plug R&R
Ol'Jim
02-18-2013, 11:13 AM
Hello friends. Girlfriend TB with the inline 6 cyl 4.2 eng has hit 100K, and has developed a hesitation when cold started and begin to drive away. (North Texas, so not "cold" weather, lows around 30-40). I am going to replace the plugs in it, since they are due anyway, but have a couple Q's for those knowledgable about these vehicles/engines, or newer tech EFI driveability issues. Prob is not bad, and after warm, no issue at all. Could it actually be 02 sensor, or even worn TPS? The feel is like on a cold carbureted engine that has a bad accelerator pump, and/or no choke.
No trouble codes or indicators present.
Also, I was wondering how much of the stuff on top of the engine I have to remove to replace the plugs, I can't even see them. Is this 4.2 really a DOHC? and if so, are the plugs on top, or driver side?
Don't have a manual, and the Autozone DIY info is completely generic, and gives no info on how to gain access to the plugs, only how to remove/reinstall them once you get to them.
Thanks guys. As always, I will appreciate any info/advice you can provide. -Jim.
No trouble codes or indicators present.
Also, I was wondering how much of the stuff on top of the engine I have to remove to replace the plugs, I can't even see them. Is this 4.2 really a DOHC? and if so, are the plugs on top, or driver side?
Don't have a manual, and the Autozone DIY info is completely generic, and gives no info on how to gain access to the plugs, only how to remove/reinstall them once you get to them.
Thanks guys. As always, I will appreciate any info/advice you can provide. -Jim.
maxwedge
02-18-2013, 07:53 PM
Remove the engine top cover, the you will see individual coils, they must be removed to access the plugs, care with the connectors to the plugs also, do this engine cold. Many things can cause this hesitation, if the tps were bad usually a code would pop up, may be not always, though. A full scan may show something, also clean the throttle bdy. Use AC Delco double plats, or Denso same.
Schurkey
02-19-2013, 01:51 PM
The original plugs are Iridium, not platinum/double platinum.
When I pulled the plugs out of my 90,000 mile '03, they looked so perfect that I checked the gaps, painted some anti-seize on the threads, and screwed them right back in. The original plugs were tough to loosen--they would each "pop" free with a lot of force, then they screwed right out. Scared the hell out of me, I kept thinking the threads in the aluminum head would be damaged. (No, the threads looked good) Even if, like me, you put them right back in, I wouldn't want to leave them in longer than 100K without removing them and re-applying anti-seize.
I have no plans to pull them out before 150,000 miles (or more!) for a second inspection. Currently have 120,000+ miles, runs like a top.
The new plugs I bought back at 90,000 are still sitting on the shelf in the garage.
Yes, you'll have to remove a shipload of plastic crap from the top of the engine, and then you'll get access to the six ignition coils directly over the plugs. As I recall, each coil has a wire harness, and a single bolt holding the coil to the engine.
When I pulled the plugs out of my 90,000 mile '03, they looked so perfect that I checked the gaps, painted some anti-seize on the threads, and screwed them right back in. The original plugs were tough to loosen--they would each "pop" free with a lot of force, then they screwed right out. Scared the hell out of me, I kept thinking the threads in the aluminum head would be damaged. (No, the threads looked good) Even if, like me, you put them right back in, I wouldn't want to leave them in longer than 100K without removing them and re-applying anti-seize.
I have no plans to pull them out before 150,000 miles (or more!) for a second inspection. Currently have 120,000+ miles, runs like a top.
The new plugs I bought back at 90,000 are still sitting on the shelf in the garage.
Yes, you'll have to remove a shipload of plastic crap from the top of the engine, and then you'll get access to the six ignition coils directly over the plugs. As I recall, each coil has a wire harness, and a single bolt holding the coil to the engine.
Ol'Jim
02-19-2013, 04:50 PM
Thank you for the advice & info, guys.
Autozone had AC Delco 41-103 Iridium's for $7 each. They tried to sell me the Bosch Platinum's for the same price, but with a $2 rebate per plug. The $12 back would have been nice, but several friends have had troubles with Bosch plugs, and I have seen cautions against using them by posters here on these boards, so stuck with the ACD's.
Was helping my son put a new front end on his Chevelle, we got that done, but ran short of time & daylight, so I will save this job for next weekend.
The hesitation in the Trailblazer is kind of odd, I guess my above description was not a very good analogy. It is not really like a lean stumble at all, more like a significant delay in throttle application. As far as I know, these things aren't "fly-by-wire" on the throttle control, but it feels like it doesn't miss or bog at all, it's like it keeps idling for maybe a half second after you give it some gas. Stays nice & smooth, but nothing happens for a brief period, then it goes. This is only during the first few minutes of operation, like if you had to drive a few blocks to get out of your neighborhood - Every time you hit a stop sign, then try to go, it just acts like it waits a second before the throttle actually begins to open. But it is not stumbling or bogging down.
Any ideas? Will try cleaning the throttle body. I heard injector cleaner is a waste of $$, because all gasolines have federally-mandated high detergent levels these days?
Thanks again, -Jim.
Autozone had AC Delco 41-103 Iridium's for $7 each. They tried to sell me the Bosch Platinum's for the same price, but with a $2 rebate per plug. The $12 back would have been nice, but several friends have had troubles with Bosch plugs, and I have seen cautions against using them by posters here on these boards, so stuck with the ACD's.
Was helping my son put a new front end on his Chevelle, we got that done, but ran short of time & daylight, so I will save this job for next weekend.
The hesitation in the Trailblazer is kind of odd, I guess my above description was not a very good analogy. It is not really like a lean stumble at all, more like a significant delay in throttle application. As far as I know, these things aren't "fly-by-wire" on the throttle control, but it feels like it doesn't miss or bog at all, it's like it keeps idling for maybe a half second after you give it some gas. Stays nice & smooth, but nothing happens for a brief period, then it goes. This is only during the first few minutes of operation, like if you had to drive a few blocks to get out of your neighborhood - Every time you hit a stop sign, then try to go, it just acts like it waits a second before the throttle actually begins to open. But it is not stumbling or bogging down.
Any ideas? Will try cleaning the throttle body. I heard injector cleaner is a waste of $$, because all gasolines have federally-mandated high detergent levels these days?
Thanks again, -Jim.
Schurkey
02-19-2013, 10:55 PM
Thank you for the advice & info, guys.
Autozone had AC Delco 41-103 Iridium's for $7 each. They tried to sell me the Bosch Platinum's for the same price, but with a $2 rebate per plug. The $12 back would have been nice, but several friends have had troubles with Bosch plugs, and I have seen cautions against using them by posters here on these boards, so stuck with the ACD's.
Good choice.
The hesitation in the Trailblazer is kind of odd, I guess my above description was not a very good analogy. It is not really like a lean stumble at all, more like a significant delay in throttle application. As far as I know, these things aren't "fly-by-wire" on the throttle control, but it feels like it doesn't miss or bog at all, it's like it keeps idling for maybe a half second after you give it some gas. Stays nice & smooth, but nothing happens for a brief period, then it goes. This is only during the first few minutes of operation, like if you had to drive a few blocks to get out of your neighborhood - Every time you hit a stop sign, then try to go, it just acts like it waits a second before the throttle actually begins to open. But it is not stumbling or bogging down.
The Trailblazer 4.2 is ABSOLUTELY Throttle-by-wire. They have horse-sh!t throttle response. In Park or Neutral, you can stamp the pedal to the floor, release it, and the engine won't start to accelerate until your foot is already coming back to idle. Terrible.
Even so, what you're describing seems to be abnormally bad.
Any ideas? Will try cleaning the throttle body. I heard injector cleaner is a waste of $$, because all gasolines have federally-mandated high detergent levels these days?
Thanks again, -Jim.
Federally-mandated detergent levels are not enough in many cases. Thus the coalition of manufacturers backing "Top Tier" gasoline.
http://en.wikipedia.org/wiki/Top_Tier_Detergent_Gasoline
Autozone had AC Delco 41-103 Iridium's for $7 each. They tried to sell me the Bosch Platinum's for the same price, but with a $2 rebate per plug. The $12 back would have been nice, but several friends have had troubles with Bosch plugs, and I have seen cautions against using them by posters here on these boards, so stuck with the ACD's.
Good choice.
The hesitation in the Trailblazer is kind of odd, I guess my above description was not a very good analogy. It is not really like a lean stumble at all, more like a significant delay in throttle application. As far as I know, these things aren't "fly-by-wire" on the throttle control, but it feels like it doesn't miss or bog at all, it's like it keeps idling for maybe a half second after you give it some gas. Stays nice & smooth, but nothing happens for a brief period, then it goes. This is only during the first few minutes of operation, like if you had to drive a few blocks to get out of your neighborhood - Every time you hit a stop sign, then try to go, it just acts like it waits a second before the throttle actually begins to open. But it is not stumbling or bogging down.
The Trailblazer 4.2 is ABSOLUTELY Throttle-by-wire. They have horse-sh!t throttle response. In Park or Neutral, you can stamp the pedal to the floor, release it, and the engine won't start to accelerate until your foot is already coming back to idle. Terrible.
Even so, what you're describing seems to be abnormally bad.
Any ideas? Will try cleaning the throttle body. I heard injector cleaner is a waste of $$, because all gasolines have federally-mandated high detergent levels these days?
Thanks again, -Jim.
Federally-mandated detergent levels are not enough in many cases. Thus the coalition of manufacturers backing "Top Tier" gasoline.
http://en.wikipedia.org/wiki/Top_Tier_Detergent_Gasoline
jdmccright
02-20-2013, 10:04 AM
I'd clean the TB's IAC valve and the TB itself. A sticking butterfly can cause the hesitation.
Bosch platinum plugs are awful as they are not gap adjustable as they wear due to the ceramic that surrounds the Pt tip. I've used Autolite Pt for all my vehicles with no problems, but that's my opinion.
Plugs are fairly easy to reach on top except for the forward- and rear-most plugs. You'll have to unbolt the A/C wiring harness to move it out of the way of the front coil pack. The rear pack removal is hindered by the hood seal's overhang.
Good luck!
Bosch platinum plugs are awful as they are not gap adjustable as they wear due to the ceramic that surrounds the Pt tip. I've used Autolite Pt for all my vehicles with no problems, but that's my opinion.
Plugs are fairly easy to reach on top except for the forward- and rear-most plugs. You'll have to unbolt the A/C wiring harness to move it out of the way of the front coil pack. The rear pack removal is hindered by the hood seal's overhang.
Good luck!
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