Spark Plug

[logepoge1]

I moved this to here from trailvoy based on recommendation by [a friend]

I have a 2003 Chevrolet Trailblazer LT EXT inline 6. It has 174000 miles. We bought it a month ago. We changed the throttle body(heavily caked in black gunk) and since it was so dirty Im thinking about changing spark plugs. I ordered the AC Delco Iridium plugs(Im only getting 14.1 mpg on the highway and apparently these plugs help someone according to user testimony), but am hesitant to change them because I am worried about breaking something. I am not a mechanic in any means(and a college student, so no money if something goes wrong) so how should I go about this? What material is our L6 vortec 4200 made of(is it weak enough for threads to strip removing the plugs if seized?)? My dad says he doesnt understand why I am changing them if getting no misfiring but I am trying anything to get the mpg back, without spending a whole lot of money(such as COI).

 

[The_Roadie]

WELCOME! You were invited to come here by somebody who might lose that account if the evil owners of trailvoy knew who it was. We're a non-profit site managed by pure enthusiasts, who fled trailvoy after they were bought out by a greedy corporation who turned it into a giant ad farm.

Anyway, you could have cleaned the throttle body for $5. Sorry to hear you bought a new one.

Our own member and fellow moderator MAY03LT has posted a Youtube video about spark plug changes. Check all his videos out and see what you're comfortable with.

https://www.youtube.com/watch?v=hB95ERNaUUk

If it's 4WD, also make VERY sure you change the transfer case fluid every 50K, not 100K.

 

[IllogicTC]

Because the plugs only last 100k anyway. And who knows if the original owner kept up on this? If the old plugs have a number like 41-9** I believe, they're ancient. I'm sure you got the 41-103 as a replacement, yes? It is important that you DO NOT ATTEMPT TO GAP THEM. You can check with a feeler gauge to see if they're properly set at the factory for the proper gap. If it's out of spec, some people use a pair of pliers to adjust the ground strap without touching the center electrode, while at least one other guy just exchanges the plug for a different one and checks it for spec.

The job is very straight-forward. You've done the throttle body, which means you were already 75% of the way to reaching the plugs before. The intake resonator box comes off, and then the six ignition coils. I believe the head is aluminum, but really material doesn't matter so much if you're very careful. You should never remove the plugs while the engine is hot, there is a stamping on top of the engine next to the firing order also reminding you of this. Before removing any plug after getting the ignition coils off, it is important to inspect inside each coil well. Ensure there is no water, oil or debris before beginning spark plug extraction. If you notice a plug with excess rust on it, this could be troublesome to remove without breaking the plug leaving it partially in the engine head. If you notice any dust or anything use compressed air and a cloth to remove before beginning spark plug extraction.

There's torque specs around here somewhere, too...

 

[MAY03LT]

Welcome to the site!

Looks like you got some sound advice already. Plugs 1,5, and 6 have given people grief but with the right tools it's not too bad.

I don't think replacing the plugs will help your mpgs, but since their history is unknown it's not a bad idea to change them. One maintenance item that's hurt my mpgs is the fuel filter. It's recommened every 30k miles (per manual). A couple of anonymous youtube nobodys had some choice words about my experience with the fuel filter-mpg relationship, but I have the data to back up my claim. All they have is what they've read on the internet or what their cousin who used to be a mechanic told them.

 

[Wooluf1952]

Welcome

In case you haven't heard:

http://gmtnation.com/forums/topic/218-welcome-to-gmtnationcom-heres-the-story/

I will also add, without a maintenance history, you may also need the upper O2 sensor. Especially if those are the original plugs.

 

[KNBlazer]

Welcome

In case you haven't heard:
http://gmtnation.com/forums/topic/218-welcome-to-gmtnationcom-heres-the-story/

I will also add, without a maintenance history, you may also need the upper O2 sensor. Especially if those are the original plugs.

From personal experience, I would recommend replacing O2 sensor as well, my mpg's were bad as well... on the plugs, once you break the seal, turn slowly, if you feel resistance, tighten it 1/4 turn and then loosen it again untill you have no more resistance...

 

[Robbabob]

One maintenance item that's hurt my mpgs is the fuel filter. It's recommened every 30k miles (per manual).

These trucks have a fuel filter? Okay, time to change ours...

Welcome to the Nation!

If you do encounter a tough one, 5 & 6 seem to be mothers if never removed, I have read on my Dodge forum to use PB Blaster and let it soak overnight. "They" say any of it that gets into the chamber will not harm anything. The top dogs here will edit my post if they disagree, so I hope I am correct.

When you do get to putting in the new ones, use thread lubricant to ensure a smooth removal the next time.

Enjoy the new home!!

 

[MAY03LT]

The top dogs here will edit my post if they disagree, so I hope I am correct.

You mean edit what you posted? We don't roll like that. Roadie edited the OPs post so the other site doesnt ban the shill.

 

[Mark20]

Welcome to the Nation.

Driven by people who appreciate their rides.

I am approaching the 100K point myself which means plugs and the other preventative maintenance. Personally I had not realized the fuel filter is way past due so that will be on the list.

 

[The_Roadie]

You mean edit what you posted? We don't roll like that. Roadie edited the OPs post so the other site doesnt ban the shill.

Exactly. Our tradition is to mock the posts we don't agree with....I mean EDUCATE members using persuasive arguments with footnotes and annotations to our academic references. An open and transparent debate.

 

[Lckent48]

Torque specs
Spark plugs 13 lb ft
Coil bolt 89 lb inches-less than 7.5 lb ft-don't over tighten

 

[KNBlazer]

Welcome to the Nation.

Driven by people who appreciate their rides.

I am approaching the 100K point myself which means plugs and the other preventative maintenance. Personally I had not realized the fuel filter is way past due so that will be on the list.

Some of our trucks don't have serviceable Fuel Filters, I think it was 2005 or 06 when GM went intank only... I have a 2004 and do have an external filter, right underneath on the drivers side...

 

[IllogicTC]

Some of our trucks don't have serviceable Fuel Filters, I think it was 2005 or 06 when GM went intank only... I have a 2004 and do have an external filter, right underneath on the drivers side...

05+ have in-tank filter, seems to coincide with the removal of the fuel pressure regulator on the fuel rail, instead doing regulation in-tank and having a returnless system. This is how we ended up having a TSB about sediment settling in the fuel rail and causing misfires on cylinders 1 and 6 during hard acceleration or braking.

 

[logepoge1]

I didnt buy a new one. Sorry. I cleaned it. Worked wrong.

 

[IllogicTC]

I didnt buy a new one. Sorry. I cleaned it. Worked wrong.

It's cool, either way you had most of what needed to come off for spark plugs off once already, and that should help your confidence that it's not an overly-daunting job. You save a buttload not taking it into the stealership for plugs.

For giggles back in IA, I had taken my vehicle to the place I got it from and pointed out all the recommended 100k mile service things and asked what they'd run me (I had a good 7k miles to go still). The plug change alone, including parts, was listed at something like $150-200. I remember it was rather expensive. "Oh it's because we have to remove this and that to get to them." I can understand an independent mechanic where all they do is fix stuff charging rates to support their whole business and themselves, but this was a successful dealership that had a car lot sprawling across 3 blocks and a full service center and parts department, serving up and servicing GM and Chrysler marquees. I don't think they'd exactly need to ream you for something that took me $30 and an hour.

 

[MAY03LT]

"Oh it's because we have to remove this and that to get to them."

That's similar to my work adding .3 labor per coil when doing a single coil/all plug swap. Everything is already apart for the plug replacement, the coil has already been heavily marked up, and they want to twist the knife by adding a labor cost for the coil. Unfreakingbelievable.

 

[Robbabob]

I meant to say, 'if I was wrong, I wouldn't want my advice to be used then hurt the OPs engine.' I know how y'all roll, read the humor many times! I don't mind putting myself out there to be mocked, erm corrected, it's all a learning experience and thick skin may be required at times.

edit: I guess y'all agree with using PB when necessary...

You mean edit what you posted? We don't roll like that. Roadie edited the OPs post so the other site doesnt ban the shill.

Exactly. Our tradition is to mock the posts we don't agree with....I mean EDUCATE members using persuasive arguments with footnotes and annotations to our academic references. An open and transparent debate.

 

[IllogicTC]

That's similar to my work adding .3 labor per coil when doing a single coil/all plug swap. Everything is already apart for the plug replacement, the coil has already been heavily marked up, and they want to twist the knife by adding a labor cost for the coil. Unfreakingbelievable.

So what they're saying is it takes nearly 2 hours just to swap all 6 coils alone? I mean, that's just the labor on the coils, not including the plugs or the other disassembly. They must have a hard time getting those locking tabs off the connectors

 

[The_Roadie]

It's the classic lie I mean debate...about flat rate versus hourly repair charges. I just hate it when I hear dealer stories about somebody who dropped the vehicle off, got a call 4 hours later that it was done, and the flat rate labor charge added up to 8 man-hours labor. Either they were tag-teaming the repair (unlikely) or they pocket the difference. Of course, the companies claim that makes up for the poor mechanic who takes LONGER than book rate to do a procedure. Well, that goofball shouldn't be learning on your dime, but they're also not worth being paid full rate at the dealership. But you as the owner don't get a discount on the hourly rate when they put a noob on your truck.

Last time my truck was in a dealership for a warranty repair it was for a new fan clutch. Took the asshats four days of whaling on the nut with an air chisel and they killed the water pump in the process. Hope GM only reimbursed them for 2 hours.

 

[MAY03LT]

I meant to say, 'if I was wrong, I wouldn't want my advice to be used then hurt the OPs engine.' I know how y'all roll, read the humor many times! I don't mind putting myself out there to be mocked, erm corrected, it's all a learning experience and thick skin may be required at times.

edit: I guess y'all agree with using PB when necessary...

Gotcha man. I know there's guys on here that totally disagree with how I handle brakes on any GM with antilock brakes (open bleeders/pinch hoses when compressing caliper pistons) but I would NEVER edit out their opinions.

And yeah PB ftw.

So what they're saying is it takes nearly 2 hours just to swap all 6 coils alone? I mean, that's just the labor on the coils, not including the plugs or the other disassembly. They must have a hard time getting those locking tabs off the connectors

Yuppers. They've never had an I6 that needed all 6 coils, but yeah they are bad for double dipping flat rate quotes. They charged 3.3 for plugs wires on a ford 5.4 (not the 3 valve version), And they wonder why they're going under and I'm looking for a new job.

Of course, the companies claim that makes up for the poor mechanic who takes LONGER than book rate to do a procedure. Well, that goofball shouldn't be learning on your dime, but they're also not worth being paid full rate at the dealership.

My best story of goofballs who shouldn't be technicians is when my former work gave a punch and hammer technician a car with an electrical problem. 3 hours in and he's asking anyone if they have a test light. 3 hours later. Blown fuse for FCM headlight driver supply ckt. Yikes.

 

[BlazingTrails]

One of the main problems that was causing my bad mileage was the catalytic converter. they are only supposed to last about 100k before they should be replaced. Anytime you do anything major like that it is a good idea to reset the PCM and let it learn the new conditions. -Brandon

 

[logepoge1]

PCM was reset. I unplugged the two fuses for it for 30 minutes like I was told.

 

[MAY03LT]

Converters don't last up until a certain mileage. If that was the case I'm 78K overdue.

 

[Sparky]

My cat got over 190K before I replaced it, and the only reason I did was the pipes were rotted out. The cat itself was OK.

 

[IllogicTC]

Driving habits and conditions, and runtime conditions of the engine and the upkeep of the engine and emissions/exhaust system have SOOOO much more to do with the cat's health than an arbitrary mileage. I'm sure there's people who've gotten ridiculous mileage off a vehicle with little/no cat issues.

 

[logepoge1]

Found a mechanic who would replace for $50 if I provide the plugs, which I got on amazon for $6 a piece + $2 rebate off each plug. Way better than what the dealership offered me($200 if I provide the plugs). I will probably do this but focusing on motorcycle at the moment moneywise.

 

[logepoge1]

Got them changed. Went from 13 mpg to 17.