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2004 gmc envoy_sle_xl
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Discussion Starter · #1 ·
My first post - please feel free to provide constructive criticism. I haven't worked on many vehicles since I was a certified mechanic 25 years ago. I'm grateful for this forum, and I have already learned much by reviewing similar posts. I'm going to start with the manifold problem. At first I thought it was a donut - but after removing the shield it appears to be the manifold gasket or - as I have discovered here - a cracked manifold. So last night I started the task of removing the manifold, but I didn't get very far. The nuts holding the triangular connector between the CC and the manifold are larger than 9/16, but too small for 5/8. I tried metric sizes as well. Am I stupid? Do I just need to get myself a 19/32 socket?

Also, suddenly the truck has no power. It starts and runs smoothly, but my OBD is showing a 0756 error (2-3 shift solenoid). Should I believe that, or are there other possible reasons for that code.

Thanks for your help. In return, I'll be glad to answer any computer questions you have!
 

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2003 chevy trailblazer_ls
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Welcome to the forum. Can't help on the socket size but sudden loss of power can be caused by a plugged cat.
 

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It's probably 15mm sized. Use a hex socket. 15mm is a common size used on GM. A manifold leak could have the engine controls messed up.
 

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Discussion Starter · #4 ·
Update...

Well, I removed the exhaust manifold last night. Not too bad - two hours with hand tools. The biggest PITA was one of the flange bolts holding the CC to the manifold. I couldn't get a socket on it until I had the manifold separated from the head, because there was very little space between the pipe and the transmission lines. I didn't break any manifold bolts, but I did discover that the one furthest to the rear was already broken, and that's where the gasket had disintegrated and left a gaping leak. And of course, the manifold was cracked. So this morning's project is to remove the broken bolt. I have about a quarter inch of bolt protruding from the head. Then I have to find a manifold. And I'm thinking it might not be a bad idea to replace the converter - I'm at 100K.

I have attached a couple pictures. I'm going to replace the oxygen sensor while I have easy access to it.

Any suggestions are welcome!

Greg
 

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They make bolt extractors that lock on to the stub of broken bolts but I don't know if you have enough for one to get a bite on. You probably don't have room to drill in to the stud without a right angle drill attachment.
Here is a link to one way to do the job. I would make a drill bushing to fit in the manifold bolt hole with a smaller drill size for starting a pilot hole if the stud was broken or cut off flush. Use lots of drill cutting oil so the drill and broken stud stay cool. If the stud gets hot it will probably only get harder. Mark the drill so you don't drill too deep. After drilling the pilot keep increasing the drill size just short of the threads and then use an Easy Out or other bolt extracting tool.
With the stud sticking up like you have I would make a drill guide (I have a lathe) that fits over the stub so the drill centers on the stud.

http://mightymo.org/Proj_BrokenStudRepair.htm

http://www.sjdiscounttools.com/ald4017p.html
 

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If you are fast you can tig/mig tack another, short, bolt to the 1/4 inch you have to work with. The thermal shock should loosen up the threads in the head.
 

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Search the threads here for others with broken bolts in the cylinder head. Seems to be a common problem. I read somewhere on here that they use a high temp loctite. I also read on here some moderate heat applied would be helpful. ALot of guys also wrote about overnight penatrating oil. Also go back and forth with that bolt to clear the threads as removing.
 

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Discussion Starter · #8 ·
The saga continues...

Yesterday was a day of mixed results. My local dealer was no help, but I was able to find all my parts at a dealer in a nearby town. About $250 got me a manifold (with all studs), gasket, donut and O2 sensor.

Thanks for the advice on the broken stud. Yesterday I was able to get a pretty good clamp on it with vise grips, but couldn't break it free. I thought about heating it up, but the head is aluminum - isn't that a no-no? I did some looking, and found that Sears has a stud removal tool which gets great reviews from users. I'm making the 20-mile drive to pick one up this morning. Hopefully I'll have good news to report later today...

Greg
 

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Discussion Starter · #9 ·
Manifold replacement is complete. I managed to get the broken stud out without too much trouble - of course, to get a 5/16" today I had to spend $40 on a kit of stud removal tools. Now I have one for every size stud ever made.

It's running quietly again now, and it idles smoothly at ~600rpm - but there is still a problem. It won't rev above 2000rpm, and has no acceleration at all. I've never experienced a clogged catalytic converter, but I'm thinking that maybe that's why the manifold cracked and popped a gasket. The other possibility is timing. I just replaced the cam actuator a few days ago. As I was reconnecting the wire to the new one, I noticed that the connector end of the actuator rotates - is this normal? When I put it on I thought it was in a fixed position.

So far no codes - but I need to determine why I have no engine power. Suggestions on where to start?

:thx
 

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You can create a exhaust leak before the converter to check for performance improvements. Try removing the O2 sensor in the manifold and running without. If performance improves you know you have a restriction in the exhaust. Typically converters clogging are a result of another underlying problem, So just because your done with this part you may want to make sure the engine is properly tuned and no trouble codes are present.

I had a few questions of my own. Was the manifold in stock at the dealer? Did you use heat or penetrating oil on that broken stud? Just curious how that all worked out for you.
 

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Discussion Starter · #13 ·
I'm feeling confident that its the CC. I inquired today at my area parts stores. I want a direct-fit replacement, and this forum convinced me to avoid Eastern's $50 universal one. GMParts web site has OEM for $355. Walker makes one (#55476). Autozone and Advance both said it 'hadn't been released to them yet' - but my local place said they could have it here the next day for $245. I found it online for $228, but I'd rather buy local unless someone has a better idea.

FYI - the manifold (#88890560): My area GMC dealer could have gotten it in a couple days for $157. I checked the local Chevy dealer, who didn't have one but told me that the dealer 20 miles away had one in stock. I called them, and had it in my hands in an hour for $170. Not bad for a Saturday morning.

The broken stud was a pain, but could have been a lot worse. I had just enough room to get a stud remover on the protruding end by tapping it on with the side of a hammerhead. Then I carefully got socket over the remover and used a 1/2" breaker bar so I had plenty of controlled leverage. I expected it to slip, but the remover held fast, and it came right out. I'll add a picture when I have a chance.

Greg
 

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Discussion Starter · #14 ·
Catalytic converter was the problem. Replaced it and everything is back to normal.

Thanks for the help and suggestions. :thx
 
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