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2008 GMC Denali crew cab HELP!!!!!!!

I love my Chevy Chevette!
Posts: 2
Joined: 09/12
Posted: 09/04/12 03:41 AM

Anyway here it goes.....

I recently purchased a 2008 gmc denali crew cab that has been modified from Arizona via Southern California.  Modifications include bored and stroked 6.2L gas (376) to 416cid.

CRS434740006100 chevy LS2 Lat crank 58T
CRS 612503D2000 ESP 6.125 2.100 ROD no offset
Dyno tuned for over 500hp
60 lb/hr fuel injectors
comp cam gross valve lift (intake .566) (exhaust .568)
diamond pistons COMP valve springs
L-92 severe duty exhaust valve set of 8
L-95 stainless steel intake valve
aeromotive in fuel pump
dynatech headers
dyna tech mid pipes cat converters
procharger dc1 supercharger
pro charger intercooler
snow performance methanol water injection stg 3
Transmission has cryo treated has a freshen converter
4:10 gears
truck has been dropped 3.5"
custom drive shaft
22" custom wheels
305/40r22 tires
14" Baer Brakes

All work was done at 9500 miles currently it has approx 11500 miles. When I received the truck from southern California and drove it back to Calgary Alberta Canada. I fell even more in love with this thing I've been wanting this truck for a very long time. The body is immaculate its brand new.  

Anyway enough sob story the reason for the email is for advice.  When I brought the truck home it stalled on me several times on the way home (3hr drive)  So I booked an appointment with a high performance shop here in town who specializes in custom GMC and chev products truck went in and was 2 weeks late coming out with very little change.  My engine check light came on a few days later, so I brought it back to them to fix and they did some histogram tuning on it.  Seem to be working ok.  Put approx 30 kms on it and long story short I ended up losing compression in my #8 cylinder and my exhaust was glowing red hot from the cat forward to the engine.  I have not tore the engine apart yet.  But I have a feeling that the exhaust valve might have failed... They told me it would cost me $15,000 to fix with that said I'm going to do it myself.

With only 2500 miles on this thing I would assume that this engine should last alot longer then what it did.  I personally think its the performance shops fault for making the fuel/air mixture to lean and causing the valve to burn up. But I know i will have a fight on my hands for sure if I approach them about it...

I guess in the end my questions are do you have any advice on what else the cause could have been, and what can I do to make the engine last and not have to do another rebuild.

I do have all the receipts for the truck and the work that has been done. I'm fairly knowledgeable when it comes to engines but not so much the high performance stuff.
Please help I really don't want to lose more of my shirt on this...

Stu Healey  

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V-6 Camaros rule!
Posts: 111
Joined: 09/11
Posted: 09/06/12 08:16 PM

Stu: Welcome to the forum...

Stu you should race cars, and you'll see what losing your shirt is all about. That's why I learned very early on to do as much as I could by myself,for myself...With all that preaching done... Grin  Cool

Not knowing what those speed shops did or what any of the parameters were before the performance shop's did what they did to it you will never know who to shoot...With it being at different places where do you start.

It could also be an injector nozzle clogged and made that injector go lean. It could be the voltage isn't correct to that injector. The injector pulse width could be so short it shut the fuel off, to that injector. Do you see where I'm going Stu. It can be a muriad of he did this, he did that. Or the injector just went FUBAR. It's really hard to tell what happened first.How an injector leans out , the nice spray pattern they have,is usually cut down to a very thin wet stream, and it just dribbles out. Confused  



I know this will wake up the neighbor's,...LOL... but you have to start doing something. You say you can dive into this stuff. OKAY... Blush

Drop the exhaust first and see if a cat is plugged up.
See if a cat plugged up via a meltdown...or who knows what?
If it did now you have to find out why. Did it go full enrichment, and melt the Cat. Or did it go so lean it melted the cat. The newer cats take a lot to melt them down. Confused

After checking the exhaust for a plugged cat.
Next run the engine to operating temperature if you can, without the exhaust tube glowing red, and see what the temperatures are in those cylinders. If you can pinpoint that cylinder, then pull the injector. Blow the area around the injector hole so no crap falls in the injector hole.If its a lean injector that exhaust tube will glow red-hot real quick.

I would remove a known good injector, and compare them both physically, and if you can get them flow tested. Unless it's obvious that that injector went to extreme heat, and is melted or cracked or maybe it just failed. Or if you can't figure which is the lean one. Switch the holes.DON'T FORGET TO MARK WHAT HOLE IT CAME OUT OF.

Again not knowing what was done to the parameters you maybe shoveling CHIT at the tide. I wish these speed shops would stick to what they know, and what they don't know tell you the customer they don't know. Is that so hard? Good Luck...I'll bet your getting nowhere with them now.... Grin  Cool

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I love my Chevy Chevette!
Posts: 2
Joined: 09/12
Posted: 09/07/12 07:41 AM

Hey Bob thx for the feedback....

As of right now the speed shop that tuned it for me agreed to store it for the winter and to find out whats going on with the engine. The cat was taken out and it was not plugged. Compression test has been done and found #8 cyclinder to have zero compression.  All the others are plus or minus 40psi.  Which tells me this motor has been hurt for awhile (My guess is the person that bought it before me tortured this thing without methanol.  The speed shop that built this thing specifically told me if you run this truck without metanol injection hurting the engine is ineventable.  Although the injector theroy could be a good one as well I will keep that in mind for sure.

I will be glad when this nightmare is over.  I certainly learned alot about this experience.

Thx again for the feedback  

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V-6 Camaros rule!
Posts: 111
Joined: 09/11
Posted: 09/08/12 02:21 PM

Cool I guess that's good and bad news....

With #8 cylinder dead it should be easy to figure out what the problem is. My observations from being around drag racing and stock cars nearly all my life.

1.The cam went flat do to improper breaking in procedure.
2.The valves burnt from running lean.
3.The valves were adjusted to tight. Keeping both valves off their seats too long,and never closing.
4.Or the worst thing that could happen the injector burned a hole in #8 piston.
What happens to an injector (If this is the problem)the nice spray pattern it should have goes away, and the nozzle pattern has droplets of fuel or a straight pattern to it. So the piston top gets so hot it burns a hole through the piston top...A properly working fuel injector cools the top of the piston.  Blush

I hope they find the problem with #8 dead they should.It could also be the injector was not firing do to a wiring connection?  Either way GOOD LUCK...


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V-6 Camaros rule!
Posts: 111
Joined: 09/11
Posted: 09/08/12 11:10 PM

The 40PSI indicates to me the cam is FUBAR. If I were you when rebuilding it stay away from methanol of any type. That stuff is for a once in awhile shot to get more power from the engine.

Something obviously went wrong with it big time. Methanol added to an engine goes way back to the fighter planes of WWII. They used it to get more horse power from the engine. I personally don't like Nitrous but there are guys in the field that know how to use it. Be carefull with power adders! My 2 cents.


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