Ok forum peeps need some chevy truck help.. badly

Ok so here is the deal. I have a 5.3L V8 2005 Chevy Avalanche with 80k on the odometer. The truck has never once had a single problem. Oil always changed with synthetic and on time, etc, etc..

So coming back from Infineon this last Tuesday I get a CEL code that read P0303 which is misfire on cylinder 3. So I do the standard things, change plugs, swap coils, all to no avail. Idle is still rough and the code pops up again.

So I take it to the dealer as I am too busy right now to diagnose it and we needed the the truck back ASAP. I was hoping it was a clogged Cat but no such luck.

Dealer gets back to me and says it failed a leakdown with loss of pressure on the intake valve in cylinder 3. On the avalanche forums, a burnt intake valve is a very uncommon problem (not one person has seen one) with the 5.3L chevy motors so we think that the next issue could be carbon deposits on the valve causing it.
Also I would expect if it was a burnt valve I would have seen other codes like knock alerts and such for lean condition which I have not.

So, what should I do? I was thinking of trying some kind of hard core deposit cleaner that you let soak for 20 min kind of thing, as I have read this can help, not the fuel additive kind but something stronger/faster, but I am not sure what or where to get it. The other solutions I have heard is to media blast through the plug hole with walnut shells with the intake valve open to help clear off the deposits (though this seems sketch) and lastly I just pull the head, tear it down and clean the valve or replace..

Any thoughts, ideas, The thing is if I have to pay the $3k to the dealer for what they want to do, which is pull the head and then diagnose. Austin's race season and AMA for sure is over for now as that would take a big chunk of the budget set aside for the upcoming race next month. So any ideas we welcome..

thanks
Eric

 

Sea foam it.

If it's got deposits that will clean it out.

Someone on the Chevy forums must know how to use the vacuum system on the truck to get it into the valves.

 

Wow, bummer to hear that it's going to affect your son's racing. What about using Seafoam to clean out the carbon deposits?

 

Thats what I was looking for .. seafoam..
I am all over it..

yeah its tough, we are on such a tight budget this year, wife's been out of work for 17months and we have cut back as much as possible to keep racing. So when something like this comes up it throws a wrench in the plan..

Do you guys know if Seafoam and the the system to use it is something you can get at a local parts store or is it an order online deal?
thanks!!

 

Autozone carries it!

 

What grade of fuel do you burn in it? If I run 93 octane in my 5.3 Z71, I get carbon buildup. Found this out via the dealer the first year I owned it. I run 87 only now. 198,000+ miles and counting.

btw, this is what the dealer used to remove buildup.

 

careful getting to many deposits out with cat's on it don't want to cause more issues.

 

I run 87 as well, I heard the same issue and so went back to 87. I try to run mostly shell, but to be honest driving all over for races I have been hitting Pilot and Loves a bit as well.

As for the cat issue, that was one of my concerns. The Seafoam cleaner doesnt warn of any possible cat issues... but.

That is the thing, this truck has never once had a single issue, 80k and not even one visit to the dealer, and now this.. thats what makes me lean to the deposit issue and not a burnt valve/guide/seat.. etc.

 

If you don't have any luck with the Seafoam treatment, try to find a local repair shop/dealer with a Motorvac machine. It is a 3 part decarbonization process the was one of the best. If done correctly, it cleans carbon deposits very well. Should be under $200 most areas. Trying to find some one that does the complete 3 step process properly is key. I don't work for them, but spent 20 yrs in the auto business as a tech and service manager.

Good luck.

 

I've used seafoam on several vehicles....you will get huge plumes of smoke if you do it right. Never had a cat issue with it.

I also use it every 3-4th tank in my wifes car.

 

Thanks guys..
I am picking it up from the dealer soon and I will give it a shot tonight.

Do you guys think, if the Seafoam doesn't work after the first application is it worth it to do it a second time? Or just do Lar's suggestion and/or pull the head?

 

Something to keep in mind...it is a machine. Things to break, and most times do so suddenly without warning. Have you taken it to another shop to get a 2nd opinion. Of course don't tell them that is what they are doing. See what they say!:up:

 

I did it on an older Volvo 5 cylinder turbo with 200K on it. I poured a can in the tank. Then I pulled a vacuum line ( volvo sites tell you which one) and got a piece of clear hose and attached in place of the short vacuum line. Next I had a buddy get in the drivers seat and start the car and keep the revs around 2000. I would dip the hose into the can of seafoam so it would pick up the fluid....but would pull it out before the car could die. I did this for about half the can...and then allowed the vacuum system to pick up all the fluid it could until it died.

I left the car off and let it sit for about an hour.

When I started it, which was a little difficult, it ran a little rough and I had HUGE plumes of smoke. I then got in it and took if for a nice long drive on the freeway.

After it cleared out the car ran amazing!

Then I changed the plugs and did all the tune up stuff.

The stuff is amazing.

 

First; Do you trust the dealer? This isn't common which naturally leads me to think it could be hokey. After the work you did, did you clear the codes?

Leak down tests are easy. I'd have the codes cleared, run some Seafoam etc. and tke to a shop you trust to clear any codes and do another leak down.

 

A broken valve spring could cause the code and I have seen that happen more than once.

 

A mechanic that I trust told me I needed to replace my plug wires on my 2002 Explorer as they were getting old. I bought a set from Auto Zone and the truck ran fine for about a year. Then I started getting a persistent P0303 error for a misfire on cylinder 3. I replaced plugs, replaced the coil unit, checked compression, etc, etc... I even checked the resistance on the plug wire and it seemed okay. And why shouldn't the wires be okay - they were only a year old? Turns out the boot on the wire had split and was arcing. I replaced the plug wires and the misfire is gone.

So maybe try swapping your number three wire with another plug wire before you spend a lot of money on it?

Good luck!

Jim

 

thanks guys
I dont have a reason not to trust the dealer. The way I see it dealers these days, though maybe still not 100% are usually on top of most issues, the fear of litigation keeps them stand up, though like in my case they will default to the biggest fix to keep themselves safe. IE pulling the head, rather then risk things like seafoam.

As for the plugs/wires/coils I did the swap already and cleared the codes (I have a code reader) a few times..
When I first had the issue I put in fresh OE plugs, swapped coils on cylinder 3 and 5 but the code popped back up for cyl3 again. It did fail the leakdown in cyl3 so I think we have narrowed that down to some loss of compression at its most basic. From a leakdown we should be able to tell the cause and if the dealer diagnosed it as an intake valve I suspect they heard air coming up the intake.

That all being said. Valve springs are an interesting thought, but wouldnt that stick the valve shut, so it wouldnt then fail the leakdown in that case correct?

As for the fact its a machine, I hear you.. Things do tend to just go.. from racing we all know that. But 80k miles with never an issue and good care lead me to think its not a part failure, just from my gut feeling.. I guess I will see after the seafoam. if that doesnt work then I wil pull the valve cover first and check the springs, then the head if they are fine.

Looks like I have a weekend project.. great, just what I wanted.. hehe

 

Would the dealer work with you if you traded it in... Not saying that's your best option. Maybe take it to another shop, let them have a look as well. I've been burnt by dealerships before, ended up going to local "mom & pop" type garage's and have had much better results, and less of a hit on my wallet. Good luck, bummer to hear about the bad news

 

If the valve spring was broke...it would allow the valve to stay open. The tension of the spring against the keeper does just that...keeps the valve closed. The cam then rolls over the bucket overcoming the spring, opening the valve. So depending on the rate of the leak they probably have a good assumption. If it was a very slow slow leak, the carbon build up could be a good possibility. Obviously, if the gauge drops to nothing quickly...then you have a major issue.

 

haha.. yeah of course it would.. the valve spring thing.. its been a long day..
backwards me