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Yet another P0307 code

A

AVnKC

Full Member
Joined
May 25, 2004
Messages
194
Location
Kansas City, KS
I've done lots of reading here... Fantastic info!  My truck is misfiring and only does it when warmed up.  Runs fine for at least half hour, then starts misfiring.  I'll say what I'm doing and maybe you can help me tell the dealership to do to help them speed things up...

2002 Z-71 5.3L 4x4
140,000 miles
Dynatech's SuperMaxx long tube headers with high flow cats
DirectHits
MagStar gold plug wires with high temp fiberglass
Volant cold air intake

I don't think it's the cats, they've been on for...crap  50,000 miles (maybe)
Directhits have been on for 90,000 miles, changed plugs 2 times so far.
Replaced fuel filter last week.
Replaced upstream O2 sensors 3 months ago. (Engine was throwing O2 errors and causing misfires.  felt the same as it does now but different codes.  That seemed to fix the problem until it got warm outside)

From what I've read I probably have a fuel contamination problem.  I ran the last tank as far down as I could and filled up with 31.8 gals.  I may also need to clean/change the MAF. I've got cleaner today for it and the air intake.

If that doesn't work, I'm thinking of having the dealership do these items:
  1. When the lines are removed, cap the fuel rail off to retain any fuel that might be contaminated. Remove the rail, drain it into a clear container and inspect for contamination.
  2. If contamination is found, follow the Fuel System Cleaning procedure in Service Information.
  3. Once the fuel system is cleaned, refill the fuel system with new gasoline.

http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,77636.msg1191817.html#msg1191817

I'm also thinking it may be heat.  Though the temp gauge never shows it being hot.
http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,40883.0.html#bot
 
A misfire in cylinder 6, when was the last time you ran fuel injector cleaner thru it. If you change Spark plugs and wires try that. When you have that many miles carbon buildup can be a problem. Fuel injector cleaner does more than clean the injectors it also cleans carbon off valves and the heads. It's a cheap fix try it.
 
I'll do that!  Need to fill up anyway!  I was thinking HEAT as well, if there's water in the gas leftover for some reason, that should get rid of it right?
 
glad to help
 
Well the fuel injector cleaner hasn't done anything yet.  Put 200 miles on the truck and if anything it's getting worse. 

Like I said before, it runs fine when it's cold and for about 10 minutes when it reaches temp.  After that misfires/chugging down the road.

I read another thread that it was a "HEAT" issue, but the only explanation I could gather is they changed out the cat's and it fixed it... 

Any advice???    :help:
 
Ya may need to get it on a Engine analyzer, might be a coil going bad. But find out what's wrong before you buy more parts
 
MichiganSilver03 said:
Ya may need to get it on a Engine analyzer, might be a coil going bad. But find out what's wrong before you buy more parts
Click to expand...

Easy check, swap coil, wire & plug from cylinder 7 to a different one, see if the code changes :)
 
I got the same code on my 02 5.3L .
Mechanic told me right of the bat it was the intake manifold gasket.
He said because of the bad gasket design and plastic manifold.
And that he has replaced 10 gaskets so far with the same code.
I am going to do it myself and while I have the manifold off,I will service
the injectors. >:D
 
Thank you!  I'll mention that to them when I go back because their "solution" won't fix my problem.  They told me that my headers have burnt through the spark plug wires and causing it to ground out and not spark.

I agree, it did burn through it, 20,000 miles ago and I moved them away.  :mad:  So to prevent it from being the least bit of a problem, does anyone know of a material/insulation to wrap headers/wires?  The wires I'm using are wrapped with fiberglass and have already burnt through once.
 
I'm not a huge fan of header wraps.  However, you can get braided coverings for plug wires or ones premade that way (although I haven't checked for the LSx-style motor).
 
The intake gaskets can be an issue. GM has updated them because of it. It causes that cylinder to run lean. No 7 cylinder is also known for failing(usually under boosted conditions). I would do a compression check also. You can also check by getting an infra red thermometer and see if the temps vary between #7 and the others.

Good luck, Mark
 
The intake gaskets can be an issue. GM has updated them because of it. It causes that cylinder to run lean. No 7 cylinder is also known for failing(usually under boosted conditions). I would do a compression check also. You can also check by getting an infra red thermometer and see if the temps vary between #7 and the others.

Good luck, Mark

Where can I get an infra red thermometer?
Can you rent one?
Also who has a illustration of the intake removal and assembly.

Thanks  :wave:
 
Well I hope its fixed.  Didn't figure it was the plug wires, but I replaced the plugs and wires and the problem hasn't come back yet.  Running good!!!  Had to goto NAPA and get some extra fiberglass heat shroud to put around the plug wires. 

Pics when I get the damn cable to hook up my camera.
 
Pics...  That heat shield still working.  Is a little burnt now, but holding up.
 

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are you still running the directhits? i am thinking about getting a set, but this is the only thred that is uptodate. i have an 03 z71 and would like more hp, but dont have a lot of money. did the directhits help fuel milage and power?
 
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