High flow cats or just cut em out?
 

Looking for a little advise on what I should do with the cats on my 03 GMC 4.8.


I recently took my truck in to have it checked out to see where my coolant is going and see why it seems as it has no power. I couldn't find a leak or smell it anywhere. And I have had to put a gallon of antifreeze in the thing since July 3rd and it is just a dog. It doesn't seem like it has the power it should.
The diagnosis became a blown head gasket and partially clogged cats.


So here in OK we dont have vehicle inspections anymore so should I just cut the cats out or spend the money to have high flow cats installed?


The truck is pretty much stock except for a CAI and little 40 flowmonster. I did recently come across a Hypertech III Power Programmer but have yet to program my truck simply due to the head gasket and cats.

What heads are on it? Is coolant getting in the oil?

Imo i would just get a set of sw longtubes any y pipe for about the same price of new cats installed if you went that route.

Long tube headers with an ory.

Depends if you want to stink like gas everywhere you go. Power difference between ory and cats is negligible too

I am not sure on the heads. What ever a stock head would be on a 03 GMC 4.8, and the oil is clean.


I have a muffler shop wiling to install some high flows for around $350.00. Not sure if I can find some descent headers and y for less than that. That's why I asked about cutting them out.

Speed engineering headers and Y pipe are 349. You WILL love them.

Hit summit for proper 3" band clamps, you need 4 of them and ebay for a set of header bolts.
Use Kroloil to soak your oem manifold bolts for a week before removal. Spray them before heading to work and when get home from work..

none of mine broke and came out Very easily.

1. Who in OK is doing your diagnosis? Are you aware of the problems with Castech heads?

2. For $350 you can get Speed Engineering stainless headers and ORY for your truck.

3. The Hypertech is junk. If you don't believe me I'll read the stock tune out of your truck, then install the Hypertech tune, then read it out and compare the two and show you how little it changes. Plus it can't turn off the codes you will need turned off with an ORY. Even if you put muffler shop cats on it there is a good chance you will still set 420 and 430 cat codes. I see it all the time.

4. Here is the GM Bulletin on the heads. Although you would probably be getting coolant in the oil if that was the problem. I would inspect them anyway.

#06-06-01-019B: Information on Gradual Coolant Loss Over Time with No Evidence of Leak Found - (Jun 12, 2007)


Subject: Information on Gradual Coolant Loss Over Time With No Evidence of Leak Found


Models: 2004-2006 Buick Rainier

2001-2006 Cadillac Escalade Models

2001-2006 Chevrolet Avalanche, Blazer, Silverado, Suburban, Tahoe, TrailBlazer Models

2001-2006 GMC Envoy, Jimmy, Sierra, Yukon Models

2001-2004 Oldsmobile Bravada

2005-2006 Saab 9-7X

with 4.8L or 5.3L VORTEC® GEN III, GEN IV V8 Engine (VINs V, T, M, B, Z -- RPOs LR4, LM7, LH6, L33, L59)




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This bulletin is being revised to include engine RPO L59. Please discard Corporate Bulletin Number 06-06-01-019A (Section 06 - Engine/Propulsion System).


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Some vehicles may experience a gradual coolant loss over time. A very low percentage of cylinder head(s) manufactured with an embossed Castech logo may develop a porosity crack in a very specific area.

Inspect the cylinder head assembly to determine if the casting was manufactured by Castech. This can be accomplished by inspecting for their casting logo located on top of the intake port, under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.

Important: If the cylinder head(s) are Not a Castech casting, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.

Refer to the following illustrations on how to identify Castech casting and/or the very specific areas of the cylinder head(s) for a coolant leak from porosity.

Just a little heads up with adding headers and ORY to that current muffler or even just cutting the cats out, it's going to have a TERRIBLE rasp at part throttle.

OK, now I am concerned about the heads and if the shop that made the diagnosis is aware of this problem and if they have taken proper diagnostic steps.


If it were the head and not just a gasket, would there be more of a chance of coolant in my oil?


As far as the exhaust goes, my wife has put her 2 cents in and it sounds like I am going with the high flow cats. She does not want me to remove them and then have get a tune done so my engine light will stay off.


As far as the Hypertech III, I figured for not having to spend any cash it would make some kind of a difference since I cant afford $400.00 for a tune job plus the exhaust repairs at the moment.

She's really going to be pissed when a P0420 or P0430 cat code pop up with those muffler shop cats. And you know you don't have to spend anywhere that for a tune around here. Sorry, can't help you anymore.