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Discussion Starter #1
Hey guys,
2004 Frontier V-6 VG33ER
Im experiencing high fuel consumption, low power and I have received a check engine light, scanner code was catalytic converter.
I believe I have one or more cats that need replacing.
Looks like there are 4 catalytic converters, my questions;
Can I replace the entire exhaust with out cats ??
Is there a header system out there for my truck ??
What have you guys done short of spending $2k for an entire new factory Nissan exhaust ??
Thanks
Gregg
 

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NF Mod/Nissan Master Tech
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9,504 Posts
Well, there are a couple of things to consider and without more info, it's hard to say whether you need a converter or not. For example, if the engine is running too rich...which would cause high fuel consumption...it would cause catalytic converter efficiency codes to trigger (P0420/P0430). You would expect to see those codes in such a case, but it doesn't necessarily mean that one or more of the converters is/are bad.
Have you owned this vehicle long? What do you consider "high fuel consumption?" I ask because all of the VG33ER engines suck down premium fuel like it's going out of style and 12-13 MPG combined is about average on a supercharged Frontier. If it is considerably worse than that or if you are seeing black smoke out of the tailpipe, it would be worth figuring out what's going on before you condone the converters as the problem. For starters, you can use an exhaust back-pressure tester installed at the upstream oxygen sensor bung to test for any restriction in the exhaust. If you don't have one, you might be able to borrow one from a local part store's tool loaner program, if available to you. Autozone and Advance Auto Parts usually have such a program. One thing they will have in a tool loaner program is a fuel pressure test gauge, which you can use to make sure your fuel pressure is in spec. If the fuel pressure is too high, you have either a bad fuel pressure regulator or a problem with the fuel return line to the tank (clog or bent line). You can also use it to do a fuel pressure leakdown test to make sure the fuel injectors aren't leaking. Also, make sure the vacuum hose is connected to the fuel pressure regulator AND there is vacuum being pulled at the hose. Also, remove the hose from the regulator (which can be tough to get to being at the back of the engine) to see if there's gas in it; if so, the fuel pressure diaphragm has failed and gas is being sucked through it and into the intake. The upstream oxygen sensors or a faulty MAS can cause the engine to run too rich. So can worn spark plugs or poor compression. If you need any info, NICO Club's site will give you access to free, online, Nissan factory service manuals for your vehicle; most of the information as far as engine management will be in the "EC" section.
On to the exhaust questions... There are headers available for this engine. If you are going to eliminate the converters, make sure it will pass your state's inspection practices. Technically, eliminating or gutting any catalytic converter is considered tampering with a federally controlled emission device, therefore "illegal," but some areas are more thorough than others. If you live in an area that complies with California emissions inspections standards, not only will you not be able to eliminate any converters, but their replacements will need to be genuine Nissan parts or C.A.R.B. certified aftermarket parts. If state inspection is not an issue, Doug Thorley makes a nice set of ceramic-coated, long-tube headers for around $500/set. They do have a bung for the EGR passage pipe which will need to be plugged since the VG33ER doesn't have one. Also, if you plan to not use any converters, you will need to install "CEL eliminators" or oxygen sensor "simulators" to keep the ECM from triggering catalyst efficiency codes. Magnaflow makes headers that include an integral, upstream converter, but they are ridiculously expensive at around $700 each! If you have the original-style exhaust manifolds on it, you will also have to replace some of the exhaust manifold studs, installing shorter studs where the long studs are. For the rest of the system, a custom exhaust shop can bend some new pipes for you. Depending on your body style, you may have options from Magnaflow or Gibson, but I do know the Magnaflow muffler is around $600! An exhaust shop can use a Flowmaster or other muffler options, if you wish. Good luck!
 

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Discussion Starter #3
Excellent reply,
Thank you.
I've got my work cut out for me.
Ill keep you guys posted.
 
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