2003 5.3 misfire problem

New here but not really :) I've read as a guest for quite sometime just never joined. I own 2 Duramaxes, my son owns the 03 & now he has a problem. He tells me it started as rough idle a couple months ago so he changed plugs & wires. Friday night he limped it home as it would not go any faster then 20mph. I drove it yesterday & it was flashing the mil & just wouldn't go. Checked the wiring seems ok, checked for vacuum leak around intake, changed Fuel filter & cleaned MAF & new air filter.
Logged it with EFI Live and 1,3,5 & 7 are misfiring. I'm lost & now he's got my truck. He says he's taking it to the dealer Monday but I was wondering if anybody has any ideas.
Thanks in Advance

The driver's side cat is plugged. Unhook the y-pipe and road test it. Common problem. It's covered 8/80.

I'll have him check that, can you get aftermarkets? Where? I can find any Dmax part but need help with this truck.
Thanks

You can get aftermarkets but be prepared to have them replaced every 12-18 months for DTC's P0420 and P0430. Aftermarket cats have so much less parent/precious metal content they don't last long. IMO they're a waste of $400. You could remove the cats and install headers and an off road pipe yourself along with a tune from someone else for about the same price as parts and labor for stock cats.

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Originally Posted by GasGuzzler

You can get aftermarkets but be prepared to have them replaced every 12-18 months for DTC's P0420 and P0430. Aftermarket cats have so much less parent/precious metal content they don't last long. IMO they're a waste of $400. You could remove the cats and install headers and an off road pipe yourself along with a tune from someone else for about the same price as parts and labor for stock cats.

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I'd assume the tune would eliminate the sensors by the cats? How about a by passing the cats & a tune? Headers & Y pipe sound good but It depends on his bank account not mine. Any company you'd recommend for the headers

A lot of guys use Pacesetters. They come in coated (very nice looking and expensive) and painted (cheaper). Other companies include Stainless Works and Dynatech. They're more expensive but are generally very nice. You could cut the cats off and put in a "test pipe" if you know someone willing to weld it for you. Then you could get a tune for more performance and fuel mileage as well as cutting out the rear sensors. In an extreme $$ pinch you could patch in some test pipe yourself and install O2 simulators but I would not advise that....pretty cheesey.

Thank You I will share this when he gets back in my truck :)

Great call, plugged DS cat. We dealt with both of them at once.
Thanks a bunch

Cool. Thanks for posting the fix.