Since I started driving my dually this spring there has been an exhaust rattle, well I drove it up north this weekend towing my camper. All the way up there it just didn't seem to have the power it used to, but I just thought I was so used to driving my duramax that I figured it was normal. After awhile though it started running hot. Didn't think much of it as it was really warm out and I was pulling some long grades. By the time I got to my destination the exhaust rattle got worse, just thought it was vibrating on a crossmember or something. Well yesterday on my way home, it seemed even less power and continued to get worse. Just 15 miles from home I have a long steep grade that normally I can pull up 45-50 miles an hour up, this time I was at max 25 mph and really struggling, I didn't think I would make it up, plus it was up to like 240 degrees. I nursed it home and put it up on my lift to check out the exhaust. Come to find out the rattle is coming from inside one of the convertors. So I figure that is what my problem is, something broke off inside and is partially plugging it up, is that something that could happen? During the whole trip the check engine light never came on. The truck only has 57000 miles on it, aren't convertors supposed to last like 100000?? I have never messed with converters before so I don't know what is really inside them.

So here are my questions, wtf do I do? My truck has 2 of them, can I just replace one at a time or do they both need to be replaced? Can I eliminate them? I am not in a state that has emissions testing, but would it cause computer problems, the 02 sensors are before the cats. Can I put one aftermarket cat on it? I can't afford an oem one but have found aftermarket universal ones reasonable.

if the 02 before the cats, y not cut a whole in it tear out the porcelin and re weld it up and have it be a free flowing cat? cheap and inexpensive

I normally just take them out and put some exhaust pipe back in place of them when they get clogged up. My Ford did this about 2 years ago.

The rear O2's will set off your check engine light if you gut or remove the cats. You can get O2 sensor simulators to replace them, or have them custom-tuned out of your PCM.

Richard

mine doesn't have rear 02 sensors, just the ones in front of the cats.

If it's factory, it has rear O2's. Trust me on that. OBD2 (1996-up) uses it to measure catalyst efficiency.

Maybe someone already deleted 'em?

Since the cats are staggered on a Vortec true dual setup, the rear O2's are staggered, too.

EDIT - huh, forgot to ask and you didn't mention, is this truck gas or diesel? I haven't seen the later model diesel setups to know for sure whether they use rear O2's.

Richard

It is a 2000 7.4L gas, I have owned the truck since brand new and never removed the rear 02's, there are bungs in the pipes for them but no sensors or wires back there. Don't know why they arent there, I have never had it in for service so no one but me has worked on it.

Here is a sensor from autozone they list ones with and without sensor after cats.

Part Number: 15732
Weight: 0.4 lbs
Warranty: 1 YR
Application: Without California emission
Sensor located after catalytic converter
Notes: Universal 4 wire; heated; 2 required
Fit: OE SmartLink
Sensor Type: Heated
Wires: 4
Length - Sealing Surface To End Of Connector: 28.4 inches
Shipping Information: Overnight and Two Day shipping are not available for PO Box, APO/FPO/DPO or US Territory addresses.

above 9500 gvw trucks 95-2000 came availible without supplemental restraint system(airbags) and doec not have rear 02 sensors. i have a 2000 setup the same way, and towing the camper mine went out just like yours did. i took them out and hollowed out the porcelin, but they were too damn loud after, they made a horrible hollow sound. i did like lock said, just put a piece of pipe in its place, and walla, your done. it will not hurt calibration, and will not affect the computer either. what it will do is give it more spunk though. these fu$$ers are too restricted from gm. want even more power, do the injector swap and get a cam/lifter kit with the timing chain setup made for the later 7.4 like ours from summit, and it will be what a big block was meant to be later, brian

Thanks, I think that is what I am going to do, I think I have extra pipe at home to do i up.

The 7.4 has terrible numbers as far as torque and HP for what it is. As I remember my 5.3L yukon has more HP and just a little less torque, just isn't geared right or it would tow my camper decent, I was dissappointed in it this weekend, but when I couldn't hardly get home with it I knew something was wrong. My diesel has so much torque I just figured I was used to that but my dually shouldn't be this bad. GM really detuned these to get emission standards or whatever they needed.

the 7.4 in these trucks are dogs stock. gm put too much restrictions on them 4 sure. i reworked my entire setup piece by piece, and am happy with the outcome. i got the cam kit from summit, ford bosch injectors, removed airbox and built cold air intake, deleted cats, wait4me tune on the computer with all the torque management removed from the program, true duals with headers and magnaflow mufflers(all 3") and it is quite powerful and wayyyyy more torque than gm even imagined like it should be. it gets a little better gas mileage than stock, but it is a big block and not a honda i think even with an all stock truck, the tune is a much needed mod, especially towing the camper. later, brian

I took them off last night, one was ok but the other the stuff inside had broken into 2 pieces and had majorly deformed and was plugging off the exit, so I am confident that was my lack of power issue, don't know why it didn't trip the ces light but oh well, got me some straight pipe in there just need to weld it all up.

All this talk, now I am going to have to look under mine to see if I have O2 sensors after the cats...

it would trip the ces light if it had rear o2 sensors, but mine never came on when it happened to me either. okc, does your truck have supplemental restraints(airbags)? if so, it wont have the downstream o2 sensors. later, brian

Now I'm confused. In one post it seems like you're saying if the truck came without airbags it also came without rear O2's, and in the next one it sounds like you're saying the opposite? Maybe I just read it wrong. And I'm only half awake.

Anyway I don't see how the airbags would have anything to do with the O2's or why the truck would be equipped that way. Every 95-up I've seen that is a regular duty 3/4 ton or heavier came without air bags. I've heard some had airbags as an option but so far I haven't seen them. My '98 C3500 has a driver's side air bag but only because someone busted the column and replaced it with whatever they could find, the airbag isn't hooked up, but it would fool someone that just happened to peek into the window, ya know?

As far as the rear O2's, every OBS dually I've seen with a Vortec engine has 'em, I'm definitely not arguing with you about them because by no means have I seen them all. Just going off what I have seen.

Richard