Plugged Up Cat?

BowTieDude · February 9, 2007

I'm starting to think my truck might have a partially plugged up catalytic converter. It's never had tons of power, especially when taking off from a stop. I've read where other people on here could spin their tires from a stop even without a tune, but mine wouldn't dream of doing it. I've always thought it was probably due to the 40 flowmaster the previous owner installed taking away to much back pressure, but now I'm not sure. Every now and then when accelerating from a stop it seems to have much more power and gets up to speed much quicker than usual. It's rare when it does this, but it definitely feels stronger.

I'm wondering if it's possible that one of the cats is partially blocked, but sometimes the stuff moves around enough so that it's less blocked? I know the cat on the pass side has been cut out and replaced by the previous owner, but looking at it from the outside it's about as rusty as the factory one. Also, the SES light isn't on, so the PCM must not see a problem. Is it possible to have one clogged, but the computer not catch it?

I'm going to do some routine maintenance on the truck (Plugs, wires, fuel filter) and see if that makes any difference. It appears to have never had the plugs or fuel filter changed and it's got 164,000 on it! I'm not looking forward to taking the plugs out if they have been in there that long.

ken1mod · February 9, 2007

Plugging cats behave just like a plugging fuel filter. Power drops to zero over the last 100 or so miles. Happened to me in alaska.

Ken

Draenor · February 9, 2007

I'd check out what the SES light is about. Try to get some DTC's. Autozone and the like will pullem for free. Then you can see where you need to look.

dewfpo · February 9, 2007

What rear axle ratio do you have?

With that many miles I would suspect lazy O2 sensors (front).

DEWFPO

c502cid · February 9, 2007

Never had it's fuel filter changed? I'm surprised it is running at all. Do the basics first like you planned and go from there.

BowTieDude · February 10, 2007

What rear axle ratio do you have?

With that many miles I would suspect lazy O2 sensors (front).

DEWFPO

3.73 rear axle. Yeah the O2 sensors probably need changing too, but I'm short on funds right now. I'll have to do everything in steps.

Never had it's fuel filter changed? I'm surprised it is running at all. Do the basics first like you planned and go from there.

The fuel filter "appears" to have never been changed, but I don't know that for sure. It's certainly been on there a while in any case, and I think it's an AC-Delco, so I thought it might be the original.

It seems some peoples idea of routine maintenance is gas and a tree shaped air freshener.

98 Z71 SLT · February 10, 2007

Start with the basics, especially on 164k miles.

Air and Fuel filters, plugs, PCV, ignition wires.

Don't guess; especially with no DTC's happening.

dewfpo · February 10, 2007

Yeah, with 3.73's you should have plenty of zip. After the tune-up, filter's, etc... as mentioned above....if you still don't have power, you can put an analog voltmeter on the O2's and see if they are lazy. Lazy O2 sensors typically don't set any codes, but kill fuel mileage and performance if everything else is up to snuff.

DEWFPO

Rolandd · February 10, 2007

y 95 with 180,k miles would jump off the line, so you are on the right track to start with the basics. The cats are probably not plugged and not doing much either with that kind of milage

BowTieDude · February 13, 2007

Just thought I'd give an update:

I got the fuel filter changed today, and it needed it too. It was somewhat restricted when I tried to blow through it. It wasn't the original, but it had been on there a long while. It was an AC-Delco filter, but it was the newer part number GF481 not the GF626 that would have come on it new. Can't tell much difference in power, maybe a little better, but that's probably just my imagination.

I've got plugs and wires on order, they should come in by Wednesday. It may be awhile before I get them put on though because they're calling for highs in the 30s here until the weekend, and it can just wait.

I went with these NGK plugs. They weren't much more than the copper core NGK plugs that many on here use, I figured they might perform a little better or at least maybe last longer? Anyone use them?

Thanks again for all your help guys.

Z71SIERRA · February 13, 2007

I just had plugged cats on my 02 Sierra and my computer never threw a code. I had a dramatic loss of power and did all the common sence fixes (fuel filter, clean the throtle body, check the maf) and nothing fixed it. Took it to my dealer and he found plugged cats. Replacement was free because they are emission control gear and the truck runs STRONG now. Just be warned that the computer dosent always throw a code when the cats are plugged.

chev9644 · July 31, 2007

My 96 K1500 silverado 5.7 Vortec keeps giving me a code "P0430 = Catalyst Efficiency Below Threshold (Bank 2)". I've replaced the O2 sensors fairly recently so i don't think that is the problem. This truck has 163,000 miles and the catalytic convertors have never been replaced. Does that sound like the problem and if so is there a fairly cheap universal replacement for both catalytic convertors? I know the factory set up with pipes to the manifolds is $300-$500 so i'd rather cut out the old cats and weld in new ones if possible. It also has a "P1403 code = EGR valve pintle position" could this be causing the P0430 code to happen?