Diagnosis help please!

Alright guys, here's my predicament. My truck (99 1500 5.2 4X4 60k miles) has been losing oil, and has general lack of power at times. Easy enough on that one........I've ordered the Hughes kit for my Plenum and will be doing that next weekend. I've also got an exhaust leak that I will be welding shut at the same time. New Plugs and wires also will be done at this time.

I haven't gotten any codes pulled yet but probably will just to verify but here's what happened. Going up an incline on the interstate, the truck loses power and speed. This past weekend I was gong up this incline and I gave it the gas to get around a car because I had others coming up behind me. It downshifted and went but I heard a pop sound. After that while idling it was super rough as if it wanted to shut off but never did. I got it home and the rough idle continued.

Today I crank it up and she's idling fine. Kinda curious as to if anyone else has had this issue and what it could possibly be. Also while doing the Plenum anyone else got any good ideas to go ahead and knock out while I'm in there?

Edit* The Cat will be gone completely in the near future, so that is already in the works because I'm close to sure it's clogged.

I strongly advise against deleting the cat. Your truck will not run correctly without it. You will not gain any measurable amount of horsepower by deleting it

The cat itself does nothing for operation. It's the side affects of the free flow vs the engine requirements. Too much flow capacity the system loses scavenging ability and 02 reads more oxygen in the system causing it to richen the mix.

Without some power modifications, yeah don't bother. If you've got some stuff done, go for it. That is if you have enough to require the flow.

Myself, my signature outlines my bolt on engine. Difference between cat and no cat on my setup is minor at best but it is slightly better without, but mine warrants the flow

During plenum fix, do yourself a favor and do a tuneup. No time easier to get the cap and rotor done (use brass terminals) as well as wires. Swap in some good copper core plugs. Oem works fine, ngk is good, autolite is good. Preference at that point assuming all plugs you'll look at are copper core and the same heat range

Main reason for removing the cat is of course better flow. However, with a proper resonator/muffler combo you can still retain the back pressure the engine needs to operate properly. They just don't clog up like a cat will. Plus cats can be expensive and I'm trying to ball on a budget.

Cats will last well past 200k+ unless you're burning oil, like the plenum does. High flow cats are cheap as hell too and our factory cats really don't have all that much restriction in the first place. It's not "backpressure" you're looking for either it's scavenging. Backpressure is a simple way of explaining the relationship of airflow velocity and restriction and how they affect each other. Think of exhaust as a bunch of little balls of exhaust gas, we'll call em pulses, 1 for each cylinder in 1 cycle of the firing order. Now say at idle, about 700rpm-ish, you have a bunch of these little pulses. Assuming no mufflers no cats just straight pipe, once each little pulse is expelled from the cylinder that ball of gas is trying to expand. In a small 2" pipe there's not a lot of room to expand and that energy spent attempting to expand as well as the energy that expelled it from the cylinder causes this little pulse to move at a high velocity through the tailpipe. Scavenging is when velocity is high enough that it creates a slight vacuum effect behind it that helps to pull the next one out of the cylinder more completely. More pull = more efficiency. So small pipes are better? At low rpm yes. At higher rpms, like 2000rpm for normal driving or 6000 in performance scenarios the volume of gas is much greater and while that little pipe may have been great at idle it'll strangle the engine at this point. Larger pipe has a greater capacity for flow and at higher rpms lends to better scavenging without choking the engine.

So that you've read that book, why do you care or why does it matter? Because your exhaust system should be a balance of your engine setup and intended purpose. 300hp daily driver engine will suffer with a dual 4" setup while an 800hp competition engine will thrive. That comparison will flip and be the opposite with a single 3" pipe.

Considering these trucks make 245hp at the crank and about 180hp at the wheels from the factory, unless you're doing further modifications, an otherwise stock truck without a cat and a straight through our lack of a muffler is overkill. Factory pipe is 2.5" and the factory keg intake doesn't even support that capacity potential without other things like larger throttle body, rocker arms with more lift, headers, etc. Resonators and many straight through style mufflers increase velocity over that of straight pipe from featuring less surface friction while chambered mufflers do the same through restriction that acts like your thumb on the garden hose without changing the capacity.

For daily drivers I generally recommend using a mix of pipe size cats and mufflers to tweak flow based on the build and desired sound. You like flowmaster 40/44/50 series mufflers and your state inspects for cats, go about a 1/2" over needed free-pipe size. Like glasspacks and you're definitely going to cut out the cats "cuz you don't need them blasted government doohickeys (insert tobacco spit sound here)", don't change pipe size or don't go more than 1/4" bigger.

If that tobacco spit comment offends you btw, i apologize. I'm from small town Iowa where every ******* kid drives an 88 K1500 Chevy with true dual 3" straight pipe, 1 barely hanging on with a clothes hanger, and thinks it's just the hottest **** in town. Then they try to race me and i make em look like a ***** while i have an extra 1500lbs in the bed and I'm the *******

That and your truck will give everyone around you headache and or sick.

Not cool. I'm not some tree hugger but I've never walked out side and said " I wish the air was less clean"

dapepper9 said:

Like glasspacks and you're definitely going to cut out the cats "cuz you don't need them blasted government doohickeys (insert tobacco spit sound here)", don't change pipe size or don't go more than 1/4" bigger.

If that tobacco spit comment offends you btw, i apologize. I'm from small town Iowa where every ******* kid drives an 88 K1500 Chevy with true dual 3" straight pipe, 1 barely hanging on with a clothes hanger, and thinks it's just the hottest **** in town. Then they try to race me and i make em look like a ***** while i have an extra 1500lbs in the bed and I'm the *******

Click to expand...

*spits I do enjoy ******* off my HOA, my minibike has a 212 on it with a straight pipe and no governor. No emissions testing down here is SC. If they implemented emissions testing down here half the population would think they had to go back to school to pass something for tha gah dang guvment. Oh and when my exhaust on my other 1500 broke off the hangers I hung it back up with a bungee strap.

I'm the type that's just pure *******, giving people headaches is a passion of mine. The front plate of my 2WD even says Redneck on it.......

Might be better off changing that front plate to "moron"