1997 K2500 454 Rough Idle, Loud Afterfire

Erik the Awful said:

Check to make sure your distributor hold-down is tight. The backfiring is a pretty good indication the timing is off, and the intermittence sounds like the distributor might be rotating on its own.

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So I checked it, and you're right! The distributor is loose. When the engine was warm, I pushed it to another position, and the truck idled smooth, although generally when the engine is warm it runs a lot smoother anyways. After letting it cool for a few hours, experimented again and sure enough, it idled fairly smooth, with an occasional pop, but not nearly as bad as before. However, it's definitely not the only problem, and I'll have to see how it runs tomorrow morning, as that's when it's usually at its worst.
My mechanic claimed to have set the distributor, though, so either he did a terrible job or it loosened itself. Now I'm kinda stuck, though - A: I don't have the tools to tighten the bolt properly, so going to have to buy some (need to get myself a good socket set anyways), and B: Other than going by ear, I have no way of knowing what angle it needs to be at. I borrowed a friend's scan tool but I couldn't find the cam retard reading (it's a bluedriver, so I'd expected it to, based on the price).

Schurkey said:

You'd check for rich/lean by looking at the O2 sensor voltage.

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I'll let you guys figure it out, but the exhaust smells less gassy than before, although even before the smell wasn't too strong. I wouldn't trust the O2 sensor on my truck though, judging by the state of the exhaust. I crawled under there a while back and found one of the sensors unplugged. Plugged it in, made no difference.

Schurkey said:

Fix the EGR
Fix the exhaust leaks from the converter forward.
See what happens.

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I want to get a brand new exhaust setup, as the pipes are badly rusted, and plus that means I can install a new EGR hose that works (the current one is rusted on both ends). I'm worried though that I'll put it on, fire it up, and one afterfire will blow holes in my brand new setup. Those pops are loud enough to be considered illegal firecrackers (NY...) in their own right. Or is that unrealistic? And is it worth it, or would I be better off patching everything up? And plus, while I should, I don't have a welder or jack stands (yet), so anything more than nuts & bolts will either mean relying on a friend who has the tools but no time, or burning through my paycheck on tools.
Or would it be better to find a shop that does exhaust? And should I go with stock or aftermarket?

I am so out of my league (and my budget). Makes for good experience, though, and I like to think of the cost as regular tuition to mechanic school. No pain, no gain!

Your mechanic probably did set the distributor, although it sounds like he may have missed the step where he tightens it down after setting it. I wouldn't think asking him to finish setting it would be out of line. A good scan tool is needed to dial it in. Looking the Bluedriver up on the web, it does not indicate that it can read timing, so it may not. Torque can with the correct OBD adapter. A Tech 2 can also do it, but you're not likely to find many of those out in the wild.

Trying to patch an exhaust that has rusted through is an exercise in futility. The sections that have rusted through need to be replaced. Most, if not all, of the sections of your exhaust should be available as pre-bent assemblies. With a lift, torch, and welder, a shop could have you out the door in an hour, generally for a pretty reasonable price. It would require a great deal more pain and suffering to do it yourself on your back. There's a lot of performance that can be wrung out of the exhaust on that engine, but you need long tube headers to make it worthwhile. If you're not going to put them in, you might as well just replace what needs replaced and call it good.

Manmeyco said:

So I checked it, and you're right! The distributor is loose.

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Awesome! Feel free to guess how I know to check for that.

Erik the Awful said:

Awesome! Feel free to guess how I know to check for that.

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Hours of head-scratching & fiddling under the hood, I'll bet. Everyone's a genius in hindsight.

Carlaisle said:

Your mechanic probably did set the distributor, although it sounds like he may have missed the step where he tightens it down after setting it. I wouldn't think asking him to finish setting it would be out of line.

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Yup. He should do this for free. His fault that it wasn't done properly the first time.

Carlaisle said:

Trying to patch an exhaust that has rusted through is an exercise in futility. The sections that have rusted through need to be replaced. Most, if not all, of the sections of your exhaust should be available as pre-bent assemblies. With a lift, torch, and welder, a shop could have you out the door in an hour, generally for a pretty reasonable price. It would require a great deal more pain and suffering to do it yourself on your back.

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All true except for the "out the door in an hour, generally for a pretty reasonable price" part. A '97 with a 454 should have two catalytic converters, and the whole mess is unreasonably priced.

If your exhaust is rusted, it's probably non-original. The original pipes were stainless steel. They get replaced with "aluminized" steel tubing, and that lasts about three years and rots to pieces.

When it was me, I installed all four O2 sensors which killed about six codes that previously would re-set after being cleared. The sensors were about $90 for the four, combined. I had to clean-up the damaged threads in the pipes because the sensors I took out were (probably) 160K-mile originals.

Carlaisle said:

There's a lot of performance that can be wrung out of the exhaust on that engine, but you need long tube headers to make it worthwhile. If you're not going to put them in, you might as well just replace what needs replaced and call it good.

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I don't think this is right. The WORST part of the original exhaust was the MUFFLER. It was horribly restrictive. 2 3/4 pipe inlet, necked down to about 2" internally.

Buddy of mine bought a '97 K2500 that had stock exhaust in good condition. He scrapped the muffler, and said it made WAY more difference than the very expensive Gale Banks headers he installed later.

My '97 had an aftermarket muffler that was totally blown-out when I bought the truck. I installed a different muffler and tail pipe, but I never had the original muffler to compare to. 'Course, this may be the situation for the OP as well, if his exhaust is rusted badly, it's probably not original.






I said previously that you need to fix the exhaust leaks from the converter forward. That was not correct. You need to fix the exhaust leaks from the muffler forward, because the rear O2 sensors should not be allowed access to air, which would screw-up their output and potentially set a code.

I don't think my truck has mufflers (not surprising based on how it sounds), underneath there's 2 entirely separate pipes for each side of the block - plain pipes from the block to what I'm mostly sure are catalytic converters (O2 sensors before and after them), and then plain pipe all the way to the end (2 separate outlets even). It makes sense that it's not stock.

Schurkey said:

All true except for the "out the door in an hour, generally for a pretty reasonable price" part. A '97 with a 454 should have two catalytic converters, and the whole mess is unreasonably priced.

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A shop replaced mine with custom bent pipe from the manifolds back in an hour and a half, but it was a really good shop and the guy could have been on drugs.

"Reasonable" is relative, but I could have spoken more clearly. New parts cost what they cost. Compared to me buying the pieces and crawling around underneath the truck, cutting out all old junk and then wrestling the new stuff in and getting it connected I thought what I paid to have it done for me was a very reasonable price.

Schurkey said:

I don't think this is right. The WORST part of the original exhaust was the MUFFLER. It was horribly restrictive. 2 3/4 pipe inlet, necked down to about 2" internally.

Buddy of mine bought a '97 K2500 that had stock exhaust in good condition. He scrapped the muffler, and said it made WAY more difference than the very expensive Gale Banks headers he installed later.

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No doubt the OEM muffler is a choker, but I've never heard anyone say the muffler made a bigger difference than long tube headers. Interesting.

To get the exhaust replaced, should I go to any kind of shop in particular (aftermarket, specialty, chain shop), or should any shop that does exhaust be good? And do any of you know of a good shop in NY tri-state area?

You need to decide what you're going to be satisfied with.

Aluminized steel is cheap and short-lived. Stainless steel is expensive and durable. Some grades of stainless polish nicely for that "show-car" look--and some don't.

Mandrel bends flow nicely. Crush-bends are a flow disaster. I don't know of any "muffler shop" that can do mandrel bending. I bet there aren't a dozen mandrel-bending exhaust shops in the whole USA. Practically every shop uses a hydraulic crush-bending machine. If a shop offers mandrel bends, they're almost certainly buying the bends from an outside supplier, and then welding them to sections of exhaust pipe.

An alternative to having a "muffler shop" custom-make an exhaust system for you, you could go onto Summit or Jegs--or your local NAPA or Advance or O'Reillys and buy exact-fit aftermarket replacements for your pipes ready to bolt in place. Either install them yourself, or talk to the shop you'd be hiring to see if they're willing to install parts you've supplied. You may get the speech about "do you bring raw steak and eggs to a restaurant and have them cook 'em?" and that's a valid response. When I was parts-shopping on Summit for the exhaust on my truck, the exact-fit replacement stuff was going to run well over a thousand dollars; but that included two catalytic converters--one in each pipe, plus the muffler/tailpipe, gasket, and four O2 sensors.

Some examples which may or may not be correct for your vehicle.
https://www.summitracing.com/parts/mpe-95470/overview/year/1997/make/chevrolet/model/k2500
https://www.summitracing.com/parts/wlk-50430/overview/year/1997/make/chevrolet/model/k2500

https://www.summitracing.com/parts/mpe-95471/overview/year/1997/make/chevrolet/model/k2500
https://www.summitracing.com/parts/wlk-50308/overview/year/1997/make/chevrolet/model/k2500

Aside from exact-fit aftermarket pipes, there's the semi-universal stuff, and that tends to be less expensive.







In the end, what I did was keep my original catalysts and pipes, and merely replaced the sensors, muffler and tailpipe. SO FAR, the catalysts seem to be OK, which somewhat surprised me as I had a dead-miss in cylinder #8 when I bought the truck. I stole the OEM stainless steel single-inlet muffler and single tailpipe from a salvage-yard vehicle, and used a 2-into-1 "Y" pipe to connect it to the existing twin converter pipes.
https://www.amazon.com/gp/product/B07BK5H4DT/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Welded it all together with some shims because the original pipes are 2 3/4 which is an uncommon size. What I did is not for everyone. Probably wouldn't work well in a rig that tows heavy loads, but I'm just pushing snow with it, so I never really need more than half throttle. (and the noise of the blown-out muffler was making me barking insane. Now it's nice 'n' quiet.) It's all stainless, so it'll be there awhile. Including the $90 for the O2 sensors, but not counting my labor or the M18-1.5 taps and re-threading tools, I don't have $175 in this.

Schurkey said:

Some examples which may or may not be correct for your vehicle.
https://www.summitracing.com/parts/mpe-95470/overview/year/1997/make/chevrolet/model/k2500
https://www.summitracing.com/parts/wlk-50430/overview/year/1997/make/chevrolet/model/k2500

https://www.summitracing.com/parts/mpe-95471/overview/year/1997/make/chevrolet/model/k2500
https://www.summitracing.com/parts/wlk-50308/overview/year/1997/make/chevrolet/model/k2500

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What's the difference between the Walker and Magnaflow brands, why is Magnaflow $100 more? And it asks me for cat placement, why does it have 6 options (driver, pass., left, right, front, rear)? Mine are under the passenger side, but why does it only 'fit' if I select Rear?