84 K10 Hates its New Exhaust: Help!

[SourTooth307]

Saturday afternoon I installed a custom exhaust system on my 84 K10 and now it runs awfully......

The truck was running with a set of Flowtech headers, and some flex pipe that ended right after the cab making for a pretty loud (and illegal in NJ) exhaust system. I added new Flowtech headers, two new Flowmaster universal cats, and two Dynomax super turbo mufflers with outlets ahead of the rear wheels. I also installed new AC Delco sparkplugs and wires since when ignition wires come off, they don't like to go back on.

Now I have a truck that pops, backfires, and sputters when you try to move it. It basically limps everywhere it goes and I'm not sure why. I'm hearing things like the timing, or the Edelbrock carb I have on it is the wrong application, but if all these things were true, why would it have ran beautifully before the change? I've never seen an exhaust system have this kind of effect on a vehicle before. Any help would be greatly appreciated. Thanks.

[1981Stepside]

Sounds like it might be a crossfire. Perhaps one of the new leads got burnt and it arcing out on the headers or block?

[old Rusty C10]

are you sure you got the firing order right? are the wires loose in the cap or on the plugs? did you use the right plugs?

[SourTooth307]

Yeah I know the firing order is right, I went online and verified it. I think I might have my answer though. The old headers (same style) were wrapped in a fabric tape about the thickness of a belt. I think this was providing a barrier between the headers and the ignition wire boots and prevented arching or shorts since they're so close they actually touch. I'm going to rewrap the headers when I get home and try again. Crossfiring is what it feels like is happening. I'll prolly change the cap/rotor too just for fun since I did everything else......

[gramps77]

firing order. If its backfiring, AND sputtering, youre firing order isnt correct.
What kind of plug wires did you install?
Its fairly rare for it to be plug wires these days.
If your plug wires are not insulated AND touching your headers, youre gonna melt one of them, ask me how I know. Wait, dont do that

[donut]

May as well look for cooked wires also...

May still have the old set that melted out in a bucket.

[walkerb]

Mufflers on backwards?

[TheBlueBomber]

I had this same problem with my 305 when I replaced wires... i swore up and down that I had the firing order correct and I did!!! It just so happens the dizzy was off by one. So I my order was "right" but it was just one spot off the dizzy lol...

[SourTooth307]

Originally Posted by walkerb

Mufflers on backwards?

Now that's an idea. How do you tell which part goes on first? I think I have the offset part facing the front, and the centered part facing back.

[walkerb]

There should be an arrow pointing towards the back of the muffler. Might even be the cats too

[SourTooth307]

Originally Posted by gramps77

firing order. If its backfiring, AND sputtering, youre firing order isnt correct.
What kind of plug wires did you install?
Its fairly rare for it to be plug wires these days.
If your plug wires are not insulated AND touching your headers, youre gonna melt one of them, ask me how I know. Wait, dont do that

I installed a set of AC Delco heavy duty pregapped plugs and Autolite wires. It was doing this before I changed them out though. I had to remove the wires when we changed the headers and I'm pretty sure I put all the wires back the way I found them. I even made sure I kept that order when I installed the new set by doing it one plug, one wire at a time. I found a diagram of a 350 from 1984 (assuming that I have a stock engine) online and even made sure I had it set up the right way. I know my truck originally had a 305 but it was swapped out for a 350 by one of the previous owners and from the looks of things under the hood it looks like a GM 350 engine. I'll have to check it again when I get home from work but I'm 99.9% sure I have it right.

I honestly didn't know mufflers could be installed backwards, we did it that way for fitting reasons. If that's all it is I'm gonna feel really stupid......

[SourTooth307]

Originally Posted by walkerb

There should be an arrow pointing towards the back of the muffler. Might even be the cats too

The cats had arrows so I know we put those on right. The mufflers I'm pretty sure we have on backwards......

[SourTooth307]

http://www.summitracing.com/parts/wlk-17731/overview/

These are the mufflers I used. According to the description the inlet is offset and the outlet is centered. If that's the case I have them on right. Back to checking the firing order I guess.....

[walkerb]

Bummer. Guess its not the "easy" fix.

[walkerb]

You think the distributor may have moved putting the wires back on?

[66/87chevy]

Originally Posted by SourTooth307

I installed a set of AC Delco heavy duty pregapped plugs and Autolite wires. It was doing this before I changed them out though. I had to remove the wires when we changed the headers and I'm pretty sure I put all the wires back the way I found them. I even made sure I kept that order when I installed the new set by doing it one plug, one wire at a time. I found a diagram of a 350 from 1984 (assuming that I have a stock engine) online and even made sure I had it set up the right way. I know my truck originally had a 305 but it was swapped out for a 350 by one of the previous owners and from the looks of things under the hood it looks like a GM 350 engine. I'll have to check it again when I get home from work but I'm 99.9% sure I have it right.

I honestly didn't know mufflers could be installed backwards, we did it that way for fitting reasons. If that's all it is I'm gonna feel really stupid......

OK so are you saying the truck was running like this before you changed out the exhaust, wires, and plugs ???

[SourTooth307]

Originally Posted by 66/87chevy

OK so are you saying the truck was running like this before you changed out the exhaust, wires, and plugs ???

No, the truck ran beautifully when I drove it over to my friend's place with the old exhaust system which consisted of Flowtech headers, some flexpipe, and what looked like a couple old Cherry Bomb mufflers that ended right after the cab. We disconnected the spark plug wires and removed the whole exhaust system. Then we replaced the headers with the same brand and style and added two universal fit cats and two mufflers before replacing the old wires to their respective locations. After doing all that the truck ran like crap. Then just to make sure we didn't damage any of the ignition wires when we popped them off, I replaced them along with the plugs for good measure.

[SourTooth307]

Originally Posted by walkerb

You think the distributor may have moved putting the wires back on?

I suppose anything is possible, I tried to be as careful as possible when handling everything. I wonder if the truck can have some kind of custom firing order other than the factory spec. I noticed someone had hand written the cylinder numbers on the distributor cap but I didn't pay them any mind feeling confident I had the wires plugged in right according to what I read.

Here's the diagram I used.....

[KQQL IT]

I'd make #1 is #1 on the cap.
Or pull the distributor and start over.

[nekkidhillbilly]

Originally Posted by walkerb

Mufflers on backwards?

that only works with something like a flowmaster that isnt a straight through.

[KQQL IT]

I'd make #1 is #1 on the cap.
Or pull the distributor and start over.

[SourTooth307]

Originally Posted by KQQL IT

I'd make #1 is #1 on the cap.
Or pull the distributor and start over.

Yeah the colors on the diagram are really hard to distinguish so I printed it out in black/white and wrote the numbers on the diagram of the cap and drew the wires on. Even distinguished each one with a Hi-Liter. I did this last on Saturday night so who knows, I might've traced a wire incorrectly and assumed it was right. I know I didn't make any corrections but maybe I have to......

[66/87chevy]

I'd bet your wires are all off by one on the distributor. I've done this same thing before. Start with #1 on the cap and go all the way around. Good luck!!!!!

[SourTooth307]

You'll hear one way or another. Lol.

[SourTooth307]

Well'p....... I had cylinders 7 and 5 mixed up and the mufflers are on backwards.....

I swear I'm a much better mechanic than this. I've got an excellent running 89 Cadillac to prove it. Lol. Thanks for the help guys, I really appreciate it.......