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Al_C
09-14-2020, 05:08 PM
Time for some comic relief: i.e. my issue/question. We all have strengths and weaknesses; mine is diagnostics. With repair being a close second. Doing it from scratch is one thing, fixing it quite another!

As you may recall, I was more or less stuck in my driveway thanks to the highway department's decision to grind down our street and re-pave it. Well, the good news is that they finally put down the first layer on Friday. Then it started raining. It finally quit raining on Sunday, so out we went. The car hadn't run in a week or 10 days, so when it started making noises I figured it was just in need of cleaning itself out. We went out again today and I decided something was not quite right - snap, crackle, pop. And a few backfires mixed in for good measure. I usually expect (and tend to enjoy), the noises the car makes when the rpms come down, but this was in another league. And, all the noises seem to be emanating from the passenger side.

On to the diagnostic part. I can't see anything looking down through the engine bay, in through the side vent, or looking under the car. My suspicion is one of these: j-pipe cracked, j-pipe loose from the header, or a bad gasket somewhere between the header-j-pipe connection and the side pipe. Knowing that others have had issues with j-pipes cracking, I installed turnbuckle braces on both sides with the intention of preventing those cracks. Who knows...

So what is your experience? What would cause excessive popping and some backfires on one side of a slowing engine?

I'd like to get the car up in the air, so to speak, so I can better see what's going on. (your input will help in that regard, too!) To that end, my friend Greg told me that he just installed a four post lift and he wanted somebody to use it! He lives 5 minutes away. That was Sunday's trip. The goal was to get it up in the air and deal with the bell housing issue. You've heard about best-laid plans? Greg's driveway is uphill to his garage just enough that the rear end of the car is too low to get over the lift's cross-member. (The top of the cross member is 5 inches off the floor). As you'd expect, the side pipes scraped along the ramps and the bell housing hit the cross member. The solution, we believe, is to make some 8 or 10 foot ramps out of lumber so the grade is less. Now I have two things to deal with when I go back over there...

Jeff Kleiner
09-14-2020, 06:55 PM
Your turnbuckles should be keeping the J pipes stabilized but I suppose a crack is still possible, especially with the brittle stainless, but I think a more likely culprit is a gasket at the 4 port connection. I don't remember now whether I had to use any wedges or spacers but if so that doubles (or even triples) the possibility. I always enjoy your good attitude and humor when reporting the minor issues you encounter!

Be well my friend :)

Jeff

FF33rod
09-14-2020, 07:00 PM
So what is your experience? What would cause excessive popping and some backfires on one side of a slowing engine?



Had that exact problem when I first put together my 347. Started fine and then after a few seconds it would go crazy with snap, crackle and pop. I was distracted by the Sniper technology which actually had nothing to do with it. I found I had the ultimate intake manifold leak - I had left a port open on the rear of the manifold (difficult to see). The manifold is dual plane and the port was only in a single plane affecting 4 of the 8 cylinders. Good for a laugh in the end. Sounded so nice once fixed up.

Good luck with your diagnosis!

Steve

Jdav
09-15-2020, 12:40 PM
My guess is j-pipe crack. I had similar sounds when mine cracked (even with turnbuckles on)

Al_C
09-15-2020, 02:43 PM
My guess is j-pipe crack. I had similar sounds when mine cracked (even with turnbuckles on)

Unfortunately, I'm not going to be able to inspect it until the weekend. I like Jeff's assessment because that's an easier fix, but I'm planning on the worst case. JDAV, you ended up replacing your j-pipes with full length headers, yes? I have to dig out your thread on that topic...

wareaglescott
09-15-2020, 07:36 PM
My guess is j-pipe crack. I had similar sounds when mine cracked (even with turnbuckles on)

yep me as well

Al_C
09-21-2020, 04:47 PM
Well, we were all wrong. Check out the photo. It's the forward j-pipe to header bolt on the passenger side. Note the hole where a bolt should be! (sorry about the delay - I was out of town...)

https://thefactoryfiveforum.com/attachment.php?attachmentid=135371&d=1600723795

My plan is a) get new bolt, b) install new bolt, c) drive. I've been looking in the manual and on the inventory sheet for the specs on that particular bolt. I THINK it is 5/16-18 x 1.5 (flange), but I'm not certain. (the documentation is less than clear on this topic)

Anybody know for sure?

Jdav
09-21-2020, 05:20 PM
That's good news Al - definitely the easiest and cheapest fix!
I think it's a 7/16-14 (at least for the BBK shorty headers that came with my kit), but someone else might be able to confirm

In case you or anyone else following wants to do the full length swap, here's my post on it:
https://thefactoryfiveforum.com/showthread.php?36556-Swapping-Coyote-Headers

steno
09-22-2020, 07:49 AM
You might want to put a bit of high temp RTV in the joint just to be safe.

nuhale
09-22-2020, 08:08 AM
Glad to hear just a bolt... get that torque wrench out and get back out there!

kobra01
09-22-2020, 12:32 PM
What should the 2 nuts that connect the j pipe to the header be torqued to?

rich grsc
09-22-2020, 12:52 PM
Gud-n-tite

AC Bill
09-22-2020, 01:40 PM
Does that flange take a nut and bolt, or is it pre-threaded for a bolt only?

Use a stover nut if a bolt and nut is used, it won't ever back off.

Al_C
09-22-2020, 01:46 PM
What should the 2 nuts that connect the j pipe to the header be torqued to?

I believe the standard for a 7/16-14 bolt is 48 lbs. of torque.

Al_C
09-22-2020, 01:48 PM
Does that flange take a nut and bolt, or is it pre-threaded for a bolt only?

Use a stover nut if a bolt and nut is used, it won't ever back off.

The header itself is threaded. I have a grade 8 bolt with a flange head to install.

rich grsc
09-22-2020, 06:02 PM
Never use a stover nut on an exhaust stud. You will all most always break the stud or have it come out of the flange. Use brass nuts on exhaust studs.

AC Bill
09-22-2020, 06:27 PM
Never use a stover nut on an exhaust stud. You will all most always break the stud or have it come out of the flange. Use brass nuts on exhaust studs.

Yes, never on a stud. I meant they could be used with a bolt, to hold a flange together.

rich grsc
09-22-2020, 09:30 PM
Same difference, don't.

Al_C
09-23-2020, 10:23 AM
No nuts involved here (only the one turning the wrench...). Everything is nice and tight. While the car was up on stands I checked the DS, too. They were considerably looser than when I had originally mounted them. Tightened them, too. Everything sounds "correct" now.

Lesson: check these every few months. Or, figure out why they get loose and fix that. My only explanation is expansion/contraction from the heat. Vibration is negligible on this engine.

phileas_fogg
09-23-2020, 03:25 PM
...My only explanation is expansion/contraction from the heat...

That's where the brass nuts Rich is telling you about come in. Different material = different expansion rate, so they don't come loose. Since they're brass, I follow Jeff Kleiner's advice & get the extra long type: https://www.napaonline.com/en/p/NDP6001800


John

P.S. I think your idea about checking them every couple of months is spot-on.