So I'm working on tracking down some
Back fire issues. The other day I went out for a cruise hit the highway in 3rd brought
Her up to redline and hit 4th. Let out a BIG backfire/flame. As you all may know a racing beat stuff ain't cheap so I don't wanna blow a muffler up.

So I started messing around today changing some vacuum lines just
To eliminate that. I have a racing beat full exhaust with ACV still intact.

So this week I will check my exhaust bolts although I just checked them a month or so ago before my last track day. I'll finish changing my vacuum lines.

Is there any other place I should look if the above mentioned doesn't fix my backfire issue?

Thanks guys.

 

You won't blow up a RB exhaust system, so don't sweat that. Checking your exhaust for leaks is the right move. You have cats? You mentioned the ACV was still on there. Make sure that system is functioning as designed too.

 

I ran my RB road race exhaust for years without any of the emissions equipment and always had nasty afterfires on deceleration. Absolutely no harm to the exhaust.

Is your throttle dashpot working? It's my understanding that this should help prevent an overly-rich mixture when letting off the throttle.

 

Full header back with presilencer. It all seems to be working. I'll have to double check though.

 

I've been having the same issue with my SE since I put my RB full exhausts, long tube headers, pre silencer, PP muffler and the factory connecting pipe. I too have all my factory emissions stuff. After much looking about to find a leak, I had my wife plug the exhaust with welding gloves and was able to find a leak between the connecting pipe and the muffler at the top of the flanges. No matter what I did it would not seal. It appears that somehow the top of the connecting pipe flange to the muffler is "worn out" and won't seal. I also found some leaking around the gasket between the connecting pipe and pre silencer. But that was my fault for reusing a used gasket there.
I just got the two gaskets today. I also sourced another connecting pipe with a very flat flange. We'll see if it finally seals.

 

Sometimes doubling up on the gaskets can seal it up. Also make sure the exhaust is supported well on both sides, theres hanger at the end of the presilencer and one on the muffler neat the back axle.

 

Yes, I think I will order two more new gaskets and try to see what happens by doubling them up. I put it back together today and the two points i mentioned before still leaking. A lot less, but still leaking. I could not get the connecting pipe hanger earlier because it was connecting pipe part was to low from the hanger. But I was in a bit of a rush and I think I just failed to push the muffler forward and up to kinda tuck it in, which should push all the connections together better and bring that hanger up without and the whole system up, without putting pressure up on the joints that makes it want to open the joints at the top. But that will have to wait till the weekend. Into then I am open to suggestions. Especially from those who change their exhausts often for smog tests.

 

Important to inspect hangers as they stretch as they age. Experience has shown it to be best to replace all the hangers when installing RB system-especially streetport system due to its weight. Even though hangers may not be missing/broken,they will be sagged enough that weight of system is stressing joining hardware/gaskets causing stress to gaskets and premature failure.The hangers are not cheap-consider them an investment in prolonging your exhaust system life
My current streetport system on my SE(the 1st with stainless muffler) had a small leak at the joint from presilencers to muffler. I resolved this by removing muffler and using a file,found hi spots on rear presilencer flange. Sanding flange with sandpaper wrapped around a 2x4 block of wood til all hi spots knocked down and flange even. New gasket and reassemble,been good for 2+years now.

 

Is to get all of the exhaust components in place, loosely - then put a floor Jack under the Presilencer and raise it slightly until everything is tucked up nice and neatly, THEN go through and tighten everything down. This helps to keep it all tucked in neatly, and ensures that the joints are as flat to one another as intended. Also, those 2 rubber rings at the front of the rear connecting pipe can be overlooked and carry a lot of the weight of the middle exhaust components. I've found this method also works well to ensure your exhaust doesn't pull on the engine, torquing it slightly which will tend to wear on the passenger side engine mount.

Give that a shot and see how it goes,

 

I do this as well. It really helps get eveything tucked up and in there.

 

Thanks for all the suggestions. I did clean and sanded all the joints. But I definitely will get new hangers as mine are pretty saggy and stretched out. Definitely will try the jack under the pre silencer. I truly appreciate your advise, knowledge and experience guys.

 

Was reading through the 1984 Factory Training Model (*not FSM) the other night and it explained how the split air pipe works with the ACV on decel to keep fresh air going to the cat through the one-way valve built into the feed, which also provides the air pressure signal (~4-6psi) to operate your 6-port induction on an SE. If the ACV is clogged up or not flowing air properly between the exhaust ports and the split air pipe, it could be supplying fresh air from the air pump into the hot exhaust downstream where it would combine with unburned fuel to cause backfiring.

I'd be very surprised if any exhaust leaks that far back would result in backfiring - you'd really need fresh air being pumped where it doesn't belong to make that happen (*combined with an overly rich mixture: leaky fuel injectors, bad intake air temp or coolant temp sensors, or bad AFM z in that order). Curious if you got that resolved,

 

Another quick thing; the Dashpot located to the left of the Throttle Body looking at it from the PS (right next to the firewall), is there to slow the closure of the Butterfly Valves in the intake when you let off the throttle quickly. Instead of allowing the butterfly valves to slam shut, that Dashpot (looks like a steel mushroom with a metal plunger sticking out the end) has a spring and a diaphragm inside that slowly returns the throttle body rods back to idle position over the course of 2-3 seconds.

In the event that the Dashpot is bad, it could be allowing the throttle body butterfly valves to slam shut, which would dramatically cut air supply having the effect of creating a rich mixture in your exhaust. Perhaps combined with my prior post, this could lead to backfiring.

Something else to think about and literally faster to check than to explain; rotate the main throttle body rod off of the idle position and release it. See if it just snaps shut on release, or if it slowly returns to idle position. Good luck,

 

First, sorry to the OP for high jacking your thread. LongDuck, I haven't had the chance to do anything with the car these past days. Crazy hours of work. But Monday/Tuesday I plan to (my weekend). I will start my own thread once I figure something out or get stomped. But thanks again for being there, sir.

 

I haven't had a chance to take a peak. Don't worry about hijacking the thread. Seems we have similar issues. Hope to tackle mine this week!

 

ACV carbon,diaphragm high on my list if exhaust leaks eliminated. Exhaust leaks don't have to be loud enough to be heard for air to get in...

 

Love this community. Thank you all. I will post progress hopefully by Tuesday.

 

My SE is backfiring also when taking foot off the gas. Looks to be a stock exhaust with a pace setter muffler. Don't know if it is a new development or a long existing issue as I haven't had it long. This post is a great help and will do some checking on exhaust leaks and the other suggestions on here with the hangers. Is it a good idea to just replace all the gaskets anyhow as long as I am messing around with it. Did you get yours resolved?