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1986 Bronco, 351w, Edelbrock aluminum top end, Holley 600, 4" BDS lift, 35" Maxxis Razr's, stuff..
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I just mentioned flex pipe since it would be cheap and easy to test until you do you final exhaust fixes. Good luck!


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95 5.8L MAF XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Man hubs, KYB Quads, 31x10.5x15, 301K miles
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You have some really weird pressure fluctuation going on there. It's going from pressure to vacuum and back. I never saw that on the exhaust before. Are your plug wires hooked up correctly? What is your timing set at? Is your TDC mark accurate? There shouldn't be any vacuum in the exhaust. Back to the question I asked earlier about Cam installation timing?
 

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Premium Member
1986 Bronco, 351w, Edelbrock aluminum top end, Holley 600, 4" BDS lift, 35" Maxxis Razr's, stuff..
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2,475 Posts
Remember - this was a new issue, something changed to make this happen.


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1980; 347 stroker; Holley Sniper EFI
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230 Posts
Discussion Starter #84
You have some really weird pressure fluctuation going on there. It's going from pressure to vacuum and back. I never saw that on the exhaust before. Are your plug wires hooked up correctly? What is your timing set at? Is your TDC mark accurate? There shouldn't be any vacuum in the exhaust. Back to the question I asked earlier about Cam installation timing?
I might get a timing light to check. I have been experiencing diesling so I want to check the timing anyway. I am quite certain the wires are fine and the cam shaft is not retarded. Maybe this guage us faulty? Ita just a cheap one from Amazon, i wish I had another car or someway to check the gauge. I am going to do the exhaust stuff first and see what happens
 

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1980; 347 stroker; Holley Sniper EFI
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230 Posts
Discussion Starter #85
You can then do the same thing after the Cats to see if there is any restrictions in the mufflers if you want to really analyze your whole exhaust.
The issue has been solved, thanks everyone for all the advice. As a few people mentioned, one of the cats had completely crumbled apart and it created a restriction in one of the Y pipes. I got lucky and cut the exhaust right at the clog, so I was able to pull all the crap out. I cut both cats out and welded in new straight pipes and also replaced the headers. I don't think I have any more exhaust leaks and I got my acceleration back! I will have to add cat(s) back in at some point, so I will be back for more exhaust advice.
 

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78 Custom - 460 - NP435 - NP205 - Sniper EFI - HyperSpark Ignition - 4.56 Gears - Front/Rear Lockers
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Cool beans.

So when you say it was clogged, clogged with what? Was it just the contents of the inside of the cat falling apart or..? I'm not familiar with cats, so I'm just curious.
 

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1980; 347 stroker; Holley Sniper EFI
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230 Posts
Discussion Starter #87
Cool beans.

So when you say it was clogged, clogged with what? Was it just the contents of the inside of the cat falling apart or..? I'm not familiar with cats, so I'm just curious.
Yeah exactly, the contents of the cat. When I cut the cat out it was completely hollow - all of metal foil stuff broke out and that's what created the clog. Looks kinda like a metal honey comb
 

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95 5.8L MAF XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Man hubs, KYB Quads, 31x10.5x15, 301K miles
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If and when you put a Cat(s) back in you only need one Hi-Flow not 2 unless you wanna spend your money. I'm glad you worked it out, always start with the basics and work your way up to the complicated.
 

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95 5.8L MAF XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Man hubs, KYB Quads, 31x10.5x15, 301K miles
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Did you check the mufflers to see if any Cat material made it into them? Just bang on the mufflers with a rubber mallet or you fist to see if there is any rattling inside.
 

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1980; 347 stroker; Holley Sniper EFI
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230 Posts
Discussion Starter #90
Yeah I cut them out, shook them out and blew most of the depris out with a shop vac. Pretty sure I got most of it
 
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