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1980; 347 stroker; Holley Sniper EFI
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Discussion Starter #1
I recently took the Bronco on a long drive to pick up a small boat/trailer, it was about 5 hours each way. On the way home I had a lot of trouble accelerating at on-ramps, but was fine at cruising speeds. At first I thought it was because of the trailer but it really wasn't that heavy. It sounded really loud when I was trying to accelerate, sounded a lot like an exhaust leak. Acceleration problem persists today without the trailer, so I know its not that.

I can't seem to find this exhaust leak from a visual inspection, so it must be pretty small if there is one. Is it possible that a really small exhaust leak could cause a loss in power/acceleration? I can only hear the exhaust leak sound when the throttle is opened up, like after a red light (not when I'm cruising). What is the easiest way to locate an exhaust leak? I have two tail pipes. What other things should I be looking at?
 

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95 5.8L XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Manual hubs, KYB Quads, 31x10.5x15's, 301K miles
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Do you have a Cat(s)? and not a Pussycat.
 

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1980; 347 stroker; Holley Sniper EFI
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Discussion Starter #3
Do you have a Cat(s)? and not a Pussycat.
I do have one. At least I think I do (see pic), it looks like a catalytic converter but also looks kinda small. I also have two mufflers and two tailpipes to make locating the issue even harder

162470
 

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95 5.8L XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Manual hubs, KYB Quads, 31x10.5x15's, 301K miles
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If your Cat is clogged or becoming clogged it will start showing up under load and will create exhaust leaks upstream of the cat. You will need to use more and more throttle to keep up speed under load/going up hill/pulling away from a light or stop sign.
 

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1980; 347 stroker; Holley Sniper EFI
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Discussion Starter #5
If your Cat is clogged or becoming clogged it will start showing up under load and will create exhaust leaks upstream of the cat. You will need to use more and more throttle to keep up speed under load/going up hill/pulling away from a light or stop sign.
Is there anyway to test if the cat is clogged? I would just replace it but it looks like its welded in
 

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95 5.8L XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Manual hubs, KYB Quads, 31x10.5x15's, 301K miles
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It looks as if that one is in one half of the Y-pipe from the driver's side and is right under the engine/trans, not a very good place for it and where is the one on the passenger side pipe of the Y-pipe? When they get or are getting clogged they get really hot. If it is clogged you'll have to cut it out and replace or whatever you want to do. There is usually a cat at in the end of the Factory Y-pipe and some Aftermarket Y-pipes, So the question stands, why would you need that one or why is it in that location and where is the other one?
 

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1980; 347 stroker; Holley Sniper EFI
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Discussion Starter #7
It looks as if that one is in one half of the Y-pipe from the driver's side and is right under the engine/trans, not a very good place for it and where is the one on the passenger side pipe of the Y-pipe? When they get or are getting clogged they get really hot. If it is clogged you'll have to cut it out and replace or whatever you want to do. There is usually a cat at in the end of the Factory Y-pipe and some Aftermarket Y-pipes, So the question stands, why would you need that one or why is it in that location and where is the other one?
I just took another look, and yeah you're right - there is two cats on each side of the Y-pipe. The passengers side goes up and the cat is near the starter, the drivers side crosses under the transmission. I couldn't tell you why its routed that way, it was a custom built exhaust that the PO put in.

I attached a couple more picture, sorry the pictures suck. Its dark and cramped under there.

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78 Custom 351M NP435 NP205 Sniper EFI Hedman Headers Magnaflow Muffler 4.56 Gears Grizzly lockers
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Not trying to bash or anything, but that exhaust setup looks terrible and could be improved a lot. Is it y-ing together and then y-ing back apart?
 

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1980; 347 stroker; Holley Sniper EFI
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Discussion Starter #9
Not trying to bash or anything, but that exhaust setup looks terrible and could be improved a lot. Is it y-ing together and then y-ing back apart?
Bash away, I didn't build or isntall it. and that is exactly what happens, the two Y's are about 1 foot apart, maybe because there wasn't space for two pipes under the cross member? (see picture)

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Space is the reason its built like that. But also, they could've done it better. You only need one cat on the single pipe, then a single in dual out muffler.

Are you sure the noise is exhaust and not a loose rocker arm or dead lifter? They can sound similar. Fire the engine up and take a 2'-3' long piece of pipe or tube and use it as a stethoscope to pinpoint the location of the sound. Exhaust leaks don't cause power loss.
 

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Discussion Starter #11
Space is the reason its built like that. But also, they could've done it better. You only need one cat on the single pipe, then a single in dual out muffler.

Are you sure the noise is exhaust and not a loose rocker arm or dead lifter? They can sound similar. Fire the engine up and take a 2'-3' long piece of pipe or tube and use it as a stethoscope to pinpoint the location of the sound. Exhaust leaks don't cause power loss.
Not positive at all if its an exhaust leak, just thought it sounds kind of like one. I read somewhere that an exhaust leak will create less back pressure and can reduce power? But I really don't know.

Only probably with locating it, is when its idling I cant really hear it. Its only when its under load, like accelerating or up hill, so that makes locating the sounds really hard to pin point
 

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95 5.8L XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Manual hubs, KYB Quads, 31x10.5x15's, 301K miles
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If your engine is basically stock there is no need for 2 high flow cats and 2 Y-pipe junctions with 1 pipe connecting the 2. That 1 single pipe is the restriction in the exhaust if you want to call it a restriction. Anyway that cat going under the Trans is COOKING the Trans and the Fluid, not a good thing. You should/could replace the forward homemade Y-pipe and the 2 cats with an Aftermarket Y-pipe and connect that to the existing rear part of your exhaust. You can purchase a Catted Y-pipe or a Non-Catted Y-pipe whatever your heart desires, that is IF your cats or a cat is clogged.
 

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Yo Ian,
Loss of power by Ford;
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Iggie quick test ( for diagnostic trouble codes, VAF meter, Fuel Pressure Regulator, injectors, fuel sender. Injectors, suler charger, turbocharger, etc as required.
See Vacuum leaks test, general for carbed vehicles @ Make vacuum leaks hiss-tory
Iggie EFI INFO.

Ask for other component tests if vacuum leak is resolved.

1980-1986 F Series/Bronco Carburetors, Chokes & EFI by Gary

1980 Bronco Fuel System Illustrations by Gray @ 1980-84 F-Series & Bronco


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Contact Walker fir info on your Bronco;
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1980; 347 stroker; Holley Sniper EFI
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Discussion Starter #14
@BigBlue 94 come to think of it, I do have what could be some lifter noise when its idling. You replied to my other thread about adjusting the timing because of knock/dieseling. This 'knock' sound could be lifter noise maybe? I will try and get a video so you can hear the sound it makes when I'm accelerating.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Not positive at all if its an exhaust leak, just thought it sounds kind of like one. I read somewhere that an exhaust leak will create less back pressure and can reduce power? But I really don't know.

Only probably with locating it, is when its idling I cant really hear it. Its only when its under load, like accelerating or up hill, so that makes locating the sounds really hard to pin point
Backpressure only helps with fuel economy... A top fuel dragster has absolutely zero backpressure and they make thousands of HP.

An exhaust leak shouldnt get louder under load. Only with rpm.

A dead/collapsed lifter, bent pushrod, or loose rocker will indeed destroy power.

I bought a 90 F150 with a lifter tick once. Low oil seemed the culprit. Threw a few quarts in and drove an hour home. It never would get above 60. Got home, swapped the bald 33" boggers out for 31" street tires and drained a quart of sludge out of the oil pan and some oil. Did a full oil change, and the lifters cleaned themselves of sludge and pumped back up. Truck would do 90mph now and no issues.

I was driving a 79 z28, at nearly double the speed limit on the highway when the 350 bent a pushrod and valve, and the rocker arm rotated 90°. Power went down so far I could barely make it home.
 

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Discussion Starter #17
Backpressure only helps with fuel economy... A top fuel dragster has absolutely zero backpressure and they make thousands of HP.

An exhaust leak shouldnt get louder under load. Only with rpm.

A dead/collapsed lifter, bent pushrod, or loose rocker will indeed destroy power.

I bought a 90 F150 with a lifter tick once. Low oil seemed the culprit. Threw a few quarts in and drove an hour home. It never would get above 60. Got home, swapped the bald 33" boggers out for 31" street tires and drained a quart of sludge out of the oil pan and some oil. Did a full oil change, and the lifters cleaned themselves of sludge and pumped back up. Truck would do 90mph now and no issues.

I was driving a 79 z28, at nearly double the speed limit on the highway when the 350 bent a pushrod and valve, and the rocker arm rotated 90°. Power went down so far I could barely make it home.
I will do an oil change and use some lifter noise additive tomorrow and check the ticking noise.

I am assuming I can just remove the valve cover to take a look, it would at least tell me if the rocker arm is rotated. Can I run the engine with the valve cover off to see if the rocker arms are all moving or will oil fly everywhere?
 

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I see you have a 347 so you don't have a stockish engine. What size cam is in the engine? What is it's Rpm range it was built for? Low rpm, mid rpm or high rpm? What gears and tire size? What stall Torque converter? How many miles on the engine? The Cats?
 

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Discussion Starter #19
I see you have a 347 so you don't have a stockish engine. What size cam is in the engine? What is it's Rpm range it was built for? Low rpm, mid rpm or high rpm? What gears and tire size? What stall Torque converter? How many miles on the engine? The Cats?
So the PO had the engine rebuilt so I don't know have answers to all your questions. Camshaft spec is attached. Previous owner claimed the engine was rebuilt in 2015, don't know how many miles but less than 50k for sure. I don't know what the ratio is, I think its the stock ford 9" if that helps, and 33" tires.

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Discussion Starter #20
Okay so I tried to record the sounds for you guys, not sure how well you'll be able to hear through my phone video.

This first video is it idling in the driveway. Tell me if you think there is any lifter / tapping noise. There is also a faint rumbling sound that I thought was the exhaust leak. You can hear this low rumbling louder at the very end of the video when I'm on the right side of the car. Rumbling sound is way louder when I'm accelerating in the second video.

This second video is me accelerating up from a red light. You can also see on the LCD screen RPM in the center. There is definitely less power than normal and its a way louder / deeper / rumbling sound. Hopefully you can hear that. You can also see on the LCD screen the TPS, I need to open the throttle up to about 35% to get the RPM up. In the parked video, the TPS only goes up to about 5%

Third video is be revving up in park to a similar RPM range for comparison. In park there is almost no rumbling sound.

Let me know what you guys think this sound is and what might be causing the loss of acceleration.
 
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