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Old 08-20-2002, 09:58 PM
89Custom
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Default exhaust manifold leak: rough idle?

This is my first post. Owned my 89 one year (120k - all stock except 32 x 11.5) and last month started hearing this clicking noise under hood when accelerating. Friend says its an exhaust maifold leak (is not a knock).
Around same time, idle in gear started to get rough and some hesitation on acceleration. Otherwise she runs fine and flies down the road. Hasn't got any worse in the last month, but is annoying I changed plugs and dist cap and cleaned throttle throat. Runs better overall but still rough. I'm planning to pull codes.
Would exhaust leak affect idle and performance? Or are they separate things going on. What causes manifold leak and do I have to replace entire manifold or just a gasket?
I cant see any cracks etc. Any suggestions most appreciated. I'm amazed at all the info in here!!
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Old 08-20-2002, 10:14 PM
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Default Re: exhaust manifold leak: rough idle?

A number of things can cause a manifold leak, motor age, heat, vibration, bolt broke, etc., and it could be a gasket, or a warped or cracked manifold, or.....

I would guess this can be checked with a gauge no matter what the cause.

The clicking though, I'm just wondering. Sometimes problems in the FI system can make for a different (and louder) ticking noise from the fuel rails. Definitely pull codes if you can.
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Old 08-20-2002, 10:32 PM
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Default Re: exhaust manifold leak: rough idle?

seeing that your truck is ~13 years old, it's definitely possible that your cat is "spent" and is restricting flow. it could be that there's so much backpressure that you blew your manifold gasket, though if it seems to have power at low rpms then i doubt its really that bad. one other thing to definitely check is the air check valve on the little pipe that runs from head to head at the back of the engine. you cant really see it but if you look right behind the intake manifold you can see a rubber hose that hooks into it. my valve broke in half and was dumping exhaust in the engine compartment, which made a really loud click/clack when the engine was under load. also my manifold has several cracks that make a higher pitch clicking but not as throaty. other options are a cracked EGR pipe on the passenger side manifold or possibly the pipe coming from the cat to the other check valve by the diverter valve. check that whole thermactor system carefully, theres lots of crap that can go wrong with it. when my check valve broke off it let hot exhaust melt through 5 of my vacuum lines, which could definitely cause rough idle and hesitation.
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Old 08-21-2002, 07:54 AM
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Default Re: exhaust manifold leak: rough idle?

I had an '85 with a 351 in it. I kept burning out the heat riser, that little spacer with the valve in it between the manifold and exhaust pipe. It helps the motor warm up faster in the winter. That little bugger was not cheap. I ended up doing away with it, and putting dual exhaust on the truck.
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Old 08-21-2002, 09:50 AM
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Default Re: exhaust manifold leak: rough idle?

I have a similar problem with my 88 302, the air check valve was completely melted, it sounded like an exhaust leak to. had to pull the upper intake to get to it wasnt as hard as i thought it would be. the part was $80 bucks from ford and wont be here till thursday. I wish i could get rid off all that emissions stuff, just not sure how it would run with it all off and how hard it would be to get off. anyone done this and how has it been working out for you?? no emissions here where i live .
Good luck with your exhaust leak
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Old 08-21-2002, 05:29 PM
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Default Re: exhaust manifold leak: rough idle?

it will run fine. i ripped out all the lines from the smog pump back to the cat and plugged the hole down in the exhaust and it's peachy, and i can actually get to my passenger side spark plugs! for now i just left the check valve back there but when i get around to it i'm going to plug those holes in the heads and be done with it. you got ripped big time on that part, i paid ~$20 for mine at advance.... but if you get a threaded cap to put on that tube hopefully you can take it back and get your loot back.
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Old 08-21-2002, 08:56 PM
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Default Re: exhaust manifold leak: rough idle?

hey there M-B

i just finished putting the headers on

my bronco--unfortunately the rest of the exhaust

basically flaked away while i was hackn and whackn

the tube going into the exhaust after the first cat

snapped off, are you saying just plug it and remove the pipe

any help would be great im just about to put the h-pipe back

up, im also going to run just one cat--is that ok or is

there probs with this, straight pipe to muffler then exit

out at the normal local,

thanks bud

KILLLLLAAAAAAAAA
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Old 08-21-2002, 10:26 PM
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Default Re: exhaust manifold leak: rough idle?

Hey 89Custom

Yes it will make your truck idle badly, especially if it gets bad enough. I'm pretty sure I warped my manifolds so when I removed them I stuck in gaskets where there had been none before. Cured the noise for about two years, had to do it again this past Spring.

My 86's 17 year old original cat is probably restrictive, like someone suggested, but it ain't getting changed until the test next year.

Slap in some gaskets and make sure your Ford dealer has some extra manifold studs as mine were real thin and several needed replaced.

Sixlitre
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Old 08-23-2002, 05:11 PM
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Default Re: exhaust manifold leak: rough idle?

muddy what did you use to block the holes where the tubes went back to the cat. my 88 has 2 cats on it, i think there alittle clogged so in a month or two going to swing by the muff shop and see about getting the exhaust redone. set of headers and 3" to the back. i figure one high flow cat would work fine instead of the two.
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Old 08-23-2002, 07:50 PM
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Default Re: exhaust manifold leak: rough idle?

i have removed all the rubber hoses, valves, and vac lines in that system period, except the check valve on the head cross-pipe. there is one hole between the first and second cat that will need to be plugged, but somehow between my injection pipe ripping off and mud/rust, it has fully sealed itself and almost looks welded... weird. i'm wondering if the exhaust shop didnt weld it the last time i had it in, but that would be a PITA to get to. anyway, just make sure you either plug the line going from head to head OR leave the check valve in place, which is what i did. i'd like to pull that stuff off completely and plug the holes right at the heads but i'm slow to get anything done that doesnt help me put chunks of mud on my roof [img]images/icons/laugh.gif[/img] the only thing i have left to do is run some new lines for the EGR valve system, which is easier than trying to block off those TAB/TAD solenoids. right now i have that whole vac line segment plugged at the intake manifold tee, but i'm sure it would trigger a check engine light without the EGR working properly. mine has been on solid for 3 years now so i cant tell you for sure [img]images/icons/wink.gif[/img]

i have yet to block off the smog pump ports, and i went through some DEEP water today which is not good because i dont know how sealed its bearings are. i'm going to run a hose from the intake to the exhaust but as i recall they are 2 different sizes so you cant just slap one of the old hoses on there.
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