can a cracked manifold cause my jeep to have a rough startup and then idle funny for like 10 seconds..but after it stops idling funny its like brand new again and it runs great.

 

Usually they sound better, but I don't know about the idle.

 

cracked exhaust manifold will cause rough idle at start up due to not having enough back pressure. once the manifold heats up the metal expands and the crack seals some what, restoring the back pressure, whick fixs the idle and makes the funny popping sound go away. jeeps are notorious for cracked headers due to crappy motor mounts that sit to close to the exhaust. the exhaust heat ruins the rubber in the mount.

 

hew man thanks.. i just bought a set of headers now i have to put them on..uggghh they are a pain in the *** haha

 

no problem. replace your motor mounts when you do your header or you'll just crack the new one. what happens is as the rubber mushes in the drivers side mount it drops the engine down which makes the intermediate pipe push up on the exhaust manifold. due to the high temps headers get they cant take the extra stress from the intermediate pipe pushing up on em and they crack.

 

oh and after you put the header on, run it for about 50 miles till everything is nice is hot then go re-torque all the manifold bolts, while HOT. what this does is help the bolts seat. as the block heats up the bolt holes on the block expand allowing you to torque em down better. if you dont you'll just blow a manifold gasket and your compression will be off, giving you horrible gas mileage.

 

okay thanks alot man..any tips on gettin the manifold off..they are a pain haha

 

easiest way ive found to do it is remove air filter, throttle cables, all electrical connections, label your fuel injector connections (1-6) and remove fuel line (need 3/8" line tool) manifold bolts are 5/16" .leave TB and fuel rail on air intake, unbolt intake only. (there are 3 bolts that bolt to header only, leave those until later) once the intake is out of the way you can unbolt the header from the intermediate pipe, then unbolt the header from the block. dont let crap get into the intake ports.

 

I think the bolts are 9/16 or maybe even 14mm

 

could be...it's early still...quoted from memory...well what i think i could remember hehe