check compression
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Joined: Mar 2011
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check compression I need to know what needs to be done to check compression safely on my ls6? I know how to use a compression gauge. I need to know what to unplug or what fuse or fuses to do this safely without screwing with my tune,pcm etc. do I pull the fuel pump fuse? ignition,unplug coil packs? I'm thinking I over reved and bent a push rod or might even burnt a valve. because when I let off it it goes blub blub blub instead of a smooth decal. or should I change the exaust gaskets. did that once used the stock mls problem developed again. I was wondering what I've done is let of it at high rpm and let it decal with engine. in the old days of Harleys if you let off like that you could burn a valve like that . I was wondering if that were true with or ls motors? I only have 20k on this brand new crate motor . I just hope I don't have to pull the heads for a burnt valve that's why I'm thinking compression test . am I too old school or too paranoid. you young guys know this better than I do . please help the oldman out. thanks ahead of time.
unplug coil packs and injectors...
you dont have to pull the fuel pump fuse, but it certain doesnt hurt anything to do so
checking pushrods is really simple...
pull valve covers, undo rockers, pull them out...roll them on a flat surface(usually a glass surface is guaranteed to be flat)
there is a function on place in the stock pcm called Decelration fuel cut off...you may be hearing it, or not hearing it depending on if certain conditions are met...
it sounds different with clutch in than with clutch out...
cars are not like motorcycles...you will not burn a valve from deceleration
you are over thinking all of this...
why do you think you have hurt something? are you driving it in a way that would cause damage?
did you let the engine bang the rev limiter of an extended length of time?
are you running aftermarket mods with no pcm tuning done to compensate for the mods?
right now your questions are too open ended and we need to know more details.
you dont have to pull the fuel pump fuse, but it certain doesnt hurt anything to do so
checking pushrods is really simple...
pull valve covers, undo rockers, pull them out...roll them on a flat surface(usually a glass surface is guaranteed to be flat)
there is a function on place in the stock pcm called Decelration fuel cut off...you may be hearing it, or not hearing it depending on if certain conditions are met...
it sounds different with clutch in than with clutch out...
cars are not like motorcycles...you will not burn a valve from deceleration
you are over thinking all of this...
why do you think you have hurt something? are you driving it in a way that would cause damage?
did you let the engine bang the rev limiter of an extended length of time?
are you running aftermarket mods with no pcm tuning done to compensate for the mods?
right now your questions are too open ended and we need to know more details.
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Joined: Mar 2011
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thanks, soundengineer. you helped me once before on another subject, 1) bounce off rev limit every now and then,but shift imedeitly rev limit in tune set @ 6800 rpm stock ls6 took into consideration the aprox 300 rpm difference on the stock tack.arh headers,slp lid,amsoil air filter,85mm vette maf,36lb injectors,gmmg cat back,arh catted "y" t56 (liberty's magic) s60 3:54's ( I road hunt foreign cars,god bless America!) the blub,blub, blub is on deceleration only. when I let it run in garage yesterday noticed water from exaust on floor close to where I had to weld the "y" junction last year.thanks for the upbeat note on the bike comparison air cooled versus water cooled. that's why I wanted to do compression test to avert pulling all the push rods or do you think pulling the push rods is a better idea? gosh I really don't want to unbolt anything internal on my virgin motor if you think compression test is more precise in that if there is a big difference in compression per cylinder that it would through process of elimination I would find the bent push rod in a particular cylinder if there was one. yes you are right I over think stuff.
I know you are claiming to be old and all...but holy run on paragraph batman...
Try hitting the enter key once in a while to make a new line, and try using a Capitol letter at the beginning of a new Sentence.
Decel fuel cutoff removes fuel while under hard deceleration.
Do you have hardened pushrods, or are they stock pushrods?
If they are stock, you shouldnt be going over about 6200
Its easy to check them... like I said...pull the rockers off, and pull them out...roll them on a flat surface. Its a simple and easy test.
When you put them back in, you just put the rockers back on and torque the bolts to 22 ft/lbs, Nothing else is needed, no special procedures...
feel free to do a compression test...it certainly cant hurt anything to do it.
and you wouldnt necessarily be able to see a bent pushrod on a compression test...depends on how bad it is bent...
also, it wont keep the valve from closing, it just wont open quite as far...
Try hitting the enter key once in a while to make a new line, and try using a Capitol letter at the beginning of a new Sentence.
Decel fuel cutoff removes fuel while under hard deceleration.
Do you have hardened pushrods, or are they stock pushrods?
If they are stock, you shouldnt be going over about 6200
Its easy to check them... like I said...pull the rockers off, and pull them out...roll them on a flat surface. Its a simple and easy test.
When you put them back in, you just put the rockers back on and torque the bolts to 22 ft/lbs, Nothing else is needed, no special procedures...
feel free to do a compression test...it certainly cant hurt anything to do it.
and you wouldnt necessarily be able to see a bent pushrod on a compression test...depends on how bad it is bent...
also, it wont keep the valve from closing, it just wont open quite as far...
Thread Starter
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Joined: Mar 2011
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Soundengineer, Thanks for the info.I guess I need to use more than one finger on the keys.Thanks for the lifter info. Sounds so easy.That 22lb torque is all that's needed no matter where the valve event is at on the cam? I will do what you said before compression test.Also should I do the comp cam trunion upgrade while I'm in there? I was using the stock push rods as an insurance policy to prevent further damage in case of over rev in case I miss a gear. I'm used to yanking the shifter like the old Muncie's.I guess I need to work on that too.
