TheGreat4.8

I posted on performance trucks but not getting much advice, just need some experienced advice on this issue.

I recently swapped a new(er) 4.8 in my sierra that i found sitting in a salvage warehouse type deal, it had been sitting for at least 2 years but the bottom end looked in good shape and it had good compression so i took it for 400 bucks.

Swapped in a new oil pump and timing chain just to be on the safe side and threw her in, it drove good for about 15 miles then on the second trip to get pizza it just died creeping through a parking lot with no warning.

now when it runs it has a distinct valvetrain knock/tick that is there cold or hot and has that awful lean burnt smell from the exhaust, surges under load, hard starting and pretty much drives horrible.

Oh yea and i can tell from the way it pulls and sounds that it is pulling alot of timing so no power anywhere.

and yes this is a turbo build but i have the charge pipe left open to keep from getting into boost until i fix this issue, only code that is showing is MAF low input and that doesn't matter because i have a SD tune.

Can a collapsed lifter or bent pushrod cause this to run so horrible?

1dirtybird

iTrader: (7)

Do another compression test, pull the covers, check springs rockers and p/r's.

Then pull the valley cover and take a peak at the front lifters they go 1st with lack of oil.

Also you got a magnetic drain plug? drop the oil and check for metal.


Motor may have been hurt even before you got it.

Dirty

TheGreat4.8

Alright i did a little investigating with the valve covers off on both sides and cannot find any crazy amount of play that i expected to find, so i took off all the rockers on the passenger side and pushed on each push rod to find every lifter is hard with no give but on the cylinder 2 lifters have a little squish to them like what you would find on a non pumped up hydraulic lifter.

I ran out of time today so didn't take off the drivers side rockers but they all feel pretty firm, one thing i noticed is the passenger side valve cover is not oily as the drivers side almost dry not sure if that makes a difference because there was oil all over the push rods and rockers.

Wouldn't i be able to feel some slack between the rocker and pushrod if i had a collapsed lifter? This sucks

TheGreat4.8

Some more info, when i first started this engine i had very good oil pressure like 80 lbs from the start but over the last few days it has gone from 40 lbs down to 20 lbs at idle, i cannot get it to go above 20-25 lbs cruising now, coincidence?

1dirtybird

iTrader: (7)

You use the big or little o-ring in the oil pump kit for the pick-up? on the truck pick-up tube you want to use the little one.

Yes if the lifter is spongy it could be collapsed or bled down. They should be pretty firm. Is it an exhaust lobe or intake? Check the plug too.

TheGreat4.8

When i did the oil pump swap i didn't know which o ring to use, the new one came with one that looked a little thicker, but the original looked fine it was green or blue ish can't remember so i used the original but could an o ring be fine and then just let loose all at once?

The squishy lifters are both valves on the #2 cylinder.

1dirtybird

iTrader: (7)

Check the valve hight on that cylinder as compared to the others. May have tuluped (bent) the valves due to a heat issue in that cylinder. (lean condition or steam pocket) it basicly makes the valve longer thus putting more pre load on the lifter and collapsing it.

And yes if improperly installed or the wrong o-ring is used you may have good pressure for a short time then it just drops. Ive seen it both ways great then nothing or non to a little on 1st start ups.

Also change the oil filter, who knows what was in the when it was pulled.

TheGreat4.8

I went ahead and bought a new pump and the thicker red o- ring that the local chevy dealership said was for my year, anyway 4-5 hours later and a lot of cussing at the hard to reach pickup bolt i cranked it back up to find i had only gained about 5 psi and still doing the whole lifter knock.

Now there is no doubt in my mind that this o-ring is installed correctly because it was tight as can be and i had checked it 3 times before bolting it up, but there it was doing the same thing as before.

I've also checked the valve height and all are identical, also i have not checked the filter, i know kinda backwards but that old o-ring was really bothering me so at least i know for a fact my pump and o-ring are good.

Tomorrow i am checking the filter and oil but I'm really doubtful of that, but i have read of some bypass pressure valve? are there ways to check this piece is functioning right?

b16acrx1988

You can pull the valve covers and roll the motor over and watch all the valves, have you checked all your pushrods? I really didn't lose much oil pressure with my collapsed lifter but you could hear a bad tap right where it was, but the systems I did have were right after a race it started bad so I shut her down checked oil and all was fine. So I started it up and it was surging like you say especially under a load, running really rough significant loss of power, I think it went into limp mode. It took me pulling the heads to actually know for sure what happened, and what was wrong but it ended up being a turned/collapsed lifter. looky at pic

1dirtybird

iTrader: (7)

Man I think you need to pull that valley cover... but yes you can check the oil pressure with a mechainical gauge. Either pull the existing sensor or get a vett oil galley cover (rite above the fitler) that is drilled and tapped (for the temp sensor) or drill and tap the front of the block for a fitting.


Most of the quick things have been tried.... You do a compression test again yet on that cyl????

You may have found the reason the motor was pulled in the 1st place.



Dirty

TheGreat4.8

Not yet i don't have the equipment to do a compression test but i have since pulled that garbage fram filter and threw on a purolator and gained a good 10 psi at idle and it winds up to 40 lbs at 2000 rpm so i think i'm good for pressure now but still knocking.

The motor was good for the first 15-20 miles with no valvetrain noise whatsoever so I'm thinking it sitting dry in a warehouse for a few years is to blame, good thing is i have a whole other 4.8 worth of parts minus rings that i can take a cam and lifters from if need be, i just hope these busted lifters don't chew my cam up in the 5 or so miles i have to take it to park.

98blkz28

I will tell you that, my ls1 just died from a start at like 2-3k shift...and started ticking got worse and turned out to be a spun bearing...my mine just lost all power.. but as far as the low pressure i didnt have any change in mine..

I'd check compression, and manually check the oil pressure..if it still does it you may have to disassemble the motor

TheGreat4.8

Well i will be tearing the passenger side and possibly driver side head off sometime this week and throwing in some good lifters, head gaskets, and head bolts.

Now as far as removing the head and reinstalling it with a new gasket are there any tips or how to that anybody has for me before i go and slap it back on?

I know that surface machining is out of the question with the motor still in the truck but i want to make this the once and only time i have to take this head off so any input on this is appreciated.

b16acrx1988

Non metallic scraper, and clean very well. I have some that I use at work made of plexiglass, but you can use a windshield ice scraper.... I used a razorblade also just was very careful with it.
http://www.ls1howto.com/

1dirtybird

iTrader: (7)

just use a green 3m finger disk then a blue scotch brigh disk. Do them both and check the cam lobes. Also mesure the lifter bores to check the clearance.

TheGreat4.8

My next post will be pictures of what i found, all my lifters and lifter bores look good as well as valves, chambers, and piston tops. With what i found i was baffled not finding any bad lifters so i decided to pull the cam out.

The cam pulled out and i found the front most cam bearing all loose and chewed to hell with the oil holes closed off, almost like welded!? it was loose in the block i could move it front and back with my finger so there is my oil pressure issue.

I got the sucker out and checked the rest farther back and they are all worn with copper rings in them.

I think this motor is going back to where i bought it...

TheGreat4.8

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1dirtybird

iTrader: (7)

Thats Neat! motor prolly has a ton of miles and had very infrequent oil changes. bet the main bearings look super duper too.. usually the rod bearings give in before the cams though