RichS

If you put a 3/8 rocker in place of the 10mm stud I bet that is your issue. Probably too much preload holding the valve open a bit. Since you already have the 3/8 rocker and cant find an oem one you could replace the stud with a 3/8 one and then use the adjusting nut that came with the new rocker. You will have to adjust the preload not just tighten it. You can put a want ad in the for sale area to locate a oem rocker.

Sidewaysc4

Okay i did use a 3/8 rocker... i put out a thread to see if anyone has an oem one on here... ive never baught or sold anything here so, not really sure how it works if someone does have one.

mtwoolford

Okay, I'm a curious guy, so a number of years ago I pull the valve covers off my then new to me LT4 and find one rocker arm completely off the valve stem, and another partially off. I replaced 2 (or 3?) oem 10 mm stud type roller rockers on my LT4; I sourced them at the dealership and back then they were like $75.00 each...ouch. But that was only the tip of the problem. Further investigation showed that the last three lobes on the camshaft had failed and the lifters had worn an actual grooves into each cam lobe...and others were beginning to show signs of failure...on an engine with less miles than yours...

I would take the intake manifold off and pull each lifter in turn...any roller that shows any sign of wear or damage, pitting, etc, guarantees a damaged cam lobe. Lacking that, I would turn the engine over slowly by hand and make sure the valves all opened the same amount, any rocker that moves less than its similar companions is riding on a bad cam lobe.

but with that said I don't think your problem is valve train related...my engine ran amazingly well even with 3 cam lobes missing in action. I think it's electrical.

one overlooked, but inexpensive, item is the short low voltage wiring harness that plugs into the Opti; Its kinda delicate, and plugs vertically into a female boss on the Opti and yes I know its a "Weathertite Connector" but all manner of crap and water can collect there, and sure you replaced the Opti, but the male plug can still be dirty, damaged, corroded..

Sidewaysc4

Why would the idle and dieing issue only arise after the rocker swap is my question?? Other than the 5k studded issue, my motor ran great until i parked it for a month and replaced that rocker???

mtwoolford

Did you encounter any problems installing the non oem rocker?

my long hand math, no calculators here! tells me than a 3/8 ths inch stud is 9.525 mm, so, assuming the fulcrum in your non stock rocker is a nominal 3/8ths inch, and you installed it onto a 10 mm stud there may be some issue there, like maybe it's not seating on the pedestal?

the GM part number for an LT4 rocker arm is ARM KIT VLV RKR p/n 12557779; try goggling it, you may get lucky finding yet another "one year only" LT4 part

mtwoolford

no egr, but there is a large plate and gasket on the end of the intake manifold where an egr could go, maybe a leak there directly into the intake?

mtwoolford

it really doesn't sound like an mechanical issue, it does sound like an electrical issue...and I realize the coincidence of replacing the rocker and having the engine run like crap, but that doesn't necessarily mean it was the cause.

RichS

Do a compression test on the cyl you put the odd rocker on. If it's over tightened the valve will be open not sealing causing low or no compression. The rocker fulcrum is different on the stock rocker vs the 3/8 one. You could also try loosing the nut a turn or two and try to start it to see if it takes some of the preload off. A new 3/8 screw in stud is also cheap.

Sidewaysc4

Ill do a compression test when i get home, what is the average numbers?

Sidewaysc4

***ANOTHER UPDATE GUYS***
I did a compression test on that cylinder, and it was 140-145 psi. Idk what the normal pressure is so let me know... after that i started it up and it sounded like it was running "okay" so i took it down the road and it wasnt dyining when i came to a stop it would either get close ( around 3 or 400 rpm) and bounce back, or idle way high constantly (around 2k) until i touched the throttle to accelerate again. Then just sitting at idle(out of gear at the house) it was good right around 700 but about every 30 seconds it would drop like it wanted to die to about 400 then bounce back to 70 and back and forth... any thoughts?

1800Wing

Have you looked at the fuel pressure when it starts to stall ? When I encounter problems like this I always start with the basics....failing ignition or starving for fuel will give you the problems you describe. Eliminate one before proceding with the other.

later, tiny

Sidewaysc4

Honestly didnt think to even check, thanks. I will hook a tester up tomorrow and let you know, maybe the regulator is bad?

antfarmer2

Pull the vacuum line off the fpr and smell for fuel.

wikdwizard

Not saying it is the problem, but I did not see that you replaced the fuel filter during your tuneup?

mtwoolford

that's probably within the ball park, it certainly isn't bad, but "normal pressures" is hard to define, mostly you want to see all cylinder pressures and look for any variation, for instance once cylinder real low, bad valve? two adjacent cylinders real low, blown head gasket? one cylinder significantly higher than the rest, excessive carbon build up in that cylinder?