Low engine power?

And I know this is a bit of a joke but will any sort of additive help? A tech from justanswer recommend try marvel mystery oil on a oil change

i dont believe in oil additives. todays oils have all the additives we need.

Roy

Ok and should I rotate the engine with the plugs out a couple times before I start it? Just to make sure the lifters are all pumped up a little? I've never touched lifters so I have no clue, and is it a sure bet on a high mileage cam?

Oh and if I burnt a valve wouldn't it miss/backfire? The exhaust note is irregular but to an untrained ear it isn't a very pronounced difference, I would expect a burned valve or one that isn't seating to be far more noticable... Am I correct on this?

forget the burned valve. it would have come up on the compression test.
when you install them, just be double sure the push rods are in the correct position. no need to do anything else. it will start up, clack for a second and the noise will go away.

Roy

Alright do I just let it idle or rev it up on start up? The rev up I think is just for new cams right?

just let it run till it stabilizes.
yes, 1800 rpm is for new cams for break in, not your case here.

Roy

One last question, will the lifters come right out of the guides or do I need the remove the guides to get them out?

And again thank you so much for your help, you clarified a lot!

remove the guides to get them out. the guides keep the lifter from rotating.

Roy

Is there any way to verify its the lifters? I called a Couple Chevy dealerships and none of them heard of replacing the lifters while replacing intake gaskets

I did the LIM gasket and the upper plenum gasket and I changed tge plugs, now its got a top end on cal 3, and the car has low power
Compression good
Oil pressure good
Spark/plugs good
Injectors in working order
Vacuum is good but at idle it sits at about 19-20 inhg and it fluctuates constantly 3-4"hg

Symptoms
Low power
About 22mpg avg, was at about 25-27mpg before this happend
It has a bad hesitation on acceleration
Rpms usually sit at 750-800 at idle but now it will drop to about 550 when brake is applied in drive and will go back to.normal when foot is off brake(intermittent)
Valve clatter very pronounced on cold start ups
Doesn't want to hold revs when it hesitates, it gets to about 2 grand on accel and will just drop.off and make tge car hesitate
Rpms will jump 200-400 when I let my foot of the gas at cruising speeds 25-45 does it all speeds but more noticable at 25-45
I will occasionaly have power randomly but after the car gets driven for like 20-30 min it hesitates and has low power


I do have power if I make the car downshift, but it still doesn't have the power.it used to.

Iv done
New intake gaskets
Plugs/wires ac delco
Air filter
Seafoamed it (helped a.little on power/mpg)
Oil is clean
Coil good
Maf/map good
Can't find any intake leaks
I feel like ive been running in cirlces, but I'm like 99.99% positive its a valve train issue, any ideas on how I can be 100% sure what it is before o tear into it again

the give away is the fluctuating vacuum. the noise is a collapsed lifter and the valve is not opening enough. you most likely will have to open it up again and replace the bad lifter. it just wont pump up.

Roy

Would it be safe to try a quart of marvel mystery oil on an oil change to see if I can get it pumping up? And can a single Lifter be replaced? Can I it be replaced without removing the intake manifold?

What would you try first before blowing 500 bucks digging into it.... Again!

you can try the additive but i doubt it will work.
yes, you can replace 1 but i recommend replacing all.
no, the intake must come off again.

Roy

Dang when I pull the lifters do I have to remove the guide? And what's a recommended procedure for prep of new lifters and a break-in precedure? Or point me out a place to find this info

Sorry for a lot of questions, but is it damaging to drive it like this for long?

I'm curious is it possible to misalighn a pedestal mounted rocker arm? My car isn't breathing right at all. And I have a pretty pronounced valve train noise from a lot of my rockers. If I pull the covers again what should I look for? On cold starts the valve train is noisy and exhaust is a loud puffing noise, no miss just noisy and a major hesitation/lack of power.

This started after doing a lower intake gasket.

Ps there's no coolant that goes through the intake manifolds

Any testing tips would be great instead of saying go to a mechanic... I'm here cause I would Love to fix it on my own over paying a 100 dollar diagnosis (which I've done 2 times to hear them say "we don't know!") its not worth it...

what motor?

3.5 v6 flex

you did the gaskets yourself?

Yea it wasn't too difficult, I had to fix a crossover leak and I went ahead to replace the manifold gasket, just for the sake of been in that far. The car took a couple tries to start then it started up and was making noise, I think it was the lifters but I'm not sure. Right now it just seems like I have some excessive clearances in the valve train. I checked pushrods and only one had some stress marks and it was very slightly bent, could only fit a post it note under it on a level surface

i see this is a repeat visit. https://www.2carpros.com/questions/2007-chevrolet-impala-valve-clatter-hesitation-low-power-bad-mpg

Yep. And do you have any insight?

not at this time. will keep in mind and see what pops.

Alright. Basically I was leaning towards a running compression test, a cylinder Leakdown, or get a dial indicator and measure cam lobe lift and compare it to stock height. Sound like I'm on the right track?

sure, doing anything positive increases the chances of finding the issue.

i recently did a lower intake manifold gasket on my car and i replaced the plugs/wires, air filter, and all the gaskets along the way. After i was finished i started the car up and at first the car was really noisy in the top end but it quieted down after about 10-20 seconds, but it was still there.

I was worried i messed something up so after about 2000 miles i tore it down AGAIN, replaced gaskets with ac delcos, all the pushrods were in the correct location, no broken parts. as i was putting the pushrods back in i noticed one of the pushrods had a little stress mark on it, i put it all back together without changing it because it was on the front head so it is easy to get to. i go to start it and it was running just fine but it seemed to have a smooth idle but it felt like it was loping a little (no rpm fluctuations) and i still had a hesitation and no power.

basically my question is, can there only be one pushrod messed up? if it was bent wouldnt it cause a miss? could it bend and not bend a valve? how could it bend?

I dont know anymore its driving me nuts though...

compression was good, lowest was on the cylinder with the weird looking pushrod but the numbers were like 205 to 195 so i didnt think it was bent.

forgot to add to... when im coasting along and i let my foot off the gas the rpms jump like 200-400

Yes a push rod can be bent and not damage a valve and just one can be bent.i would scan for codes for the erratic tach.if i understand your post?you are concerned about the tick noise right?

im more concerned about the power loss and hesitation, i was worried about the tick but after not finding any damage the second go on the LIM gasket i was more curious as to why its got no power

and at idle my rpms drop to about 550 and returns to about 650-750 when i let off, i dont think its normal bc it was never noticeable, now i can visually see it drop. and when im coasting and the rpms jump i can kind of feel the engine go with it (if that makes sense?) iv been told by alot of people its an electrical issue, but this never happend until i did the LIM gasket, so its driving me nuts having crap mpgs, no power, and a complete loss of driving excitement(complete frustration now)

well sounds like possibly a convertor restriction i would have it tested at exhaust shop

is there any chance a bent pushrod can make the cat go bad?

i see what you are saying.that you had no issues before you changed the gaskets.so why did you change the gaskets to begin with was it leaking?

before all of this i had a hesitation and about a 4-5mpg drop in economy, after about a week i had a big coolant leak comming from the coolant crossover, which at the time i thought was a headgasket leaking(also bc the intake manifold had some seepage). once i got down and noticed the coolant leak was from the crossover and not the head i was really irritated since i bought all the gaskets/materials needed to do the head gaskets. so i went ahead and did the intake gaskets too thinking it would help get better mpg. on top of that i did the plugs/wires too, right after i did the job the first time i started said having problems.

ok if all vacums are on and in the right place no bent or kinked fuel lines all plugs plugged in correctly no codes in ecm check fuel pressure and ignition module