best way to unstick valves

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Jan 4, 2023
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a few months ago my car had a sticking lifter that caused a misfire. i replaced the lifters, and a few weeks later I quit running lucas UCL. today the misfire came back. it only misfires when first started, once it warms up the misfire dissapears. i don't want to tear the car apart again, so should I just seafoam the intake manifold? run lucas again? the valve that stuck open was only barely not sealing, so the car ran alright with it leaking. when I took the rockers off the lifter was stuck, (the lifter is between the rocker and the valve stem on this engine) and the valve took some tapping to get it to seat fully. i think the valve stem has some varnish on it where it should fit into the guide, from it's time hanging open, so the valve sticks sometimes. im considering putting it back on the UCL to see what happens. it only started misfiring again today, and it only did it on one start, so I don't know if I should even worry about it.
 
Physically clean the valves (walnut blasting)?
Solvent clean the valves (induction service)?
The old trick of misting some water into the intake (poor man's decarbon)?

How do we know it's the valve sticking in the guide, not a carbon buildup down seat situation?
 
Physically clean the valves (walnut blasting)?
Solvent clean the valves (induction service)?
The old trick of misting some water into the intake (poor man's decarbon)?

How do we know it's the valve sticking in the guide, not a carbon buildup down seat situation?
the engine is port injection, and I had the intake manifold off to do the lifters. the valve that had hung open was actually the cleanest valve, i guess it got the deposits blasted off from the leaking compression. there was no seat deposits or burned valve. it did have some varnish on the stem though, same as all the valves. the head could be torched but the car starts and runs perfectly smooth since I did lifters, exept for today. maybe the engine just stopped in the right spot and the valve didn't want to move from it's "comfy spot" where it used to hang open. the misfire could be something else also, but i did gaskets plugs and wires
 
the engine is port injection, and I had the intake manifold off to do the lifters. the valve that had hung open was actually the cleanest valve, i guess it got the deposits blasted off from the leaking compression. there was no seat deposits or burned valve. it did have some varnish on the stem though, same as all the valves. the head could be torched but the car starts and runs perfectly smooth since I did lifters, exept for today. maybe the engine just stopped in the right spot and the valve didn't want to move from it's "comfy spot" where it used to hang open. the misfire could be something else also, but i did gaskets plugs and wires
Maybe dose the fuel hard with a PEA (Techron/SI1) rich fuel additive, or Yamalube RingFree , or similar
Take it out for a nice long drive, and give it the old Italian tune up?
Take it out of OD, keep the revs up for a few miles on the highway?
Rev the everliving **** out of it?
Going off your signature, we're talking about a 3.5 6G74 V6 right?
 
yes it's a 6g74, i rev it out on every highway ramp, half for fun, half because I don't wanna merge at 45mph. it spends 10 minutes at 2000rpm and 5 at 2600 every time I drive it. i will try the techron if it acts up again. i love this car so much but something is always broken.
 
well the misfire magically dissapeared, i think that cylinder just has chronic sticky valves from when the car sat for 4 years. ill probably run some b12 chemtool through a vacuum line, that stuff cleans varnish good in my experience.
 
well the misfire magically dissapeared, i think that cylinder just has chronic sticky valves from when the car sat for 4 years. ill probably run some b12 chemtool through a vacuum line, that stuff cleans varnish good in my experience.


Well that’s information out of nowhere. This vehicle sat for four years?
 
yes, it sat in my grandpa's backyard from 2017 to 2021. i bought it, charged the battery, new thermostat and throttle position sensor and I've been driving it since then. a few months after I bought it it developed a cylinder 4 misfire that only happened sometimes. once I did lifters, plugs, and intake gaskets it dissapeared. I've never run anything through the intake manifold, but plenty of seafoam/mmo/lucas/b12 through the gas tank. also this misfire doesn't happen in the summer 🤷‍♂️
 
I also like the idea of trying GM Top engine cleaner. Another thing to try is mixing TCW-3 oil with the gas at a ratio of 1/640. That's one ounce of oil for every 5 gallons of gas. That might help clean and lube the valve seats and stems.
 
tcw3 will probably help, but I want to clean the valves, so they move without help from oil. i want to fix the problem rather than hide it. i do have a jug of tcw3 for my diesel cars
 
I would do engine flush and oil change and then maybe try that old trick of spraying water mist into intake to decarbonize the engine. Also i would add a bottle of fuel system cleaner into the gas tank, that way your intake valves would getting cleaner as engine runs.
 
If it is in fact a valve problem, not a dirty injector or failing coil.
I would try Mmo in the oil to clean the part of the valve stem exposed to the oil, and either Chemtool or Amsoil power foam to run through the induction side to clean carbon off the back of the valve face.
I've done this on a small block Chevy that had low compression on a couple cylinders due to leaking valves and it brought compression back to spec.
 
TCW3 or MMO in the fuel may help a sticky valve. Synthetic oil in the crankcase may also help.

I had a turbocharged car with variable turbine guide vanes. (a custom setup that I fabricated) After some years, the variable guide vanes got really sticky and failed to work. I used quite a bit of two stroke oil in the fuel and I could not believe it fixed the problem.
 
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