Waste gate question and an observation

[millsroger]

Snooping this morning under the hood on my 94 L65. Got a question---wastegate actuator on a GM-4 is kinda stuck in the middle except when it has full vacuum on it, then hard pulled. I think it should open all the way without vacuum by an internal spring or ???? Can someone verify that??? Got 20" vac from pump, same at the actuator. When I pull the vacuum line the actuator only moves about 1/4". I can push it by hand all the way but with resistance and it moves back when I let go. I think it's shot but want opinions.

While in there, I took the turbo intake elbo off to check airfilter and look for blowby out the crankcase vent pipe. Clean aircleaner and almost no blowby, slight air flow but near none, good news. Anyway, I read to check if there was side or end play on the turbo shaft so I tried to feel for any----none, also good news considering 245K on the truck.

Now, here is what I observed, very stiff to rotate the compressor wheel and it stopped immediately when I gave it a spin. Fire up the engine and I can hear it start whistling when I rev it a bit so it does work. Just when I watched it as my wife shut it off the turbo came to a stop in about 3 second. Not so good news!

Got some coffee, sat down and scratched my head for a while. Here is what I did and the result. I took the oil feed line loose and rotated the turbine by hand, oil slowly seeped down. I put some Seafoam in the fitting and did it again and again, like about 6 times. Then, almost like magic, it started spinning more and more free. After about a dozen cycles it no longer got better.

I put the oil line back on and fired it up. Now, it starts whistling almost immediately when I rev it a bit, and when I watch it on shut down it keeps spinning for a good 12-15 seconds. Haven't driven it anywhere yet so I don't know if there is any change in performance.

Just a DIY if you think the turbo is getting stiff.

 

[buddy]

Thats some good news on the turbo shaft spinning, probably a lot of guys that could benefit from that. I imagine the inside got gummed up from hot oil boiling at some point or setting a long time, dirt and dust, ect..

My GM4 wastegate lever got sticky about halfway open, so that it wouldnt always close the gate all the way, which led to some smoke and slower spooling. I had the ATT so I never fixed the GM4.

 

[millsroger]

Have driven it now and can say it made a difference. Used to be able to feel the turbo come in at about 2500, now it feels like it is pulling hard from the git go. No real lag except when cruising at 50 in OD and I mash it. That's even hard to feel due to the kick downs, kind of like the turbo is spooling before the tranny figures out what gear to be in.

Re the waste gate---mine wants to be in the middle with engine off, can push it both directions but it wants to return to the middle when I let go. From a pic of the waste gate itself, I think it should be loaded to the full open not the middle, with vacuum pulling it shut. Gonna compare it to a new one and prolly just replace it.

 

[bison]

Most likely the turbo exhaust wheel shaft is packed in with hardened soot inside at the seal area and between the heat shield between the housing and the wheel.
The seafoam prob softened it up for a bit.

The vacuum actuator is prob shot,unhook it from the wastegate and see if the gate moves freely

 

[millsroger]

Could be Bison, will keep an eye on it. If you are right it wll start to bind up again, hope you are wrong tho, I'm hoping it was just sludgy gunk in the bearings.

 

[bison]

Not enough bearing surface there for gunk to take hold IMO,there won't be any sludge if the oilchanges were done on time.

 

[millsroger]

Truck came with all maintenance records, guy was anal about it, engine oil and filter at 5k, trans at 10k intervals since new, means you are prolly right. I spose I need to find a kit or a really nice used one. Later on, it will be getting some upgrades but need to build up a piggy bank first.