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Troubles with Turbo

JohnShead

JohnShead

Member
Messages
64
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40
Location
Kingsport, TN
Yesterday I changed the center section of my 20 year old GM4 turbo. The bearings were wearing out in the old one but it was still making good boost, 14PSI when climbing hills with EGT less than 800°F (pyro sensor in the down pipe after the turbo). Now I have screwed my TurboMaster to the end of the threads and my maximum boost is only around 6PSI and the EGT goes right up to 800° with WOT on flat ground, it would probably go higher but I lift to prevent it since that's the end of the green arc on my pyro gauge. If I screw the TurboMaster out the boost is lower of course and there is a lot of black smoke with anything more than about 1/3 throttle, I didn't notice the effect on EGT as I only drove a couple of blocks, saw the smoke and screwed it back in. I get a bit of black smoke when I mat it while cruising but none from a stop. There is also a new giant sucking sound that neither the old turbo nor the ATT that I used to have made. It's drivable but I really have to watch the EGT. Any ideas what's going on would be appreciated.
 
John, How well did it spin by hand before you re-assembled it? I've not rebuilt one before but I've had the centersections out of a couple. It's fairly obvious when one isn't spinning freely. Double check it and compare with the older Center Section. Other than that, I don't know what to say. Too bad this didn't come up in February, I was in Tehachapi, Lancaster and Oxnard/Ventura the 2-9th.
 
It spun very freely, the old one still spun easily but you can hear something rubbing inside, I assume its a bearing going bad unless its the oil seal. The noise it was making is the reason I replaced it. I spun the new one from the air inlet also after assembly to make sure it wasn't rubbing against anything and it's still turns freely.
 
I looked for boost leaks and everything is tight. I didn't put any sealant on the turbine side of the center section, it didn't look like any was there originally, it doesn't look like there is any exhaust blowing by there. I'll check the v-clamp when I get a chance but there are no new exhaust sounds that might indicate a leak.
 
You may have a clamp loose on the intake (pressure) side of the turbo. Make sure the boot went on properly and didn't "blow off". Check the air filter to turbo connection as you can have the bottom half go into the turbo rather than around the turbo generating a dirt leak and more whistle. Yes this ruins the intake piece.
 
I think I've got it as good as it's going to get. In the past I had to cut off the end of my upper intake to install my ATT. When it failed and I had to go back to my GM4 I used a piece of 2.5" silicone hose to connect the cut off piece back to upper intake and I only used one clamp directly over the cut. This time I didn't quite get it lined up right and it was blowing out from under the hose. I still don't have as much boost as my old turbo though and this turbo makes a lot more noise, it sounds like it's blowing into a barrel. I'm getting about 7PSI and the EGT is in a much more comfortable range. I think this center section is probably not the right one for my turbo. It will work for now while I'm waiting for Dennis K to rebuild my ATT.
 
Are you cutting open your oil filters and doing UOA? There has to be a reason to eat 2 turbo's. From your avatar pic I assume you replaced the engine - did you replace the oil cooler as well?

As much as I put 6.5's through the only GMx turbo I wiped out was done when the oil mixed with coolant due to a rod beating holes in the cylinder.

Not saying it isn't just bad luck but it never hurts to make sure that's all it is.
 
I did not replace the oil cooler, the one I have was pretty new and after the old motor failed I had my oil analyzed, not from the filter but from the drain plug, and it came back with <.1% water contamination. I did have 38ppm Silicon (labeled as Moderate abrasive) and 1663ppm Calcium (labeled as slightly high additive metal), all wear metals were very low.

I plan on running a new oil line for the turbo from the oil plug just above the oil filter connection as recommended by Dennis K of ATeam Turbos. He suggested that the factory location is at the end of the oil gallery after feeding all of the lifters and rockers etc. on the right side of the engine and the remaining oil available for the turbo may be inadequate. The plug by the filter is right after the oil pump so it would be full flow.
 
How did the last engine fail? If it puked a bunch of debris into the oil cooler, well, they can't be flushed clean and this may be the source of the problem.

Anything special on the replacement engine? New/used/rebuilt and by who? Head studs?

How is the oil pressure?

Another thought is a low volume oil pump on a piston oil squirt block.

Silicon - Did you do any engine work and use 'gasket in a tube'? This will spike silicone levels. How does the UOA look now?

These engines priority oil the cam bearings thus bad cam bearings loose oil pressure.

What kind of oil and any additives? Like Marvel Mystery Oil? (MMO is known to cleanly flat wipe out ATT turbo's.)

Again, just some guesses.
 
1) maybe you have the wrong center section, most model years are slightly different from one other.
2) maybe your waste gate does not close all the way(carbon build up in the shaft bushing or on the flap valve)
3) check for a leaking doughnut or rusted out flare in the exhaust cross over
 
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