Overboost - why?

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turbojimmy

New member
Hi all,

My truck has been overboosting for quite sometime now. Even a POV doesn't react fast enough to keep it from shutting down. I'm constantly adjusting the POV and it doesn't seem to help.

I have an ATR exhaust and an RT cat (not gutted). I know other people have hi-flo cats and exhaust and don't have these problems.

Last year, when I still had my Ultimate, I tightened up the wastegate rod about a turn and a half to get it to the factory spec plus about half a turn tighter. Figuring this was the problem (now that I've pulled the Ultimate out), I got in there last weekend. Turns out the rod was too loose? WTF? So, I turned it back to factory spec and put it back on.

The good news is that wacky flucutation in boost under steady throttle is GONE. Boost is solid as a rock - it runs awesome. BUT, the overboost is still there (now worse, obviously).

What can I do? Is there some other wastegate I can use? It seems silly to go through that trouble on an otherwise stock truck. I figured if the WG was bad, it would be flopping open, not stuck shut....

TIA for any suggestions,
Jim
 
T

turbojimmy

New member
No on both.

But I just got my new Datamaster key. Laptop crashed so I had to re-install it on a new machine.

On some of my older datamaster runs, though, you can see the boost consistently higher than the "target". With the Ultimate, it would be a couple of pounds higher max than the chip wanted to see. With the Ultimate, though, it didn't matter. With the stock chip, it makes it unhappy.

I'll try to do some logging today.

Thanks for the reply,
Jim
 
Daron

Daron

Active member
Just a thought, but why not wire your wastegate Open to rule out a back pressure issue. It would likely take forever to build boost but I would ASSUME that after a good run your overboost would slowly show its face. Keep in mind, I havent done this so not sure how succesfull it would be.

You can test your wastegate actuator with a Mity Vac pump. The manual has a rather detailed adjustment procedure that suggests replacement if adjustment parameters cannot be met.

Good luck,
Daron
 
T

turbojimmy

New member
On 2002-02-24 09:23, Daron wrote:
Just a thought, but why not wire your wastegate Open to rule out a back pressure issue. It would likely take forever to build boost but I would ASSUME that after a good run your overboost would slowly show its face. Keep in mind, I havent done this so not sure how succesfull it would be.

You can test your wastegate actuator with a Mity Vac pump. The manual has a rather detailed adjustment procedure that suggests replacement if adjustment parameters cannot be met.

Good luck,
Daron
Click to expand...

I'll have to read the manual again. I have a Mity Vac pump, too. I read it once, and it didn't make sense to me - something about 1.5mm of travel (MILLImeters) - doesn't seem right.

I could wire it open, too, and see if it overboosts. If not, it's gotta be the actuator, right?

Thanks,
Jim
 
Daron

Daron

Active member
I could wire it open, too, and see if it overboosts. If not, it's gotta be the actuator, right?

Thanks,
Jim
Click to expand...

It may take quite the freeway run to get it to boost up, but if it never overboosts then yes the assumption could be that one of the items in question would be the actuator.

Could it be possible that your wastegate is stuck? Mine gets sticky every now and again. It only rears its ugliness when the turbo is warm. Dig exposed this issue sometime back.
Good luck,
Daron
 
T

turbojimmy

New member
It may take quite the freeway run to get it to boost up, but if it never overboosts then yes the assumption could be that one of the items in question would be the actuator.

Could it be possible that your wastegate is stuck? Mine gets sticky every now and again. It only rears its ugliness when the turbo is warm. Dig exposed this issue sometime back.
Good luck,
Daron
Click to expand...

Yeah - that's actually a pretty good possibility. I've only noticed it when it's warmed up. I'll have to hammer on it while it's cool and see if it overboosts. What's the cure if it's the WG sticking?

Thanks,
Jim
 
Daron

Daron

Active member
Dig sourced some GM "High Temperature Lube" and reported that helped. I carb clean mine real good and that keeps it moving nice for a while.
Daron
 
C

croosr

New member
Yeah, a sticky wastegate is a good shot. My WG would be stuck after each cold start. I'd play with the throttle to bring the boost up to 15psi a few times and finally the WG would free up and then would operate normally, until the next cold start. The 'Dig high temp lube fix' helped, but didn't solve the problem. We finally pulled the turbo and did some 'clean up' machining on the WG hole in the turbo casting and polishing on the WG shaft. I guess there was some roughness that would collect junk, rust, etc. and would make the WG sticky. After that, it worked great, once the Dig chip got calibrated. Good luck.

Howard
 
T

turbojimmy

New member
On 2002-02-26 18:01, croosr wrote:
Yeah, a sticky wastegate is a good shot. My WG would be stuck after each cold start. I'd play with the throttle to bring the boost up to 15psi a few times and finally the WG would free up and then would operate normally, until the next cold start. The 'Dig high temp lube fix' helped, but didn't solve the problem. We finally pulled the turbo and did some 'clean up' machining on the WG hole in the turbo casting and polishing on the WG shaft. I guess there was some roughness that would collect junk, rust, etc. and would make the WG sticky. After that, it worked great, once the Dig chip got calibrated. Good luck.

Howard
Click to expand...

Okay - I think I'm convinced it's a sticky wastegate. It's only doing it after some hard driving or a lot of highspeed driving - i.e., when things are hot. There's a decent amount of carbon around the shaft - could be interfering when it's hot.

And, the cruise has gotten weird. It's surging now when I try to maintain a constant speed - boost, then sudden correction, booost, sudden correction, boost.....

So what's the cure? Do I have to take the DP off and lube up the WG?

TIA,
Jim

_________________
1992 GMC Typhoon: Stock, 13.7 @ 96
1987 GN: PT51, PTE 50#, LS1 MAF, T+, Ext., THDP, TT 3" duals, Walboro, Comp Cams 206/206, Level 10 trans/TC
http://www.turbojimmy.com

<font size=-1>[ This Message was edited by: turbojimmy on 2002-02-27 11:55 ]</font>
 
turbodig

turbodig

Active member
On 2002-02-27 11:54, turbojimmy wrote:
On 2002-02-26 18:01, croosr wrote:
Yeah, a sticky wastegate is a good shot. My WG would be stuck after each cold start. I'd play with the throttle to bring the boost up to 15psi a few times and finally the WG would free up and then would operate normally, until the next cold start. The 'Dig high temp lube fix' helped, but didn't solve the problem. We finally pulled the turbo and did some 'clean up' machining on the WG hole in the turbo casting and polishing on the WG shaft. I guess there was some roughness that would collect junk, rust, etc. and would make the WG sticky. After that, it worked great, once the Dig chip got calibrated. Good luck.

Howard
Click to expand...

Okay - I think I'm convinced it's a sticky wastegate. It's only doing it after some hard driving or a lot of highspeed driving - i.e., when things are hot. There's a decent amount of carbon around the shaft - could be interfering when it's hot.

And, the cruise has gotten weird. It's surging now when I try to maintain a constant speed - boost, then sudden correction, booost, sudden correction, boost.....

So what's the cure? Do I have to take the DP off and lube up the WG?

TIA,
Jim
Click to expand...

I've had a long, painful experience with
this...

My stock turbo started siezing in '95. After
a lot of experimenting, I found the GM heat
riser lube. While it helped, it was too little
too late to keep the WG from nearly welding
itself to the housing.

So, I got a 20g turbo, and put it on. *It*
started siezing not long after.

This one, though, wasn't as bad. The heat
riser lube has been really effective in
keeping that WG moving, although it has been
somewhat of a constant maintenance item. If
I don't goober it up in the fall when it
goes into storage and in the spring when I
take it out, I end up having problems. It has
gotten a lot better in the last couple of
years, I don't have nearly the problems I
used to have.

I guess I'd try the heat riser lube, and work
the flapper back and forth a bunch to get it
working smooth. It's gonna take quite a few
treatments to get it working well. Heat riser
lube actually seems to work even when the
turbo is hot, which is pretty amazing.

I also found some 2000 deg never-sieze that
refineries use. This also seems to work well.

Over time, constant use will work it out. The
two common items that I've found over the
years that seem to accelerate siezing, are
long-term storage, and leaded gas.

If you have to fix it, you can get the flap-
per out of there. You'll need a dremel or die
grinder, a punch and a wire welder. Can be
done at home, with those tools.

Later,

Dig
turbodig@yahoo.com
 
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