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Discussion Starter #1
Replaced the boost solenoid a long time ago when I actually accidentally had a MAP sensor unplugged. Occasionally when hot I'll have no boost or it will have the boost farts, where it will be zero until about 2000 rpm and suddenly the boost kicks in, leaving a giant trail of black smoke.

Unfortunately this only seems to be when driving. Both the vacuum pump and the wastegate actuator are original but function fine until when hot and only sometimes malfunction when hot.

The remedy for this is a blast of WD-40 into the solenoid and a long blast into the vac system. Haven't done this since last summer and this solution is very temporary, couple weeks to a month in the summer and frankly irritating. Because it usually happens when smoke is not desired, like in Friday traffic jam, or when I want to beat on the truck or when towing.

The truck is tuned hot so it sees peak 11-15 lbs of boost at times , and it's possible that boost vs intake temperature kicks the truck into derate possibly? Yesterday I got an SES light which I'm attempting to read today. Bluetooth OBD scammer number 9 must be dead :(

Possible fail points could be the MAP sensor, vac pump, wg solenoid that just sucks, or wg actuator.
 

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My truck is pretty much stock with exception of a turbomaster. I always was driving blind in my 97 without gauges and was surprised when I mounted the pillar gauges to find out I had zero boost most of the time. Truck was a dog just passing people on the highway empty. Then I was really surprised towing maybe around 10k in OD I was barely getting 5 psi, then when dropping in 3rd gear boost went to zero. I then did the "turbo master" mod and got rid of the vacuum set up. Like a whole different truck. Always peppy on the highway empty running a couple pounds. Down shifting when trailering gives more boost always. It's set to maybe 12-14 psi max. Never seen it go above 15 anyway. Once or twice I've gotten a boost code can't remember what it is. But never had any derate.
 

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My truck is pretty much stock with exception of a turbomaster. I always was driving blind in my 97 without gauges and was surprised when I mounted the pillar gauges to find out I had zero boost most of the time. Truck was a dog just passing people on the highway empty. Then I was really surprised towing maybe around 10k in OD I was barely getting 5 psi, then when dropping in 3rd gear boost went to zero. I then did the "turbo master" mod and got rid of the vacuum set up. Like a whole different truck. Always peppy on the highway empty running a couple pounds. Down shifting when trailering gives more boost always. It's set to maybe 12-14 psi max. Never seen it go above 15 anyway. Once or twice I've gotten a boost code can't remember what it is. But never had any derate.
Robert, did u turn up your pump or add a chip with your TurboMaster? Have been considering deleting my vac system and go mechanical.
 

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I would check the wire connections at the solenoid plugs while the motor is running for poor connections...

Mine is OBD1 and I believe the turbo & vacuum setup rod may be slightly different but I added an external helper spring to mine that keeps mine boosted so if that vac system chits the bed mine will never go to zero. I just added a spring that would be used for an old wooden screen door works like a charm, so I have both.
 

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Discussion Starter #7 (Edited)
I can swat the top of the solenoid with my hand and the boost will come on, yet if I pull the line off the actuator, I lose all vacuum to the actuator. Have to hook it back up and swat the solenoid for it to come back on.

Sprayed it with wd40 on Tues and it was acting up by Friday. It was acting up in the driveway so I was able to mess with it. It's working now but function is pretty sketchy don't trust it.

After many years of hanging on to the stock system for fuel efficiency, im starting to have enough going wrong with the truck that I won't be able to to replace the vac pump when it goes. Going to see if I can find my old boost solenoid, I kept it ....

Crankme do you have a picture of your semi spring gate?
 

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Looks like the boost solenoid may be bad?
Did you check all the vacuum lines?

I did what @structures did 12 years ago with a TM from Heath (NOT homemade) and never look back.
I know most member here will flame you when we suggest the mechanical wastegate aka TM.
The cost and time to maintain and troubleshoot the vacuum system is just not worth the time. Plus the system is aging 24 years old to be exact in my truck. It is well above the life expectancy that GM ever put in this truck. IMO.
 

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... I still use the vacuum actuated wastegate.... there is a bit of a saftey factor to it as well as efficiency.

Not to say I dont plan on going to a mechanically actuated wastegate (relatively soon)

...to each is their own... and dont fix it if it's not broken.... :thumb:

And troob, if you need a boost solenoid PM me I think I have a spare or two if your spare dosent turn up or does not work (also... can we not get these on RA??)
 

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yep, I agree that removing good, working parts may not be the best plan, and if the vacuum control system only needed the boost solenoid, I’d just replace that. But once you start getting vacuum leaks from the aging plastic fittings like I did, a TM can be a quick and effective fix.
 

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Discussion Starter #12
Thanks everyone. Been having trouble with the forum eating my replies with expired tokens so I'll make this quick.

I decided to douse inside of the turbo actuator and.that seems to have helped but it's starting to fail again. Boost is strong one day and sort of flimsy the next. I may have weak vacuum in general and a little lubricant is just buying time. Trying to find or make a vac gauge. I have spare solenoids and spare vac lines just can't find them on the time to mess with it.

The turbo has been making a very light screeching sound on throttle lifts. Found lots of shaft play.What was a very tight cartridge when I ported it 10k ago is now loose as a goose. It seems like it's gotten worse hopefully there is Time left in it. I know gmx turbos are renown for being loose... Hopefully it's just a leak. need time to hunt boost leaks maybe that's what it is....
 

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Discussion Starter #13
I found the spares last night tucked inside a filter box I'd looked past 20 times.

Both spares act up as well. They work at first then get weak and zonk out as soon as the heat gets to them, I assume. My vac lines all seem to be in good shape, actuator holds, etc.

I guess its new solenoid time. Whats funny is, I have a window track spring that somehow got left from a scrapyard run laying on my passenger side footwell I can make an impromptu boost helper deal like crankme69!
 

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Discussion Starter #15
Yes vac pump is working. A spare boost solenoid from a Paleyjim fixed the issues. The failure on these things is sooo weird.
 
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