boost problems help!!!

[Steve-0]

k here's the scoop, couple days ago my truck started acting up and well my boost gauge was screwed so couldn't really see what it was doing yesterday i bought a new one and just finished putting it in and took her for a drive.

k now this is what it's doing when i take off i get my lil tuff a black and off the truck goes builds it's boost up to bout 13 pyro's sitting at around 1000 lil higher, then all of a sudden boost drops down to 0 truck bogs out hard and out comes the black. then if i let off it seems to smarten up a lil but now i only got bout 5 psi and holds there then once and a while i guess whenever it decides to if i give it some throttle one time it will get boost then drop or it won't even get boost and again just pours out the black, any ideas would be great. i guess more so what would be the best place to start looking for the problem

[ZZ]

I just read here somewhere about a similar problem and the vacuum pump was faulty.

[a5150nut]

What rpm is this happening at?

[brypay]

Check your boost solenoid. Depending on your truck you will have 1 or 3 similar looking black boxes on the drivers side above the valve cover; it's the one nearest the front of the engine if yuo have 3. Your problem reads like a boost solenoid problem but could be a failing vacuum pump or a faulty vacuum line. The waste gate controller could also be going.
My first guess would be the boost solenoid.

[Steve-0]

ya i know the three solenoid they were replaced bout 3 days ago, heh so i unno unless it's a faulty one or the connection itself, but i just drove 350kms tonite and i noticed with the thing even at a 100km/h and i go to pass there's nothing then bang all of a sudden after awhile it kicks in and up goes the boost then all of a sudden after it hits bout 13 it bogs down and boost drops to 0, then with the peddle still down it will hit boost again even at 140 km/h then looses it again . so i unno i'm going to check a few things tomorrow and see what happens but ya kinda turning into a piss me off special

[Bnave95]

ya i know the three solenoid they were replaced bout 3 days ago, heh so i unno unless it's a faulty one or the connection itself, but i just drove 350kms tonite and i noticed with the thing even at a 100km/h and i go to pass there's nothing then bang all of a sudden after awhile it kicks in and up goes the boost then all of a sudden after it hits bout 13 it bogs down and boost drops to 0, then with the peddle still down it will hit boost again even at 140 km/h then looses it again . so i unno i'm going to check a few things tomorrow and see what happens but ya kinda turning into a piss me off special
When this happens,do you get a SES li8ght on the dash? Recheck your vaccum lines.The rubber connector are tight and the plastic lines had not cracked,rubber ends are'nt split.

[Steve-0]

no ses light on but a buddy of mine was saying that what it seems like it's doing is overboosting and then the computer is shutting it down, has anyone heard of that before like let me know. thanks

[DmaxMaverick]

You could have a vacuum leak. The wastegate solenoid operates in a continuous cycle, applying and releasing several times a second when near the boost cut out pressure. If you have a leak, it could be building up OK when on steady, but can't keep up when it starts to modulate. The wastegate solenoid/valve could also be sticking, causing it to stick between cycles.

[ak46champ]

I had the same problem with mine, it was the waste gate solenoid. You can buypass the solenoid by just hooking up the vacuum line directly up to the line that goes to the wastegate. I suspect that will tell you if it was the wate gate solenoid ($30 anyway). That will keep the waste gate closed all the time. My wastegate solenoid broke and I havent fixed it yet. I just hooked it directly up to the vacuum pump. Prior to doing that I hooked up a vacuum gage in various conditions and found that the vacuum kept the wast gate closed all the time. Either with a load or with out. Mashing the pedal or babying it. That was done prior to me breaking the plastic tubes where the vacuum line hooks to. Hense the reason why it is broken now. I was trouble shooting another problem in the process.