Low Boost

[94bluehd]

I used to be a regular user of the forum but all of the good tips helped me go 40K without many problems. All at once, I went from 7-10 boost to 1-3 and that's it! Is there a simple answer. I know it is not the gauge or a leak in the line to the gauge, I checked that and am getting excessive smoke. Any good ideas for trouble shooting procedure??

Thank you.

[Robyn]

Howdy and welcome back.
Check your vacuum pump and be sure its running a steady 26 inches (No wiggly needle allowed)

Check to be sure you have vacuum to the wastegate actuator.
If the pump is working ok and there is no suction at the actuator, check the plastic lines that run from the pump to the solenoid on the rear of the LH valve cover (Wategate solenoid) then be sure the line to the actuator from the solenoid is good.

If all this checks be sure you have vacuum at the solenoid and then if there is nothing at the actuator the solenoid is probably bad.

Vacuum pumps do go away as do the wastegate solenoids.

Also make sure with the engine off that the linkage on the wastegate is free to move back and forth.
If the wastegate has vacuum and the lever will move by hand (engine running) then the actuator diaphram is probably toast


If all this stuff works and the waste gate lever is closed tight then it could be a damaged waste gate (as in burned off)

Probably the vacuum system though.

Give it a go and let us know what you find

Robyn

[More Power]

GM says in their manuals that 15" vaccum is the minimum allowed when measuring at the vacuum pump. The several I've put a gauge on all delivered 20-23" of vacuum, and the needle on the gauge will swing about 2-3" as the engine idles. This is a diaphragm vacuum pump that is operated by an eliptical cam, so it will cause the needle to swing a little between strokes when measured at the wastegate actuator on the turbo. This needle swinging effect is more pronounced at idle, and it's all perfectly normal... :)

Jim

[chambie]

I had the same issues awhile back with a 97 3500 dually. I had really low vaccum, and was blowing black smoke when i asked for power. I was getting 23 in. at the solenoid, but less than 10 at the wastegate. If the pump, lines, and solenoid are ok. check the voltage at the solenoid. you should have a constant 12v + at the solenoid. This comes from the ignition switch. The pulsed ground signal comes from the pcm. If it isn't getting pulsed correctly, you will need to change the pcm. That was the case for me. I chased this problem for quite awhile before i got it figured out. I got lots of info from this forum. Truck runs like a top now. Hope this helps.
Lindsay