Surging Turbo

[Lawn Cher']

Quick question...

In my '97 K2500 Suburban, when cruising at highway speeds under what should be a fairly constant load, I hear my turbo spooling up and down at a fairly even and quick interval of every one or two seconds. It is even more obvious now that I have an open intake and 3.5" straight pipe. It has 173k miles and I replaced the vacuum pump somewhere between 100 and 120k. I'm suspecting the vacuum solenoid, but am open to other ideas. Wouldn't that tend to just fail rather than have a strange cycling symptom? I don't have any black smoke pouring out either, so I know it works under acceleration.

Thanks!

-Mark

[Bennie]

i would suspect a leaking line if not the solenoid-vaccuume switch. either one could be intermitient.

[Scrufdog]

The factory programming of the ECU will cycle the wastegate open and closed to keep boost below 7-8 PSI. The keep it from cycling either get a new program (ECU/chip), get a manual wastegate controller, or both.

Before you do any of those however, get boost and egt gauges.

[94sub]

Replace the vacumn lines first. Many people overlook this and add expensive hard parts with no improvement. They are only $15.00 from the dealer and are the best place to start. Remenber that they are plastic and get hard and crack with all the heat.

[Scrufdog]

or spend the $5 it costs to make a manual boost controller, and eliminate the vacuum lines, and solenoid.

[Scrufdog]

actually the best way to start checking to see if there are any actual problems is to get a vacuum tester gauge, and check for at least 17 inHg (inches of mercury a.k.a. negative PSI) at idle on the line going to the wastegate. If that checks out then the vacuum system is not leaking and the up/down your hearing is, in fact, the factory programming

[stumppuller]

did u check line for leaks?