DTC 78 - wastegate selenoid fault

[kevin77]

Ok,

I had a turbomaster boost controller on my turbo and I couldn't get it tuned down enough without loosing too much power. So I removed the turbo master, put the wastegate actuator back on and hooked up the vacuum lines again.

everything is fine until I hold it at about 75 mph - the boost keeps building and it throws a code - I was monitoring the boost with a tech1 and according after throwing the dtc 78, the boost did not drop. According to the DTC 78 description on alldata - it is suppose to drop boost.

I figure I am down to one of two things:

1) I have the vacuum lines crossed at the selenoid

2) the wastegate on the turbo is worn out?

Am I missing something? or are these my only two alternatives?

Kevin

[gmctd]

Raw vacuum into the center port on the solenoid, wastegate actuator on the side port

25"vac at the pump, 15"vac at the wg actuator.

[JohnC]

If the boost doesn't drop off while DTC 78 is set, the wastegate must be stuck shut (rod pulled in). With the engine off the arm should move freely through about 90 degrees. This could also explain why the Turbomaster didn't perform correctly also.

[kevin77]

I measured the vacuum on the wastegate actuator and got 25", so I switched the vacuum hoses around on the selenoid - the little brass thingy in the selenoid now goes to the vacuum pump.

I checked with the vacuum gauge and it now read 20" - I took it on a test run up to 70-75 mph and it now seems to be operating correctly - the tech 1 said it was running at the least 20% and about 6 psi - If I drop it down to lower speeds the boost drops too.

Kevin