So Ive had my car boosting about 22 at spike ever since I rebuilt it. Sometimes it would spike to 25, put out a cloud of fuel smoke and bog.

I had a leak in the intake hose between the airbox recently so I replaced that hose. When I did that I put a new n75 in that was attached to the hose as I bought it. It was out of a 98.5. After I ran that the car seemed to run a little better as I didn't have that leak after the maf anymore. It was more steady boost but still spiked to 22.

The giac tune I have is for 16. Before my rebuild it seemed to hold steady at 16, for the day it ran right before It blew.

Now today on the way to work it seems as the n75 broke. Its the same symptoms as when the hose to the high pressure side of the turbo came off, like the wastegate wont open at all. boost will keep climbing over 25 if I dont let off and that's only at half throttle in first. On the freeway I cant boost at all, because the shock to the turbo is so abrupt.

I unplugged the n75 as well as ran new lines to the wastegate and turbo. Neither of those did anything. Still haven't thrown a code. I figure the n75 is bad as it is the boost solenoid which controls the vacuum to the wastegate. Has anyone had problems like this with the giac tune either? Im going to try running my friends mbc on my car tomorrow in place of the n75 to see if it works.

 

I have my old n75 if anyone thinks I should try that as well

 

Could be a bad N75 valve or the WG actuator arm tension is too high causing the wg to be open less for the same pressure supplied. That could have happened during the build. Arm might not even be connected anymore.

If you want to test this, you can bypass the N74 valve by putting the 2 vac lines together. That should cause the car to boost to 5psi only, if it is higher then that there is an issue with the WG.

 

Sweet, thats what I was looking for, a way to test em out. Ill do that and report back on what happens.

 

Did it and car ran about 7 to 10 lbs. Guess when I put the new turbo on I never checked the wg arm.

 

Mike, is there somewhere specific the wastegate arm needs to be or is it a trial and error kind of thing adjusting it up and down?

 

Pretty much trial and error. There are was to set it using a compressor to see when it starts to crack open.

 

I guess Im just gonna run a manual boost controller instead. I don't want to mess with the wg cause its too hard to get to.

 

I was having the exact same problem. I replaced the N75 valve but it seems like it already broke again. Did you adjust the wastegate arm or just throw on a MBC? And if so how did everything run with MBC installed