Clint's 944

ARGH...I need help!

I can't seem to control my boost levels. First gear will peak around 10psi, Second around 12, third around 15 and fourth shoots way past 15 but I let off before.

So far I have...
1. I pulled the control line off the wastegate and it would peak at 10psi. So, it has to be a control issue right?

2. Checked the MBC and it looked pretty old and dirty so I ordered a rebuild kit from lindsey and replaced all of the internal parts. Same issues....

3. I disconnected the control line from the MBC and ran the car and there is plenty of air coming through the MBC and varies with **** setting. Same peak at 10PSI

4. I blew into the control line to see if it was leaking or maybe pinched and it seemed to hold pressure fine. I drove the car and held my finger over the line and can feel a small amount of air coming out. If I cap it with my finger I gain about 1-2 psi.

Any of you guys have an idea where to look next? I am at a lost, I'm thinking the wastegate diaphragm may have a tear in it?

Thanks for any help!

ibkevin

Interesting.. I've found the same in my car in gears 1-3, but 4th does not shoot anywhere.

I'm running an EBC and a new cat has provided topend zoom, but the low end peak is ~1bar.

Could there be a stock exhaust collapse? Running a 3" here so no chance of that.

Tom M'Guinn

What kind of wastegate are you using? With the stock wastegate, if you pulled the lines you should get max boost...

Clint's 944

I have a 3in exhaust, no cat and running a lindsey dualport wastegate.
Saw another post from Lindsey that said if you pulled the control line, the wastegate would run off the spring (10psi). If it did, then it was a control issue.. ie the MBC but that has been rebuilt and I still don't have boost control.

Prior to this, I would hit 10-12 psi in first, 14-15 in second and 15 in third through fifth.

Tom M'Guinn

I see. Dual ports are different that way. Sure you have the lines configured correctly for that wg?

Clint's 944

They are hooked up right. I've been running the setup for a year without any issues. This is a new issue that came up last week.

If the diaphragm was torn in the wastegate...
A: would the wastegate still function in single port mode?
B: would the pressure from the control line keep the valve closed or open?

ibkevin

This sooo sounds like my problem. I did a vacc check on the Tial diaphram because I suspected a leak but the diaphram held to I suspect the solenoid valve, i.e; control.

Again, my system is a few years old and would put your *** in the seat easily when it was new.

Clint's 944

So, today I vacuum checked the ports on the wastegate.
The top port holdsvacuum. No loss after 5 minutes.
The side port (control port) will not hold vacuum, but I assume this is normal.

So, the wastegate should be good right?

What else can I check?