86 951 Driver

Went to watch the KC Chiefs training camp today up in St. Joe, MO. It is about an hour drive. The weather was perfect, but I wanted some a bit more fun than the miata so I took the 951, obviously. I put a Vitesse chip and 3 bar FPR in last weekend, set the boost to 15 PSI and have been grinning from ear to ear the past week or so. It has been running great. Well on my way to St. Joe I stopped for some gas, about 3 miles down the highway I realized I left my gas cap there. I pull a U-turn and try to get back up to highway speeds when my car pops, and starts to stutter. I thought it was something big. Open the hood and my hose for the Recirc valve blew off. I reconnect it and tightened it down well. Car runs fine, boost is where it should be.

After training camp the wife and I got lunch, on the way there the car ran fine. On the way back home after lunch I floored it and saw the boost gauge hit almost 20 PSI. I thought WTF. So I let out immediately. I tested this a few more times, but after I saw the boost gauge go past 15 PSI I would just left off. Mind you the car ran great, but I know that is more boost than I should be running. I turned the MBC down, no change. I turned it all the down, no change.

So over the course of the day my car cannot regulate boost properly. I did a lot of testing when I set the MBC for 15 PSI last weekend. I made a lot of runs in 3rd and 4th gear.

Recent changes: A month ago I put in a used LR Dual Port wastegate, hooked it up with a LR MBC set to 10 PSI to be safe. Last weekend I put in a 3 bar FPR and Vitesse AFM chip. Could my waste gate be stuck shut, or could my MBC be bad?

homerj

i would say mbc is bad if it worked fine after the lr waste gate install. i had same problem. bought a fancy one and still didnt work. ended up getting lr mbc and worked great. mine failed over night. seemed to work until i adjusted it one day. hope it helps

86 951 Driver

MBC was new when I put it in. It was a few years but never used. Could it just need a rebuild?

User 52121

My bet is that one of the WG lines fell off. Most likely the one on the top port. Check your vac lines.

86 951 Driver

I'm going to get under the car after work today to check, but I pulled on the lines and could see they were still connected to the wastegate. Could I somehow bypass the MBC and connect the wastegate directly to the intercooler pipe? Would this run the gate on just spring pressure?

86 951 Driver

I ran a few tests tonight. I hooked up the top port on the LR Dualport WG directly to the port on the intercooler pipe. I still was boosting way over 15 psi. This test took the MBC out of the equation.

I then unhooked all the lines to the wastegate which allowed the boost to go well over spring pressure. I assume this wastegate is stuck?

Carlsbergas

I had something similar my boost went from 15psi to full 22psi and my boost **** just didnt work even if i dialed back to minimum i still had 22psi when i came back home, i found out that one of the hoses from lr waste gate disconnected from my intercooler pipe


When i connected it back i was able to regulate my boost again

86 951 Driver

None of my lines have melted or come off.

I unhooked both of the lines to the wastegate and that I think should run the wastegate on just spring pressure. Isn't that correct?

Chris White

Simple test:
both lines going to the wastegate should be sealed - they should not 'leak' air. You can either blow into the lines with your mouth to see if they leak or use a Mity Vac and see if you can pull a vacuum. if they don't hold pressure or vacuum then you have a leak in a connector, line or a ripped diaphragm inside the waste gate.

86 951 Driver

I just got off the phone with Dave @ Lindsey Racing, he recommended the same thing. I don't have an air compressor so I can't test applying boost to the diaphragm. I will be testing this tonight.

Chris White

you don't need an air compressor - just blow on the end of the line. If you can keep blowing then its leaking, if you can't blow any more then its good.

User 52121

When you connected the top port straight to the banjo, what did you connect the side port to? Did you leave that open to atmosphere or was it connected somewhere?

86 951 Driver

The side port was connected to the MBC. The MBC was not connected to anything at the other end. I figured this would be the same as being open to the atmosphere. The MBC was all the way turned down.

86 951 Driver

Dave mentioned that if I apply air pressure to the top port I should be able to hear the wastegate open and close. I should hear a bang noise. If I don't hear that then most likely the diaphragm is shot.

86 951 Driver

I did a little more testing tonight. I took my Mity Vac and pulled vacuum on the top port. It held vacuum no issue. After that I rigged up a setup to pressurized that same line. I could hear the valve shut when the pressure was released. My only thought would be the valve is not opening all the way.

Any ideas?