Hard clunk and unstable boost

[rdjarvis]

Good morning!

I just picked up a 98 GST with some questionable parts on it. The only markings on the "16G" turbo are AR70, a no name FMI, KN filter and an old turbosmart MBC. It seems to hold boost just fine below 10psi but when you get on it the boost gauge tops out above 20 and a loud, aggressive clunk happens. It feels like the car hits a brick wall and all power stops. Then it drives just fine at low boost/rpms. I played with the MBC and no change. I took the MBC off completely, no change at all. Please any advice would be awesome!!

 

[boost97gst]

Do you know what injectors you have? What fuel pump? No tuning solution i assume.... A wideband? If none of the above then you simply can not run that much boost on stock injectors,pump.

 

[rdjarvis]

Thanks for the input. I just put the car up on jacks and I'm gonna take all the " questionable parts " off, run a boost leak test and start reinstalling everything. Just for peace of mind. The injectors and fuel pump did cross my mind. Would the lack of fuel cause the aggressive "clunk" and complete power stop? It felt like the brakes were being slammed on. I guess I should go ahead and get some sort of tuning software too.

 

[boost97gst]

I have never owned a stock dsm but it COULD be fuel cut you're feeling. IDK honestly. Heard its like hitting a wall

 

[Colt4G63 also]

I've felt it, and that's what you're feeling. That's too much boost for no tuning solution. If you can turn it down to 10-12 psi you should be fine. Twenty is too much.

 

[rdjarvis]

That's what it feels like. I'll get working on it. Thanks for all the help!

 

[mean4g]

you might also look into a boost leak check, and checking the plug gap. Recommend BPR7ES at .025" if you plan on running 20 pounds..

 

[Marchev]

16g turbos are notorious for boost creep, when you keep them internally gated. That's why even when you take the MBC off it still spikes. Sounds like someone decided to just slap on a bigger turbo without any other mods

 

[rdjarvis]

You guys are great! Thanks again for all the input!

 

[rdjarvis]

Installed an Eprom ECU and DSM link is up and running. I'm putting in the Walbro 255 fuel pump and 1150 FIC injectors this morning. Time to see if this fixes the problem... Let the fun begin!

 

[livedsm4g63]

It will fix it.
Right now, that is the same setup on my 1g. I only see 45% duty cycle at 22psi. . Id rather not need the extra duty cycle, and have it, then need it and not have it.

 

[rdjarvis]

I got all the parts in thinking it was going to be easy....then...after two hours cursing the HP Fuel line on top of the tank I found out the bottom fitting spins, unlike the top. That was annoying. I should have read ALL the threads before.