Boost spike to 14psi on bone stock FD, any ideas?
 

Got a local guy who has a bone stock fd.

His primary turbo boost to 14psi. So his boost pattern is 14-8-10 or something like that. He said his secondary turbo isn't boosting all that strong but the primary spikes to 14psi.

Wondering if anyone had any ideas. Car is completely stock, has precat on it and all that stuff.

Thanks,
Darren

maybe the pill in the precontrol actuator line turned and now its either a bigger or smaller opening.

That could be very possible, those things are so damn small. Simply just pop off the house and re-seat the pill I take it?

yea just pull the hose from the compressor to the bottom actuator and look through to see if the light is right through the middle or not. oh yea when i took mine off my car the pill slid out pretty easily and i didnt notice and then found it on the floor.

Just remove the line completely and put on a new empty line to test in a safe manner. If the car is still boosting about 10psi you most likely have a crack or break in a line leading to the wastegate control somewhere earlier in the system. Those stock pills are a PITA to get out of the stock vac line.

Possible clogged cat or precat.

Make sure the precontrol hose isn't leaking.

Dave

NOT...

Dave

Replace the pre-control line, don't reuse it.

had the same issue on a stock car and somehow was gone once the cat was replaced

How could a bad cat cause 14PSI primary boost?

I realize my response is contrary to the fact that opening the exhaust is more likely to cause a spike. However in my experience when I changed out the cat I went from a 14-8-8 pattern to close to a 10-8-10 pattern. Since his car is stock it may be beneficial just to swap out the cat prior to manipulating the twins.

The cat makes no sense.....it is 1000x more likely to be a problem with the pre-control line.

My impression is that the turbo pre-control is for the purpose of spinning up the secondary turbo in advance of actually using its output. I thought a failure of that control line would result in the secondary turbo not spinning up, and would cause its slower response to demand. How am I wrong?

If the pre-control failed to open the secondary spool up would suffer, but that "extra" exhaust would flow thru the primary turbine causing an over-boost (before a delayed transition)...

Yeah his secondary turbo runs like ass, so he says. I gotta take his car for a spin.. but it has 70k on that engine.. and I don't have time for shit.

Interesting, and that's the *only* thing that changed, then I believe you. But it's entirely counterintuitive.

Inspecting the cat would be a reasonable first step, rather than replacing it. Failed cats almost always become apparent after a little bit of poking around at it.

Dave

don'tlift,

Thanks for your response. I didn't realize the blocked flow to the secondary would be "re-routed" to the primary's turbine.