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2G Bad bang above 14psi

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DSMrightontime

Proven Member
40
5
Dec 11, 2014
Atlantic, Virginia
So, I removed the boost restrictor in the boost control solenoid and I went from 12 to 18 psi, BUT, when I hold past 14psi the engine bangs violently and loses power for a second. It immediately returns with boost holding at 12-10 psi. What gives? It feels like the must violent Rev limiter ever. Anyone?
 
when I hold past 14psi the engine bangs violently and loses power for a second
Well, I thought i was following the free mod section on this site as the primary steps before I went with the real mods. The smart remark isn't necessary or helpful. If removing the boost restrictor shouldn't be done until after heavy mods are completed, why is that one of the first steps after maintenance in this site's upgrade path? Jeez

If you were following the upgrade path, did you also notice the part where it said you can safely increase boost 1-2psi? If so, then it should make sense why the car wouldn't hold past 14psi, no?

As far as why the car was cutting out, it's anybody's guess. Like the others have already mentioned, you're most likely experiencing fuel cut. However, detonation, poor ignition, boost leaks, or multiples of these issues could be the cause.

You also have a FMIC, which will increase efficiency and provide for a more dense intake charge. This becomes a problem when most of the other parts on the car are stock. Hence, supporting mods being an important part of even the "free" upgrade path. There's a reason FMIC and hard piping is not on that page. If you followed the path verbatim, you'd probably be fine. But, that's not the case here.

Additionally, if you want to limit boost to the lowest it will go, connect the wastegate actuator nipple directly to a boost source, as I mentioned earlier.

Here's the deal, dude. Most of us have probably been at a point with a DSM where time, money, know-how, or all of the above limit a build. At least, I know that's been the case for me personally. Back when I started modding DSMs, there weren't nearly as many assholes on forums like these telling me what not to do. You won't find many of the guys who have been around a while giving you some tough love for the hell of it. It's because most of those guys have seen scenarios like this play out time and time again. And because of that, the "why" is usually secondary to reversing whatever issue overzealous tuners create. It's natural to want to turn up the boost, but as you found, it will often create issues rather than positive results. If left unchecked, those issues could become serious problems. Be glad you're not left with the latter.
 
Removing the BCS restrictor (done properly) should only raise boost by about 2 psi max. Typically, with the restrictor removed, I have seen a spike to 15psi (on three separate 2gs), then settles to 13 psi. The restrictor alone should not be the culprit. Boost cut is definitely what you are experiencing.

I would:
  • BLT perhaps to 18 psi
  • Check waste gate operation. You may have a sticking actuator.
  • Check your plugs and plug wires.
  • Put a wide band o2 sensor at the top of your mod list.
 
Last edited:
A quick follow up, and the reason I wanted to determine why I was experiencing the issue;

  • BLT perhaps to 18 psi
  • Check waste gate operation. You may have a sticking actuator.
  • Put a wide band o2 sensor at the top of your mod list.
Dead on! Found significant leak at a coupler. Fixed

Spiking returned and progressed to a total fail in boost control. Waste gate opens fine manually with actuator arm removed. I believe that only leaves actuator failure, correct?

Plugs and wires are good.

Wide band o2 is at the top of the list...
 
you can test the actuator by 'blowing' into the line connected to it. you can use a compressed air nozzle, if you turn down the supply pressure to 14 psi, to blow into the line. Just blow into the line and watch the actuator move. the movement should be smooth and the arm should extend all the way.
 
Yup, that was it. Arm was stuck. After spraying the arm with liquid wrench and manually freeing it, I hit it with 14 psi. It drug slowly about 1/4" then would kind of let go and extend a little faster. I swapped it with a spare and it's good to go!
 
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