Weird Boost Issue
 

So I hope I can describe this properly...

The car will make normal boost most of the time (22ish psi) but once in a blue moon it will make 14.5 psi peak, and only 14.5 psi. Thats what the stock E4 boost level is about. Once it starts making 14.5 psi the car will not allow me to get over it at all. Sometimes restarting the car fixes it instantly, other times I go in at night and when I go to drive it tomorrow it is back to normal. I assume it's some sort of wastegate issue but the inconsistency and rarity of it makes it hard to diagnose. I have tried two separate boost control methods. My regular EBC and an MBC. Issue persists on both. I also wanted to stress that this is very rare, happened tonight for the first time in over a month.

The car is tuned, has no boost leaks, strong compression, and probably any other thing you'll ask.

Boost control is handled through an AEM Truboost.

Thanks for any possible solutions, I couldn't find anything that matches my issue online.

DO you have Tephra Mods? Do you have the CEL set to flash on knock? What does logs say if your logging. Could be getting bad Pump Gas, and hitting high knock, which will cause low boost. That is stock WG pressure. Look there.

Tuned on Ceddy. Octane stays at 100 through the whole pull, I have no consistent knock. I assure you the issue is not tune related.

Does your knock sensor flash when this happenes?

Most of the time, EVOscan will stay at 100 octane, even if it's not. I have never got that setting to read write. But sounds like you know what your doing. Carry on.

I have had it change.

Anyway, I found the issue. Going to need to replace the wastegate actuator. The wastegate is rusting out and sometimes sticking. Apparently a somewhat common issue on older Evo 4s as the way the hood vent and heatshield are designed the wastegate just gets tons of water on it. Supposed to get worse over time. Going to replace it with a Kinugawa unit or just finally buy an Evo 9 turbo.

Thanks everyone.

And sorry Race if I came across as a bit of a dick, didn't mean to sound like one.

No worries. Glad you figured it out.
However, you still may need to adjust that tune with the new WG...

Possibly. Have to buy one first. Assuming that the new spring is still the standard 1 bar/14.7 psi setup that the TD has stock I should be fine. Adjusting a tune takes a couple minutes anyways.