Boost going past 25 psi, why?

[Jeff822]

I have an evo III big 16g turbo with all supporting mods set at 18 psi, but today i floored it and boost didnt stop at 18 and hold, it shot past and kept going and going untill it was well past 25 pounds so i let off quickly when i noticed it, i know i have a boost leak somewhere, and right now i am on stock sidemount and all stock piping since i just sold my old intercooler+piping to buy a dejon full race fmic kit with short route piping it will be on my car tomorrow, but why would my boost jump like that? boost creep? the turbo is brand new had it on my car a little over 1 month, what could it be?

 

[RipperXX]

Maybe one of your lines from your MBC blew off or has a leak via dry rot?
Maybe the adjustment screw on the boost controler fell out?
Waste gate working correctly?

I assume you are useing a MBC (I didnt look at your mods) but at least it was on stock pipes.. hell dont worry about it throw some more fuel at it and call it good seriously though. The few things I mentioned above are all I would know that can cause it to suddenly sky rocket out of the blue.

 

[JaxTalonTSi]

What your experiancing is boost creep. This is a common issue with alot of the EVOIII 16gs. Mine did it as well. Some people have reported that installing an 02 sensor housing with a tubular dump on it helps fight against the creep issue, if not get rid of it totally.

Somtimes a faulty manual boost controller can cause boost to creep as well.

Also, a boost leak will not cause boost creep.

 

[dalatinromeo]

Maybe one of your lines from your MBC blew off or has a leak via dry rot?
Maybe the adjustment screw on the boost controler fell out?
Waste gate working correctly?

Def check these three things first, and post back the results.

 

[Jeff822]

I'll check the boost controller lines today, i dont think it is broken it is brand new also, but i'll check it, and will do a boost leak test today after i get my new intercooler on.

 

[olmytsi]

If it creeped there, than yes it's creep. If it just shot there, than it's a boost control issue.

 

[CanadianTSi]

If it creeped there, than yes it's creep. If it just shot there, than it's a boost control issue.

This is correct, if it went to 18 and then slowly went up from there its creeping, if it just shot straight up to 25+ then it sounds like a hose for your MBC popped off or something.

 

[crunchymilk]

definitely boost spike. Happened to me when I accidentally kinked the boost source line to the MBC. Check all the lines, has this always happened?

 

[Jeff822]

No, it has never happened before only when i was still on the t-25, all the hoses are still in place, i didnt check to see if they were kinked yet, i will do that in a few minutes, ever since i took my front mount off i try not to go past 10 pounds, once i get my intercooler on i'll have my local tuning shop take a look at everything to make sure its all working good, btw the dejon intercooler i got will not fit my car without some modifications to move the trans and oil coolers and the trans dipstick so i will have to send it back and get the street kit i guess, they shouldve been more specific and said on there website that the kit will not fit automatics without more midifications. thanks for the replys

 

[oldman]

What your experiancing is boost creep.

What part of his post made you so sure that he has boost creeep?

Some people have reported that installing an 02 sensor housing with a tubular dump on it helps fight against the creep issue, if not get rid of it totally.

O2 dump is the worst solution for boost creep aside from adding a CAT. An O2 dump will do very little to help combat boost creep unless it's a minor case of creep, like 2-3 psi, to begin with.

Somtimes a faulty manual boost controller can cause boost to creep as well.

Mind explain how a faulty mbc can cause boost creep?

Also, a boost leak will not cause boost creep.

This I agree.

definitely boost spike. Happened to me when I accidentally kinked the boost source line to the MBC. Check all the lines, has this always happened?

"Boost spike" refers to when boost shoots past the setting and immediately settles down to setting. What Jeff822 is experiencing is what is commonly refer to as "out of control boost", "all out boost" or "infinite boost". The only things that can cause this is:

1. Little to no pressure signal going to the wastegate actuator.

2. A defective actuator.

This is only true if the original statement of "but today i floored it and boost didnt stop at 18 and hold, it shot past and kept going and going untill it was well past 25 pounds" is true. If it pauses for a second at 18psi before it creeps up as RPM increases, then it's boost creep.