Boost Spike and map limit activation

Hi all,

I am facing a boost spike condition .. Using an MBC , HX 35 . I have set the map limit from 5000 rpm to 7400 as 280 KPA

Some times the map limit gets activated at 5400 some times at 6700 .. Is it a wastegate problem that it isnt opening and the desired boost is not holding and its spiking ? or am i missing some thing ?

what are the cons of shutting off map limit ??

Even with a MBC you should get reasonably consistent boost. You'll always tend to see a slightly higher boost in higher gears, but generally you should be within perhaps 10 kPa. If you're seeing inconsistent boost pressure from one pull to the next, I'd be suspicious of the boost controller, the wastegate, or your plumbing.

I'd start by getting the MBC out of the system and plumb the wastegate directly to boost pressure. Prove that under these conditions the boost is consistent and repeatable. This will eliminate the wastegate as a potential fault. If that checks out fine I'd suggest the MBC might be your issue.

The MAP limit is there for engine protection. Ultimately it sounds like you have some issues to work through and disabling the MAP limit is a bandaid rather than a fix. Understand that disabling the MAP limit will leave you with no protection if the wastegate fails completely.

Thanks Andre for the response.

It turned out to be faulty wastegate.. While checking, i also found some restriction in wastegate dump tube.

Now holding stable boost.

I'm glad you found the problem!