boost drops from 19 psi to 14 psi

['89beretta]

This may be a stupid/common question, and after doing quick search, it might be a boost leak that's the culprit. Tell if I'm wrong. Most people have the problem of boost creeping up. My problem is boost falls.

MBC set to 19 psi, but by 5500 it drops to 15 psi and by 6500 it's at 14 psi. Is this normal? (see mods in profile). It seems to hold fine in the lower rpm: example, on the freeway in 4th gear, flooring it holds from 3000 - 5000 just fine, 19 psi. As rpm rises higher, the boost drops. I was under the impression that if I had a leak I wouldn't be able to hold that high of boost at all.

Is there anything I can do to the stock wastegate to hold boost better? One of the reason's I though this might be normal is because on Evos the boost spikes to 19 but drops to 16. This isn't life or death, just wanted the car to run a little stronger in the upper rpm range. Thanks.

 

[ECLIPSE4x4]

I would not run the T-25 that high regardless.

What boost controller are you using?

Also the EVO drops in boost becasue the ECU regulates that.

 

[Defiant]

[QUOTE='89beretta]MBC set to 19 psi, but by 5500 it drops to 15 psi and by 6500 it's at 14 psi. Is this normal? [/QUOTE]
Yes. The motor's outrunning the boost coming at it.

 

['89beretta]

14b, not t25. Home made ball and spring type MBC.

So there's no quick fix for this huh? Thanks for the reply. Just wanted to make sure this was a normal thing.

 

[ECLIPSE4x4]

My bad, I didn't pay attention to the year car.

Stock BOV, or is it crushed?

I am also going to go against Defiants beliefs here... I don't believe in the home made boost controllers. They seem to also have issues. I have a hallman and never once had issues with boost creep or boost bleeding.

Have you ever did a boost leak check? If not, go to www.vfaq.com and look up how to do a boost leak check.

 

['89beretta]

Stock BOV, not crushed.

A homemade MBC seems to work for a lot of people since it's the same basic design as the name brand ones. Other than losing boost, it's pretty accurate. 1/4 turn for each psi.

I'll have to make my way to Menard's (like a Home Depot) one of these days to make a Leak Tester.

It'd be interesting to see if other's have this problem with cheap/homemade MBC's.

Thanks for your input.

 

[Thomas91169]

It'd be interesting to see if other's have this problem with cheap/homemade MBC's.

yes.

i had freinds using home made pos mbc's that always had problems with them. i finally convinced them to get real ones and it solved all their problems. one guy had the same as you(boost drop) and the other couldnt properly regulate a 56 trim with a bleed type mbc. they both got ebay ball and springs and were fully satisfied with accurate and consistent boost.

 

['89beretta]

Yeah, my MBC is off ebay, but it's obviously not a brand name. I'm assuming it's homemade because I paid $10 for it.

I've been looking at the Joe P. Also, finally made a leak tester and found two leaks, one coming off the intercooler and the other on a hose off the BOV. Hopefully this will help me hold boost.

 

[oldman]

1. 19psi on stock 450cc on a 14b might be pushing it though it probably has nothing to do with your boost dropping off problem, I suggest turning it down to 16-17 psi until you upgrade the injectors.

2. Do a test run with the actuator nipple open. This should result in all out boost so feather the throttle to keep it at 17psi. If problem solved, the mbc is in question. If problem persists, go to 3.

3. Perform a intake leak test like everyone suggested, fix all leaks until system is able to hold about 20psi for a reasonable amount of time. If problem persists after this, you probably have a dying turbo running out of steam at higher RPMs.

Good luck.

 

['89beretta]

I'm seeing no knock at 19psi even on the stock sidemount and 450's. That is until the temp goes above 80 degrees or the sidemount gets heak soaked, then I just never go WOT.

I've never thought of #2. That sounds pretty dangerous, but hey, I'll give it a shot. I've done the intake leak test and fixed my two leaks already, and that didn't really help the boost dropping.

Like you say, could just be a dying turbo. I know this is the original factory turbo, and the car's got 123,000 miles on it. I'll try #2 and hope I don't blow anything.

Thanks for the suggestions.

 

['89beretta]

You were right Oldman. Maybe bad boost controller. Took the hose off the wastegate, feathered at 17 psi until redline. That was scary though. The temptation to floor it was there.

I'll look into a new MBC.