Won't boost past 10psi, low power off boost

s70glt novice[Will] · Post by **s70glt novice[Will]** » 13 Feb 2013, 18:45

Hey all, been awhile since I last posted.

Been keeping up with the FF's though, love them.

Anyway, I have a 98 t5 with a 19t and ard blue tune. 3' exhaust, fmic, blah blah blah.

Manual swapped as well.

Anyway, I built my own MBC (mistake) and used a rubber ball, needless to say this got jammed up at the bottom and would not open up.

Here's the scary part: I hit at least 20psi (probably more) at 1/3 to 1/2 throttle. So after changing my pants, I took that off.

Hooked my ard tcv back up and now I only get about 9-11psi (depends on gear) at wot, with an afr of about 13.7 (again, at wot)

Reset the ecu and no change. I'm a bit lost on this one.

Some background: Before the mbc, i would see the boost fluctuate between 15-18 or 10-15psi at wot. back and forth like a kid in a jumpy house. The mbc fixed that, but had its own problems.

I'm telling you this because now it will hold 10psi until at least 4.5k (thats as far as im going at wot) so no more fluctuations.

I also have noticed my off-boost power seems low. Require more pedal up hills and doesn't seem to accelerate as it used to.

13.7 also seems a bit lean for 10psi, but I don't have much experience

Does anyone have any ideas? Although 10psi is much more manageable, I'm beginning to miss 18 :/

Post by **matthew1** » 13 Feb 2013, 19:10

Howdy Will, welcome back.

s70glt novice[Will] wrote:Some background: Before the mbc, i would see the boost fluctuate between 15-18 or 10-15psi at wot. back and forth like a kid in a jumpy house. The mbc fixed that, but had its own problems.

If you need an MBC to fix something, and you take the MBC away, the underlying problem is still there. You're just going to have to do some painful work to ferret out the problem.

13.7 is rich, no worries there

. (Air Fuel ratio Fast Friday for all you closet tuners out there.)

Any codes?

s70glt novice[Will] · Post by **s70glt novice[Will]** » 13 Feb 2013, 19:18

No codes. And thats the thing, I've traded one problem for another.

The 13.7 means (to me) its software, and not hardware. Otherwise if it thought it was at a much higher psi, it would be much richer. Correct?

Thanks for the help.

Oh, is it possible im in limp mode somehow?

Post by **matthew1** » 13 Feb 2013, 19:26

I don't know what 13.7 means. You could have a "pre-code".

You need to strip down to factory until you find what component is not functioning correctly.

s70glt novice[Will] · Post by **s70glt novice[Will]** » 13 Feb 2013, 19:32

My dog ate my code-scanner soooooo.

Also, i was referring to the afrs.

For example, if there was a boost leak and the ecu thought it was seeing 18psi, but only saw 10, the afrs would be in the 10s.

Or if the wastegate wasnt functioning properly. (which im suspecting)

s70glt novice[Will] · Post by **s70glt novice[Will]** » 13 Feb 2013, 19:47

So, there are no hints as to what this could be. Its exactly as if I have a 10psi tune and everything is working perfectly

Post by **jblackburn** » 14 Feb 2013, 12:14

How old is the O2 sensor? How old is the compressor bypass valve on the turbo?

s70glt novice[Will] · Post by **s70glt novice[Will]** » 19 Feb 2013, 22:28

HA! I had the idea to check the CBV before i read this.

Still looks new, aside from grime on it, which i cleaned up and then reinstalled.

Re configured the mbc and its now much better, tuned into a steady(ish) 15psi.

I decided to leave it after removing the cat and replacing my resonator (this time the right way around, don't ask)

I noticed a sulfur like smell after tuning in the mbc and coming to a stop (this is with the cat still installed)

So i figured it is rich at wot.

Also, PO said front 02 is new Bosch. Not sure exactly how old, irrc, like 1.5-2yrs. So it should still be good.

Also i think my afr gauge sensor is going out, as it reads 14.7-15 at idle/light cruise and only drops to about 13.2 (lowest) at wot. With two runs, both identical settings, it read (and didnt change at all when wot) 14.0 on one and 13.5 on the other. So either my car is running lean, my sensor is broken, or I'm a worried nervous wreck about afrs.

For now im keeping the mbc on, as the sulfur smell indicated it was rich. Feels strong under boost as well, much healthier then with the cat.

Any tips? I'd plan on pressure checking the system, but its lean on the gauge and rich by smell. Oh god im going insane.

s70glt novice[Will] · Post by **s70glt novice[Will]** » 19 Feb 2013, 22:29

Oh, off topic, installed the ipd upper torque mount bushing as mine had completely separated.

Feels so good man. Starting and shifting is so much smoother and less back and forth, and i dont feel like i suck at stick! haha

s70glt novice[Will] · Post by **s70glt novice[Will]** » 20 Feb 2013, 19:12

Everything fixed itself somehow during a mountain road drive.

CEL went off. I noticed afrs dipping into the 12's for the first time under some light throttle (compared to wot, not DD)
and decided to go for it. VOILA! 11.5 at wot and felt great!

Don't ask me how I did it, i'm not sure. It may just be a "good" moment for my MAF, and wil fail again. I hope not *crosses fingers*

Thanks for the help guys! Wish I could say how this was resolved.

If i had to place a bet, I'd say change the MAF if youre reading this with the same issues.

Best of luck