Boostin Funny

[94Jettameowpsst]

Okay, im seriously pissed right now. I have a 90 talon tsi and i was cruisin along, well boostin along w/ my boost set to 16 and all of a sudden, no boom, no sound, but my boost dropped to 11.....im like wtf. I stop and check for leaks, broken vaccum lines, etc. NONE I been havin problems w/ my spring stickin in my mbc so i took it apart, then put it back together ( worked before ) nada. I got my boost to rise to 14, wont go higher or lower. I disconnected the actuator vaccum line to try to pinpoint the probmem. Well, i DO think the wg is indeed working cause my charge piping blew apart (never does this) but my gauge only reads 11 psi the whole time and my vaccum is 21hg. What is the problem?????

 

[oldman]

I suspect the mbc being the problem here so let's try a couple of things:

1. Connect the pressure source directly to the actuator to bypass the mbc and describe the result. Boost level should be held at around 10psi, the stock actuator setting.

2. Disconnect the hose to the actuator from the mbc and test drive. Be carefull with this one and don't let the boost go pass 16psi because you're still on stock fuel.

If #1 holds boost at around 10psi and #2 shoots over 16psi before you let off, then it's almost certain that your mbc is not functioning. If 1 or 2 does not hold true, post back what you found and we'll go from there.

 

[94Jettameowpsst]

Well, i just did a couple pulls in my car and the results thus far lead me to believe that my boost gauge has failed.
I hooked the vaccum source straight to the actuator and wouldnt ya know i got 10 psi, steady
I then hooked the mbc up so the line off the side wasnt connected to the wg and im kinda stumped. My boost gauge read 13-14psi, but my bov was MUCH louder and my car became all choppy and sputtered.
Then i hooked my mbc up normally set at like 16-18psi dont know cause i just adjusted it a little, and my car doesnt feel like its runnin 16psi. It feels like 12-14. At idle, my vaccum is 18-19 then 21 when its heated up. On decel its 21 as well, idk whats goin on here help me out??

 

[oldman]

Well, i just did a couple pulls in my car and the results thus far lead me to believe that my boost gauge has failed.
I hooked the vaccum source straight to the actuator and wouldnt ya know i got 10 psi, steady
I then hooked the mbc up so the line off the side wasnt connected to the wg and im kinda stumped. My boost gauge read 13-14psi, but my bov was MUCH louder and my car became all choppy and sputtered.
Then i hooked my mbc up normally set at like 16-18psi dont know cause i just adjusted it a little, and my car doesnt feel like its runnin 16psi. It feels like 12-14. At idle, my vaccum is 18-19 then 21 when its heated up. On decel its 21 as well, idk whats goin on here help me out??

1. We can now conclude the wastegate is operating properly.

2. When you disconnect the line to the actuator did you plug up the mbc or at least turn the mbc all the way up? If not, it would be like a boost leak when you go WOT. Let's try the second test again, correctly this time. You're looking for all out boost so easy on the throttle. If you in fact get a smooth all out boost, I'd say you need a new mbc. If the car still won't boost over 14-16 then perform a real boost leak test and fix all leaks. I would also check plugs and wires as well if you have not already done so.

 

[DSM Loki]

the sputtering he desribed sounds to me like fuel cut from it boosting above what the stock fuel pump can flow. or if it sputtered at idle it'd be a boost leak, either way, more testing needs to be done

 

[94Jettameowpsst]

Well i didnt do this test, but infact it is my mbc. I Adjusted the knob yet again to run "more boost" and im holding 15 in 1st and 17 in the rest of the gears. Ill be making another one this weekend but also i noticed i had my wg, booost gauge, and fpr all tapped into the same vaccum source. I fixed the problem sorta for now, but ill keep you updated. Thanks for the help

 

[DSM Loki]

have you rewired your fuel pump? if not 17 psi is higher than a safe level

 

[94Jettameowpsst]

its not rewired yet, it will be this weekend but im not touching my mbc right now...dont wanna take the chance of my boost dropping again. I did a log and only got 6 counts of knock in 3rd around 5400. I didnt mention i have an automatic fpr, but 16-17 IS a bit much for the injectors getting 96% IDC. Also, the sputtering was under acceleration and im assuming was because my boost was rocketing. How many psi will i be able to run just w/ the fuel pump rewire? (hopefully that will lower my IDC)

 

[94Jettameowpsst]

Well, i found the source of all my problems, a hole big enough to stick 2 of my fingers into my one coupler right before my fmic. I didnt see em cause they're under the clamp.

 

[oldman]

Well, i found the source of all my problems, a hole big enough to stick 2 of my fingers into my one coupler right before my fmic. I didnt see em cause they're under the clamp.

Do a real boost leak test, trust me you probably have more leaks.