low boost pressure

[NJeuro]

my car is acting pretty weird when the motor is cold i have full power and boost gradually when it warms up i only get like 8psi max . I know theres no boost leaks the only thing i can think of is when the car is warming up the wastegate sticking open not allowing to build up any boost pressure .. Its a k04 turbo I wanna know if theres any more things can cause this issue im having

[texasboy21]

Have you scanned the car for codes? Did you preform a boost leak test? I had a similar issue and it was a damaged portion of the wiring harness.

Log the actual and requested boost and the N75 duty to start.

[NJeuro]

I have done boost leak test all ok when it's cold . I have codes for no cat that's it . I'm just running a hallman boost controller n75 connector is connected electrical connector but no vaccume lines going to it

[Matt Devo]

well, why are you running a MBC/EBC vs the N75? The N75 is going to give you superior driveability it just about every situation. It's quite possible that the MBC is causing an overboost condition, kicking the ECU into limp mode, and that's reset the next time you drive the car (which happens to be when it's cold)

[NJeuro]

I re routed the n75 valve in parallel with the mbc still issue present .
I scan for codes im getting 118 coolant temp sensor and a 02 sensor code would that cause the car go into limp mode ?

[J Boy]

The MBC is most likely your problem sir

[texasboy21]

I have done boost leak test all ok when it's cold . I have codes for no cat that's it . I'm just running a hallman boost controller n75 connector is connected electrical connector but no vaccume lines going to it

I bet its your MBC. You will need to loop a vacuum line or cap the lines on the N75 to prevent a boost leak.

[NJeuro]

The boost controller is about 3 weeks old I doubt it went bad .. I turned the boost up and now it's running 25 psi apposed to 22psi .

[Charles.waite]

Not the point.

The MBC does not play nice with the ECU.

Get rid of it.

Do you have proper software even? or is the MBC your tuning method...

[NJeuro]

Giac tune k04 and I'm running with a Mbc

[texasboy21]

Have you tried clearing the codes and removing the MBC from the equation? Our ECUs do not like MBCs.

[NJeuro]

I've had this setup since I own the car no problems I cleared the codes come right back

[customa4]

The fact of the matter here is that you can remove the MBC from the car and see if that helps the situation. Just try it. I understand your car was running perfectly before but now it's not. The easiest way to test if there's a problem with the MBC is to remove it and see if the condition changes. You said you turned the boost up to 25 PSI on the MBC, did you turn it back down to see if it changed anything? My suggestion and a few others is to get rid of it and see if it fixes your problem. It's the easiest solution and could very well be your problem.

[Charles.waite]

You said you have a k04. Maybe the waste gate broke and it overboosted, throwing the car into limp mode.

Of course if the n75 is fully disconnected and the mbc is actuating the waste gate then the only way the low boost could be happening is if the waste gate is cracking too early from being broken or out of adjustment, or because there is a large boost leak.

[NJeuro]

Going to remove the Mbc tomorrow see what happens . I think when the engine is getting hot the wastegate is sticking open but not sure

[NJeuro]

I removed the Mbc completely hooked up the n75 up car still running low boost pressure when warming up

[blownb6]

it could be the tune , here read this from the s4 tuning wiki


IAT effect on requested boost

ME7.1 will adjust the specified load limit depending on IATs. As IAT's go up, ME7.1 brings the max boost up a bit so that the driver can't tell that the car is slow in hot weather. It can do this because the stock boost curve is relatively conservative, and there is plenty of headroom. Also, at some point, if IATs go high enough, max specified load is pulled to prevent knock.


KFTARX - IAT correction for maximum specified load


However, if you are running a lot of boost, and always want maximum performance, there is no point in increasing boost when it is hot, let alone reducing boost when it is cold. Also, as IATs rise, even with a perfectly flat KFTARX and LDIATA (see below), you will see more requested boost because the ECU knows that a higher P/R is required for a given cylinder fill (PV=nRT for you thermodynamics nerds out there). It is unknown if there is a table for that calculation. To compensate, you may want to taper KFTARX across the board as IATs rise to keep your requested boost sane. In particular, be aware that the maximum requested boost is slightly above the maximum MAP reading. Readers who understand PIDs should recognize that really bad things happen when the measured output cannot reach the setpoint...



In other words, the tune can be tuned to have less boost when the car is cold....

and yes our cars dont like mbcs, again due to the ecu and the tunning , the psi is set by rpm threshold and mbc works a bit different

[old guy]

There is one thing you can try. Get the motor up to temperature to where you are only getting 8 psi of boost. Either clamp off or disconnect the waste gate pressure signal line. Go for a short spin and see if you are still restricted to 8 psi or if you immediately have full boost. Don't overdo it since you will be running unregulated boost.

If the boost comes back you have a controls issue.

If the boost stays at 8 psi you probably have a waste gate issue.

[NJeuro]

old guy i already disconnected the vaccum line of the wastegate when the car is warmed up and i get boost back ..what are the pids for request boost and actual boost pressure on vag com going to try narrow this down.

[old guy]

old guy i already disconnected the vaccum line of the wastegate when the car is warmed up and i get boost back ..what are the pids for request boost and actual boost pressure on vag com going to try narrow this down.

Try logging block 115. That will give you actual versus requested. It's a good place to start. If the actual is lower than the requested you may have a defective N75 since you already confirmed that the waste gate is capable of providing full boost.

[JBM]

I will have to check this, b/c right now my car is not boosting and sounding like a dentist drill...is that a blown K03? Car has roughly 123K on it. Should I go to K04 or GT28? more power but I don't need balls back up inside of me HP.

[customa4]

The dentist drill sound is from the turbine grinding against the housing. You probably have some type of FOD. You'll want to change the turbo soon because the sound will not get any better. Mine was making the dentist drill sound and this is what it looked like:

[GOODBYNAAIR]

I will have to check this, b/c right now my car is not boosting and sounding like a dentist drill...is that a blown K03? Car has roughly 123K on it. Should I go to K04 or GT28? more power but I don't need balls back up inside of me HP.

Dont wast your time with the k04, go GT2860/71r and dont look back, I never will! If anything close to a K04 go F21 best of both worlds.. just my $0.02

[NJeuro]

i dont have any abnormal sounds from the turbo .. I just tried logging it the 115 i have to purchase the full version to view that kinda sucks

[Charles.waite]

i dont have any abnormal sounds from the turbo .. I just tried logging it the 115 i have to purchase the full version to view that kinda sucks

Your compressor or turbine fins could be trashed/bent which destroys the turbo's ability to move air, thus not letting it build boost. Pull your TIP and see what the fins look like. If you can't get to it, get an inspection borescope from Harbor Freight/ebay/amazon and stick it down the TIP and check out the fins.

[WTFISAKSERIES]

Hey i have the same problem. when i start it and go i have fully boost then i hit a red light and it goes back to 7-8psi but after driving for about a half hour some times long some times sooner its weird. I am running a stock k03 TT injectors APR DV, straight cat to TT TUNING down pipe to Magna flow duals and a revo tune 18psi. When i do have boost the car runs amazing super stock but has balls. I usually always have boost by the end of the day . The only codes i have is for the 02 sensor? My n75 is connected The hose arm all brand new i just put the k03 back in 5 months ago car was running fine. Then the no low boost and when i want it its not there. I have a brand new one OEM n75 from ECS i haven't tried it yet. Because i dont think its my n75 but i will try it tomorrow and see what happens any info on my set up would be great!! I just got my FMIC an i wanna fix this while i am installing. What do you guys think about the boost pressure Thrust sensor

[WTFISAKSERIES]

Please help!!!!!!!!!!

[Charles.waite]

Please help!!!!!!!!!!

Kind of sounds like your n75 is on te fritz. Slap that new one in post haste. Any codes?

[WTFISAKSERIES]

Only code is p0420 i have a straight pipe no cat my o2 sensors are onnected and i am thinking about buyinh 2 of the mini cat adapters has any one tride these a friend of mine say they work even with out the honey comb inside. Okay ill put it in tomorrow! But as i was driving after a few min. warm up i had boost and ass boost was at about 15 psi it just jumped to 6-7psi so yea iam thinking it the N75! I let you know !! thanks again!

[WTFISAKSERIES]

okay I change the N 75 valve and I had boosted when the car was a little warm then it went back to 7 psi then I got on the highway shifted from 3rd to 4th held it till about 4000 rpm shifted to 5th and I had full boost again but when the boost comes back on it usually stays on until I shut the car off now with the new N 75 valve I had full boost I drove about 4 miles and once I slow down an i went around a corner and it was back to stock 6-8 psi. so should I try the boost pressure sensor or should I let the car adjust to the new N75? or is my waste get getting stuck open?!?!

[customa4]

Read this thread from post #27 for some troubleshooting steps. http://www.audizine.com/forum/showth...=1#post9016067

[A4Maine-iac]

I had similar issue with my GT2X. Was the wastgate. The diaphragm was leaking after it heated up. Was just worn out. After its warm see if it holds any boost. Disconnect from N75 to wastegate and attach to compressor. Slowly turn up the psi and see if it is holding.

[WTFISAKSERIES]

Now if its the waste gate. Can i get one from ebay or should i go with the new internal waste gates that are aluminum and springs can be changed an can be used on many different turbos
or just got get a OEM one

[Charles.waite]

Now if its the waste gate. Can i get one from ebay or should i go with the new internal waste gates that are aluminum and springs can be changed or oem

You can order a stock pressure waste gate actuator from ATP turbo I believe.

[WTFISAKSERIES]

You can order a stock pressure waste gate actuator from ATP turbo I believe.

is it universal or do they have them for the borg warner k03?

[WTFISAKSERIES]

You can order a stock pressure waste gate actuator from ATP turbo I believe.

I FOUND IT!! Ithink i am gonna go with this one http://www.atpturbo.com/mm5/merchant...egory_Code=WGT

[Charles.waite]

I FOUND IT!! Ithink i am gonna go with this one http://www.atpturbo.com/mm5/merchant...egory_Code=WGT

Just remember you need to reset it to crack at the proper 5-6 psi rather than 12-14.

[customa4]

I FOUND IT!! Ithink i am gonna go with this one http://www.atpturbo.com/mm5/merchant...egory_Code=WGT

Did you confirm your wastegate is bad? Did you pick up an OEM N75 to replace the old one with?

[WTFISAKSERIES]

Yea i learned the hard way I RECEIVED THE TURBO IN THE MAIL CLOCKED IT AND PUT IT ON WITHOUT never touching the wastegate. i installed the new one and it was boost 30 psi blew the turbo in k1000 lol opps

[WTFISAKSERIES]

Did you confirm your wastegate is bad? Did you pick up an OEM N75 to replace the old one with?

Yes! I bought the OEM N75 from ECS and installed it and the same problem boost when i first start the car as it fully warms i have low boost and anywhere from 15 mins of driving with low boost to 2 hours of driving it will come back on to 18 psi spicks at 21psi and drops to 18psi and then ill have boost till i shut the car off for at least 20 mins. If i shut the car off while i still have the boost only for a few mins and start it ill still have boost most of the time. BTW does any one know where the boost thrust sensor is located ? Does it go on the intercooler piping? pics below of the sensor

BOOST THRUST PRESSURE SENSOR