boost control problem

[spammy123]

ok i installed my 550 injectors the other day and now my boost wont go down. i don't know if the injectors have anything to do with it and it was just coincidental that it started after that but, i replaced my mbc, and ran a boost leak test. the boost will not go down, it spikes upto around 26 psi. i checked the arm of the wastegate and it doesnt seem to be sticking or anything like that, i would asssume something is wrong with the wastegate, but i don't know what else to check. any help would be greatly appreciated

 

[uberstrafe]

what are you using to control those 550's?

 

[No_Skillz]

Easiest way to rule out MBC or Wastegate is to hook up a vac line directly from the boost source to the wastegate.

Start with that and we will continue to narrow it down from there.

 

[snowborder714]

Which MBC did you install? Where are you getting your boost source? Did you install it correctly (side nipple to wastegate and end nipple to boost source)? Did you try adjusting the MBC?

uberstrafe, it says in his profile he has an S-AFC.

 

[the_mork]

Check to make sure that there aren't any tears or holes in the vacuum line going to your wastegate. The injectors themselves shouldn't be a problem so this is probably just coincidence.

 

[spammy123]

thank you for all the responses. to clear some things up, i am no longer running safc, i am running dsmlink now, fofrgot to change my pro. i am running a homemade boost controller, but it has never given me any problems before, i replaced the one i was running with one of my friends, who also never had problems with it. As far as hooking a vac line directly from the boost source, do you mean hooking up the line from the "T" straight to the wastegate nipple? i will try that if thats the case. i replaced all the vacuum lines with the boost controller. so i know none of them are leaking. thanks for the responses

 

[snowborder714]

Where are you getting your boost source? You mentioned a tee, but where is that coming from?

Also, did you drill the bleeder hole in you MBC?

 

[No_Skillz]

As far as hooking a vac line directly from the boost source, do you mean hooking up the line from the "T" straight to the wastegate nipple? i will try that if thats the case.

By this quote I am assuming that you have your MBC teed into your BOV line, which is generally frowned upon. I would highly recommend (in fact I would say it's the only right way to do it) running an uninterrupted line from your BOV to your intake manifold. Your pressure source for your MBC/Wastegate should come from somewhere located as close to the compressor as possible. Some people tap for a nipple on the j-pipe.

When I say "run direct wastegate" I mean hook up a vac line from your pressure source directly to the wastegate. This will cause boost to be set at wastegate pressure, usually ~10-12psi.

When you do this, you also need to strictly define boost spike vs boost creep vs boost dropoff vs uncontrolled boost:
Spike - Pressure "blips" somewhere higher than your wastegate/mbc is set but quickly normalizes.
Creep - Boost reaches wastegate/mbc pressure and is stable until upper RPMs where it slowly starts to creep up.
Dropoff - Same as creep, except pressure drops in upper RPMS (not the case here).
Uncontrolled - Boost immediately rises with no sign of stopping when turbo starts to spool, and you LET OFF before you let it get to 20+psi.

Let us know which one you are experiencing after you run direct wastegate pressure.

 

[snowborder714]

By this quote I am assuming that you have your MBC teed into your BOV line, which is generally frowned upon. I would highly recommend (in fact I would say it's the only right way to do it) running an uninterrupted line from your BOV to your intake manifold. Your pressure source for your MBC/Wastegate should come from somewhere located as close to the compressor as possible. Some people tap for a nipple on the j-pipe.

I assume that's where the source was too.

I don't agree that the pressure source should be as close to the compressor as possible. The line from the MBC to the wastegate should be as short as possible so the wastegate reacts quickly and precisely. But I had my source from the j pipe and was having inconsistent boost issues - different peak psi's at different RPM's. After posting some logs on the link forums and talking with JeffGST, we determined that that was my problem, so I switched the source from the j pipe to the head. Ever since I have yet to have any problems.

Here's what Jeff said on the topic:

Always take your pressure source from as close to the cylinder head as possible. The intake manifold source is perfect.

Reason : You want the pressure source AFTER the intercooler. This is because there is a pressure drop across the core. If you take the boost source from the J-pipe, then you will be taking the reading from a source that will drop in pressure after it travels through the intercooler.

Example:

EBC is set at 25 PSI
25 PSI at the J-Pipe (Pressure source is taken from here)
Boost Travels through intercooler
Exit pressure out the intercooler is only 22 PSI

In this case above, the boost will only be 22 PSI in the motor, even though the EBC is set to 25 PSI. This is because the boost source is taken pre-intercooler. This causes very inconsistant peak boost pressure because changes in the weather will alter how much of a pressure drop there is through the intercooler core.

The larger the turbo, the larger the pressure drop through the core. This is why it is always best to take the pressure source as close to the motor as possible so that you get consistent boost peaks.

 

[thom2white]

dido on the direct wastegate plumbing for process of elimination of the boost controller

 

[spammy123]

thanks guys ill try those couple of things, and what im experiencing now is uncontrolled boost, it immediately cilmbs to 24+ psi

 

[No_Skillz]

Here's what Jeff said on the topic:

This has certain merits, but is an older school of thought.

Having a boost source as close to the compressor as possible frequently means that you are running the shortest possible vac line to the wastegate, allowing fastest reaction. Also, this is a potential means of protecting your turbo - if you have boost leaks and the pressure drop is rather large, the wastegate will still open and prevent overspinning, especially if the turbo is a smaller variety. This setup also eliminates another factor which contributes to boost spike - i.e. your MBC is set to 20psi off the manifold, however, when the turbo first spools it may reach high levels (lets say 25psi) due to the delay of pressure from the volume it has to fill. Although the wastegate opens at 20psi off the manifold, that 25psi is already in the system and will eventually reach the manifold.

This method, however, requires stringent BLTs for best results.

The only benefit of running off the manifold that has been proven is that your MBC/EBC setting will be the exact match of the pressure entering the clyinders. However, since the boost gauge is usually tapped at the manifold, this becomes a non-issue since you will be seeing the exact pressure on the gauge.

 

[spammy123]

update, i hooked the wastegate directly to a boost source. the boost held at 10 psi. so i eleiminated the wastegate as being a problem. should i just get a brand new boost controller and try that? it doesnt make sense that 2 controllers that worked before would just suddenly not work tho. my friend said i should reroute my vacuum lines, any suggestions on where to route everything for the bov and wastegate? thanks in advance

 

[JeffGST]

Having a boost source as close to the compressor as possible frequently means that you are running the shortest possible vac line to the wastegate, allowing fastest reaction.

Fastest reaction? Do you really think it takes that long to fill a vacuum line with pressure?

This setup also eliminates another factor which contributes to boost spike - i.e. your MBC is set to 20psi off the manifold, however, when the turbo first spools it may reach high levels (lets say 25psi) due to the delay of pressure from the volume it has to fill. Although the wastegate opens at 20psi off the manifold, that 25psi is already in the system and will eventually reach the manifold.

No way. If your boost pressure spikes to 25 and then drops back down to 20, then that is a very inefficient wastegate that has nothing to do with the length of the line. I can set my T67 as low as my wastegate pressure which is 22 PSI. When I hit 22 PSI, it will stay there rock solid and not move. (MBC + Tial44) At this low boost pressure the wastegate is directing a ton of exhaust gases away from the turbo.

The length of the vacuum line is irrelevant to boost spike issues. Installing a vacuum line that is 3 to 4 feet longer in length has an insignificant effect on holding stable boost pressures.

To the OP, what MBC is this? Did you test the MBC out yet? Take the MBC out of the car and take it to an air compressor with a gauge. Even a cigarette lighter tire pump will work. All you need to do is add pressure to the MBC through the vacuum hose and wait for the MBC to open. When it opens take a look at the gauge to see what pressure it finally opened at.

Also make sure you didn't install the MBC backwards.

 

[spammy123]

i will test the MBC, it still doesnt make sense that it doesnt work on my car though, i had the car running fine with my original MBC 4 days ago, then it stopped controlling boost suddenly, then i try another MBC that worked before and that doesnt work either, then i test the wastegate and that proves to be no problem. i will double check that i don't have a faulty MBC tho. anyone got suggestions on my vacuum lines though? i was thinking of just tapping the J-pipe, for the wastegate, is there anywhere else that is a better option for a boost source?

 

[thom2white]

If you have the skills and tools, yeah tap in a fitting into the J-pipe somewhere, an aftermarket compressor housing usually has a fitting it it. As far as a possible explanation to the sudden change in performance, something could be obstructing the vacuum line somewhere (mud, telon, RTV, debris, who knows), restricting the flow to the WG making it take longer to open, the ball and spring could of malfunctioned (rare), the bleeder hole in the Boost Controller is clog, or the controller it's self has a leak. We usually take the stance that if you have a problem that you can't explain, start all the way back at the beginning and work through it the way you know it is supposed to be. Usually it will work fine when you remove the ambiguities from others shotty work.