View Full Version : calling all tru tech guyz... im stumped

12-26-2004, 03:16 AM
ok.... first time in a year swap has acted up. Ive been through everything and cant figure it out. First, here's my setup:
11psi set by MBC
PIM sensor STILL connected
T-VSV STILL connected
idles great @ -20

I was coming back from tampa the other night, air was cool, so i got on it a little bit... noticed only hitting 7psi when i KNOW im set for 11. Figured mabey i had creeped up to fuel cut and partially thrown myself into limp mode. Shut off the car, restarted, all was fine. Was going up to NC thrusday to see family, noticed it doing the same thing. So ive been playing with everything all weekend. First i thought it was a boost leak, but ive checked EVERYTHING. Then I began to think sensor related.. so ived tried disconnecting the t-vsv and the pim sensor. No difference. Besides, I'm not throwing any codes. For the past couple days its been moody... sometimes itll let me right up to 11psi, then not 5 minutes later i can only boost up to 7psi. Been trying diff things all day today and I can't get over 7psi at ALL now. Its possible my boost gauge may be shot, but unlikely... bc I def can tell that im not at 11psi. Talked to Clayton and the general consensus is some kind of timing retard. But from where? It's still limiting me when the ECU has been reset and pim sensor has been unplugged. Knock sensor mabey? but again, im not throwing any codes... and i can boost fine up till 7psi. I also had a bit more oil than i should in my intake pipe from the idle control hose, and a tad bit of white froth under the oil cap today. :squint:

Im stumped guyz. Any ideas?????

12-26-2004, 04:00 AM
Do you have any reason to believe the MBC is doing anything and that your wastegate is functioning properly? What happens when you take the MBC out and just have a line going straight from the turbo to wastegate?

12-26-2004, 04:43 AM
First you need to disable your TVSV.

That will isolate that and point the problem at your MBC.

If disconnecting doesnt help, remove the mbc, plug the wastegate on both ends, and boost... If your turbo surges up past 11 psi easily then its your MBC.

Just be careful not to overboost with the wastegate disconnected, its more of a troubleshooting measure.

12-26-2004, 04:48 AM
How cold is cold?

12-26-2004, 04:57 AM
if temps are unde 32F the ecu will lower boost, and refuse to open the t-vis. that could be the cause.

im worried about the white froth, tho... headgasket?

12-26-2004, 05:21 AM
hmm white froth, inconsistent boost...this could be a potential HG issue. How is your engine temp gauge? Stock gauge kinda sucks but it might tell you something.

Could also be the boost controller. See if it is gummed up with any oil.

Do you notice a loss of power aside from less boost, hesitation, or does it feel like the car is being 'pulled' back? If yes there is potential for timing retard. However with no codes there might be a reason for this. The ECU is probably doing it's job.

Off the top of my head, this is what I suspect.

Cool dense air caused head gasket to blow/not hold, air leaking past gasket (loss of boost) causing localized boiling in the coolant. Coolant temps are very high b/c of this, engine either detonates and the KNK sensor causes retarded timing AND/OR the ECU sees the coolant temps and retards timing accordingly. You must be careful. When the ECU retards the timing, EGTs skyrocket.

So don't get hard on the throttle until you figure this out. **very important** You could melt/crack a piston.

First step is to do a compression test and a leak down test. That will help you rule out a few things. Check your coolant level.

12-26-2004, 07:01 AM
I missed that froth comment..scary..

12-26-2004, 07:58 AM
Start running through the normal headgasket tests. Check your oil for coolant, check your coolant for oil, check your exhaust for the sweet smell, and run the bubble test with your radiator cap off, and look for more then usual air pockets within your coolant. Could be your headgasket, could be your VSV acting up in my opinion cus the colder weather?

You could eliminate the MBC, run the normal hose to the wastegate, and see how she runs/boosts. Maybe the spring in your MBC is gummed up? Take her apart and make sure it looks alright.

12-27-2004, 12:21 PM
hg was my original idea... however, temps are fine, and im not loosing any coolant. i beleive the froth under the top of the cap is moisture. in colder temps it will take much longer for me to reach normal operating temp, taking longer to evap any moisture in the mix, as it rises it settles under teh cap until evaporated.

THIS IS DEF AN ELECTRICAL ISSUE. I can disconnect the battery, (clearing out the ecu) and then reconnect and i boost just fine... for a little while... then shortly i go right back to 7psi.. and its not a hard jerk like fuel cut typically is. its just like im set at 6-7psi and cant boost past it. (not that im trying and beating on it) So this is def sensor related.

12-27-2004, 04:38 PM
Disable that VSV dude.

When dealing with boost issues you gotta bypass that.

If disabling fixes it, good. If it doesnt, pull the wastegate and boost freely and if you climb higher than 7 psi in a hurry then you KNOW its your boost controller.

12-27-2004, 05:10 PM
tried both of those... unfortunatly it still enables the cut. Its def sensor related. but w/o thowing any codes... i dont know what to look for. itll still do it with the PIM sensor disconnectd. the only other item that retards timing/limits boost (other than the VSV) is the knock sensor right? and that would throw a code

12-27-2004, 05:26 PM
Dude, if you unplug your vsv, remove the wastegate from the system (so it has no boost control) and disable your fuel cut, there is NOTHING in the system to prevent you from boosting.

Not even your knock sensor can do that.

If you were having knock/knock response, youd see the boost register, but you wouldnt feel it.

If you cant get any more than that much boost no matter what, your turbo is failing (like mine), your headgasket is blown, your mechanical timing is off, something along those lines.

Those 2 items are the only boost control items in the system.

12-27-2004, 06:06 PM
this is tru... i guess its quite possible i might have a crack in one of the vacc lines that reside under intake manifold on the back of the block. although i have checked them several times... could be something i cant see. guess its time to replace everything in the area. Im down to process of elimination at this point.

12-27-2004, 08:24 PM
Does it run well at 6psi?

12-27-2004, 10:12 PM
You could eliminate the MBC, run the normal hose to the wastegate, and see how she runs/boosts. Maybe the spring in your MBC is gummed up? Take her apart and make sure it looks alright.

What he said... its boot contowar related.

Took a ride in the car today.. I'll put money on it. Just do like I said, put it back to completely stock, then go back through your setup one part at a time.

12-28-2004, 04:01 AM
it sounds like the car is being put in low boost mode. what type of gas do you have in it? how cold is the weather?

with the stock turbo control, the waste gate is set to 7psi. if the ambient temps are 32F+ degrees the tvsv will let the car boost up to 11psi. if ambient temp or fuel grade is judged to be too low the car will stay at 7psi.

if you installed an mbc, you must disable your tvsiv (the extra hose on the wastegate) or you will get inconsistant boost control.

12-28-2004, 12:59 PM
not necessarily, as long as you are not boosting outside the parameters of fuel cut, many people (myself included) have been sucessfull in leaving tvsv enabled. after alot of trial and error im with clayton that it is most likely controller related. still havent figured it out yet though. i have cleaned and reinstalled controller twice and its still being moody

12-28-2004, 02:14 PM
Again, is it running like ass at 6 psi, or not.

12-29-2004, 07:59 AM
I have very little faith in MBCs. Mine was set at 12 PSI, but I boosted 15 psi. TOok the controller out completely, just vaccuum from wastegate to turbo and guess what.. still 15 psi... :hehe:

12-29-2004, 12:38 PM
running beautifully at 6psi. im sure its the mbc now. ive cleaned it twice. I dont like bleed mbc's so im using a pressure control (ball and spring) bc it will spike less and is more conistant. I beleive my spring is just worn out tho.

12-29-2004, 03:42 PM
That could be. Is there a breather hole in it?

12-29-2004, 04:02 PM
That totally sounds like the mbc. I don't think it would have to do with a breather hole at this point, I've seen dsm guys run without one and are totally fine until like 15psi.

12-29-2004, 04:30 PM
yeah i have a breather hole... and its not clogged. i originally had to clip my spring when i got it bc it wouldnt boost below 20psi. this was typical with this brand of controlller. its been doing fine for about 6 mnths... then it started acting up a week ago. Possible the spring is just worn out?? Ive cleaned it and turned up as tight as it will go and now im at 12psi. So I should be fine. Gotte be the spring... nothing else i can think of.

12-29-2004, 06:05 PM
Am I making this up, or did I once hear that when you cut a spring, it actually loses it's ability to coil/recoil faster than if you did not cut it?