Like the title says (I try to be somewhat descriptive in my titles, regardless of the buttload of boost questions recently).. I've got a '90 TurboII that is being really stupid with the boost..

before it would (on the stock gauge) read about like 1-2 psi, and about 5.5 on a mechanical gauge. Now after installing a boost gauge, the stock gauge is reading like not even 0 at "full" boost, and this gauge is reading about 5. Also (it may have done this before) it is hitting "max" boost and then backing down BEFORE I shift.

 

oh yeah one more thing. All my vacuum stuff on this side is running off of one vacuum nipple on the engine. Is that a problem? It's running the stock boost gauge, the blowoff valve, and the aftermarket boost gauge. All off of vacuum tees.

 

what kind of shape are your cats in?

 

I hate to say it, but everyone asks that. I have absolutely no way to determine what the cats look like short of cutting up the exhaust. Is there a simple way that someone could share with me?

 

you made sure the boost control solenoid is hooked up right ? its by the oil filler neck and connects to two hard lines on the front of the engine and goes to the wastegate actuator

 

Yeah I'm pretty sure it's correct. I doublechecked that before I redid it. Only thing is, where do those two hard lines go to? I'm not absolutely sure that the OTHER side of those 2 hard lines is connected correctly, and I want to make sure they are.

 

Ok, few things. The duty solenoid is activated by the ECU? If so, the ECU gets its boost pressure from the pressure sensor, correct? My stock boost gauge reads REAL low, so is it possible that the pressure sensor is bad (even though I've heard if they read anything at all, they're still good), and that the ECU thinks it's only at 1 PSI of boost so it doesn't tell the duty solenoid to bleed off extra pressure to the wastegate actuator, because it doesn't think it's at 5.5psi, but rather only 2?

 

I doublechecked the duty solenoid again, seems correct.. Still only hitting around 5 psi. I'm about 99% sure the problem lies with the duty solenoid not bleeding off extra pressure, but the reason WHY I'm not sure of. If it's the duty solenoid itself, or if it's the pressure sensor not telling the ECU what the real pressure level is. Please someone help here.

 

*bump*

I know someone out there has the answers

 

Sorry, but low boost and "boost bleeding" at high rpms is a dead giveaway for clogged cats and/or exhaust piping. My TII did exactly the same thing, and it turns out that my precat is somewhat clogged (but still working), and a piece of the main cat's internal THE SIZE OF MY FIST had become loose and was stuck in the Y-pipe....

You really need to take the exhaust off and take a look. No other way really...

 

I agree with "The Ace"

Either that or your DCS is fucked up. try unplugging and removing the DCS then plugging up each of the two vacuum lines leading to the DCS. Now take it for a spin. Are you still having boost problems? If the answer is no, switch that DCS for a manual boost controller. When you take your car out... with the DCS removed and plugged you can over boost your engine if you are not careful...So watch that boost gauge. I don't want to be responsible for you blowing your engine.

 

I was thinking of doing that. I think I'll check it the proper way first with a voltmeter, and see if it opens when power is applied to it.

 

I checked the DCS and it was at like 39 ohms resistance, where normal I guess is like 30-34. I'm going to try the old one I've got sitting around, and if that doesn't have better resistance, or doesn't work, then I don't know what I'm going to do.

I do consider the clogged cats a possibility, BUT it seems awfully peculiar that it boosts right to 5.5 psi and then hangs there, then slowly goes back down. Any other ideas or simple ways I can test the cats for clogs? Or just get a full exhaust?

 

Also, plugging up both hoses in the DCS isn't going to fix the problem, is it? I would have to leave at least the one hose open (that tees from the wastegate). Am I correct in my logic here?

 

last bump.

By the way, I just changed the Duty Solenoid Valve to one that was within spec, and it still doesn't boost correctly. Is this an indication that the problem is 99.9% sure the cats clogged?

 

either that or your turbo is flaky

 

same thing used to happen to me. its partially the turbo's fault, but it was mostly because of the cats. when i straightpiped the sucker, i only got it a little bit, where i used to boose maybe 1 or 2 psi.

 

so, Funklord you think it's the cats, and maybe possibly partially the turbo?

 

Drop the main cat and look inside of it. If the precat went, it would have clogged up the main cat.