[sccowboy]

Does anyone know how quickly the vacuum pump should achieve full vacuum on the reservoir to maintain proper pressure on the WG solenoid? Long story but I have been chasing a drivetrain malfunction 120308 for low boost pressure. I have smoke tested, replaced the intercooler, WG does not appear to be sticking, and replaced the WG solenoid. I am thinking that the vacuum pump may not be recovering fast enough on the WG side when on the road however, I have also verified the following:

- Check vacuum at output of pressure converter for wastegate valve (-450 +/-50 hPa at 50 % duty factor at idle speed)
- Check whether wastegate valve moves stiffly
- Check vacuum at input of pressure converter for wastegate valve (target value -900 to -800 hPa)

I have not changed out the charge pressure sensor yet. This started when I found oil in the vacuum cannister under the engine cover and found that the supply nipple on the pump had a bad check valve. Not wanting to spend a ton of money, I found a replacement nipple online and removed/cleaned my original pump. I am able to achieve 23" or so psi to the WG solenoid but at idle it seems like it takes quite a while to get there from 0". My thought it that under actual road conditions, when the WG solenoid is applying or venting vacuum rapidly, it cannot recover vacuum pressure fast enough. Thoughts??

Thanks!

[95blkmax]

If you found oil in your vac canister and lines, your vacuum pump has internally failed and must be replaced. The fact that it takes higher RPMs for it to achieve enough vacuum for your turbo to spool further reinforces that (as the vacuum pump runs off the end a camshaft on your N20). The turbo is putting out the right PSI later in the powerband, but down low it's lagging. It all points to a faulty vacuum pump.

You did the right thing in cleaning out the canister, lines, and replacing the solenoid. But IMO the root of the problem is still present and it's just a matter of time (how quickly totally depends on how far gone the pump is) before all the components are full of oil again.

As to your original question- It shouldn't take more than a few seconds really. On a cold start, you should achieve full vacuum long before the RPMs begin to drop down below 1000 rpm. So we're talking maybe 3-5 seconds

[sccowboy]

Thank you so much for that information. I agree with your assessment and that makes total sense. The lag down low allows for the DT malfunction and the reduction in output. I will replace the pump and let you know if that clears it up. I forgot to mention in my OP that I also replaced all vacuum lines with new silicone ones. Again thanks!!

TW

[sccowboy]

Well I replaced the pump and it immediately achieves full vac pressure however, still getting the dang DTM low boost pressure. Makes no sense at all. I suppose I will smoke it again and keep looking for where the boost is leaking and maybe take my borescope and watch the WG control arm to see if it is indeed moving when rpm's go over 1900. Any other suggestions at this point would be greatly appreciated.

[juld0zer]

Seized or damaged turbo at either end will do the same. Restrictions at either end will also cause boost issues if the vac (control) elements are all good.