850 Turbo Zero Boost

Post by **Nevada1906** » 01 Aug 2017, 23:24

I took the bypass valve apart and the diaphragm was fine, so i reassembled it.

Post by **abscate** » 02 Aug 2017, 04:11

I'm not positive this will work but perhaps you can confirm boost pressure by looking at the output on the boospt return hose on the Boost. Solenoid.

Boost pressure comes from the turbo casing, goes up to the boost solenoid, and then is switched to either the wastegate (boost requested) or the air intake ( no boost). You should be able to confirm pressure at the air intake line to test for blockages

nickm · Post by **nickm** » 02 Aug 2017, 05:43

The waste gate flap has failed? You would need to pull the dump pipe to check or pull the actuator arm off and wiggle the flap to see if it is seating in the housing.

Post by **Nevada1906** » 02 Aug 2017, 11:24

Everyone, thanks for your help.

Because of availability and frankly extortionate pricing of the stock piece, I've got a MAC solenoid on the way.

Post by **abscate** » 02 Aug 2017, 12:28

Its exanguinating, not extortionate. We are a stickler for accuracy here on MVS...

Post by **scot850** » 02 Aug 2017, 13:06

The TCU at this age is past it's best. The valve's fail in them and then the turbo does not get the signal to boost. Are there any parts yards around you where you can even pull a used one to try? 850's have a different shaped one to the V/S70's but I believe they can be interchanged even if it is not pretty at least to check it out. I have several but it would take a while to get one to you.

Good luck with the aftermarket part.

Neil.

Post by **tryingbe** » 02 Aug 2017, 20:06

I'd pull the vacuum hose at the actuator and see if you can make boost before buying a TCV replacement.

Pull the downpipe and look inside the turbine housing to see if the punk is still in place.

Post by **Nevada1906** » 04 Aug 2017, 09:32

scot850,

I considered going to a junkyard, but when 850s show up in the yards around here, they're pushing a quarter-million miles. Best to just replace the part with something new. Thanks for the offer, but I need to get this sorted out by Monday.

Post by **Nevada1906** » 04 Aug 2017, 10:03

tryingbe,

I hear what you're saying, but the factory part did its job for King and country - it lasted nearly a quarter-million miles. Best to replace it and eliminate that particular question mark.

At least if this isn't causing the problem, it's one more thing I can check off the list the next time something goes wrong.

Post by **scot850** » 04 Aug 2017, 23:37

Don't disagree on the chance of a good TCV being in the junkyard, but they may be good enough to know if you are going in the right direction. I think I pay about $5 for them. I would agree a new part is preferable as it is probably overdue being replaced, but throwing new parts when not sure a part is faulty gets expensive quickly (as me how I know....!), so it was a suggestion to keep diagnostic costs down.

Neil.