For a while now I?ve been chasing a problem where the zed is building boost slowly. It used to be an auto (auto turbos etc). At first after searching I thought I had a boost leak, and a boost leak test revealed a few minor leaks here and there which I?ve fixed but with no major improvement. Next I thought it may be the recircs leaking boost so I blocked them off just for testing, again no improvement. It is currently my daily so finding time is difficult but someone suggested it could be a blocked exhaust. I was sceptical and tried it cause I had nothing to lose and wanted to hear it anyway. But it barely made a difference. I have also replaced all PCV lines and valves (more just for maintenance). Also no error codes. As you can tell I?m fairly rookie but I have a good understanding and mechanical ability. Still learning about zeds. I am now thinking it could be wastegate related or maybe turbos on the way out. Basically during a 3rd gear pull (less noticeable in lower gears, especially 1st) starting at 2k rpm, it makes 0.1 bar fairly quickly and then slowly climbs to full boost which is roughly 4 ? 4.5k rpm. It is running 0.9 bar up from stock boost using boost jets. Also once full boost is finally reached it slightly over boosts to 1 bar and the boost needle is wobbly the whole way. From memory full boost used to be 0.9 bar by 2.5k rpm. Thoughts?
How much mileage is on the engine? What is the compression like? Is the boost gauge stock or aftermarket? If it's hitting 1 bar (14.5psi) the turbo's are supplying boost. Perhaps it's been boosted a couple of times too many & it's starting to slow down?
The odo reads 147 xxx currently. I havent done a compression test, I'll try and get one done this week. And the boost gauge is aftermarket (apexi). I really hope thats not the case but could be a good excuse for a rebuild.
What did you try? Most common cause for blocked exhaust is the biscuit coming loose in one of the cats and rotating before lodging itself firmly. The other main cause for slow boost (apart from massive boost leak or blocked exhaust) is a seized turbo I guess it could be possible that one or both of the actuators have become disconnected from waste gates, that would cause slow boost but should be easy to diagnose from under the car.
I ran the car with just the dump pipes. So would the car still reach full boost with one seized turbo? Is there any way to test waste gates to make sure they're doing their job?
When I got my z one turbo had been clocked and it was holding a wastegate partially open. It would only make 8-9 psi on the one turbo and struggled to do that so if by full boost you mean this level then it may be a dead turbo however if you can make more than that I would be looking for either a boost leak or maybe a rag in the intake lines somewhere or some other issue
Yes but slowly. Use compressed air in the vacuum line to the actuator, as you add and remove air you can see the actuator rod move.
NO , The side with the seized turbo is effectively a massive boost leak. any boost being produced by the good side is being lost through the open throttle body on the seized side. I seized a a turbo on one side and the engine had no boost or power at all. A faulty operating waste gate as IB mentions could cause slow boost . Have you tested with a different boost gauge, the one you have might be stuffed if its wobbling all the way.
Re: Compression results According to the FSM 171psi is the standard pressure in a TT. Based on your test results: #1 is down 15psi [9%] #2 is down 22psi [13%] #3 is down 23psi [13%] #'s 4, 5 & 6 are down 21psi. [12%] The percentages are approximate. These figures would be within specification (128psi is the minimum).
Ill test the waste gates with compressed air as mentioned. I don't think it would be a rag or similar because this was a gradual change from having good spool to slow spool. I will also try another boost gauge. Might do another boost leak check too before I go pulling turbos off.. I should be able to tell if either turbo is seized by removing dumps? I'm about to buy a ute/ daily so should have more time to work on it where I won't need it the next day
yep take off dumps and rotate turbine wheel. should be able to move pretty freely. if it touches or grabs its engine out time.
