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Need help diagnosing lag issue

2K views 4 replies 4 participants last post by  RoboTuner 
#1 ·
Hi everyone,

I'm a new member of WRX Tuners. I'm in Colorado and need help diagnosing a lag issue.

My car is a 2002 WRX Sedan.

Performance mod list:
JDM EJ205
ID 1000 Injectors with IAG rails
Fuel pressure regulator
VF30
Grimmspeed uppipe
Borla header
Cobb downpipe, cold air, boost control
Apexi exhaust
Process west top mount
Gfb mach 2 diverter
255 walbro pump

Problem:

I got a custom tune for my car.

Day 1: It was running great, 18-19psi at 3,000rpm. I drove it conservatively and did one 2nd gear pull to try everything out. I know you're supposed to wait and "break in" a new tune.

Day 2: I try a 3rd gear pull, psi was great then I hit 4,000rpm, loud pop happens in the engine bay and boost drops. At first I thought I blew the engine so I pull off and take a look. No smoke so I start the car up again and everything runs fine (this was 4 days ago). I try to accelerate again and that's where the problem lies, all of the gears have the same lag: 3,000rpm = 3psi 4,000rpm = 10psi 5,000rpm = 18-19psi

The past 4 days have been a thorough check of everything on the car.

We did a vacuum leak test, all hoses checked out and all connections were solid.

We put the air compressor on the end of the exhaust to see if there was a blown gasket or something like that on the back end. There was an uppipe and header leak, that was re-torqued but didn't change anything.

We will be checking the wastegate tomorrow.

If anyone has had a similar experience or could explain the loud popping in the engine bay and boost lag that would be extremely helpful.

Thanks!

- Sean
 
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#2 ·
We just tested the wastegate and it opens at 5psi of compressed air. We blocked off the hose to prevent any air from entering the wastegate and took it for a drive to see if the boost would hold but unfortunately the boost lag was still happening.
 
#4 ·
GSMNZ, it looks like they tried to force the wastegate shut to see if it would build boost which would completely bypass the boost control system altogether.

I think you guys did a good amount of tests. At this point, I would consider dropping the downpipe so you can inspect the back side of the turbo so you can make sure the wastegate flapper is still attached to the arm and also to make sure that the turbine wheel isn't coming into contact with anything. Another thing to check would be all the connections between the turbo and throttle body. I know you said you did a vacuum test, but have you done a boost leak test? Try to cap the intake and give a couple psi to see if it holds the pressure. A pretty major boost leak could cause the symptoms you're describing, and you would know right away if you try to get it to hold pressure.

If the turbo is fine and there's no boost leak, I would think about doing a compression test.
 
#5 ·
The td04 will build up to 6psi with the flapper full open/disconnected, so the vf shouldn't be much more. Sounds like the wastegate isn't connected at all


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