Boost drop - weak wastegate spring??

[bosco659]

Had my MKIII on the dyno this w/e for tuning and found that I am losing boost. Car boosts great to 14.5 psi at about 3200 rpm but slowly loses boost to redline, actually it drops off pretty quickly after hitting 14.5. Boost will drop to about 12 psi by the time I hit redline.

No hose leaks, Greddy Profec B boost control, CT26- 54 trim, 550's, Lexus afm, Walbro FP, SAFCI. Tested wastegate actuator and the diaphragm does not leak. Thinking it may be the spring that is getting weak and cthe actuator cant hold the wastegate closed once the exhaust starts to flow.

This condition has really surfaced lately (maybe at the end of last seaon). Before it would hold a steady 14 - 15 psi to redline (according to the gauge anyway).

It was suggested that I try to shim the wastegate with washers to preload the spring a bit and that might help hold the boost. Any thoughts? If you agree to shimming the wastegate, how many washers do you think I should use? Actual recommended thickness of shims / washers would be helpful as all washers are not the same thickness.

A search of the forums still leaves me puzzled.

Thanks

Vic
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[silvergsx623]

It does sound like the waste gate spring is old and can't hold closed to boost. Replace the waste gate or preload the spring.

If you choose to Preload just start off with a thin washer, test it if it still drops. Then add another , test it and see. Etc...

 

[bosco659]

Thanks, I will try that. I did check for boost leaks but did that visually. I will do a pressure test of all components this weekend.

 

[Whasian]

Check the wastegate port on the exhaust side of the turbo housing, if there are cracks on the housing you can bet that is where your leaks are coming from.

Whasian

 

[bosco659]

Thanks, if the wastegate port is cracked (and I know most do), I will most likely leave it until next year and do my turbo / engine upgrade. :icon_frow