Boost Control Actuator....Leak-down Testing?? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat
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Old 03-01-2008, 12:12 PM   #1
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Default Boost Control Actuator....Leak-down Testing??

I don't know if this is the right term, but in trying to determine where my trouble with a Code 57 on my '92 Park Ave Ultra with Type 1 SC, I came across something with my BCA and thought I'd ask.

I'm calling it leak-down testing. Here'* the story......I removed my BCA and squirted a bit of WD40 into the upper and lower ports and around the actuator rod to freshen up the seal. And after I started pushing the rod up and down I could hear air pumped in and out of it.

Now, with the rod pushed up I put my finger over the lower vacuum port and released the rod. I started to see foaming bubbles around where the rod exits the cannister. And the rod slowly pushed out towards its normal position.

I tried it a few times and it kept doing it. So I guess the internal spring pressure in the cannister is forcing air out of the lower chamber. BTW, I didn't shoot a lot of WD40 into the ports, I think most of it came from over spray around the rod seal. I was using the WD40 as sort of an external cleaner.

Well anyway, I hooked up a vacuum guage to the lower port and a hand-held vacuum pump (a great Harbor Freight brake bleeder) to the top port and pumped about 17 Hg on the vac pump'* gauge. The vac gauge on the lower port went to about 7 Hg but then slowly started dropping.

Has anyone tried this before? OK, I have a little leak in mine, it'* not a major leak. But could this leak cause problems with boost and my Code 57, which I think is the ECM'* way of saying it can't cut the boost when it wants to.

Another thing I tried while testing the whole boost control issue that I think is very helpful to test for ECM control is to have the engine running at idle and put the car in reverse. The ECM will cut boost and the control gate will return to the lower stopper; that is to say it moves it down to the left while looking directly from the front of the engine. If you are doing this yourself, make sure the brake is fully engaged and the car doesn't move when you get out! Better yet, get a helper for this test.

Doing this test on my car, at idle the gate does not fully hit the lower stop. And maybe that'* not a big deal.

Well, I cleared my Code 57 and it'* time to take her out for a spin! I hope this helps.
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