Intermittant issue

[GaryR]

Had my car at Watkins Glen a couple weeks ago and it ran flawlessly for most of the day. The last session, in the pit-out, I hit the throttle hard (I usually whack my brakes here a few times before hitting the hot track) and when it reached the boost kick-in it started bucking like a bronco, running rough. Tried again, same thing. Pulled over and when revving at a stop it's smooth as silk. Was the last run so brought her home.
Took her out of the trailer and check all my air lines, etc. and all looked fine. Took her up my street and same thing, as soon as boost starts she bucks. I noticed, just before the u-turn I was going to make, the sound of an open wastegate dumping. I have a new Tial with a .6 Bar spring and an Autopower PSI guage plumbed in. The guage has proven to be very accurate and she holds 11 PSI at boost from 2800 RPM to redline normally. After turning around I pushed it and she ran perfectly... could the WG have been stuck open and caused this? I'm going to put in a Boost controller this winter but have 2 more days at limerock coming up..

Also - I have no OB switch, that's where my guage is plumbed in for now, and the wire is grounded properly. If I disconnect it it dies as it should...

Thanks for any input!

[spuggy]

Originally Posted by GaryR

could the WG have been stuck open and caused this?

Can't see how - you'd just have a hard time building any boost, surely?

Also - I have no OB switch, that's where my guage is plumbed in for now, and the wire is grounded properly. If I disconnect it it dies as it should...

Dang, that would have been too obvious...

Don't they run badly on boost if a fuel pump dies because the good pump can't get enough flow through the bad one?

[patkeefe]

Gary:
I lost the stem seat ring in my WG last month at the Glen. I didn't experience any of the bucking you describe. I essentially had an open wastegate all the time. I have had that bucking when there was a pressure leak in the turbo outlet tube, fwiw.
Pat

[9dreizig]

I had the same thing, unfortunately fixed a bunch of stuff so not sure what it was, but I suspected the diverter valve which was all chewed up.. Put it back together and it ran fine..

[GaryR]

Thanks guys, let's see if it pops up again this Friday at Limerock!

[GaryR]

An update - It DID pop up again at Limerock, and kept happening on/off since...

I was talking with Dan Jacobs last week, going over stuff for the 3.0L he is building for my SC, and told him what I was going to try on the 930 (I have a new Leask Adj. WUR and was going to install it to see if that cured the issue). He had me go over all the symptoms again and asked if I had a spare CDI box to try instead (or he would have loaned me one). By chance I did, out of my race car. Went home that night and after cleaning the contacts up tossed in my spare. Damn if she, after sitting two weeks, pop off and sit there purring like a kitten! I waited until the next morning as I had some engine tin to get to Dan (I had bead-blasted and painted), and took her out. Figured if it ran bad I would get to Dan's and LEAVE her there.. well, she ran GREAT! It was wonderful hearing all those noises and getting pushed back into the seat again... Took a nice 24 mile ride on dry roads and came home smiling... until I remembered now I have to sell her..