Overboost Switch
03-22-2013, 07:36 AM
#1
Burning Brakes
Thread Starter
Overboost Switch
I have a fairly stock 86 930. Borg Warner S200 turbo, Tial waste gate with OEM WG muffler, Borla exhaust, BL WUR, Fabspeed IC - all relatively new, all bolt on stuff. Stock headers. Car makes 320 rwHP. I have a KN cone filter instead of the box, and a new BOV.
I generally don't drive the car hard, but yesterday I had to do some hurry up traffic merges and I hit the boost limiter twice, once in 3rd and once in 4th, at just under 5k rpm. It surprised me, given the Tial and the BOV. Is this normal? With the WG muffler, the loudish Borla, and the KN sucking air, the Tial doing its job is hard to hear.
I generally don't drive the car hard, but yesterday I had to do some hurry up traffic merges and I hit the boost limiter twice, once in 3rd and once in 4th, at just under 5k rpm. It surprised me, given the Tial and the BOV. Is this normal? With the WG muffler, the loudish Borla, and the KN sucking air, the Tial doing its job is hard to hear.
03-22-2013, 09:29 AM
#3
Burning Brakes
Thread Starter
Hi Chris: no electronic controller, just the BOV and WG for control. I do have a MSD rpm box to control the WUR, but otherwise, straightforward CIS.
Steve
Steve
03-22-2013, 12:04 PM
#4
Burning Brakes
Join Date: Apr 2006
Location: Central Washington State
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The very first thing to do is to check that the bosst signal line to the WG hasn't come off. Did you happen to notice what your actual boost was when this happened (while dicing/slicing/merging with traffic under full boost, which does tend to preoccupy a person)? If indeed you were over 1.2 bar boost or thereabouts, then the overboost switch was doing it's job. If you weren't even at .8 bar, then the switch has weakened and is tripping too soon.
Is the switch really the culprit by tripping too soon, or is the turbo actually overboosting due to the WG not functioning? Take the switch out of the equation; disconnect the single wire and ground it, then run the car up to boost - but do this somewhere where you can watch very closely the actual boost in order to get the hell off the gas if it looks like it's going past 1.0 bar (which would tell you that the WG isn't functioning correctly).
Bettter yet, take the switch off and bench test it with compressed air and an ohm meter connected across the terminals. Look for the switch contacts to open at around 1.2 - 1.4 bar (if I recall that's about what a new switch will do....probably less with an old one).
Is the switch really the culprit by tripping too soon, or is the turbo actually overboosting due to the WG not functioning? Take the switch out of the equation; disconnect the single wire and ground it, then run the car up to boost - but do this somewhere where you can watch very closely the actual boost in order to get the hell off the gas if it looks like it's going past 1.0 bar (which would tell you that the WG isn't functioning correctly).
Bettter yet, take the switch off and bench test it with compressed air and an ohm meter connected across the terminals. Look for the switch contacts to open at around 1.2 - 1.4 bar (if I recall that's about what a new switch will do....probably less with an old one).
03-22-2013, 04:26 PM
#5
Burning Brakes
Thread Starter
Thanks Mark, checked hose from WG to IC and no prob. boost gauge hose looked good too.
Didnt get to see boost gauge when it happened as I was merging in between two 75 mph trucks practicing their NASCAR drafting on I81 both times.
Didnt get to see boost gauge when it happened as I was merging in between two 75 mph trucks practicing their NASCAR drafting on I81 both times.
