1985-1998 [Subscribe to Daily Digest] |
Salutations:
Not necessarily - but it is often the case and it relates to how the BPC fails.
The BPC shares it's hot wire (#2) between two solenoids. One of the solenoids has both it's wires (#3 and #2 split) routed over an internal air vent to the wastegate.
I think this disturbs the airflow such that the control disk favours the wire side vent and eventually it cuts a groove in the vent ring over time (hard steel disk - brass vent ring).
Sooo - in not to long a time - it cuts enough meat out of the vent ring to let the disk come out of the vent and chafe through the wire - then starts cutting the wire and fusing the wire jackets. It's a pair of single wires in cloth and rubber - but by the time anyone opens them up to find out - it's just a greasy rag tube, some powder and two exposed and very brittle wires down the middle with a notch cut out of the side.
In some cases, it would cut the power wire first and I suspect then tilts the disk up against the solenoid case and feeds 12v directly back to the APC on the control circuit (#1 or #3 BPC pin).
In other cases, it cuts the control wire and simply fails to base boost - (#3 BPC pin goes dead) - until it works it's way out so more and cuts the 12v wire and then eventually cooks out the lower solenoid or APC as above.
It's a crap shoot and why I think it is really wise to pull the loom connector when you start to get erratic boost. You know its happening when your BPC starts to buzz a lot noticeably at idle. That is the control disk cutting, then riding in, the groove.
Usually - you get erratic boost for a bit - then base boost. Squirting anything that can close the circuit (say brake cleaner) in there, I think at least, actually helps short it (and everything else) out more quickly.
It should be a very dry environment in there normally.
Anyway - the only way to tell for sure is to test the loom connector for resistance when grounded to the chassis - I think Bazil Burns said #1 and #3 female(s) on the loom connector show 0 ohms when your APC is wallyfux - infinite if it's ok. But it could be exactly the opposite - so check with him.
I'm working on mod'ing the BPC so that it doesn't float the control disk to one side in operation - which I think will make them last a lifetime because it would then be a frictionless valve as, I think, it was designed to be in the first place.
It is almost like two people who didn't speak to one another did the drawings for a third person manufacturer.
Again - if you have a dead BPC to contribute to the research, it would be greatly appreciated. I'll pay for shipping to my bench. Flag me through the site below.
Dexter J
posted by 24.222....
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