overboost relay

[Noah930]

I'm always thankful for this board. I had a no-start issue last week. I swapped the yellow overboost relay in the engine compartment for a spare, and the car started right up.

But now I want to replace the spare I had stashed in the frunk. Our host sells two versions: the Porsche-branded one and one made by Wittrin. Is there any difference? Is one any better than the other? I didn't want to get into a situation like the Bosch coils, where the German ones are good, but the Brazilian-made ones seem to be junk. Not something I want to find out on the side of the road.

[pkabush]

You likely already know this but if not, you can bypass the OB switch with a jumper wire.
I can’t recall the terminals for sure but I want to say 30 jumped to 86. Don’t quote me on that though. Also, it may be different on later years. Mine's a 81 so, no Lambda
Anyhow, for those who don’t know, that’s a hack that’ll keep our cars running in the event that the switch fails. Not sure on the quality of the aforementioned part.

[Alan L]

The switch is just forming an earth contact which allows the fuel pump relays to run.
In o/boost it lifts the contact in the switch - breaking the earth circuit - relay shuts down, pumps stop. just earthing the wire on the switch will get things running. But you have no o/boost protection.
Alan

[Noah930]

Yeah, I couldn’t recall which terminals to jump while stuck in a parking garage. Later a friend joked I shoulda just started jumping contacts randomly until stuff started sparking. The no-start thread stickies at the top of this forum says it should be 87 to 87a. Someone else thought it was 86 to 87a.

[Alan L]

You don't need to touch the relay.
Pull the white wire on the o/boost sw, and earth it. Job done.
Alan

[T77911S]

its 30 to 87a

the OB rly provides a path to ground via the OB switch for FP rlys to energize.

the OB rly works in the de-energized position. the air flow sensor energizes the OB rly to turn OFF the FPs when the engine is NOT running. this same ground path also goes through the speed rly under the seat for the rev limiter.

grounding the white wire wont do any good if the OB rly is either energized or the contacts (30-87a) are bad.

your contacts are probably dirty on the old one.
remove the cover and clean them with some 600 paper and see if that gives you a spare.

[mark houghton]

go to post #5 for a picture of where to jump. I once got stranded and did not have a piece of wire but scrounged around on the road and round an aluminum pull tab from a beverage can....managed to straighten it out and insert as needed. A McGiver kind of thing. A guy can run all day long bypassing that relay but yes, you lose the overboost protection.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/887500-dead-h2o-2-save-your-ass.html

[T77911S]

you still have overboost protection with the OB ryl jumpered.
the over boost protection comes from the switch on the IC.

the OB ryl is there to turn off the FP if the engine is not running but key is on through the sensor plate switch

[mark houghton]

Originally Posted by T77911S

you still have overboost protection with the OB ryl jumpered.
the over boost protection comes from the switch on the IC.

the OB ryl is there to turn off the FP if the engine is not running but key is on through the sensor plate switch

Correct, my brain was mis-wired when I said what I said. What you don't get is the safety feature of the fuel pumps shutting down in the event of an accident where the engine has stalled but the ignition key is still in the on position...perhaps puking fuel all over the place.

[T77911S]

I think it more possible to flood the engine or cylinder if you have it running too rich or a leaking injector.

[Jeff NJ]

I could swear I posted earlier, but it's not here?
Well, I wrote that I had an issue with my yellow relay and bought a new one, but pulled my original apart. I found a few broken solder connections on the board and easily resoldered them back together and it was good as new and in my parts box as a backup that I trust.
So give that a shot, you never know.

[T77911S]

yes, that's always good to do, same with the speed rely under the seat. solder joints are a common problem with electronics.