O2 sensor delete tips.

[T77911S]

not really sure what to title this but for those that have removed the O2 sensor and would also like to remove the electronics under the seat and want to keep the solenoid valve that blocks vacuum to the retard pot when on boost, i have a way to keep it.
i wanted to remove the speed relay under the seat since it tends to fail, usually due to bad solder joints, but it still provides a rev limiter. so i installed an MSD with an adjustable rev limiter built it.
to bypass the speed relay pull the back off the connector. i love these connectors because they are so easy to work with.
you can either remove both wires from pins 1 and 2 and solder them together or like i did, pull one wire off and solder the 2 together in the pin itself. no insulation needed.

this next one gets a little involved, but is easy.
it works off the throttle switch and the O2 relay on the panel in the engine bay. the thing i dont know right now is does the valve open with 12v or does it close with 12v.
open the connector on the fire wall of the engine. pull pin 5 and remove the 2 wires. one wire goes to ground, one to the switch. put the one to ground back on pin 5, the other wire is soldered directly to the wire on pin 11. i used heat shrink to insulate the joint.
pin 5 is the "common" on the switch for either normally closed contacts (5 and 4) or normally open contacts (5 and 6).
pull pin 6. one wire goes to a temp sensor adn the other to the switch. remove the one to the sensor.
now here is the neat thing. pull pin 10 and remove. depending if you want the closed contacts at idle or the open contacts at idle, you just plug 4 or 6 into the hole for pin 10.
pin 10 is power from the O2 relay.
here is a run down.
power goes from the O2 relay on the panel to pin 10. then to either the contact that was in either 4 or 6. then to the throttle switch to the common connected to pin 5. then to connector for the valve then back to ground.
the connector is the one with a red/blue wire and a brown wire.

to summarize since i know my explanation is not that good.
remove the ground wire from pin 5
wire 5 to 11
remove brown/green(?) from pin6
remove pin 10
for 12v to valve at idle, put pin 4 in pin 10 slot
for 12v at about 3/4 throttle, put pin 6 in pin10 slot

this is totally reversible. this is only for those that want to remove all the electronics under the seat and want to keep the solenoid valve for vacuum retard

[mark houghton]

Good writeup. Anyone that can decipher the wiring of these cars I hold in high esteem. Pictures would have been a plus.

[T77911S]

thanks. if you have any input as to the solenoid valve being open with 12v or closed with 12v i could clean it up some, not to mention my car.
i still need a valve for my own setup.
it took me a little while to figure out how to use all original wiring without doing anything that is permanent.

[JFairman]

The vacuum solenoid is a pierburg change over vacuum solenoid with 3 vacuum line connections origonally made for Mercedes with one side vented to atmosphere with a little curved hose pointing down so water doesn't get into it.

Depending on how you connect the vacuum lines it can be open when given 12 volts or closed when given 12 volts.
It has nothing to do with boost retard, that is a mechanical function when boost air pressure is supplied to the outer connection of the vacuum advance/retard pot.
The inner connection or retard pot side on USA '86 through '89 930's retards timing at idle and during deceleration and the rest of the time it does nothing. Put air pressure to it and it has no effect on it.
Try it with a mighty vac tool that creates vacuum or air pressure and watch it while it's removed from the distributer to prove it to yourself.

The vacuum solenoid in the retard pot vacuum line blocks intake manifold vacuum from reaching the retard pot for around a minute after a stone cold start and it by removing vacuum retard ignition timing is advanced between idle and around 1500 rpms and that raises idle speed along with the cold start aux air TB bypass valve being open at the same time.
You don't need it. It helps make a smogged out stock 930 start up and run better when cold.
The other pierburg vacuum solenoid on smogged out late eightees 930's operates the left and right air pump diverter valves.

If the smog crap is removed and static idle speed timing is retuned to around 12-15 degress btdc without having too much advance at 3500 rpms idle speed is much stronger and there's no need for the vacuum solenoid in the retard pot line.

[T77911S]

but...apply BOOST to BOTH advance and retard pots and the timing does not retard.


althougth the diagrams i have seen shows the advacnce going to the thermo time valve on the back of the motor, i routed my vacuum retard to it to perform the function the solenoid
provides to the retard pot when cold, to raise the idle RPM.

you (or I) would think there would just be a valve in the pot itself so that boost does not have an effect on timing thru the retard port, so unless mine does not work right, there does not seem to be one.