Removing the tamper proof plug

[William Miller]

A freind is comming by tonight with a 83 targa.
We plan to adjust the fuel mixture screw.
It's unlikely, that it's still there, but if it is does anyone have any tricks to removing the tamper proof plug that is supposed to be in the top of the mixture control unit? (This is bassically supposed to be a broken off bolt.)

I've looked in the manual but they expect you to remove the whole unit and drill a hole in the plug and remove it with a screw extractor.

I have an idea but wanted to see if anyone's done this with the mixture unit in the car?

My car is a euro and has the little rubber plug on a stick.


BTW anyone tuned the mixture with a dwell meter connected to the test harness? This is mentioned in some of the Bosch FI books that I have read.


Any help is appreciated!

[Steve W]

You could drill a small hole in the plug, screw an appropriate wood screw in partially, and use some pliers to pull it out.

You could set the mixture with a dwell meter. Plug the dwell meter in the test plug, and turn the mixture screw until the lambda valve modulates at around a 50/50 frequency.

[William Miller]

Thanks steve. I think the plug is threaded. I have an extractor, but need to find a way to drill the hole at a right angle and there isn't mich room.

does it matter which lead of the dwell meter get's connected to each wire on the test plug?

[Steve W]

I think the plug may just be a slip fit into the hole. I don't remember if wire polarity matters, as it's been years since I worked with CIS, but it probably doesn't matter which way the wires go in. If it doesn't read one way, just reverse the wires and try again. The lambda valve is nothing more than a modified electronic fuel injector, and you are just trying to adjust the mixture screw so the valve has a 50% on and 50% off frequency.

[William Miller]

OK on the frequency valve.
My car is a euro. no tamper proof plug.
The shop maual indicated that the plug was a special bolt that is screwed in and broken off.
I'll look closer. I hope it't already gone. Probably is.
Thanks again!