Lambda sensor coax cable question
 

The green wire that goes to the lambda brain on my 1980 SC is a coax cable. Does the O2 sensor connect to the inner wire of the coax cable, the outer wires, or both?
Tanks in advance
SmileWavy

hi!

I'm not familiar with your set-up, but typically the center wire in a coax is the (+) signal, and the mesh (outer wires) is ground. Use a voltmeter to check things out. Use the continuity setting, ground one lead on something metal, then test the two wires. Which ever shows a change on the display (shows continuity) is ground.

Brad

Is the oxygen sensor wire similar to the infamous green distributor signal wire in terms of wire gauge thickness, etc.? And where does one find this sort of wire?

Brian

It looks to be larger in diameter than the ignition wire, but of the same type of construction.
I have no clue where to find it except maybe to check with electrical equipment distributors.

I was looking at something like this RG142/U here.
Brian

According to Bentley, the center conductor is connected to pin 2 of the lambda box and to the oxygen sensor at the other end. The shield is cconnected to pin 4 of the lambda box, unconnected at the other end.

Thanks Scott.

If one wanted to replace and re-loom the green shielded coax distributor-CDI signal wire, would the RG142/U be a suitable replacement? A little help, EEs?

Brian

Brian,

The RG-142 is a good choice because of the high temperature resistance of the Teflon insulation, however, the large diameter of 0.195" means it will be pretty stiff and rather difficult to bend and route in tight spaces. Teflon-insulated coax is stiffer than typical polyethylene-insulated coax.

RG-179 and RG-180 are smaller in OD [at 0.100" and 0.140"] and also Teflon-insulated for high-temperature service. They are much easier to bend and route.

Thanks, Warren. What about the RG316U at this site? I can't find a source for RG-179 or RG-180 by the foot.

Brian

Brian,

Yes, that should work fine ... only 0.002" smaller than RG-179!

Warren, great. Thanks for the confirmation.

Brian

Theory is confirmed, the O2 sensor needs to be connected to only the inner wire.
I installed a new connector to the inner wire and the lambda brain is now functioning correctly.

I also did an injector flow test. #4 was flowing about 20% more than the rest. I replaced it with a good used injector.
The mixture is steady at 14.5 to one, but it wants to run richer under part throttle. the O2 sensor is compensating and keeping it where it should be.
I can get it to pass smog now but I am still wondering why it wants to run richer under throttle than at idle.
No vacuum leaks, I set it at 14.7 to one at idle with the O2 sensor disconnected, and as soon as i get going it goes to 13.5 to one.
The O2 sensor will adjust that but I sure would like to solve the problem instead of compensate for it.
The only thing left is the fuel distributor. I disconnected the throttle switch for a run to see if that made any difference, it didn't.