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WinRice WinRice is offline
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Join Date: Jun 2005
Location: Colorado
Posts: 700
I do a retune and test every 2 years, so I have this down pat.

The cat will not work well unless the AFR is held very close to 14.7, and that's what the O2 sensor and the other parts of the lambda system do for you. It works on idle up through mid-range.

I only have the specs for my '86, so you need to find them them for your '89. There is a sticker on the rear crossmember when you open the engine cover. To adjust, you need to measure the CO before the cat, with the O2 sensor unplugged, car fully warmed up, and set it to something like 0.4-0.8% (or whatever the '89 spec is) at idle. As your adjust, you need to reset the idle speed to stay in spec, usually around 950 rpm. Then you plug the O2 sensor in and watch the CO as you slowly run it up and down from idle to about 3000 and it should stay around 14.7 AFR.

BTW it helps to have fresh plugs, set the timing, and make sure your WUR and system pressures are all up to spec first.
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1986 911 Turbo
3.3L, K27HFS, Tial 46mm, TurboKraft Intercooler, 964 Cams, Monty Muffler, MS3Pro Evo, M&W Ignition, Zietronix WBO2 Data Logger, Wevo shifter, coupler and motor mounts.

Last edited by WinRice; 04-20-2010 at 12:26 PM..
Old 04-20-2010, 12:22 PM
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