CIS help?

[Orin Eman]

> 
> Having trouble with my semi-newly aquired 87' 5ktq (MC-1, mac 11).
> 
> I've been chasing down a missing at idle and at low speeds.  So far I've found and corrected a few vacuum leaks, and broken wires at the idle/wot connector.
> 
> I can get the engine to run pretty well now, with the missing almost completely gone, if I set the duty cycle for the CO% at about 70%.
> 
> If I try to set the mixture at the recommended 48%, the engine runs poorly, the idle speed drops, and the missing is very pronounced.  When doing this, the % seems to vary a lot, and getting a good reading is not very easy.  If I disconnect the oxs (new BTW), the mixture does not seem to sit at a steady 50% as I would expect.
> 
> I also have found that when I set the mixture to where it should be (48%ish), the frequency valve starts intermittently buzzing, with the misses corresponding directly with the buzzes.

This kind of sound is usually associated with really low duty cycles - like
10 to 15 %!

Measure the O2 sensor voltage with it disconnected from the ECU and
set the mixture for about 0.5V... then see what the duty cycle is.

> Am I to be looking for a vacuum leak, incorrect fuel pressure, burnt valves, bad injectors, different meter?  Something is definitely not right, but I can't seem to identify the problem.

What kind of meter?

Orin.