Bad grounding, codes 12 and 21, on '94 JGC?

Well I finally crawled under the car with my DVM. I noticed I had about 3.5 ohms of resistance to ground for the signal wire on the oxygen sensor. I looked at the electrical schematic in Haynes and it looks like all the grounds are spliced at "K4" then grounded to chassis. I couldn't find any chassis grounds besides the one coming off the negative battery cable. Is there another location for the ground? What does a "K4" splice look like and what is it near?

I spliced a wire on the MAP sensor ground and tied the wire to the intake manifold. My erratic idle has disappeared and check engine light hasn't come on yet after 16 miles of driving. I think I might have found the problem. I would like to fix the root problem though. Prior to adding the ground, the check engine light would come on every time I drove the car.

Thanks, Kirk

This is what I posted a few weeks ago with no response:

My '94 Jeep Grand Cherokee has been acting up. The check engine light comes on and goes off irregularly. When I check the flashing light I get 12 and 21 as the codes. The vehicle is pre-OBDII.

I hadn't disconnected the battery at any point, so I don't know why disconnected battery code would record. I replaced the O2 sensor and it didn't seem to affect the check engine light being on or off. So I doubt it was the O2 sensor causing the problem.

When the check engine light is on, the idle tends to be rough and below 500 rpm. Upon start up, if the engine revs to 2000 RPM by itself, then comes down to an irregular idle, the check engine light will come on shortly thereafter.

I do notice some other erratic things like the oil pressure gauge fluctuating greatly and the voltage meter on the dash is consistently below

14 V when the check engine light is on.

At no time does the vehicle suffer from low power or the ability to drive at highway speeds.

I cleaned the battery terminals, checked the electrolyte levels. The voltage across the battery terminals at idle or revved up doesn't get above

13.8 V using my digital voltmeter, Haynes says the voltage should be between 14 and 15 V. When the engine isn't running the battery measures about 12.8 V. So I presume the battery is good.

The battery hasn't ever discharged noticeably.

From the Haynes discription the Voltage is controlled by the PCM which is separate from the alternator. Does anybody have a similar experience and successful repair strategy? I am trying to avoid playing the musical parts replacement tune again.

This '94 GJC 4.0 liter has 138000 miles on it.

Thanks in Advance, Kirk