1989 Dynasty 3.0 liter :
I am experiencing drivability issues ( starts ok, cruises OK , then rough engine, black smoke, rough idle, stalls, cannot restart for long time, then next day sometimes all OK for a 10 minutes drive.)

Years ago, it threw codes for MAP sensor .
Installed new MAP sensor and all ok for several months .
Then same issues again.

I suspect MAP sensor circuit; not necessarily the sensor , but rather either vacuum signal to MAP sensor or electrical circuits are intermittent.
Sensor has just 2 wires, not three wires.

Bench tested MAP sensor --> passed, as voltage changed with changing vacuum supply.

Can someone educate me on the electrical circuit and the vacuum pathway?
I suspect that PCM sends / receives electrical and will adjust air/fuel mix accordingly.

I suspect that vacuum comes from intake manifold , but do not know if the vacuum pathway within the EGR valve system will create havoc with the MAP sensor system.

Trying to whether there is misinformation input or determine source of bad input to PCM to mess-up the A/F ratio.

Heavy black smoke associated with rough idle if it starts at all.
Then, all ok next day.
Update:
Yesterday, engine stalled after long warm up. Would not restart, crank crank--> no fire up.
Today, cold start immediately. Turned off before it went into closed loop.

 

Try wiggling the connector to the MAP sensor.
Many times I've had a poor connection at the MAP cause these issues. I usually pull the connector, clean everything, reinstall with some DE grease, ensure it's tight, then lock it in place with a zip tie. This usually solves the problem.

 

Yes, the wire connection is suspect.
I did clean the 2 wire connector at the MAP sensor when I replaced the MAP sensor.
Worked for several months.

I suspect the issue is upstream of MAP sensor .
I do not know the electrical circuit upstream; is it a straight shot to the PCM?
The 2 wire connector gets buried in a black plastic sheath loom and disappears from site as soon as the 2 wires leave the MAP sensor.
Is one of those wires connected to an engine ground? or do both go to PCM?

If my issue is a corroded connection to engine ground, then I should be able to handle it.
If the issue is due to a faulty PCM connection or due to a faulty PCM , then I am in this a lot deeper than anticipated.

An alternate cause of the malfunction might be due to a vacuum leak ( in EGR ?) that causes bad vacuum signal to the MAP sensor. I believe that would fool the sensor into thinking that the engine vacuum was weaker than reality.
That would cause the MAP sensor to incorrectly inform the PCM that my engine was under a load condition even though it was at idle.
That would cause PCM to command richer fuel mixture--> heavy black exhaust.

I do not know what the cause of a possibly bad MAP sensor input into the PCM might be occurring: vacuum? electrical? bad PCM?
It is sporadic in nature after closed loop kicks in.
Then extreme rough idle, black smoke, stall, no start . or extreme bad cruising at 25 mph around town --> stalls, no restart.
I experienced both.
Still no codes, no CEL yet.

 

As I said, try getting out and wiggling the connection at the MAP when the vehicle starts acting up. If the issue resolves when this is done, you have a bad/weak connection at the MAP.

 

I incorrectly posted the wiring as 2 wires when in reality it was 3 wires.
I incorrectly thought that I could trust my memory.

Today was the 1st warm day that I could get out to re-examine the vacuum and the wiring.

I let the engine warm up to enter closed loop and then started to fiddle.
I used a handheld propane source to check for vacuum leaks while the engine idled smoothly.
Result: no change in idle.
Concluded no vacuum leak at MAP, nor at intake to throttle body, nor at brake booster.
Guess that was good ,yet I was hoping to find something to correct.
Next, wiggled the electrical connector at MAP--> no change.
Traced the wiring across the back of the intake manifold as it gets engulfed in a plastic sleeve.
Peeled the sleeve. Looked new, clean.
Let idle 10 minutes and drove around 3 miles w/o an issue.
I cannot claim that I did anything to resolve the sporadic rough idle/ black heavy exhaust/ stall.
Really hoped to find a cause today.
I did not do any VOM testing today. I would guess that it would appear normal today.
The connector at the MAP sensor was melted at one side which I attributed to someone must have rested the plastic connector on a hot manifold .
The connector still held fast at the MAP clip and the electrode terminal appeared very clean.
I do not believe that an intermittent disconnect occurred at the MAP sensor electrical plug-in area.
Will do as you suggest to wiggle MAP sensor electrical connector when it acts up again.
If it does start to run rough/stall/ thick dark exhaust, should I disconnect battery to make the PCM reset?

 

You can try making the PCM reset.
I was just thinking: You said you replaced the MAP, where did you get the sensor from?
Reason I ask is I've gotten numerous sensors that were bad when I installed them. I've started pulling sensors at the JY and using them instead as they are more trustworthy than anything I can buy new.
If you need to dig into the wiring further after everything:

 

Wow. Thank you smokesxt.
That was a great electrical schematic.
Where did you get that schematic? Very clear to read.

 

Googled: 1989 Dodge Dynasty 3.0 engine wiring.