1988 VG30i Black Smoke And Loping Idle

[PUNKLOVE315]

Anyone ready for another on of these?

 

1988 Nissan Pathfinder SE 188000 Miles with manual transmission and California emissions. Engine code 12 Air Flow Meter and sometimes 11 Crank Angle Sensor. Fires right up and presents with excessive black smoke billowing out of the tale pipe and a low loping idle. If the throttle is applied it will stumble up to high RPMs. I can only run it for about 20 minutes until it completely fowls the plugs misfires and stalls. I cannot get the engine to temp to test the fast idle cam or do the FSM's voltage test for the mass airflow sensor. Do any of you know if the engine temp will affect the MAP voltage output? Also when the MAP sensor is disconnected while the engine is running the engine idles up to about 1500 RPMs and stabilizes. It also leans out the engine and my exhaust smoke clears and appears normal. Is this only because the system is reverting to preset levels. Could it still be another sensor causing the issue that is disregarded once the engine enters fail safe mode?

 

Things I have done so far.

Compression test: OK.

Fuel pressure regulator disconnected and vacuum applied: No change.

O2 sensor replaced: No change.

Crank angle sensor replaced: No change.

Air flow meter cleaned and O ring replaced: No change.

Fuel Injector O rings replaced: No change

Vacuum lines inspected found one leak and repaired: No change.

General tune up engine timing included: No change.

 

Any advice or input is greatly appreciated. I could really use the help.

 

Thanks,

 

Brett

Rome NY

[Kingman]

Ohm the Cylinder Head Temp Sensor and the sub harness. Sounds like it's reading wrong and telling the ECU the truck is in the antarctic.

[PUNKLOVE315]

So I hooked up to the one in the front behind the timing cover and it is reading 5.94 in the 20K scale. Would I be right in thinking this thing need to be replaced?

 

Thanks

[Slartibartfast]

The manual says it should read around 2.3-2.7k at 68° F, .77-.87k at 112° F, down to .33-.30k at 176°F. I'm assuming NY is colder than 68° right now, so you'll see a higher resistance than 2.7k, but 5.94k does sound suspiciously high.

 

If you want confirmation, you could pull the sensor, warm it up in a cup of hot water, then check it with the meter again.