black smoke on start up-1988 v-6/poor gas miliage? Help please

[lonfitton]

I have a 1988 pathfinder V-6, automatic. Runs well but has black smoke at tailpipe on startup and very poor gas miliage. I am located in a small villiage in southern Baja, Mexico without quality mechanics familiar with this problem. Is it possible to clean the Mas air flow sensor, or any of the other stock parts to aid in this problem? Many thanks, Lon Fitton BCS < Mexico

[PathyAndTheJets]

Yeah, if you take off the air cleaner housing, the mass air flow is screwed into the side of the throttle body.

http://www.nissanpathfinders.net/forum/topic/23251-tbi-component-listing-loctaions/?do=findComment&comment=772279

Edited April 8, 2016 by PathyAndTheJets

[Slartibartfast]

MAF cleaning is pretty easy so long as you're gentle. You can buy proper MAF cleaner, but carb cleaner or denatured alcohol should work too. Just don't use something that will leave a residue. I would expect a fouled MAF to make it run lean, though, so I would be more suspicious of your oxygen sensor.

[PathyAndTheJets]

Fouled Maf should run rich, it's a hot wire MAF right?

 

Gunk requires more amps to keep the wire hot, tricks PCM into thinking there's lots of air flow, throws mixture rich.

[Slartibartfast]

Air flowing across the hot wire cools it. Gunk insulates the wire from the air and the wire stays hot, tricking the ECU into thinking there's very little air flow, throwing the mixture lean.

 

I helped a friend with his dad's Buick a year or two back. White spark plugs, not a lot of power, went into limp mode if you drove it hard. We were sure it had a vac leak. Turned out the MAF filaments were filthy. We cleaned the MAF and the car ran fine until its unfortunate introduction to a tree.

[PathyAndTheJets]

My buddies Pathfinder went full rich after some oil from his k&n filter got on it and started catching crud. Cleaned it, ran beautifully again. But that may be because a liquid was on the wire rather than dry substances.

[Slartibartfast]

I suspect you're right about the liquid. Maybe it was boiling off or something. The gunk on the Buick MAF was pretty dry.

 

I did a general search (not just this forum) and I'm seeing threads where both rich and lean issues clear up after MAF cleaning. Interesting. There are two wires in our MAFs, more in some others apparently. Maybe the computer does some comparison between them, and the symptoms vary by which wire is dirtier?