Mechanics

ROUGH IDLE BLACK SMOKE WHEN ENGINES HOT

1993 Nissan Sentra • 4 cylinder 2WD Manual •

1993 nissan sentra
new fuel pump, distributor assembly
rough idle, black smoke when hot?
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CRisJOhn
July 25, 2011.




Check plugs and leads, sounds like a chronic misfire problem, pull plugs, faulty cylinder will have a very black and sooty plug.
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Mhpautos
Jul 25, 2011.
Thank You for your responce.
New plugs, cap, rotor, wires, and fuel pump. Checked Mass Air Flow Sensor good. Recleaned plugs. Did Two Compression tests first one when Cold (1to4) 145psi. Did second when hot 1 and 4 was 85psi, then 2and3 was 115psi. Is this good or bad?

Tiny
CRisJOhn
Jul 26, 2011.
Do a wet test on the low cylinder, just a small squirt of oil to seal the rings, if the comp comes up it will be rings if not valves, do the test hot as well.

Mhpautos
Jul 26, 2011.
Thanx
Would the the two low readings cause all four plugs to have carbon build up? Thank you for rapid responce.

Tiny
CRisJOhn
Jul 26, 2011.
Normally not, but with 2 low comps we need to establish the cause of this, a problem with an inlet valve may impact on other cylinders. If you can do or get a leak down test done, this will isolate the main problem, such as which valve is leaking or if a ring problem.

Mhpautos
Jul 26, 2011.
Removed the fuel rail (with injectors connected) Turned on vehicle with out cranking over to check for any stuck opened injectors, was test good or bad?

Tiny
CRisJOhn
Jul 26, 2011.
You must find where the compression is going first, that type of test will be fairly inconsequential at this stage.

Mhpautos
Jul 26, 2011.
Thanx

Tiny
CRisJOhn
Jul 26, 2011.
It's near midnight here in Australia, so I am signing off soon, let me know how you get on. If you need more help re post here.

Mhpautos
Jul 26, 2011.

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