ROUGH IDLE BLACK SMOKE WHEN ENGINES HOT

  • Tiny
  • CRisJOhn
  • 1993 Nissan Sentra
  • 4 CYL
  • 2WD
  • manual

1993 nissan sentra
new fuel pump, distributor assembly
rough idle, black smoke when hot?

Monday, July 25th, 2011 AT 10:37 AM

9 Answers

  • Tiny
  • mhpautos
  • Expert
  • 29,842 posts

Check plugs and leads, sounds like a chronic misfire problem, pull plugs, faulty cylinder will have a very black and sooty plug.

Was this
answer
helpful?
Yes
No
Monday, July 25th, 2011 AT 1:35 PM
  • Tiny
  • CRisJOhn
  • Member

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?

Was this
answer
helpful?
Yes
No
Tuesday, July 26th, 2011 AT 12:47 PM
  • Tiny
  • mhpautos
  • Expert
  • 29,842 posts

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.

Was this
answer
helpful?
Yes
No
Tuesday, July 26th, 2011 AT 12:51 PM
  • Tiny
  • CRisJOhn
  • Member

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

Was this
answer
helpful?
Yes
No
Tuesday, July 26th, 2011 AT 12:55 PM
  • Tiny
  • mhpautos
  • Expert
  • 29,842 posts

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.

Was this
answer
helpful?
Yes
No
Tuesday, July 26th, 2011 AT 1:01 PM
  • Tiny
  • CRisJOhn
  • Member

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?

Was this
answer
helpful?
Yes
No
Tuesday, July 26th, 2011 AT 1:08 PM
  • Tiny
  • mhpautos
  • Expert
  • 29,842 posts

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

Was this
answer
helpful?
Yes
No
Tuesday, July 26th, 2011 AT 1:14 PM
  • Tiny
  • CRisJOhn
  • Member

Thanx

Was this
answer
helpful?
Yes
No
Tuesday, July 26th, 2011 AT 1:19 PM
  • Tiny
  • mhpautos
  • Expert
  • 29,842 posts

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.

Was this
answer
helpful?
Yes
No
Tuesday, July 26th, 2011 AT 1:22 PM

Please login or register to post a reply.

Similar Questions