720 RUNNING RICH

  • Tiny
  • hoffert88
  • 1986 Nissan Truck
  • 4 CYL
  • 4WD
  • manual
  • 273 miles

I have a 1986 Nissan 720, non-hardbody 4wd 2.4L z24 motor with 273xxx miles on it. It's running really rich and I'm trying to get it to pass smog in California. The carb is newly rebuilt (less then 50 miles), new o2 sensor, new spark plugs and wires, fuel filter was changed maybe 15000 miles ago. The cat is the original from 86 but is passing the cat test involved with the smog. The mechanic that I talked to after it was smoged says its either my computer or a vacuum solenoid that controls fuel. I don't know what this solenoid is or where its located. Everything else is passing, just running rich. I don't know what else it could be. I have found 2 vacuum switches on the passenger side of the engine compartment and one it not actuating like it should be (hooked up my meter and reads 000.0 oms with engine both off and running). I don't know what the switches are for but I doubt these are the switches/solenoids the tech was talking about. For a picture of the switches and there location follow link below. Switches are part code 22360 (bottom left of picture). Please help.

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Friday, May 13th, 2011 AT 4:53 AM

21 Replies

  • Tiny
  • fixitmr
  • Member

What about a bad fuel pressure regulator? Ruptured diaphram would would suck extra gas into intake.

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Friday, May 13th, 2011 AT 5:42 AM
  • Tiny
  • hoffert88
  • Member

Where is that located? And is that something I can change in my driveway?

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Friday, May 13th, 2011 AT 6:04 AM
  • Tiny
  • hoffert88
  • Member

And is there a way to check it to see if it is bad before I go out and buy one?

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Friday, May 13th, 2011 AT 6:15 AM
  • Tiny
  • KHLow2008
  • Expert
  • 41,997 posts

Such vacuum switches can be tested. It is in fact a solenoid and if 0.00 ohms, it indicates the switch is shorted internally. Try applying battery voltage to the wire while grounding it. Note if there is a clicking noise and test with a vacuum hose to see if vacuum passes through.

Our database does not show anything about the 2 switches and from what I see, they should be attached to something else with another hose leading out.

Does the rich running condition occurs only during low engine speed or at all ranges?

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Friday, May 13th, 2011 AT 11:39 AM
  • Tiny
  • fixitmr
  • Member

Oops! Its only an 86, does it even have a VACUUM pressure regulator? Is it an electric fuel pump?

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Friday, May 13th, 2011 AT 10:57 PM
  • Tiny
  • hoffert88
  • Member

Yes it is an electric fuel pump. And those switches only have one vacuum port, but they connect to two different electrical connectors. Im not sure where the connectors lead to, I havent dug that deep into it yet.

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Saturday, May 14th, 2011 AT 12:56 AM
  • Tiny
  • hoffert88
  • Member

And it runs rich through all ranges. More so at the hi end though.

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Saturday, May 14th, 2011 AT 1:35 AM
  • Tiny
  • fixitmr
  • Member

What we really need to know is the carburetors guts, how they function. Where is the return line to tank located? Is it on the carb?

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Saturday, May 14th, 2011 AT 2:40 AM
  • Tiny
  • fixitmr
  • Member

Did you rebuild carb? What about wrong float setting?

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Saturday, May 14th, 2011 AT 2:42 AM
  • Tiny
  • fixitmr
  • Member

Looks like same carb since 83. And it does have a mixture solenoid cause ya get 1 in the kit!

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Saturday, May 14th, 2011 AT 2:49 AM

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