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Nissan 720 Surging at high RPMs and won't pass SMOG

Tiny
IDAHOGEARHEADS
  • MEMBER
  • 1985 NISSAN TRUCK
  • 170,000 MILES
Ok, so here is the situation.
11/1985 Nissan 720 Pickup, Z24 Carbureted engine, Five Speed Manual Trans, 4 Wheel Drive with federal Emissions.
I have been trying to pass a California Emissions test.
The Symptoms are as follows:
Slight surging at idle
When the RPMs are held at 2500 with the vehicle in neutral it will surge to between 2200 and 2900.
Emission numbers are well within spec for the idle circuit, but at the High Idle (2500 RPMs) My Hydrocarbon numbers are elevated and the CO numbers are higher then allowed.

The Following has been replaced within the last month:
Cap, Rotor, Plugs, Wires, Catalytic Converter, Oil, Air filter, Valves adjusted and timing set to 3 BTDC.

I suspect an O2 sensor or the Air Fuel ratio Solenoid inside the Carb. I have not yet preformed a Self Diagnostic on the ECCS.
A test of the BCDD was within specs.
A test of the O2 Sensor is to follow.
I refuse to throw parts at a problem, and this puzzle is driving me crazy!
Any Insight, or good Ideas?
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Saturday, February 11th, 2012 AT 5:58 AM

6 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check and test the air injection system
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Saturday, February 11th, 2012 AT 1:22 PM
Tiny
IDAHOGEARHEADS
  • MEMBER
  • 6 POSTS
Well 1985 did not have air injection. It used the bcdd, the tvv, and the AB valve to meter the air charge. This system also uses an O2 sensor, an air fuel mixture control valve and the e.C.C to manage the fuel delivery.
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Saturday, February 11th, 2012 AT 5:05 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check the oxygen sensor and the A/F solenoid
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Saturday, February 11th, 2012 AT 5:28 PM
Tiny
IDAHOGEARHEADS
  • MEMBER
  • 6 POSTS
Those were two parts that stuck out in my head. Do you know of a good way to test the O2 sensor and the a/f solenoid?
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Saturday, February 11th, 2012 AT 6:00 PM
Tiny
IDAHOGEARHEADS
  • MEMBER
  • 6 POSTS
Well, it is fixed! After further testing, I was able to find that it was a combination of issues. These Nissan's use a single wire Bosch O2 sensor, (mine was out of specs, and filthy) these O2 sensors ground through the body of the sensor, much like a spark plug. Nissan had added a designated ground strap to the exhaust manifold to make sure a clean ground was given to the sensor. A previous owner had removed this strap, leaving only the exhaust studs to supply a ground to one of the only sensors in the system! After a new sensor and a new strap, the truck runs great and passed it's test with flying colors. Thanks for all the help everyone. IDAHOGEARHEADS
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Tuesday, February 14th, 2012 AT 7:53 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Your welcome
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+1
Tuesday, February 14th, 2012 AT 5:56 PM

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