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720 running rich

Tiny
HOFFERT88
  • MEMBER
  • 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
  • MECHANIC
  • 9,990 POSTS
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
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  • 18 POSTS
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
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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
  • MECHANIC
  • 41,814 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
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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
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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
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  • 18 POSTS
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
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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
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Did you rebuild carb? What about wrong float setting?
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Saturday, May 14th, 2011 AT 2:42 AM
Tiny
FIXITMR
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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
Tiny
FIXITMR
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And actually all carbs with jets have an air bleed jet for each fuel jet as I recall. This serves as a way to tune it precisely I guess?
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Saturday, May 14th, 2011 AT 2:54 AM
Tiny
FIXITMR
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If that little o-ring is cut/bad that would do it.
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Saturday, May 14th, 2011 AT 3:05 AM
Tiny
HOFFERT88
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  • 18 POSTS
The fuel mixture control solinoid is what was bad when I first had it smoged. So I sent it back to national carburetor (where I got it from) to have it all rebuilt again. I apoligise for not understanding what you were talking about when you said variable jetting controls. So that has been guarenteed to be a new part (not saying that I didnt get another faulty one put in but I feel its unlikely).
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Saturday, May 14th, 2011 AT 5:41 AM
Tiny
FIXITMR
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So they gave you a faulty 1 the first time and now it's still not right? How did you determine the mixture solenoid was bad the first time?
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Saturday, May 14th, 2011 AT 3:38 PM
Tiny
HOFFERT88
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  • 18 POSTS
I took it in and had it diagnosed. They boar-scoped it and it was not physically actuating. It was getting power and was trying to actuate but no physical movement, just clicking.
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Saturday, May 14th, 2011 AT 8:48 PM
Tiny
FIXITMR
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If you knew the voltage to apply I guess you could check it out your self? And also whether it is rich or lean with no voltage applied?
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Monday, May 16th, 2011 AT 8:49 PM
Tiny
HOFFERT88
  • MEMBER
  • 18 POSTS
I am not sure. I can check my hayns book and it might say weather the solinoid is normaly open or closed. So if the solenoid is good im preaty much looking at either the catalytic converter or the fuel mixture screw on the carb itself? Cause thats really the only things that havent been changed or adjusted.
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Wednesday, May 18th, 2011 AT 3:25 AM
Tiny
FIXITMR
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If original that's an old CAT and I am not familiar with CAT life problems. 9 years? LOL
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Thursday, May 19th, 2011 AT 3:22 AM
Tiny
HOFFERT88
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Haha. Im not sure what the average is for my truck but I was reading up on the lifespan of a stock catalytic converter and it should last the life of the truck but it could be that it is bad from running so rich (depending on how long it has been running rich). I also read that its been known that replacement cats seam to go bad after 10 years due to the replacements not being built as well as the stock manufacturers are.
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Sunday, May 22nd, 2011 AT 2:06 AM
Tiny
HOFFERT88
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So the problem was resolved, the problem was the air filter being cloged. I never relized it because while doing maintance on the carb I had always had the top cover off so it was getting plenty of air to run right. I had cleaned the filter not long before all of this but I guess I had grabbed the wrong oil for the filter (a K&N filter) and not realized it so it caused all the dirt and grime to just gum up and clog the filter. So with the lid on, the carb was starving for air and more or less had the choke on all the time. R2 the filter and all is well now. Thanks for all the help.
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Sunday, August 28th, 2011 AT 6:29 AM

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