1985 Nissan Idling Problems

I currently own a 1985 Nissan 720 4x4 King Cab with the Z24 engine on it. The Idling and Stalling problems began a couple of years ago. So here's what I have done so far in trying to fix the issue

1. New Water Pump

2. New Fuel Lines cause they ripped

3. New Distributor Cap and Rotor

4. New Spark Plugs

5. New PCV Valve

6. Did the smoke test and the only places where smoke comes out is the bpt valve, the weep holes on the vacuum switches and out the top of the carburetor.

7. New Radiator Cap

8. New Anti-Dieseling Solenoid

9. Fixed 2 electrical shorts thanks to the multi meter measuring on the fuse box

10. Replaced a corroded terminal on the ecc main relay and at the same time got the anti-dieseling solenoid and the rest of the engine to receive battery voltage.

11. Manually testing the EGR and BPT valves and they both work fine.

12. Found out that the oil pressure sending unit for some reason became unplugged so plugged that back in

And after ALL THAT, the problem still occurs. However recently, I've been doing some tests and here's what happened.

1. Plugged the vacuum hoses to both the tvv valve and the vacuum control valve and problem doesn't go away

2. Hooked a vacuum gauge to one of the hoses and it reads steadily around 5-8 inhg at idle.

3. Hooked it up to one of the hoses that goes to the manifold and reads the same thing. It should read around 17-22 Inhg.

4. Turns out that the vacuum switch that is connected to the exhaust plugs was bad, took that off so now on the vacuum gauge it steadily reads around 15 inhg and revving the engine it goes up to 18 inhg and back down to 15 inhg. Something else is wrong with it.

5. Replaced both fuel filters and it did not fix it.

6. Replaced all of the plug wires with a brand new set that fit.

7. Sprayed carb cleaner around the base of the carb and the idle rpm's went up and after that, the engine kept doing it meaning that the engine is surging and not idling steadily.

8. Did timing light on all of the spark plugs. All of them have consistent timing.

9. Disconnected and plugged all the lines that go to all of the emissions control components and no effect.

I am just about ready to give up on this thing. Any ideas on what else could it be?

Have you tried buying a new car?

Your problem seems to be that your car is 32 years old.

kek.

Get a used car that someone bought new just recently. They want to sell it now. Take it at a lower price.

Weird, did you take it to the mechanic? Because you know they specialized in things like fixing cars.

I ain't taking that truck to a mechanic. Too expensive. Plus it's not registered. Stop being sarcastic My guess is that it has to do with the fuel delivery or the idle circuitry.

Idle air control ?

It could be an internal problem, like grime buildup inside the cylinders. Everything you tried to fix was external. Take it to a mechanic unless you are planning on disassembling the engine yourself.

I can tell ya this, i sprayed soapy water around the carburetor and the manifold and no vacuum leaks. Sounds like a diaphragm in the carburetor is busted. The only thing is that I'm scared to take off and dismantle the carburetor cause if i screw it up (and i don't want to spend a lot of money fixing it), off to the junkyard it goes.
Also want to point out that I've been to a bunch of websites with people having the same issue. NOT ONE CONSISTENT ANSWER.

And you should be. They are the most complex part on a car. I wouldn't recommend it unless you have gone to a class specifically for carburetors.

Exactly. I hate to see the truck continue to have this problem but we don't take it out on the road anymore, we use it only as a "property" truck as in it never leaves the property.

try /o/

Just curious, if i plugged all the lines that go to all the emissions control components, what components left have a diaphragm?

Does it have an automatic choke? Those things never worked properly.

stick your dick in the exhaust, should do the trick

well, just checked the engine this morning, found out that there is a crack in the exhaust manifold.

You said “7. Sprayed carb cleaner around the base of the carb and the idle rpm's went up and after that, the engine kept doing it meaning that the engine is surging and not idling steadily.”

When you say base, you mean where the carburetor bolts to the intake manifold?

If so, spraying carb cleaner should have no effect unless you’re spraying it into the carburetor. Sounds like you could have a bad seal between the carb and intake manifold.

I had a Ford pickup years ago with a straight six engine and I used to have to tighten the carb nuts all the time, they wouldn’t stay tight for nothing.

Well I did the smoke test and no smoke came out that area.

This is the major problem.

Nah bro, exhaust manifold isn't a huge deal.

OP, I'm going to recommend you check points and condenser in the distributor, and verify you don't have any air leaks at your intake manifold or at the base of the carb.
Be sure to check any vacuum fittings that may be getting manifold vacuum.
Check your vacuum tubing check valves are working properly, by removing and applying vacuum on each nipple.

...

Z24 engines are know for head gasket problems. Have you done a compression test?

Replace carb gasket you baka. If you sprayed the started around it and it revved up, it must have sucked it in

Though I do appreciate someone asking questions about old cars.
mine is a '66 mustang with perpetually leaking everything

92 Talon TSi AWD here. From my experience I would recommend that you also try checking the following:

-Dying fuel pump or leaky fuel pressure regulator. If the fuel pressure isn't spot on the idle can be affected drastically.

-Replace the vacuum lines. Seriously just replace all of them.

-Clean grounds and maybe replace ground wires. I'd recommend anywhere a ground connects to the body/engine to loosen it up, scrape it up a little, put some dielectric grease and bolt back down.

-Other wiring. You may need to redo some of or replace the wiring harness entirely. As wires corrode they gain resistance and this can throw off the tune. Not sure if there's a computer in there but any kind of electronic controller could potentially go bad by now and may need replacement.

-Try a compression test. If compression isn't reading what it should your valves and or rings could be wearing out of tolerance and causing idle issues. If this is out of spec you pretty much just gotta deal with it or swap/rebuild the motor.

-Oil change

yeah that too, most gaskets are suspect (and causing vacuum leaks throwing off the tune) although the headgasket would be a huge bitch to deal with but if nothing else solves it a compression test should at least let you know if the hg is suspect.

Being as how I own a shitbox D21, I might be able to help, but I need to go to sleep, so I'm just bumping the thread for now. I guess the last thread you made on Holla Forums and the thread on /o/ must not have gone anywhere? There can't be more than one asshole here with a 720.

I'll come back tomorrow asking some questions.

Time to drop a cummins in it fam

or an RB26DETT

here.

OP, is this a z24 4 cylinder with 8 spark plugs, or is this the 6 cylinder? I'm more familiar with the d21 than the 720, but both are similar.

Before I ask about anything else, have you done a compression test on the engine?

Thinking about a 4bt in my d21. Not sure how the stock 5 speed would hold up, or even if anyone makes a bellhousing to go from a 4bt to whatever the nissan manual trans is called.


I'm sure an RB26DETT could be and probably has been swapped into a 720 but I doubt it's been done on a 4x4 one and kept the 4x4 intact. I've been on forums and seen when people tried to SR20 swap a d21, but unless you have a fuckton of cash available, it's not going to be an easy swap. Shit, even if you do have a fuckton of cash, it's still not going to be easy. It might get done, but it's going to be cheaper to just import an r32 skyline.