Z24 Idles Rough Problems

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

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

15. 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.
16. 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.

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

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

18. Sprayed soapy water around the base of the carb and the idle rpm's wasn't affected

19. Found out that the exhaust manifold is cracked. Replaced the exhaust manifold and the O2 Sensor and it's still idling roughly.

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

21. However i noticed that the timing is bouncing around and it shouldn't do that. The exhaust side #1 plug has erratic reading while the rest on that side reads nothing. HELP!

Another thing to add is that the idle rpm's kept going up and down. I'm starting to think that this is a computer controlled problem like at the carb or the ECC.

bump

What year is it? If it's carbd it's not likely to have a computer (my 85 Subaru only has test wires) but I would love to see you get some answers because my Subaru is idling rough and I've replaced lots of the same parts as you to no avail. The only thing I have to add is that I changed my battery leads, and when I did at first I couldn't get as good of a ground as it had before and this poorly effected my idle.

The year of my Nissan 720 is 1985. That was the year before diagnostic tools were introduced in CPU controlled cars. It does have a first generation ECU and the carb is not injected, it's computer controlled. I'm guessing that the ECU in my Nissan's gone bad.

Brake booster is bad. It's the only vacuum system you havent check

Brake booster. Cap the line at the manifold and see if it solves it. Free to try.

Haven't yet but I thought about it.

BTW on my 85 720 pickup, on the ecu, does it have test lights and does it have a diagnostic mode?

>haven't checked but thought about it
You deserve this problem. Go check it now because I want to know.

>#21
What is wrong with your distributor, sounds like it's shorted.

I already replaced the cap and the rotor on the distributor.

Also about your spark plug again, do you have two consecutively firing spark plug wires next to each other? I've seen them jump wires and fire both or the wrong one when they're wired janky. They're wired very deliberately from the factory, make sure they still are.

>Low vacuum
Could be that it's running rich for some raisin. Look into your carburetor.

1. No
2. The carburetor is computer controlled. That is the last place i wanna look into.

Check your MAF, make sure it's giving a proper reading. Check ATC (ambient temp sensor) if it has one, which it probably does.

And I don't know much about computer controlled carbs I was trained extensively on EFI and I dabbled with friends carburated pickups and a few motorcycles but I'll be damned if there's not an idle mixture screw for you to fiddle with to see if it changes anything.

Also Throttle Position sensor, just read up a bit on 85 carbonated rice paper cars.

Oh it has a Idle mixture screw. I raised the rpm's a bit temporarily until the problem is fixed.

>21. However i noticed that the timing is bouncing around and it shouldn't do that. The exhaust side #1 plug has erratic reading while the rest on that side reads nothing. HELP!
Are you saying that the other two are misfiring or are normal. If it's misfiring it's your distributor that is faulty, chinese parts will do that.

Here's whats going on. On every spark plug on the intake side, i get a consistent steady reading. On the exhaust side, the #1 spark plug showed erratic timing, #2,#3,and #4 spark plugs read nothing.
So recap
All good on intake side
#1 Exhaust erratic timing
#2,#3,#4 Exhaust no timing

Check your exhaust coil.

Plus I keep hearing this knocking sound from inside the head where the valves are.

Could be detonation on #1 cylinder from your gay exhaust ignition coil. Or so we hope, right?

What about the rest of the spark plugs on the exhaust side that are getting no reading?

Idk it sounds like you have something inside the distributor preventing it from firing on the other cylinders. Do you have the correct distributor, are you sure it's not a faulty part? You said you checked it so I assumed it was something else desu. The only thing that controls the exhaust spark is the distributor and it's giving a poor reading to the O2 sensor so it's probably running lean or something because there's a bunch of unburned fuel leaving the cylinders that it's not programmed to understand.

Ima get you a diagram hold up Bruv. But to be Frank not sure how it can help. Their are 4 types. California, Federal, and high altitude.

Just want to point out that this is the stock distributor that came with the truck, the only things that got replaced on that distributor is the rotor and the cap (cracked).
I have Federal. And I do have the service manual

The vacuum switch changes the spark pattern. If its functioning correctly the intake sparkplugs turn off above 2000 rpm. So you only run on the exhaust side. My guess is a bad distributor, bad ecm, bad exhaust coil.

I don't think I need to replace the whole dizzy, just the icm and the exhaust coil that's inside of it.

Also not a bad time to Seafoam the engine. Alot of carbon buildup causes denotation.

In addition, why does my engine rpm's at idle go up and down (surge)?

When I had this problem it was because the air fuel ratio selonoid went bad. I recommend rebuilding carburetor. That's what I had to do.

Timing can cause surging. Did you get the little gears in the exactly right spot when you replaced it desu?