'84 Z24 suddenly won't idle

[Kingman]

Prior to this the engine was cranking over more before it started, dieseled periodically, and it idled high and I could never get it down below 1K until yesterday when it started idling low and a little rough. Today I was coming back from Portland in stop and go traffic when it suddenly died. Started it up then it instantly died again. It won't idle unless I have my foot on the gas and it sounds pretty lumpy until 2K and above. It won't start unless I have my foot on the gas either. When the choke is on it runs fine until it clicks off. Drives fine mostly except at low Rs where the engine wants to cut out under light throttle.

 

I took the anti-dieseling solenoid out and there wasn't any spring or needle in it already. I thought taking that out allowed the engine to idle, which seems to be what the previous owner did. Maybe it just needs an entirely new one?

 

Doesn't smell like it's running rich at all. It has all new tune up parts and both fuel filters are new. Float is good and where it's supposed to be.

 

250k mile carb finally bite the dust?

[ggzilla]

The valve does not let it idle but just the opposite. It cuts the fuel if the needle and spring are connected. That's why yours ran-on sometimes

 

Failing to idle can be caused by several things including:

- idle stop set too low say it got loose and btacked off

- tiny bit of water or crud in the main jet or idle passage

 

[datzenmike]

Look on exhaust manifold. Does yours have an oxygen sensor? Little green wire?

[Kingman]

No it's not a feedback carb. I did check the idle screw and it's right where I left it.

[ggzilla]

The good news is the idle circuit doesn't wear out. So it is a fixable problem most likely.

[datzenmike]

Idle screw is sealed at the factory on the stock '84 carbs.

 

 

 

Confirm that both coils are firing. If one side quits the engine will act retarded because of the longer burn time. If the exhaust side is out, replace the first fuse (10 amp) on the left side of the fuse box.

 

Find the ERG valve on the rear of the intake. Reach up inside and lift the plintle with the finger nail on your little finger. It won't bite but difficult to lift it. This will open the EGR valve. Let it drop suddenly back into position. This will dislodge any carbon or exhaust deposits and improve the seal. If this fixes the idle I would remove the EGR and wire brush it clean at a later time of convenience. If the EGR is not closed tight at idle it acts like a big vacuum leak and will ruin idle quality.

[Kingman]

What's funny is I was checking the coils and the exhaust coil isn't firing, so I checked the fuse and it's good. Did some testing swapping wires and with the intake coil wiring on the exhaust coil it fires but not the other way around. Both coils have power but not sure about the ground side on the exhaust coil. That problem might even be in the distributor.

 

I took out the idle screw and blew the port out with carb cleaner and it didn't make a difference.

 

The anti-dieseling solenoid plug where it mates to the wiring harness was finicky and making intermittent contact so I put a new plug on and now it seems to want to run better. I pulled a solenoid off a junkyard truck earlier today that works fine.

 

I think I caught a double whammy. Hate it when that happens.

[datzenmike]

What's funny is I was checking the coils and the exhaust coil isn't firing, so I checked the fuse and it's good. Did some testing swapping wires and with the intake coil wiring on the exhaust coil it fires but not the other way around. Both coils have power but not sure about the ground side on the exhaust coil. That problem might even be in the distributor.

 

 

If swapping the coil wiring makes it work then it's possibly in the distributor module or the wires to it.

 

The module is grounded and has 3 wires. One is power from the ignition. The other two ground the neg side of each of the coils. That's it. If the exhaust coil isn't firing make sure there is power on the POS+ side and try momentarily grounding the NEG side with a jumper wire and it should fire.

[iron_lungz]

sounds like the same fucking thing im putting up with

[Kingman]

The wiring diagram I have shows 3 wires going to the inside of the distributor with a ground on the outside like you say Mike. My distributor has 4 wires going to it. Blue, black/white +, white +, and red. Blue is the ground for the exhaust coil and red is the ground for the intake coil. Black/white and white are both positive wires and white stems off in to it's own plug then goes in to the wiring harness.

 

I ohmed the wires out and the wiring to the coil is good. So what's the deal with the white wire? If I touch the test leads between either positive coil wire and the white wire at the distributor the meter jumps to 60 ohms for a second then goes away and that's it.

 

Seeing as the wires from the distributor to the coil are good the module inside the distributor must be bad.

 

But to add more to the mix my choke is sticking on now. Sometimes if I fiddle with the clutch it'll kick off but goes right back on a second later. Every time I tested for power there wasn't any. Dafuk.

[ggzilla]

This is an electrical problem

Every time I tested for power there wasn't any.

 

If the alternator is not charging, the choke wire won't have any power.

[Kingman]

It's charging. I was testing for power with the engine off and the key on. The choke only gets power when the engine is running? Guess I can see the point in that...

[ggzilla]

If the choke is sticking, spray the linkage and the shaft with carburetor cleaner to free it up. The only other common reason for sticking is if someone disassembled it and didn't align the butterfly to the carb bore.

[Kingman]

It's probably something I did when I was fiddling with the carb although I made sure it was working before I put the air cleaner back on. I sprayed the linkage, venturis, throttle plates. idle circuits, etc out with carb cleaner yesterday.

 

How rediculious though. In two days it drops a coil, dieseling valve goes wonky, choke starts sticking, tire goes flat, heater switch breaks, and the window crank strips off the splines. Like fuck, maybe two weeks ago I sorted through the last go-round of crap and thought I had it pretty well sorted out.

 

What I need to do is put the Weber my step dad has sitting in his shed on it.

[Kingman]

Well the choke fixed it's self before I got a chance to look at it after work. I went to the junkyard and got another distributor but the exhaust coil still wouldn't fire. Probably got another bad ignition module. I jumped the exhaust coil to the intake coil and it fires now but the truck runs the same. I assume the coils fire at the same time and I figure if I burn up the module I'm no worse off anyway.

 

Still can't get the thing to idle below 1,600RPM and it's really choppy even then, sometimes it dies too.

 

Both coils firing

Can't find any vacuum leaks

Working anti-dieseling solenoid

Sprayed carb cleaner through the idle adjustment screw hole

No EGR control but I checked and it's not leaking

Fuel level in the float chamber sits right at the dot

 

Other than trying another carb is there anything else I can check?

[Kingman]

Thanks for the help so far, much appreciated B)

[datzenmike]

 So what's the deal with the white wire? If I touch the test leads between either positive coil wire and the white wire at the distributor the meter jumps to 60 ohms for a second then goes away and that's it.

 

 

 

But to add more to the mix my choke is sticking on now. Sometimes if I fiddle with the clutch it'll kick off but goes right back on a second later. Every time I tested for power there wasn't any. Dafuk.

 

 

The extra white wire with it's own plug is for shutting off the exhaust coil. Yup, that what it does. Unplug the connector and everything should be back to normal. If this fixes it I'll explain.

[Kingman]

Yep, took care of the coil problem!

[datzenmike]

On a dual plug motor the time required to fully burn all the gas and air is much less than that of a single plug system. Just thing of a candle lit at both ends. Because it takes less time to burn, the burn can be started much later with the piston closer to TDC. In other words the ignition advance is less with a dual plug head than a single.

 

On the later Z24 engines, Nissan deactivates the exhaust coil "to reduce engine noise during heavy load driving conditions" by using a vacuum switch that senses heavy load (throttle full open.... low manifold vacuum) The switch grounds that white wire going to the distributor module.

 

This does two things. First it stops the exhaust coil from working, in effect turns the Z24 into a single plug head. Second it has to increase the ignition timing to allow for the increased burn time of a single plug head so that power is not reduced. This is all designed into the ignition module inside the distributor.

 

Unplugging the white wire permanently removes the ground and causes constant dual plug operation.

 

 

I would say that your vacuum switch has failed and the distributor is permanently in single plug operation. If all the single plug plug switching is for is to 'reduce engine noise' I would just disconnect the white wire and run permanent dual plug. If 'reduce engine noise' is Nissan 'speak' for stopping spark knock/detonation, then it would be best to keep this feature working properly. 

[Kingman]

That makes sense, thanks for explaining it. Unfortunately having both coils firing didn't make a lick of difference and I'm thinking that coil may have not been firing for a long time. Still won't idle and it surges on decel pretty bad.

 

I also noticed something when I was tinkering around earlier. I cannot get the secondary to open.

[datzenmike]

Pull up on the vacuum diaphragm to loosen it.

 

It's the round thing in the upper right.

[Hyspeedz]

Not to hijack this, but I have the same problem. Watching this carefully.

[datzenmike]

Not to hijack this, but I have the same problem. Watching this carefully.

 

o you have a California or electronic feedback carb? High Altitude compensator?

 

 

 

Remove EGR valve and wire brush it clean. Be sure the valve is free to close properly or it will act like a big vacuum leak and ruin the idle. There should be NO EGR at idle and the valve should be closed tightly.

 

Turn ignition ON/OFF/ON/OFF/ON/OFF (not start) while listening at back of carb. If the idle cut solenoid is working you should hear a faint clicking sound from the carburetor. If the idle cut solenoid is not working, gas will be unable to get to the idle circuit.

 

Check that both coils are firing. If the exhaust is not, replace the first fuse on the far left of the fuse box. (this is the one closest to the driver's door)

 

The vacuum lines from the carb are not likely to cause issues as they are ported vacuum that isn't applied at idle. Hoses that go to the intake such as the Boost Control valve, Anti Backfire valve, Vacuum switch for fuel shut, the Vacuum switch for shutting off the exhaust plugs, vacuum supply to the air temp sensor that regulates the air mix door on the air filter snorkel and the purge line from the Carbon Canister.... these all connect to the intake and if leaking from being loose, cracked or removed will affect idle.

[Hyspeedz]

Datzenmike, not being the mechanic I would like to be, I'm pretty limited to following instructions from the Haynes manual. I believe it is a High Altitude engine (lived it's live from beginning in Colorado above 5,000'-bought new there). It has what looks like the "smog" layout on the two hoses coming into the aircleaner. I will follow these instructions concerning the idle cut solenoid and the egr as well as checking the fuse as you suggested. It happend all at once. I've had a perennial vacuum leak from a hose that would vibrate off the nipple. And I thought this had occurred again, but it did not. I tried some carb cleaner and no improvement. I'll try this over Christmas break and let you know.

 

Thanks for the suggestions.

[ggzilla]

Dec 15> Yep, took care of the coil problem!

 

Dec 16> Still won't idle and it surges on decel pretty bad.

 

Whut?