'84 Z24 suddenly won't idle

[datzenmike]

Two different guys. Hyspeedz dropped in recently with a similar idle problem.

[ggzilla]

Sorry, i should have been more clear. I meant to say:

 

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

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

 

Ah, maybe he meant the coil is now working ... but still won't idle.

[datzenmike]

Must be.

[Kingman]

Exactly, having the coil working didn't make any difference whatsoever. DDing a 5-speed that doesn't idle is a pain in the ass!

[ggzilla]

For temporary, jack the idle up to 1500 rpm. It'll probably run steady there. I've run Datsuns that way for months at a time.

[Kingman]

I've tried. Most of the time the truck still dies. I bumped it up to around 2K, so it'll somewhat hold off and on, and surge, but generally it dies even then.

[ggzilla]

So the problem is much bigger than "won't idle" ... At 1500 it is not using the idle circuit.

[datzenmike]

Pull some plugs out.... Are they white, tan/grey, or black and sooty?

 

Look on the front of the carb, there is a sight glass... the fuel level should be near the middle.

 

When running or just after shutting off, look down the carb, is there fuel dripping?

[Kingman]

Plugs are a perfect tan color been checking them since the problem started, fuel level is right at the dot been checking that, exhaust smells fairly normal, and when it's running there's fuel going through the venturi. It definitely doesn't starve of fuel when it dies.

[Kingman]

At this point I don't think it's going to get solved from outside the carb. My vehicles like to give me these issues that have a common symptom but the fix is no where near common. Always been that way.

[datzenmike]

 

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.

 

 

Maybe check this. They can clog the valve with deposits and it won't close causing a vacuum leak. Well an EGR leak but it dilutes the air fuel so much it won't idle properly.

[Kingman]

I tested it already, and it ain't leaking. Wish it was. :no:

[ggzilla]

There are two ways an an EGR valve can leak. You tested both?

 

 

An excellent mechanic can put this on the scope and figure out the cause in 1 hour.

[Kingman]

Yes and to be extra sure I sprayed starting fluid on the underside of the diaphragm, through the exhaust inlet, and through the vacuum port and the engine didn't flinch. It's not hooked up anyway since the previous owner cut the tube off the manifold.

 

Lol yes I'm sure he could. I'm not an excellent mechanic though. I'd much rather build a custom wiring harness than deal with carburators.

[ggzilla]

At 2000 RPM i doubt if that spraying would tell anything. There are better ways of testing the EGR valve, e.g. do what the factory service manual says.

 

To recap the symptoms:

* It was not running fine, wouldn't idle under 1000 rpm, but did better than now

* Then, in stop-and-go traffic, the engine quit running. Since then it won't stay running without pressing the gas pedal down and holding it to 2000 RPM or more

* the engine wants to cut out under light throttle

* It won't start unless your foot is on the gas

 

Only when warm, right? When cold, it'll start with your foot off the gas, because...

* When the choke is on it runs fine

 

 

This may or may not be a carburetor problem. It certainly is not caused by the Idle circuit or Ant-Diesel (fuel-cut) valve, because a Hitachi will idle at 1500 even if the idle-circuit is cut out.

 

 

> I jumped the exhaust coil to the intake coil and it fires now but the truck runs the same

 

yes, that's expected as the 2nd coil must run on different timing to work differently

 

 

With single-coil engines, a bad coil can cause idle problems but run "perfect" above 2000 RPM. Just sayin.

[Kingman]

It will race the engine even with the full choke on. Pretty much so with the recap. It will start with out my foot on the gas now but it'll die, with my foot on the gas I can keep it alive down to 1,500RPM but it surges. Runs perfect when it's cold and the choke is on, yes.

 

Before this happened no it wouldn't idle below 1,000. I actually didn't mind that because around 700 it lost oil pressure lol. But it did idle very smoothly and the only real problem it had was the dead spot in the throttle and the occasional run on. The day it went all gunny waggle it was running just fine all the way up until when I felt the truck shake once and the engine was dead.

 

I replaced the coils already. I had one laying around and I bought the second. I had figured that jumping the coils wouldn't do me much good other than probably burn out a transistor. But now that it's firing off the module and it's still the same I'd say that had nothing to do with it and like I said before, that coil might have not been firing for a long ass time.

 

The carb has 252K miles on it. Now that I'm not working until after the holidays I'll have more time to tinker with it. I couldn't take it apart to a point where I couldn't drive it the next day but now I can. Honestly. if I had enough money laying around we wouldn't even be having this conversation because I would have driven it home and started pulling the engine to put a VG33 in it...

[Kingman]

Haven't had a chance to look closer, but carb cleaner pours out of the bottom of the carb behind the idle screw when I spray it in from the top.

 

Yeah, I think that'll do it!

[Hyspeedz]

As I said earlier, I've been following this because I have a similar problem that appeared out of the blue. So, I've got the air-cleaner off (more work than it sounds!). I don't really know much about what I am trying to do.

 

Symptoms:

• Starts harder than usual
• Runs, but won't idle.
• Felt like a couple of vacuum lines came off
• Checked and they are all connected.
• I checked the 10 amp fuse and it's good.

Here is a photo...is this the egr (in the red box)?  

 

http://i393.photobucket.com/albums/pp19/Hiplainz/photo.jpg

[datzenmike]

EGR in mounted on top of the intake behind the carburetor. Has a metal pipe going around the back of the head to the exhaust.

[Hyspeedz]

Here's another look:

 

[Hyspeedz]

OK...that makes sense. Thanks!

[datzenmike]

Here's another look:

 

 

That's the choke heater. Choke on when cold. Electric heater warms it when started and slowly turns the choke off in about 8-10 min.

[Kingman]

I found my issue - the lower carb to manifold gaskets blew. Looks like the guy before me had it off once and re used the gaskets like a jackass. I have the carb off now, waiting for my buddy to get off work so I can get my Weber adapter out of his truck and stick a new carb on it.

[BlackCasio]

I actually have a similar problem, but I have an '81 with a Z22. I have a Weber on it, but it runs really rough and shuts off if it gets below 1000 rpms. I set it to idle around 1200 and it idles fine like that, but when driving I can tell it's not getting the power it should. 
Whoever put the weber on it only took half of the EGR system off, and decided that bending the front tube was good enough...

Do you think I should just take both of the tubes off and cap the holes until I can get a new manifold? Or does that not really affect anything?

[ggzilla]

Yay! I love it when a plan comes together.

 

 

Hyspeedz, the most common problem with "not idling" is the idle-cut valve. If the alternator is not charging fully, if the red light on partially on, then it doesn't idle. Or the idle-cut valve has the wire disconnected.

 

Hard starting is often caused by the choke not closing fully when cold. Check the engine when cold, pump the throttle one and look down the air cleaner. If the choke butterfly is not 100% closed, that's your problem.