stumped

[Chickenman]

Robert. Does this car have an EGR valve? An EGR valve that is sticking open could cause these issues that you describe.

 

If it does have an EGR Valve, disconnect the vacuum hose from the EGR valve and plug the hose with a golf tee or something. Do this when the engine is stone cold. Then start and drive the car and see if the symptoms go away. If it does then EGR valve may need servicing or replacing.

 

EGR valves can get choked up with carbon and stick open when they are supposed to be closed. They are supposed to be closed at idle and just off idle. Usually carbon gets stuck between the seat and pintle, or sometimes it builds up on the shaft and only sticks when the EGR valve opens all the way. This can cause rough running, lack of power and backfiring. Just to drive you nuts, it can be intermittent at first.

 

There is a temperature controlled vacuum switch ( Thermal Vacuum Switch = TVS )  that allows vacuum to the EGR valve once the engine is at operating temperature... so that could explain the temperature correlation.

 

The backfire may " shock " the EGR valve and allow it un-stick temporarily. It wouldn't hurt to pull the EGR valve off and have a good hard look at it. Use a vacuum pump or the old " pucker power " to test valve for free operation.

 

You can clean EGR valves with a good strong carb cleaner and some compressed air. It doesn't always work, but it's certainly worth a try if you can't find a new one. Edit: Rock Auto has them for reasonable prices. RA to the rescue again!!

 

Clean out the EGR base ports in the manifold as well. Use a shop vac to suck up the carbon as you poke it loose with a small screwdriver.

 

Hope this helps and report back with results.

Edited July 26, 2015 by Chickenman

[siteunseen]

Here's a good valve adjustment guide,

https://web.archive.org/web/20080720024048/http://www.picturetrail.com/gallery/view?p=12&uid=786489&gid=1803105

 

My attempt to explain it, post #6

http://www.classiczcars.com/topic/49655-problems-with-a-few-different-areas-of-the-car-running-poor-no-gauges/

 

I like to write the gaps down and mark the valves off as I go, some turn up at the same time so you have to jump around.

 

There's also a picture of my EGR tunnel that rotted out causing a major vacuum leak.  It was a loose connection on the tube coming off the exhaust to the bottom of the EGR.  Datsun issued a recall on this but the previous owner of mine must not have gotten it. 

 

You should take a hand held mirror and hold it under the intake manifold for a look at the underside where the EGR couples into the manifold.

Edited July 26, 2015 by siteunseen

[FastWoman]

Kudos to Chickenman for his EGR theory!  That would make sense and would be a much more likely scenario than mine.  I'd look at that first!  Sometimes the valves do get stuck, but that's usually an intake issue (from heavy varnish), rather than an exhaust issue.

 

Valve adjustment:  Every oil change?  Really?      I don't adjust mine nearly that often -- maybe once every couple of years, if that.  But if you haven't adjusted valve lash, you should.  When I got my car, I had a couple of exhaust valves that might have been held very slightly open by the too-tight clearances.  (The engine ran OK, not great.)  That said, the issue I was proposing would have nothing to do with adjustments to the valve lash.  I was suggesting you might have a valve or two that doesn't close all the way under spring tension.  If this were the problem, you might hear a rattly sound from the valve train when you lose power and a disappearance of that sound after the afterfire.

Edited July 26, 2015 by FastWoman

[78blackpearlz]

It does not have an egr anymore and i looked at where the port is plugged at and its starting to crack around the edge. I took a picture but on the mobile site it wont let me upload it so as soon as i can i will.

Fastwoman, just to make sure i am understanding you correctly, you are saying that the vlave springs might be sticking open slightly on some of the exhaust valves?

[78blackpearlz]

Ok not a great picture but its the best i could get.

Edited July 27, 2015 by 78blackpearlz

[siteunseen]

What in the world is that? You need an EGR block off plate.  I bought an EGR gasket and carried it to a welding friend of mine.  He cut one out of aluminium in the shape of the gasket.

 

Edited July 27, 2015 by siteunseen

[Zed Head]

There is another part to the EGR system, the BPT valve, that opens to let intake vacuum open the EGR passage.  If that has no EGR valve on the end of it, it would just open to atmosphere.

 

Seeing the remains of your EGR valve though, makes one wonder about the state of the other systems on the intake manifold.  Take a good clear picture of the top of your intake manifold and post it for us to ponder.  We might see something.

 

 

A thought on another potential cause - A short circuit on the injector harness.  The short opens the injectors full, flooding occurs immediately, backfire from red-hot liners on exhaust ports (N47 head) , shaking opens short, back to normal.  It's a flyer, but who knows.

[mayitin]

you are getting good advise. if its not ICM ( by the way the aftermarket one are worthless) take the fuel filter out and flow the gas into a Jar see if it has rust, if it does that is your problem . chanching the filter will only work for a little bit. gas tank must be taken out cleand and treated for rust. if not rust in the filter, look to the coil they get heated when there is no oil inside them. some ideas  

[FastWoman]

 

Fastwoman, just to make sure i am understanding you correctly, you are saying that the vlave springs might be sticking open slightly on some of the exhaust valves?

 

Perhaps a long shot, but yes.  The afterfire clearing everything up is the confusing part, and I'm grasping at that one straw.

 

The electrical theory is an interesting direction.  It could be that your CTS circuit is opening up (bad/dirty connection), causing an excessively rich condition and afterfire.  Then when a few cycles fail to combust, raw fuel and air cause afterfire, which shakes the engine and causes the CTS connection to make again.  But I don't think afterfire would shake the engine.  And if you have this sort of event, you should see black smoke out the exhaust when the engine is losing power.

 

Injector short?  Maybe.  Stuck injector?  Maybe.  I guess it could be lots of things.  But I'm trying to sniff around what would be most impacted by the afterfire.  All I can think of is the exhaust valves, as there is no EGR.

 

Is there any chance your exhaust plugs up and then clears with afterfire?  Doesn't seem likely, but just throwing it out there.

[78blackpearlz]

Sorry for the wait guys been busy its finals week,

 

But I did have a few minutes the other day and got to take a look at the z. I listened to all the fuel injectors, checked to make sure the AFM was still plugged in tight, checked all vacuum lines and wires, then pulled my plugs and found out it is running extremely lean. When I pulled the plugs they where white as could be.

 

I am waiting till tomorrow to get paid then I am going to go and pick up a fuel pressure tester and recheck it. Hopefully tonight I will be able to check and see how the fuel looks dirty. I did have the fuel tank cleaned and coated when I first got the car however.

 

It has gotten to the point where I can no longer drive my car. I know I shouldn't have driven it at all but had to with it being my only car and having to go to school and work.

[siteunseen]

You may have unmetered air getting into the manifold causing the white plugs (vacuum leak), around the EGR possibly.  When you get the fuel pressure tester, if you have the money get a vacuum gauge.  Those are two items the chain stores have on their loaner tool program.  Pay for it, use it and get your money back.

[78blackpearlz]

Thats a good idea siteunseen. Im gonna go pick up both of them when i get out of class tonight.