Ok, problems again.
 

I described this problem once before in my "newbie needs help" post, and while it had gone away, it's back, along with some other related, or non related issues. The plan is to bring the car to a Nissan dealer here in Gainesville and let them put together a list of what they find, if some of you can throw in some input I can put both lists together and see what's what. I have learned that while with my MG no one knew anything about Lucas electronics and DeHavillan overdrives, etc. EVERYONE around me is a Z expert! I find the posts here, however, to be in depth, well thought out, and appear to be coming from people who REALLY know what they are talking about.

So here go...

We're back to the backfiring thing again, after a hundred plus miles of very smooth sailing. The vehicle almost acts likes the rotor is making a full rotation without sparking. More often than not, it's a very quick sequence of backfires, like all the cylinders are not combusting as they move through the firing order.

Bear in mind, my new distributer arrives Thursday.

I pulled cap and found that my new rotor is scored (grooved out) along the outer lip, but my contact points are clean, and there is no etching on the cap itself. The rotor shaft does have some play, about 1/4 turn towards the engine, no movement away from the engine. So I blew ten bucks and got a new rotor to buy me time until the distributer arrives. Worked for about 15 miles or so, and then ran like hammared dammit all over again, if not worse.

Here's what's new part wise: Plugs, wires, cap, rotor, fuel/air filter, and most vac lines. Have run through 2 bottles of injector/gas line cleaner, as well as "dry gas" to pull out any water...

Any ideas? I've been told about everything other than I haven't thrown a sheep into my local volcano to appease the Nissan God. Like I said, out of now where it started running like a dream for 2- 2 1/2 weeks at 40 miles a day, than. BAM it stopped doing well.

Other, related, or unrealted issues.

When it's acting up it seems to be getting very, very warm in the cockpit. I didn't notice the heat when it was running right, but then again I was moving along at 50 with the windows down. Doesn't smell like anything is burning either under the hood. No odors at all actually, so that's good.

It idles really odd. Idle screw is set at whatever the manual suggests, and yet it still races at 1500-2000 rpm when in neutral, UNTIL it started running bad again, now it runs up and down from normal 500-700 all the way too 2 grand. Idle drops back down as I ease it into gear.

And that's about it, I can figure out about everything else that's wrong (wipers not working, turn signals not working, pressure plate in the clutch) but these two things have got me stuck.

I almost wonder if there's a bad groubd somwhere, or something in the EGR system has gone bad.

In closing, we were talking about what model year mine is (build date is Apr 76) I do have a four speed, but I also have the funky hood vents. so I'm thinking then it's a very early 77?

The biggest concern is the possible heat inside. Your cat converter could be clogged. These cars came with a warning light on the consol but they get disconnected. They sometimes make a skreeching sound like a loose fan belt. Your car could catch fire even after it has been sitting for a while. Check that first and then install your new dizzy.

Good point, thought the gaping whole in my exhaust would resolve those issues, but a clogged pre muffler would cause huge back pressure, which would cause the symptoms I described, right?

new dizzy is on my counter top and going in in the morning.

How do I check that converter anyway?

Only thing I can think of is a laser pointer type thermometer. If you drive it around it should heat up quickly. Look under the car and you should be able to tell if it is really over heated. The coverter is directly under the drivers seat. You can replace it with a high flow unit from Summit.

only the cali models had the cat and the warning light, but the others had a pre-muffler. you definitely have an igntion problem, and I'd bet the new distrib fixes it, but i looked through the fsm's various troubleshooting sections to see if anything else consistently came up with the symptoms you listed, plus my own experience. with what I saw, I wonder if your coil isn't going bad.
at any rate, not igniting, the gas will get pushed out the exhaust. it gets burned (backfire) typically in the first chamber it can collect in (e.g. a pre muffler or a cat), and can definitely get hot. theramz's idea of the laser thermo is a great way to see about that for sure. and yes, the hole could contribute to some of the problems you list, as could a clogged pre-muffler.
let us know how it shapes up with the new distrib!
sorry for the awful typing and grammar. i tore my hand up (11 stitches) and can't type very well for probably the next week. while i don't mind that too much, it has seriously slowed my work on the Z. :(
good luck,
Dave

:mad: The new dizzy didn't change a thing, however the note of the continuous backfires have softened a bit, no longer the crack! more of a softer thoof! So I guess that's progress, right? :confused:

Still doesn't want to idle correctly, regardless of what I do to the set screw, again, not sure if this is related or not.


So we'll get a new coil tonight and see what that does.

Oh yeah, Dave, sorry to hear about your hand man. Hope it's better soon

I guess now it's time to get a book on the fi system and start testing. Make sure the large intake hoses are connected and inspect them carefully for cracks/leaks. The afm, throttle position sensor. next in the line is the cold start valve which I tend to beleive is you source of the problem. This is a fuel injector that works like a choke squirting fuel in just behind the throttle valve. I think you can check this manually by disconnecting it after the car starts. If it runs better, then it may be that valve stuck open or because of a temp sensor that is discnnected or failed. To better understand all this you should get a Chilton book on those early fi systems.

Was thinking along similiar lines, Haynes mentions a "water tempreture" switch as a part of the EGR system, if this is the issue, it would vary the spark timing due to a false reading

What still mystifies me, is that it ran like hell, and then stopped running like hell for two weeks or so, and then ran like hell again. Whatever is wrong, corrected itself for awhile before failing again. Odd, very odd, even for a sports car :)

I just realized that if the cold start injector isstuck open, it won't do any good to disconnect it. Rather pinch off the fuel hose going to it. There are ways to check the temp sensors with an ohm meter.

Ok, for what it's worth, all six spark plugs are fouled to hell. They're only two or three weeks old. Ignitor covered with dry, black carbon, so I'm running too rich, right? but how does this play into my other problems? Gonna drop in a new set before I go taking apart anything else, figure if it runs good with the new plugs, I have my culprit.

Don't know if this will help. I have a couple of suggestions

Check the advance is working correctly by pulling the tubing off the dizzy and feel (with the end of your finger) if the suction increases with rpm. Remember to keep the tube blocked most of the time otherwise it will act like a vacuum leak and make the car run lean. then check for a leak in the advance diaphragm by blowing and sucking on a tube attached to the dizzy side.

On my carbie version I have a fast idle solenoid. It is trigger by a wire from the back of the speedo. The circuit is meant to be closed when the car is at idle (while the vehicle is still, speedo at bottom). My speedo in my old truck was sticking and keeping the circuit open therefore fast idle open.

Another cause, maybe with the idle compensator (for A/C fitted cars generally), it will have a tube from the manifold to a little box that has a electrically controlled solenoid. This will engage vacuum to a idle compensator diaphragm (near the accelerator lever). Check that this in not engaging randomly or if there is a vacuum leak in this system.

Most of this would only apply if you vehicle is carb. But there maybe similar systems on the efi but other z people can help with that info.

Happy hunting!!!! :)

I'm just about positive it is your cold start valve stuck open.

damn I love you guys :p So how do I check the cold start valve? (and i don't have an ohm meter) also thanks for the other tips, I'll look into the vaccum system as well, can't hurt.

Never mind just re read the post about all that, I'll go down and see if I can't find it in my Haynes manual, I can find the AFM easy enough, I'll just work my way back.

Ok, so here's where we're at, first of all, good news, it appears to be running much, much better, although I've yet to get it out for a good run.

Pulled apart the air intake and started cleaning, cleaned the AFM (filthy), cleaned the throttle body as best as I could without removing it from the car (also filthy). Something to note, it won't run without the AFM linked up to the throttle body? (although it's still wired in and all that).

I think I found, and cleaned, the cold start valve, although Haynes' Manual is a bit vague on where it's at. I pulled two, appeared to be, valves, both on top of the throttle body and cleaned those, one ran from the vaccum bell the other from the fuel line.

New plugs installed.

Still idles a little funky, wants to race a little then settle back down.

Throttle response is good and immediate, races well with out problem, however when I raced the engine from the accelerator linkage (up around 3k) the AFM kept shutting and causing the engine to drop idle and fuss a little, didn't happen when I did the same from the gas pedal, no did it while I was in gear driving around.

The cold start valve or injector is about 1 inch back from the throttle body. I is indeed an injector with a wiring plug connected to it on top and a fuel line to in's middle just like your other injectors. You can disconnect it after you start it up to see if it improves the fouling. AFM means air flow meter. It is opened when the engine draws in air and the position sensor on the side of it tells the computer how much air it's getting. That's why it ran worse when you took it out of the loop. The throttle position sensor on the side of the throttle body tells the computer how far open the throttle is in electronic language (ohms). All this must work together with the temp sensors and other stuff. If any one thing is wrong the engine runs like shit.

When you cleaned the throttle body, did you clean the contacts in the little black plastic housing on the side of it? Those tell the EFI where the throttle position is and accounts for various 'enrichment' levels. Opening that up and making sure of good contact and operation is pretty easy and might really help your idle (pay special attention to cleaning the idle contacts in there).
Dave

I may have, kinda went on a spree, but I'll get back under the hood and double check. And I did located the cold start injector, and cleaned up into the throttle body as best as I could reach, then cleaned through the cold start port once I had it removed.

All of it was pitch black in there.

Ok, not the cold start injector, pulled it out, disconnected the fuel line and it still didn't run right, did the same to the egr lead into the air line. And we know it's not the dizzy.

So I've given up, it's sitting at the shop now where a guy is going front to back with it, we're suspecting something in the fuel system since it fouled a set of plugs in a few weeks.

I'll keep y'all posted.

I gotta think your mass air meter is bad. You need to check this- chunk the Chilton manual and get a factory shop manual. It has been invaluable to me and I have solved numerous problems with this manual, although my current problem is still a mystery. You need a Voltmeter and 12V power source. First, you check the contacts 6,7,8,9 for continuity with the air meter frame. If you have continuity, the meter is bad. You then check for resisitance between certain terminals as noted in the manual- the resistance needs to be within spec's. Next is the air temp sensor. There is a chart for resistance within a specified range- given a certain temperature. If it isn't close then the meter needs replacing. It is not reccomended to replace just the air temp sensor, don't even know if it can be done. Finally, you check the potentiometer. You put 12V on two specified terminals then measure the voltage change across 2 other terminals as you manually operate the flap to the meter. The voltage difference should be gradual- any quick change in voltage means the meter is bad (potentiometer problem).
Finally, check the flap operation itself. it should open and shut smoothly with no binding. Get the factory shop manual!!!! I can fax the applicable sheets to you tonight if you get me a fax number. The factory shop manual is excellent.

My next suggestion would be to check the ECM itself. using a meter, you can check continuity between every sensor on the car and the ECM. It gives step by step troubleshooting. This book is what the tech's at Nissan use! Make sure that you have harness continuity between the specified terminals. It can help isolate the problem. You could have a bad ECM- this test will let you know this as well. Let me know if you would like me to fax the info.....

oh yeah..
 

All these meter tests are done with the meter off the car. Just making sure!

Waiting on a replacement AFM as we speak from Z Car Atlanta. I'll let you know what happens when we drop it in.

Just to throw this out there, since I know you are all sitting on the edge of you seats : ) Still haven't put a replacement AFM in yet, waiting to do a full electronic diagnostic before I do anything else (See AFM/ECU testing post).

But, in the interim, I did try a few other things one it started acting up on me.

Disconnected the cold start (completely) and it seems to continually want to pump gas by the way, and that didn't help at all.

Also disconnected the EGR from the air line, and that didn't have any effect either.

Just thought I'd let you all know.

You might also try checking the valve timing if none of the other things correct the problem.