Stumped... Intermittent, uneven running. Please help.

[FastWoman]

Don't get too discouraged! Instead, lean on other Z owners for support. It may take you a bit of work to get your Z straight, but you'll eventually get there. Along the way, you'll discover that these cars are really very simple machines -- even with fuel injection.

I confess I don't know where the various grounds are for the EFI. The box itself is the only one I know. You can probably find this information in the Factory Service Manual, which you can download free from www.xenons30.com.

Don't be afraid of the big connector on the ECU. All you need to know is to have the ignition OFF when you connect or disconnect it. There are a lot of tests you can perform on your EFI right from that connector, using nothing but a multimeter and info in your FSM.

In my experience (2 Zs now), you can get your car straight by simply going through it from end to end, checking, verifying, and if necessary fixing everything as you go. This may seem like quite a lot of work, but everything on the Z is very easy to get to, and as I said, it's a very simple machine.

[NiiChan GT-R]

Another possibility is your ignition module. Next time it starts running poorly, with bucking etc., stop and turn the key off. Then restart it. If the problem goes away temporarily that's a good sign that the ignition module is going bad. I could get my 76 module to do that when it went bad just by taking it to about 3200 RPM. Turn it off and restart and I could drive around all day below 3000 RPM.

The above mirrors my situation; I do seem to be able to turtle around under 3k without difficulty mostly... And the car never has difficulty starting, or issues immediately at startup. Seems to "reset" the car.

When you say "ignition module" you mean the thing next to the fusebox in the passenger's side kick panel that costs about $300, right? Or the assembly in the distributor?

I should also add that the tach never jumps around and is always accurate. When the car cuts out the gas pedal has no effect; foot on the clutch and it idles, badly. Does that discount anything?

So I've had little time to work on the car, but lots to read and map; here's my plan for Sunday:

1- leaky injector test. Check to see that fuel pressure at the rail holds once the car is turned off

2- ensure fuel pressure before and after regulator are correct

3- wiggle/clean ecu connector, see if manipulation does not improve running

4- ensure that the engine has spark by testing with timing light to see if ignition module failure shows itself.

5- measure resistance of afm pot to ensure smooth progression

6- fuel pump check valve (That's a sentence fragment, because I haven't figured out yet how I will test it)

...Please feel free to add to, or provide any feedback. I'm intimidated, but really thank you guys for the help.

I almost just wanted to stop by motorsport auto and buy a new ecu, icm, fpr and pump just on principle, as I was looking forward to taking my car to jccs, but it's too late for that now, so I have time to relax and apply thought.

Edited September 10, 2011 by NiiChan GT-R

[240260280z]

When the car dies, does the tach drop quickly ahead of the rpms?

Try upgrading to a 280zx distributor/ignition if it turns out to be your ignition box.

[NiiChan GT-R]

When the car dies, does the tach drop quickly ahead of the rpms?

Try upgrading to a 280zx distributor/ignition if it turns out to be your ignition box.

Alright, time for a bit of an update...

Regarding the above, the tach has never jumped, dropped, or reflected anything other than what the engine was doing. When the car would cut out, revs would remain steady until I put the Clutch in, at which point I'd either die or have a lumpy, poor idle slightly before dying. I'll follow-up with part two in a moment.

Here's the latest...

Timing appears correct, and I measured the vacuum, which is a steady 19 at idle, no jumping or wavering at all. Does the right things with vacuum as you rev the car, or stab the throttle. I was sort of amazed that all the little solenoids for the AC and etc. don't seem to be my problem.

I've been looking for a way to test the stock ignition module, and I'll probably still make a post about figuring out how to do so in the appropriate section. But that's the next system I set out and tackled, as follows:

Checked the air gap between the magnetic pickup in the distributor. That was fine. I proceeded to pull the ignition module from the kick panel, it seems to not be the original one to the car but is the stock style.

The box looked newish, including the connectors, but I hit them with contact cleaner and screwed them back in anyway. I just sort of stared at it other than that, not really knowing how to test it with multimeter. The plastic "jug" junction box with the distributor wires on the passenger's side engine compartment contained wires that looked a bit worse off, so I removed and replaced, cleaning the connectors.

Before my next venture of checking fuel pressure I decided to take the car for a spin...

The cutting out issue (which had returned above 3k rpm typically) then seemed to disappear, the car still ran a bit roughly, and would die (as if I took the key out) at stop lights sometimes.

I readjusted the afm by about a tooth or three that it seemed to need, and bent the idle contact a bit on the tps to ensure that contact was firm at zero throttle. Also hit the connector with my trademark cleaner. Well...

If the problem didn't seem licked, and if I hadn't had nothing but positive exeriences for the last week or so, driving a few times the 50 mile round trip to work and being fairly rough with it... Then I'd be too embarrassed to declare victory.

And even so, I'd still say I'm nervous, considering my past experience with these issues. I don't feel like I did anything, so hopefully it was one of those dumb little connectors, but I don't feel like I can be sure even after a few long trips, through heat, rain, traffic and open road. Still a voice in my head tells me I'm kidding myself if I think I licked it with just that.

I still wish I knew anything conclusive about the ignition module and I almost want to just ditch it all for a crane xr700, but I'll let this unsettling development continue for a while... Never did check fuel pressure.