1 hour ago, grannyknot said:

What test would you suggest?

pull the CSV out and see if its leaking fuel. if its warm where you are (above 70f) see if it fires while cranking the engine (it should not).

On 7/22/2019 at 3:28 PM, grannyknot said:

So the engine has been running well, I've been starting it every now and then to check for exhaust leaks, coolant leaks and such. Today I got the D/S seat installed  and started the engine to take it for the first drive, the engine started fine, ran for about 30 sec with the rpms roaming and then the rpms got lower and lower, I blipped the throttle and it momentarily reved up but went back down until it died. It started up again just fine but did the same routine and died within 10 sec, now it won't catch at all.

I didn't read back through all of the posts but this one and the following kind of suggests either an ignition module going bad, too many sparks causes too much fuel, or an ECU going bad. Tthey tend to go rich first then just die.

You mentioned what what the tachometer needle was doing when it was starting to die.  You talk about "roaming" and that's a sign of an ignition module dying.  Mine showed a jumpy needle, reading high, as it was kicking the bucket.

A $25 GM HEI module is a simple quick test, and always good to have around anyway.

Edited July 24, 20195 yr by Zed Head
perfektionist

7 hours ago, Captain Obvious said:

Did you replace all the electrical connectors in the engine compartment? If the connector to the EFI temperature sensor isn't making great connection, it'll run very rich.

Yes I replaced all connectors except the one lead temp sensor which was in good shape.

6 hours ago, Zed Head said:

You mentioned what what the tachometer needle was doing when it was starting to die.  You talk about "roaming" and that's a sign of an ignition module dying.  Mine showed a jumpy needle, reading high, as it was kicking the bucket.

A $25 GM HEI module is a simple quick test, and always good to have around anyway.

I wasn't sitting in the car at the time so couldn't see the dash tach, I was using a remote tach clipped to the #1 spark plug wire.  I have a GM HEI on the shelf but could never get it to work on the /70  240z.

The sporadic nature of your problem suggests those two electronic parts.  There's not much to the HEI module wiring, on a 280Z.  You can connect it temporarily in the engine bay with some jumper wires and a screw or two.

So have started the engine multiple times now with no repeat of the problems, starts first try every time.  I took the car out for a 10mi. run today just to push it a bit, see if I could break anything, it is running like a champ so when I got home I pulled the spark plugs to see what was happening. Looks kind of lean to me, not at all sure how to make it a little richer with an AFM.

 

Those are very clean. Could some small manifold leaks do that?

They are all even but very lean. The easy way to enrich is to put a resistor in series with the temp sensor.

 

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

°C	°F	Resistance
-30	-22	20,300 Ω to 33, 000 Ω
-10	-14	7,600 Ω to 10,800 Ω
+10	50	3,250 Ω to 4,150 Ω
+20	68	2,250 Ω to 2,750 Ω
+50	122	740 Ω to 940 Ω
+80	176	290 Ω to 360Ω

 

I'll give that a try tomorrow, thanks.

The EFI system is supposed to run clean. Other than the plug color, do you have any reason to believe you're running too lean? Were you pinging?

Is ten miles enough to really get a good plug read?

10 minutes ago, Captain Obvious said:

The EFI system is supposed to run clean. Other than the plug color, do you have any reason to believe you're running too lean? Were you pinging?

Is ten miles enough to really get a good plug read?

Other than the plug colour, no, there are no other signs, no pinging.  I've always believed that you could get a good plug read on much less than that although I could be completely wrong. The lean looking plugs are the same ones from post#44

They actually have a little bit of carbon buildup starting on the exposed metal at the ends of the threads.  Where it's cold.  The insulators look good and so do the grounding straps.  You can see some ash on the grounding straps and a little color on the insulators.  They'll be nice and tan in a few hundred miles.