Weird No Start Condition - 260Z

[SteveJ]

Background:

260Z with a 2.8L engine, Maxima 2.4L head, ZX ignition, GM TBI fuel injection with SU carburetors converted to throttle bodies

The car ran fine last Saturday. I pulled it out of the garage and parked it back in the garage about an hour later. I don't recall anything strange happening. Yesterday, I took off the distributor cap to take some pictures of the coolant temperature sensor. I put the cap back on after I finished taking pictures.

Today:

I went to start the car. I primed the fuel pump (audible) and tried starting. When it didn't fire, I thought to check the coil wire to the cap. I tried again with the coil wire connected, but it still didn't start. I re-seated the cap, checked the coil wire again, and hooked up a meter to check voltage at the coil. I could smell some fuel coming out the exhaust, too. 

There was good voltage at the coil. I hooked up a battery charger and put it in Start mode to make sure the battery voltage wasn't dropping too much during cranking. I also tried starting fluid. Still nothing.

Wondering if I fried the ignition module, I hooked up the timing light to cylinder #6 so I could look for spark while cranking. The light indicated spark while cranking.

I left the car on the battery charger while I ran an errand. When I got back, I had the wife turn the key while monitoring the timing light on #1 against the timing mark. I also used starting fluid. Timing was right, but still no fire.

Wondering if the plugs might be too fouled, I changed them out, putting NGK 7131s (not 7133). The old plugs were somewhat fouled, but I've seen worse. No fire with the new plugs. I also checked spark with the timing light on #1 and an inline spark checker on #2. The glow on #2 looked good, and the timing light still lit up. Still no fire.

Bottom line:

I have fuel, spark, and timing. I will verify compression, but I'm not sure how it would fail suddenly. What am I missing here? I will also try NGK 7133 plugs as soon as I can get them.

[Zed Head]

Any chance the coolant temperature sensor is disconnected?  Maybe for the pictures or a bump?

[SteveJ]

The CTS has a good connection.  I verified spark from the coil by placing the wire near the shock tower, and I saw a good spark. 

I took off the air filter and sprayed starting fluid down the throttle bodies, but it acts like no spark despite my other observations. 

[Zed Head]

I've mentioned this before in other posts.  I damaged my control module once by leaving two spark plugs disconnected after doing some work and restarting the engine.  After I did that the engine wouldn't start normally even though it showed spark.  It started with starter fluid only.  This was on a hot engine, I never tried when it was cold, I fixed it right away.  It had spark but the spark was weak and orange even though I had a GM HEI module.  Installing a new module solved the problem.

And, here's another odd one - try lifting the distributor cap up an MM or so.  Who knows?  He had a ZX distributor too.

 

[SteveJ]

I checked compression. I have one low cylinder, but I didn't pull the valve cover to check the valves for that cylinder.

I installed the NGK 7133 plugs (Those are the ones for the 280ZX, since I'm running the ZX distributor/ignition module) and tried to fire it up. It sounded like it was close. Tried again with starter fluid, but no change.

I replaced the rotor, cap, and ignition module. Sprayed in starter fluid. No change.

[Patcon]

It seems to me it has to be spark related

You have ether going in and you smelled fuel coming out the other day.

So it's breathing.

That leaves spark...

[Zed Head]

 

2 hours ago, SteveJ said:

GM TBI fuel injection with SU carburetors converted to throttle bodies

Are the throttle blades on the SU's opening?  How about a problem with the trigger signal to the GM ECU?  Or the injectors stuck open?

Edited November 14, 2020 by Zed Head

[SteveJ]

Just now, Zed Head said:

 

Are the throttle blades on the SU's opening?  How about a problem with the trigger signal to the GM ECU?

Even if the ECU isn't getting the trigger, the engine doesn't attempt to fire with starting fluid.

[SteveJ]

2 minutes ago, Patcon said:

It seems to me it has to be spark related

You have ether going in and you smelled fuel coming out the other day.

So it's breathing.

That leaves spark...

You would think. On the other hand, I did see a spark from the coil wire to the shock tower when I pulled the coil wire, and I did see indication of spark with the timing light and inline-spark checker. So why would a spark not be a spark?

[Zed Head]

Vacuum leak?  Have you tried shooting the fluid through a plug hole?  Where are you squirting the fluid?  I don't now the SU TB conversion, just curious.

Engine ground strap?  Other grounds?  The invisible electrical problem...

Edited November 14, 2020 by Zed Head

[SteveJ]

So to investigate the spark more, I shot some video of the #1 plug wire pulled, #2 plug wire pulled, and coil wire pulled. When I was looking at the spark from the coil wire earlier I was sitting in the car. This time I was able to see it up close.

It looks like I'm not getting a good spark. (and that's with the replacement ignition module)

Not dead, but not as alive as it should be.

[Zed Head]

How about something got jarred when you removed the distributor cap?  The reluctor wheel or the magnet or stator.  Those ZX distributors are kind of fragile when they get older.   There were some good sparks there, so the make-break circuit seems to work.  Looks like a trigger problem.