240Z WILL NOT run right

[BoldUlysses]

So this is a follow-on to this post, but i didn't want to clutter up my resto thread with too much troubleshooting, and I thought a standalone thread might be more helpful for others battling the same issue.

Long story short, my '72 240Z starts and runs fine initially, but dies after for 10-15 minutes, and won't start again for minutes at a time.  It's gotten me temporarily stranded, fortunately not too far away (yet).

Fuel system:

• Tank cleaned out
• Fuel lines blown out
• New primary filter, and secondary inline filter installed near tank
• Fuel pump recently rebuilt
• Carbs rebuilt by ZTherapy about 12 years ago, float bowls properly wet-set

Ignition:

• Stock coil
• Timing set at 10 degrees BTDC
• Pertronix points replacement kit installed

I've been assuming it was a fuel system issue, but now I'm starting to think it may be ignition-related.  It's been a couple of years since I installed the Pertronix kit, and I believe it said I didn't have to use the condenser, so it's not on the side of the distributor.  Is this an issue?  What else could be going wrong ignition-wise?  Here's the wiring to the coil area, can someone check my work?

Thanks much.

 

Edited September 11, 2024 by BoldUlysses

[Zed Head]

Ignition modules can fail due to heat then come back to life when they cool down.  You could take some cooling spray, like Dust-Off Duster, and spray the Pertronix module under the cap in those minutes when it's not restarting.  Or take a spare spark plug, pop a plug boot, and check for spark.

Wouldn't be a surprise if it was the Pertronix module.  Apparently quality dropped dramatically many years ago.  There are old posts about it.  The Pertronix I's were also sensitive to leaving the key on.  It can damage them.

[BoldUlysses]

8 hours ago, Zed Head said:

Ignition modules can fail due to heat then come back to life when they cool down.  You could take some cooling spray, like Dust-Off Duster, and spray the Pertronix module under the cap in those minutes when it's not restarting.  Or take a spare spark plug, pop a plug boot, and check for spark.

Wouldn't be a surprise if it was the Pertronix module.  Apparently quality dropped dramatically many years ago.  There are old posts about it.  The Pertronix I's were also sensitive to leaving the key on.  It can damage them.

Yeah I wasn't super impressed with the fitment of the kit when I got it.  Actually had to get a guy at work to cut a notch in the mounting plate to clear the wires when the timing is advanced.  And the round rubber grommet doesn't fit the rectangular notch in the distributor body.

I don't have a spare plug lying around, but I could use my timing light.  Will give it a shot this evening.

[Captain Obvious]

Next time it dies, you could just pull the coil wire out of the distributor cap and lay it close to one of the nuts on the strut tower. Crank the motor and see if you have healthy looking spark.

[BoldUlysses]

OK so here's how things went, roughly, earlier this evening:

1. Lots of cranks to cold start car, indicative of float bowls having to fill from having run dry yesterday.
2. Let car warm up for a few minutes, idle not great.  Choke off.  Drive it up and down the cul-de-sac.  Starts missing, bucking at anything over 1.5K rpm and the lightest of loads.
3. Pull back into driveway, remove the gas cap to eliminate the possibility of the evap system being clogged/misrouted.  Car idle seems to smooth out a bit, though this could just be coincidence.
4. Let it idle for a few more minutes, then take it out in the neighborhood again.  Immediately acts like it wants to die.  Manage to coast it back into the driveway.
5. I put the timing light on it and crank it, no start.  Timing light flashes at regular intervals.
6. Check the fuel filters.  Rear one is nearly full, but engine bay one only has about 1/4" of gas in it.
7. Let the engine cool just a bit while I remove the fuel hardlines above the manifold and give them a good cleaning & blow-out (not b/c I think they're the issue; just b/c I hadn't done it).
8. Reinstall hardlines and go to start the car.  Cranks & cranks, but the engine bay filter is filling now. 
9. Finally starts, but I'm out of time and pull it back into the garage.

Conclusions:

1. Pretty sure it's not the ignition, since I have spark the whole time.
2. I don't think the evap system is an issue, since it died while the gas cap was off.
3. The full rear filter & nearly empty front filter would seem to point to a clog in the feed line, but I can't tell you how many times I've blown out both the feed & return lines...

Still stumped.  Any ideas appreciated, as always.

Edited August 28, 2024 by BoldUlysses

[Patcon]

I don't recall but:

Are all the fuel lines new?

What is the condition of the tank?

If it were me, I would rig up a 1 gallon fuel tank in front of the radiator support. Use the system from the under hood fuel filter in. Drive it around in the cul de sac on that. If it doesn't act up it's in the rear section of the fuel system. Probably the tank

[SteveJ]

My first guess would be a check valve issue with the fuel pump if it's a mechanical fuel pump.

[ollie]

I'm going fuel pump too.  The easy test is to pull it off and make sure it's pulling and pushing vacuum adequately.  I went down an epic fuel pump rabbit hole and finally figured out the reed valve seal was the primary issue in all the ones I pulled apart.  They have to fit perfectly and while I can't recall the exact size, I believe McMaster Carr was kind enough to sell me 100 as a minimum lot.  I can have a look at the package later as need be. 

[BoldUlysses]

4 hours ago, Patcon said:

I don't recall but:

Are all the fuel lines new?

What is the condition of the tank?

If it were me, I would rig up a 1 gallon fuel tank in front of the radiator support. Use the system from the under hood fuel filter in. Drive it around in the cul de sac on that. If it doesn't act up it's in the rear section of the fuel system. Probably the tank

The fuel lines are not new, but as mentioned, they've been blown out MANY times...

The tank was cleaned & resealed with the POR-15 tank restoration kit about 12 years ago as part of my effort to get the car running again as a baseline.  The car drove many miles after resealing the tank.  Took me to work & back one day (30 mile round trip), and on several trips around the area before I parked it for the body & interior restoration.

I'm going to bypass the filters and see if that helps, if not, then I'll bypass the lines (I'll run hoses from the tank to the pump & zip-tie them underneath), and if that doesn't work, I'll do what you suggested & rig up a temporary tank.

2 hours ago, SteveJ said:

My first guess would be a check valve issue with the fuel pump if it's a mechanical fuel pump.

11 minutes ago, ollie said:

I'm going fuel pump too.  The easy test is to pull it off and make sure it's pulling and pushing vacuum adequately.  I went down an epic fuel pump rabbit hole and finally figured out the reed valve seal was the primary issue in all the ones I pulled apart.  They have to fit perfectly and while I can't recall the exact size, I believe McMaster Carr was kind enough to sell me 100 as a minimum lot.  I can have a look at the package later as need be.

I rebuilt the stock fuel pump as a diagnostic measure.  I had an aftermarket replacement on there before.  The car behaves exactly the same before & after the rebuild.

 

Edited August 28, 2024 by BoldUlysses

[ollie]

I can tell you this, if you don't have exactly the correct white seals behind the reed valves they will leak air.  I went through two separate rebuild kits and until I found the correct seals, the issues I had remained and they sound exactly like yours.  If you can pull fuel pressure after the pump that would help...but low levels in your filters are telling. 

[BoldUlysses]

3 minutes ago, ollie said:

I can tell you this, if you don't have exactly the correct white seals behind the reed valves they will leak air.  I went through two separate rebuild kits and until I found the correct seals, the issues I had remained and they sound exactly like yours.  If you can pull fuel pressure after the pump that would help...but low levels in your filters are telling. 

I have an inline fuel pressure gauge installed on the rear carb line.  Reading fluctuates between 1-3 psi at idle.

I may rebuild the pump again if my plan of attack doesn't work...  As mentioned above, the dying started with the previous pump, and I replaced it, and there was no change in the car's behavior.  I guess the previous pump could have been bad, then my rebuild kit was faulty, but that seems unlikely.

[ollie]

1 to 3 psi cold?  That's low to me, I think you're onto something.  Of all the pumps I messed with, even new ones, it wasn't until I found the right seals for the reed valves did it finally resolve.  Then I had to go back and fix all the bandaid tweaks I did the the SUs before hand, to get it semi stable.  Runs like a champ now.