Need help with my zz502

[drdave69]

My zz502 has me stumped. I had Eric rebuild the Holley and it performed excellent but it did not cure my problem. I then had F.A.S.T EFI installed (not cheap) and the issue is still present. The problem: it starts and runs fine from cold but after running up to temp and parking for a little while (20 - 30 minutes) it doesn’t want to start again and doesn’t want to idle. I have put in new plugs, ignition coil, plug wires and had the timing checked by the guy that installed the efi. What can cause this issue?

[Spooky]

Have you checked the wiring in the car? If it is old it may have a bad wire with a break or corroded inside the jacket. Heated up it expands and may be losing contact. Just throwing another possibility. You can check with a multi meter when cold then hot. My car did this with the starter wiring.

Scott

[Spooky]

Also check the grounds.

[earntaz]

Have you tried hot wiring it just to check the primary ignition wiring??

[markjohnson]

Almost sounds like a heat soak problem with the carburetor and you might want to try a thicker heat-insulate gasket between the manifold and carb.

[VintageMusclecar]

What distributor?

[miket1]

Ignition Module,, or if msd,,ignition box.

[drdave69]

By the way this is in my 1966 Corvette. The Holley is no longer on the engine. It has FAST EFI now. I recently checked the ground strap from the engine to the front crossmember and cleaned the surfaces. I also installed a second ground strap on the other side of the engine to the frame rail (with cleaned surfaces).

The 502 has the HEI that came with the engine 12 years ago. I bought another new coil this past Saturday, installed it and it did not cure the problem.

I do not know how to hotwire it but I will check the voltage when cold and hot.

Thanks for the info.

[earntaz]

On the side of the HEI cap that holds the coil you will see connections (should be on the drivers side ... if someone has jacked with it) -- one is marked IGN ... run a hot wire from a good 12V source to there. OR hook up a volt meter to this IGN source and see if you have 12V with key in the ON position -- 12V during cranking ... TAZ

[drdave69]

On the side of the HEI cap that holds the coil you will see connections (should be on the drivers side ... if someone has jacked with it) -- one is marked IGN ... run a hot wire from a good 12V source to there. OR hook up a volt meter to this IGN source and see if you have 12V with key in the ON position -- 12V during cranking ... TAZ

I'll check it with my volt meter for IGN and Crank when cold and hot.

[Big Block Bill]

By the way this is in my 1966 Corvette. The Holley is no longer on the engine. It has FAST EFI now. I recently checked the ground strap from the engine to the front crossmember and cleaned the surfaces. I also installed a second ground strap on the other side of the engine to the frame rail (with cleaned surfaces).

The 502 has the HEI that came with the engine 12 years ago. I bought another new coil this past Saturday, installed it and it did not cure the problem.

I do not know how to hotwire it but I will check the voltage when cold and hot.

Thanks for the info.

Make sure the metal ground strap under the coil is present. It goes from a coil mounting screw to the cavity in the cap next to the 12 volt power supply. I had a Cadillac that drove us crazy from someone leaving it out when they changed the cap / coil. Just an idea FWIW.

Bill

[earntaz]

Make sure the metal ground strap under the coil is present. It goes from a coil mounting screw to the cavity in the cap next to the 12 volt power supply. I had a Cadillac that drove us crazy from someone leaving it out when they changed the cap / coil. Just an idea FWIW.

Bill

Your right --

[Justoldchevys]

Is your wiring harness all original? If so the wire that supplies power to the coil is probably a resistence wire. Look at it closely you will notice it being different. You will need to remove that wire and replace it with normal wire to provide the correct voltage to the hei coil

[earntaz]

Is your wiring harness all original? If so the wire that supplies power to the coil is probably a resistence wire. Look at it closely you will notice it being different. You will need to remove that wire and replace it with normal wire to provide the correct voltage to the hei coil

Hopefully however did the conversion would know that -- or maybe not ... a lack of full 12v to an HEI will have issues.

[drdave69]

Make sure the metal ground strap under the coil is present. It goes from a coil mounting screw to the cavity in the cap next to the 12 volt power supply. I had a Cadillac that drove us crazy from someone leaving it out when they changed the cap / coil. Just an idea FWIW.

Bill



It is present.

[drdave69]

The engine was running fine when I bought it (April 2016) and did so until this time last year (Oct. 2016). That is when this issue popped up. I have since put in new plugs, wires, ign coil, cap, rotor. Had the timing checked. Had Eric rebuild the Holley and recently had the EFI installed. So far, nothing has solved the issue.

[drdave69]

I finally got around to checking the starting voltage. I pulled off the input voltage wire from the HEI and checked the voltage with key on. It is 11.8 v. In start mode it goes to 9.8 v. It is the same when the engine is up to operating temp. The next thing I am gonna check is the voltage when running but that involves removing the cap from the coil.

I also drove it about 10 miles and it also has a miss. Got to be something wrong with the ignition but I haven't figured it out yet.

[earntaz]

I finally got around to checking the starting voltage. I pulled off the input voltage wire from the HEI and checked the voltage with key on. It is 11.8 v. In start mode it goes to 9.8 v. It is the same when the engine is up to operating temp. The next thing I am gonna check is the voltage when running but that involves removing the cap from the coil.

I also drove it about 10 miles and it also has a miss. Got to be something wrong with the ignition but I haven't figured it out yet.

I'd still try to "hot wire" it ... 12V lead from + side of battery to the IGN terminal on HEI. That would isolate the ign system from all except the 12V source.

Don't know if this has been mentioned yet. Do you have an electonic tach connected to the HEI? If so, you may want to unplug it also in case the tach is causing an issue ... TAZ

[L78_Nova]

When it is hot and it "won't start" is it cranking over at normal speed or hard cranking?

Had a similar issue with freshly powder coated engine mounts frame etc. Would fire cold but not hot (cranked very slow). Poor ground through the coating. I added a ground cable from the block to frame and all is well.

[drdave69]

I'm not sure how to 'hot wire' it to the battery. Will it still start/stop using the keyed ignition switch if I run a wire to the + at battery and 12v side of the HEI? I still have the original tach in the car and the EFI has a control/monitoring module that has a multitude of 'gauges' including a tach. The wire in the HEI is part of the EFI harness.

When the engine is hot it will turn over just fine, it just takes time to fire. I usually open the throttle (1/2 - full pedal) to get it started.

[earntaz]

I'm not sure how to 'hot wire' it to the battery. Will it still start/stop using the keyed ignition switch if I run a wire to the + at battery and 12v side of the HEI? I still have the original tach in the car and the EFI has a control/monitoring module that has a multitude of 'gauges' including a tach. The wire in the HEI is part of the EFI harness.

When the engine is hot it will turn over just fine, it just takes time to fire. I usually open the throttle (1/2 - full pedal) to get it started.

Dave -- use a female spade terminal with at least 14 gauge wire. Spade terminal will plug into IGN terminal on side of HEI cap and other end to batt 12V + source. Next to the IGN terminal on side HEI cap is the TACH terminal. With this setup -- the engine is "hot wired". Turn key to fire it off -- to shut the engine off, you will need to disconnect the the IGN wire that you ran to the 12V source at battery ...

[drdave69]

Thanks. That is what I thought. I'll try that next time I monkey with it.

[VintageMusclecar]

If you "hot wire" (bypass the stock switch/wire) the ignition with a 12V source, you need to add in some sort of switch to be able to shut off the ignition.

[earntaz]

If you "hot wire" (bypass the stock switch/wire) the ignition with a 12V source, you need to add in some sort of switch to be able to shut off the ignition.

A alligator clip at battery will work for quick disconnect -- if that is what you're talking about ...

[RPOLS3]

Are you using the original starter or a new "mini" starter. If using the mini starter they typically do not have the terminal like the originals due for the 12V line that you are talking about bypassing and that could be causing the problem. If it fires right up when bypassed that will be a clue.

[drdave69]

It has the starter that came with it 12 - 13 years ago. I haven't been able to touch it lately (been sick) but I think I can just configure a wire with a female spade and battery clip to hot wire it.