Need help with my zz502

[Big Block Bill]

Originally Posted by 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.

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]

Originally Posted by Big Block Bill

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]

Originally Posted by 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

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

[drdave69]

Originally Posted by Big Block Bill

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]

Originally Posted by 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.

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.