intermittent won't crank when hot - electrical power loss
 

For several months I've experienced an intermittent total loss of electrical power in a hot engine start situation. I bought this car used in April, and first encountered this problem June. Took it to a local specialty car shop (recommended by Texas Cobra Club members). They found dead cells in the Optima Red Top Battery (two years old), and replaced it. Problem continued, and in August same shop performed total electrical test - all checked out EXCEPT a loose connection at the alternator. They replaced the smaller wire from the alternator to the battery with a 4-guage wire. Looks impressive, but the problem continues, intermittently. The shop is too busy now to look at it, so I'm looking for help

Superformance Cobra, Roush 402R, MSD ignition, GM 1-wire alternator

Each time it has reoccurred, the engine has been hot, and turned off for 5 to 15 minutes, and then won't start. 2 of the 3 times the car has just been unplugged from the battery tender, and driven for only15 minutes. One incident was August 18th, after driving for one hour, then sitting 15 minutes, and 'self corrected' almost immediately. Next was Aug. 28, and self corrected after 7 minutes - I tapped on the starter, not sure that helped. The last incident was September 13, and took 2 1/2 hours of my intermittently tapping on the starter & firewall solenoid, & 'jump-starting' it. In each case, I initially made the same following mistake, which was followed by the electrical power loss incident:

Hot engine. 5 - 15 minutes after stopping. With the car in gear, key inserted, turned to run, electrical power-up noise heard, fuel gauge starts to rise, turned to start and 'clicking' solenoid-like noise heard, and motor will not turn over. Fuel gauge starts to drop. No power. Move the gearshift to neutral, but it still wont start. Perhaps a sticking neutral safety switch?

In the last incident after 2 1/2 hour tapping & trying the kill switch (no sound) & jumping from another car and then from my Ford F 350 turbo-diesel, I finally heard the faint "power up" noise from under the drivers side dashboard. Turn the ignition key to run, but the fuel gauge did not rise. Car would not start. No clicking 'solenoid-like' noise. Turn the key back to accessory, and pressed the kill switch. As I pressed it, heard the solenoid-like click, then click again as I released the kill switch. Motor would not start, fuel gauge needle would not rise. Tried the kill switch several times: each time the solenoid noise clicked as I depressed the kill switch, and clicked again as I released the kill switch button. Motor still refuses to start, fuel gauge doesn't work. Finally tried holding the kill switch down with one hand while turning the ignition switch from accessory to run to start with the other hand, and the engine turned over and started. The dashboard lights wouldn't work however, and the running lights would not come on, however the headlights came on. I checked the fuses, and they are good. Turn indicator lights work.

Any thoughts or suggestions are greatly appreciated.

I am not saying this is it, but I had some similar issues lately. Turned out to be a bad fusible link in the power cable going to the battery from the alternator. Take a reading at the power cable on the battery and see if it reads 12V when this is happening. If not, there is likely a break in the wiring.

Phil

Trouble with that wire was my mechanic's first thought. HE replaced the entire wire with a larger 4-guage. Problem has occurred before and after that wire replacement. Not sure where the fusible link in that wire assembly is.

I had an intermittent hot start problem eventually traced to an inadequate ground connection from the engine block to the frame. Found the problem via connecting a jumper cable from the battery negative terminal to the starter directly.
Just a suggestion - it sounds like you have done very thorough trouble shooting.

I've put a multimeter in the trunk, to check the voltage at the battery Cable the next time this happens. if I understand correctly I should put the positive multimeter lead on the battery cable, and the negative lead to a ground somewhere, not on the negative battery cable.

I've put jumper cables in the trunk as well: next time this happens I'll attach one to the negative post and cable on the battery, and run the other end to touch the starter case.

Thank you both for your suggestions.

It sounds like either bad battery or bad ground. A voltmeter won't tell you unless you have a permanently bad cell you need to rest under load

David's suggestion above panned out. Had an electrical failure at a cold start. Did not try and start with the transmission in gear this time. Everything else was the same: key in ignition, turn to run, hear the electrical start up noise, and the gas gauge needle starts to rise. Turn the key to start, and hear the solenoid like click and the gas needle starts to drop, there is no power anywhere, and the engine will not turn over. Check the battery voltage: 12.75. Hooked a jumper cable to the negative battery terminal, and clipped the other end to one of the bolts securing the starter to the bell housing. I turned the key to run, heard the electrical energize noise, and the gas needle starts to rise. Moved the key to start, and the engine turns over and catches. When my mechanic troubleshot this in June, he checked the three original chassis grounding straps, and added a fourth one. The closest grounding strap is a four gauge wire running from the chassis next to the starter down to a bolt connecting the bell housing to the block, 6 inches from the starter.

Does this mean the negative ground failure is between the negative battery terminal and the chassis?

90% of the time when you have this type of intermittent problem, it is a loose connection. Usually an insufficient ground connection. It could be corrosion at one or more of the ground connections or a loose connection on one of them or paint between the lug and the connecting point insulating the connection from the chassis. Any one of the connections may be the culprit if you aren't getting a good ground connection to the starter. An easy test would be to run a heavy piece of cable from the ground side of the battery to the connection the starter uses to ground to the chassis. If you don't have a chassis ground directly to the starter, add one by putting a ground strap from one of the starter mounting bolts to the chassis. Then also connect the ground cable from the battery directly to this same connection point. If your power connections are good and tight everywhere, this should take care of the problem. If it doesn't, you will need to trace back the power cable to see if there is any loose or corroded connections between the battery connection and the fuse box.
Years ago, I had this problem and it turned out to be corrosion had gotten into the positive lead on the battery under the cable sheath where I couldn't see it until I stripped it back. Replaced the cable and all was well.

Bob