I had the head gaskets replaced about two weeks ago. The car was running fantastic for the first time in months. It's worth noting that it started without fail every time in the four years I have had it before this major procedure. The car also started fine for the three or four times I had started it after getting it back. Then, I found myself getting out of the supermarket, car full of groceries, turned the key, and the car would not start. Full battery life (indicated by the dash reading), bright lights, radio, etc. Frustrated, I popped the hood, stared the engine down (did nothing), got back in and the car fired up. Erased the episode from my mind.

Fast forward about 3 or 4 days, car had been starting fine. Got out on my lunch break, turned the key, and nothing. Frustrated, I went back in to finish the work day. When i got out, i turned the key and it started.

Next day, drove the car to work, would not start at lunch. This time it would not start when I got out of work, got a jump (despite the full battery life) to no avail. Called a tow. Waited an hour, pushed the car out out of the parking garage, and as he was backing up to get it on the flatbed, I turned the key. Started right up.

Brought it to my mechianic, who replaced the starter. He told me it started everytime he tried, but treplaced the part. $400.

Confident, I drove it out on a Saturday. Got back to the car. Of course, nothing. Coasted down a hill in neutral. Nothing. Called a tow, had it towed to the mechanic. Nothing.

My mechianic had it all day today. He said that he turned the key at least 50 times and it started all 50, right away.

Help! I don't want to go pick it up and get caught waiting for a tow for the third time. He said he doesn't know what to look for until it doesn't start. Is there anything I can tell him to look for? Does this sound like trouble anyone has had? I've spent too much money to walk away!

Is it cranking when this happens, or just nothing? If it's not cranking at all, I would suspect that your battery terminal may be corroded.

Not cranking or even clicking. When the key is turned all that can be heard with the hood open is a faint whine which I though might be the fuel pump. When the key is turned.

Since the starter has been replaced I think we can rule out the starter as the "faint whine". I'm with JC. Check the battery terminals, cables and connections.

Codes?

http://www.cadillacforums.com/forums/cadillac-tech-tips/55172-how-pull-codes-got-codes-warning.html

Could also be the ignition switch. There are posts here on them going bad and causing similar problems. If you're getting no crank and no theft system warning I would look there.

Yeah, I've been sitting here doing some research and have started to think "ignition switch." There is certainly no crank nor theft system warnings. I've tried all three keys. I pulled all the codes when I was waiting for a tow and they were all "history." Mechanic has it now. I'm going to tell him to check the terminals, cables and connections in the morning. If he still comes up with nothing, I'll take it back and risk the tow, i guess. Or should I have him replace the ignition switch? Is there any way to just check that it night be the ignition switch ( i.e OBD)?

Look at your history codes. Despite the fact that they were in history, they were still a problem that your car has had in the last 50 or so key cycles. They may even provide a hint.

That said, I'm with everyone else. Either bad battery cables/connections or a bad ignition switch....... Another thing to try when it acts up is to put the car in neutral and see if you can start it that way. If it works with the car in neutral, it would likely be a bad neutral safety switch.

Another thought. How about the neutral safety switch? Have you tried wiggling the gear shift while the key is turned to the start position?

I did try to start it in neutral when i was having the problem, but never really wiggled it with the key in the start position. It's frustrating because you can't try these things when the car is starting every time (unless I'm far from home). Which makes me wonder if I should have these parts replaced and hope that does it.

How does a new ignition switch cost?

How about a neutral safety switch?

Hmm, how about the starter relay? If that is going bad, it could cause an intermitant problem like this.

I would be suspecting corroded - oxidized blade contacts on one more of the relay contacts.

Here is a schematic diagram of the control circuit and component locations.
http://s70.photobucket.com/albums/i101/JimDphotobucket/?action=view&current=98Sevillestartcontrol.jpg

Less than an hour's labor to check all the pieces for corrosion.

go back to the start...problem started after head gasket repair-check your power and grounds especially grounds, check all connections that might have been disturbed during head repair, after all is done check your battery connections, once you have established good power, go to the easy stuff first, check the starter relay and swap it with another relay in the box...then most important..check your codes any theft code history or current could be the key to an easy diag, a theft code can go to history as soon as the car starts

I just got off of the phone with my mechanic. he said that he finally got it not to start. He was able to make it restart again, by "jamming" it into park. So he is going to replace the neutral safety switch. I hope this does it. I asked about all of the cables, connectors and terminals. He said he checked all of that before replacing the starter. He also checked everything he though might have been disturbed by the headgasket repair. I feel like we're ruling things out, though . . . let's just hope I'm close to home if the neutral switch doesn't fix the problem.

Well, the mechanic replaced the neutral-safety switch, and now the car won't start at all. He wants me to bring by all of the spare keys. At least we seem to be ruling things out . . .