2000 Grand Marquis engine would not turn off

[kingofhearts]

I have a 2000 Grand Marquis with 160K miles on it. Today I was driving down the road about 30 mph, when this loud noise, like a failing bearing, started up.
I pulled over the side of the road and put the car in Park. I revved the engine slightly and the noise seemed to follow the RPMs. The engine was idling fast, I'd guess over 2,000 RPM.
Then it got really weird. I turned off the ignition and the engine kept right on running, except a bit rougher. When I turned the ignition back to run, the engine smoothed out and kept running. I tried to turn off the engine a few more times and the engine just kept on running.

I got out and started to open the hood, and the noise went away. The engine returned to normal idle and when I tried the ignition switch, the engine shut off. No check engine light ever came on.

I restarted the engine and drove another 15 miles home. The car ran just fine, the noise didn't return and the car turned off with the ignition switch.

I suspect other people have had a similar experience but I couldn't find any occurrences with my searches.

Anybody have a clue of what happened? I suspect I haven't seen the last of this problem.

If there is already a thread regarding this problem, I'd very much appreciate a pointer to it.

Thanks in advance

[sly]

I would suspect cruddy contacts on the ignition switch and you cleaned them enough to work through all of that. I would replace the ignition switch.

[kingofhearts]

Here is an update. I replaced the ignition switch with a new motorcraft part and did several short trips around town. It was working just fine. Last night I went for a longer ride, about 30 miles, and when I got close to my destination, the starter kicked in while I was driving (I think that's then noise I keep hearing). So when I turned the ignition off, the starter keeps the motor turning over and when I put the key back to ON, the engine keeps running. I had no tools with me (doh) and I sat in the car for several minutes until the starter disengaged. Then I was able to turn the car off. On the way home, it acted up again, once on service roads and once on the freeway. While I was still on the freeway, all my dash and exterior light when out and I had to use the manual ON position to get the lights back on. Once the starter disengaged, I nursed the car home and parked it in the driveway. Just for grins and giggles, I tried to start the car up a few minutes later and the starter did nothing but the lights dimmed like there is a direct short. Well I'm heading outside to see what today brings.

[sly]

that's a new one. Never heard of that problem. Might be some wire chaffing somewhere along the crank wire (or a problem with the new ignition switch - BTW... the BWD/DORMAN/cheapo replacements actually work well for this... NOS Motorcraft may be old and brittle, unless the new part is actually new), if it's not a wonky starter solenoid.

[Mainemantom]

That is a good way for a fire to start. Glad it did not happen.

[kingofhearts]

I am probably luckier than I realize. I suspect the starter is toast and I am probably going to have to replace it. The circuit seems pretty simple and I am at a loss to figure out how the circuit can be activated when the ignition is in the ON mode. I don't think a frayed wire could do this. Maybe the starter relay is malfunctioning or maybe the starter solenoid. Here is the wiring diagram from the shop manual.

[sly]

pretty much you've got it nailed. Those are about all that can happen. The chaffed wires could cause some crap if it's in the bundle to the ignition switch... in the bundle to the firewall... or some crap shorting something in a connector along the way to the relay or solenoid. Also might have been something kicked up on to the starter shorting the battery line to the trigger line on the solenoid. Damn near impossible for some crap like that to happen with the relay.

I'd definitely take a look at the starter and the wiring going to it to make sure some bad shenanigans haven't happened.