My 99SD cuts off while I'm driving. No warning, nothing. Just shuts down- all warning lights flash as if the key is in the "on" position and the engine just shuts off. I put the truck in park, and it fires right back up and it continues on with no problems. There are no warning lights that stay on.

Here's what's I've done to the truck recently. I had a bum battery that burned out my alternator. Changed the battery, then changed the alternator. Had to change the alternator and battery again because I received a bum alternator off Ebay and it killed the new battery. I replaced the battery and the alternator and it was running well for about a week. Then on Friday evening, I did some maintenance. I checked my power steering fluid and oil, put some Lucas additive in my transmission and Seafoam in my gas tank. Saturday morning, as I was driving, my check engine light came on and I got to the nearest Autozone. There's smoke coming from under the hood and when I open it, there's a good amount of smoke coming from the alternator and black marks on it indicating there had been a small fire. I exchanged it with autozone and it hasn't been a problem- I have been checking it constantly with a multimeter to make sure it's operating correctly. Later on that evening, after driving the truck the whole day, it shuts down for the first down. Fires right back up and makes it back home. I drive for another day and a half, and it does the same thing to me this morning on my way to work.

My hypothesis is that the fire or heat from the alternator may have damaged a module of some type under the hood that is causing this. Any ideas on where to start looking first?

PS. I'm a newbie disco owner that is having fun getting to know this truck. The search function on this forum has been invaluable to me.

 

My money is on CkPS although it usually requires slightly longer to cool off.

The next time this happens, before trying to restart, check for fuel presence at the fuel rail.

 

How would I check for fuel presence at the fuel rail? And what is the guess at what's wrong if there is or isn't?

 

It's a DI, so on the passenger side of the engine on the fuel rail you will see a black cap, like a tire valve stem cap. Remove the cap and you will find a schrader valve, this is the fuel pressure test port. Push in on the valve, but hold a rag in front of it to keep you from being sprayed with fuel. If fuel sprays out your pump is working, if it dribbles or you get nothing it means the fuel pump cut out. In short, if you find you get fuel spraying out then replace the crank position sensor.

BTW, make sure the alternator is NOT on fire before checking for fuel pressure at the rail.

 

You guys are very helpful. So should I wait until it cuts off again to perform this check or should I do it after it stalls out?

 

I do not guess when conducting diagnostics on vehicles.

When the vehicle has next died on you, before trying to restart, check for presence.absence of fuel at the fuel rail.

At this point, all that is known is that the truck quits. We must follow a logical progression to rule out things that are known or not known.

Jumping to conclusions is a good way to waste $ and increase frustration.

 

And SWMBO may be watching.....