Dear Tom and Ray:
I have a 1991 Mustang GT with just under 100,000 miles. The engine runs fine on the flat desert floor, but when I try to climb out of the valley, the 302 V-8 begins to sputter and then stops completely. If it sits for a few minutes, it normally will restart, but as soon as I continue up the mountain grade, it dies again. What's going on? -- Greg
RAY: Well, if I had to guess, I'd say it's fuel starvation, Greg.
TOM: Here's what you have to do. Next time it dies, hop right out and pop open the hood. Pull off a spark-plug wire, and have a friend or a good Samaritan turn the ignition key to the start position. If you hold a screwdriver (with an insulated handle) close to the open end of the pulled-off plug wire, you should see the spark jumping to the metal end of the screwdriver. That tells you that you have spark.
RAY: I used to make my brother use his tongue to test for spark -- until he got wise to me and insisted on using his finger instead.
TOM: If you see sparks jumping, that means your problem is lack of gas. A car this age might be not getting gas for any number of reasons, but the first thing I'd suspect is a bad fuel pump.
RAY: Me, too. But before you replace the fuel pump, go ahead and put in a new fuel filter. It's something you can do yourself, it doesn't require any diagnosis and it only costs 10 bucks. Then if that doesn't fix it -- and you didn't set the car on fire -- you can try putting in a new fuel pump.
TOM: If your screwdriver test doesn't produce a spark, then you have to look at one of the electrical components, like the coil or the electronic ignition module.
RAY: But I'd bet on a fuel problem here, Greg -- it dies going uphill, when the demand for fuel is the greatest. Good luck.