1998 Mercury Mountaineer on Dec 28 it would crank but not start. The next day it started - took it to a mechanic and he could not find a problem. The same thing happened on March 11 and the next day it would start. What’s up with this?
The next time it doesn’t start, check for spark. This can be done by removing a sparkplug wire/coil pack from one of the sparkplugs and inserting an extra sparkplug into the plug wire/coil pack. Then lay the sparkplug on the engine to ground it. Try starting the engine and have someone watch the end of the spark for spark. If there’s no spark, the problem might be caused from a defective crankshft position sensor/ignition module if it has one.
Thanks, I will let you know what happens.
This may also be a fuel pump failure. It could be a bad relay, inertia switch, or pump. The inertia switch is located in the passenger side kick panel under the dash. Check for voltage there when it will not start. The power will only go to the switch for a couple of seconds when the switch is first turned to run.
As noted, you want to separate the problem into two large areas: spark, or fuel caused. Auto parts stores have several types of spark testers. One type looks like a spark plug with a clamp on it. What it really is, is a spark plug with a clamp on it. These are better to use than laying a spark plug, loosely, on the engine.
To test for lack of fuel, get a spray can of Starter Fluid. When there is a no-start, disconnect a rubber vacuum hose going into the engine intake. Spray a two-second shot of the Starter Fluid into the rubber vacuum hose, or the large intake tube. If the engine now starts, your mechanic can concentrate his efforts on the fuel system (supply, or injection, or electric).
Did you try giving it a little bit of throttle? If that makes it go, it is your IAC (idle air control) valve. From my limited observation and some scuttlebut, they tend to be intermittent at first and give more and more problems until you are driving with two feet. In addition, if you do get it started, they tend to improve when warmed up.