My Mercury Grand Marquis will not start sometimes

Maintenance/Repairs
1

Although it starts most of the time, about two times a week it will act as though it’s going to and won’t. We had it in a shop for about 3 weeks and the mechanic said it started every time for him. When I got it back, within a few days it would not start. I try after about an hour and it starts. He ran diagnostic tests and nothing showed up. I want to give this car to my teenage granddaughter and I can’t have this problem. Please help!!!

2

Not starting can mean two things.

You turn the ignition to start and nothing happens, or you turn the ignition to start and the engine cranks over but doesn’t fire.

Which is it?

Tester

3

I turn the ignition to start and the engine cranks over but doesn’t fire.

4

What year is your Mercury?

Tester

5
6

One thing that can cause an intermittent no-start condition is a faulty crankshaft position sensor.

As the engine is cranking over, the computer has to receive a signal from crankshaft position sensor that the crankshaft is rotating. If the computer doesn’t receive this signal the computer see’s no reason to operate the fuel and ignition systems so the engine doesn’t start.

A faulty crankshaft position sensor won’t always turn on the Check Engine light or set a code. That’s what makes it difficult to diagnose a faulty crankshaft position sensor. You have to have a scanner connected to the vehicle while the failure is occurring.

I have a customer who knows when the crankshaft position senor is failing in their vehicle. As soon as they start having intermittent starting problems, they call me and say, “Time for a new crank sensor!”

Tester

7

It stopped on me once after I had started it and was backing out of a parking space. Could it still be the crankshaft position sensor?

8

Yes.

If the computer doesn’t receive a signal from the crank sensor while the engine is running, the engine will shut off.

Tester

9

Makes sense. Thanks!

10

Also, next time it doesn’t start turn the key to on for a few seconds. Then turn it off. Repeat process and try to start it. If it starts, then it’s the fuel pump. A bad Maf can cause a no start issue to.

11

@knfenimore‌

The OP stated that the engine stopped while backing out of a parking spot.

How can the anti-drain back valve in the fuel pump cause the engine to shut down if the fuel pump is running?

The anti-drain back valve only comes into play once the fuel pump stops running.

Tester