Cranks but Intermittent no Start when Warm

Greetings, cold start is fine on 2008 Mercury Marquis. After a short (2 mile) drive to the store to buy some groceries it will crank but sometimes refuse to start. So the car is stuck in the store parking lot. Repeated cranking does not help. Wait around half an hour or several hours and it will start right back up. It never dies once it starts or while driving. So I sum it up as cranks but sometimes won’t start when engine is warm.

Crankshaft position sensor would be something i’d check.


We had a 2003 windstar with the same symptoms. After 2 tows to the dealer and it started right up, I worked with the dealer to be ready to help us in a no start. Had the wife stop by there every time she passed the. No start in their parking lot, they analyzed it quickly and it turned out to be a bad fuel pump.

If you can test for no-spark and for no-fuel when it’s not starting, that will narrow the possibilities.

No spark? Crankshaft position sensor is suspect #1.

No fuel? Fuel pump, or its relay, is suspect #1.

The CPS is more likely than the fuel pump to quit in a heat soak circumstance like yours.

Put a can of starting fluid (ether) in the car. When it won’t start.spray some in the air intake for about 2 seconds… If it starts right have a fuel problem. If it doesn’t, you have no spark


Thanks for all the replies. Just got two new pieces of information. First, dead cold/first thing in the morning the car failed to start at the repair shop. We have only seen a dead cold failure to start this one time. All the other times the car was warm when failing to start. Second, the car is flooding when it won’t start. So we believe it’s getting plenty of fuel. Does this narrow things down or open it wide up ?

What does the shop have to say that needs to be done to solve this. I myself would not tell the shop that they should do something that I was told on the web. If you don’t trust them to fix this then you need to find another shop.

A Crankshaft Position Sensor will sometimes fail intermittently when hot, and later fail even when cold.

Well the shop could not replicate the failure to start condition over a two week period. But when we went to pick up the car, it did indeed fail to start (when dead cold). Right away the shop tried again to diagnose the failure but could not. Then they plugged in a scanner but (unfortunately) the car started right up. It’s a reputable shop and arguably the best in town. Their position is that the car must be in failure mode for them to diagnose it. Similar to Barkydog’s (above) situation.

For what little it costs, given its crucial role in providing a well-timed spark, I would put in a new Crank Position Sensor and cross my fingers. Good luck!

I agree and have already bought ($22) an OE Denso crankshaft position sensor. Also, saw a video claiming that if the tach stays at zero during cranking then the issue is the crankshaft sensor. Anyone know if true ? CRANK Position Sensor Test - failing CKp sensor - CKp test - YouTube

1 Like