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Only has trouble on the FIRST start of the day

My car, 2000 merc mountaineer- ONLY on the FIRST start of the day (especially when cold) -have to turn the key and then sit, playing with the gas-if the little needle goes under 1, the car shuts off. After a while, the engine will start REALLY revving itself so I can stop playing with the gas so much, but, takes a good 5-10 min depending on cold for car to STAY started without my help with the gas pedal. As the car is starting, the engine shakes HARD. After this, the car starts just fine all day, even after sitting for hours.
I have changed the front o2 sensors, spark plugs, fuel filter, battery and I put in “heet” with my gas. I did also have the coil checked and it was fine.
All these repairs seem to make small positive differences, but today, with the weather in the lower teens, it took a lot of manual work to keep the car started until it was “warm” enough to do it itself.

The next time you go to start the engine after it has sat for a long period of time, turn the ignition switch to on position so the dash lights come on for two seconds and then turn the the ignition switch off. Repeat this a half dozen times and then try starting the engine. If the engine starts right up the problem is with the anti drain-back valve in the fuel pump assembly.

When this valve fails it allows the fuel in the fuel rails and fuel lines to drain back into the fuel tank as the vehicle sits. Then when you go to start the engine there’s no fuel in the fuel lines/rails to build the proper fuel pressure so the engine won’t start. When you cycle the ignition switch on and off this forces the fuel pump to run for a second or two. This then reprimes the fuel system with fuel and builds the proper fuel pressure which allows the engine to start.

If you find this is the problem, the fix is to replace the fuel pump assembly in the fuel tank.


Great! That sounds like it makes a lot of sense!!! I will give it a shot tomorrow morning!! I know I was told to replace the fuel FILTER even thought the diagnostics said nothing about that part (guess it won’t read “fuel filter” but the stuff connected to it)-would this fuel pump valve read on a diagnostic test?

Yes. You can test for a faulty anti drain-back valve by doing a residual fuel pressure test.

Connect a fuel pressure gauge to the fuel rail. Turn the ignition switch on so the dash lights come on and then turn the ignition switch off. Check the fuel pressure reading on the gauge. If the vehicle hasn’t been driven for a while the gauge will read zero. If the vehicle has been driven, then normally fuel pressure will come up and then slowly bleed off over the course of 10-15 minutes. If the fuel pressure comes up and then immediately drops back down to zero the anti drain-back valve is defective.