Cold Start Problems

[Robert Morasko]

I have a 2011 RAM 1500 5.7 Hemi. The truck recently (2 months) does not start when cold without pumping the gas peddle. After I pump the gas peddle, the truck starts and runs like brand new. After the truck starts the initial time, the truck starts like new until the truck is cold again. I replaced the battery with a NAPA battery in July 2020; battery is good. I recently had a local mechanic change plugs and professionally clean the fuel system injectors. I cleaned the mass air flow sensor and throttle body, made no difference with cold starts. I ran the truck with berryman b12 in two tanks of gas. I always run 87 or higher octane. I've owned the truck since new (128,000 miles on truck). All of the guages and lights work perfectly. I purchased a blue drive and the truck shows no codes. I recently drove the pickup 1,000 miles and the truck ran like new except when I start the truck when it is cold. Any suggestions?
Thanks,
Bob

 

[ToxicFire]

Injector issue possibly? My h2 was having cold start issues but start and rangreat when warm. Ended up needing 2 new injectors.

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[Robert Morasko]

Did your truck throw any codes? If no, how did they diagnose the injector problem?

 

[danoday]

Pumping the pedal on a fuel injection engine does nothing when the motor isn't running. . The ecm system knows the temp and sets the fuel mixture for cold starts. Assuming you have good injectors and fuel rail pressure, you may want to consider your O2 sensors. Just a thought.

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[Robert Morasko]

Hi,
I meant to say I pump the gas pedal when the engine is cranking. The truck will not start unless I pump the pedal during a cold start. The truck runs perfect after it starts the first time. It starts and runs great immediately after the first start even if not warmed up. How do I check the air sensor when the truck has no codes?

 

[jws123]

Hi,
I meant to say I pump the gas pedal when the engine is cranking. The truck will not start unless I pump the pedal during a cold start. The truck runs perfect after it starts the first time. It starts and runs great immediately after the first start even if not warmed up. How do I check the air sensor when the truck has no codes?

Next cold start turn the key 3 times to prime fuel pump NOT turning it over just turn key on and then try to start if it fires right up its your fuel pump.

 

[turkeybird56]

delete

 

[Robert Morasko]

Thanks, I have never replaced the sensors and have 127,000 miles on truck.

I turned the key on and off three times and it fired up like a new truck. I’ll confirm this later to make sure. I’ll schedule to have a new fuel pump installed, I’m not a mechanic.

 

[Robert Morasko]

Do you think it could be the fuel pump pressure sensor instead of the fuel pump? The truck accelerates and runs great after it is started. Replacing fuel pump is a large job compared to the fuel pump sensor.

 

[Fast69Mopar]

Thanks, I have never replaced the sensors and have 127,000 miles on truck.

I turned the key on and off three times and it fired up like a new truck. I’ll confirm this later to make sure. I’ll schedule to have a new fuel pump installed, I’m not a mechanic.

If the engine started like it's supposed to after cycling the key three times before cranking the engine then the fuel system is losing its prime while the truck is sitting and when you go through a cold soak and attempt to start the engine the fuel pump takes some time to prime the line and fuel rail.

Glad you were able to do some easy diagnostics to verify your concern. To confirm your diagnosis connect a fuel pressure gauge to the fuel rail, start the engine and let it run, then shut the engine off for another cold soak overnight and then look at the gauge before you attempt to start the engine the next morning. You will probably see there is either low or no fuel pressure left in the fuel system.

 

[Robert Morasko]

I don’t have a fuel pressure tool. Is there a simple way to check if it is the sensor vs. fuel pump as a staring point?

 

[Fast69Mopar]

I don’t have a fuel pressure tool. Is there a simple way to check if it is the sensor vs. fuel pump as a staring point?

If the fuel system is losing its prime after a cold soak then a sensor is not causing this issue. Inside the fuel pump there is a one-way check valve that allows fuel to flow toward the fuel rail but not backwards into the fuel pump. When this check valve fails it allows the fuel pressure to bleed off while the pump is not running. This is why the engine is hard to start after sitting for long periods. The fuel pump is having to refill the fuel line and fuel rail with enough fuel to start the engine.

 

[Hemi395]

To accurately diagnose this you would need a scantool capable of live data viewing to see whats going on during a cold start. Sounds like a fueling issues as mentioned but it would be just guessing without seeing the live data....

 

[jws123]

I don’t have a fuel pressure tool. Is there a simple way to check if it is the sensor vs. fuel pump as a staring point?

Its not the sensor its 100% the pump if it starts after priming it they dont make **** like they use to cheap plastic new pump is $300 on rockauto only get a Mopar one I got aftermarket for $140 and it crapped out within a year and i got stuck doing it again.

 

[Robert Morasko]

Thanks!

 

[danoday]

You may consider the fuel pressure regulator valve if it is not assembled to the pump it self. The regulator valve is what maintains the pressure at the fuel rail from the fuel pump. A failed spring valve will allow fuel to back to the tank.

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[Robert Morasko]

Can I add an inline one way check valve instead of replacing the entire fuel pump? If yes, where would I add this and what brand and size do you recommend?

 

[Tach_tech]

Are you pumping the pedal or holding it down? If you’re holding it down it goes into clear flood mode and disables the injectors.

Does it do it first thing in the morning after siting several hours or only a few hours?

Sounds possibly like leaking injectors,purge valve or possibly a fuel pump losing prime.

 

[Robert Morasko]

I pump the pedal to start. I now turn the key on and off 3 times without trying to start. The truck then starts cold and runs perfect. This logically indicates it is the check valve. I was thinking adding the inline check valve would eliminate the need for an entire fuel pump replacement .

 

[danoday]

I would replace, but no hurry since x3 start cycle and it works.

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