Starting issues

[stanleytalley]

Hello,
I'm experiencing an issue with my truck where it often takes up to 6 seconds to start if I let it sit for a while. However, if I cycle the key 2 or 3 times to pressurize the lines, it starts right up. The dealership diagnosed it as a fuel pump problem and quoted me $850, but after replacing it myself, the issue persists. The truck runs and idles smoothly with no error codes. Someone suggested it might be a cracked vacuum line, but I'm unsure where to begin looking for that.

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[RangerBill]

Hello,
I'm experiencing an issue with my truck where it often takes up to 6 seconds to start if I let it sit for a while. However, if I cycle the key 2 or 3 times to pressurize the lines, it starts right up. The dealership diagnosed it as a fuel pump problem and quoted me $850, but after replacing it myself, the issue persists. The truck runs and idles smoothly with no error codes. Someone suggested it might be a cracked vacuum line, but I'm unsure where to begin looking for that.

It could be leaking fuel injectors. You could try some Chevron Techron in the gas tank.

There is a fuel rail pressure sensor that can be monitored using a scan tool or Forscan. Monitor the fuel pressure after the truck has sat for a while or overnight to see if it is bleeding off.

 

[airline tech]

Which fuel pump was diagnosed as bad? LP or HP
I suspect 1 of 4 things
Bad Fuel Pressure Sensor (On-Top) of the fuel tank (LP Pump Pressure)
Bad Fuel Rail Pressure Sensor (HP Pump Pressure @ the rail)
Bad Fuel Pressure Regulator (Part of the HP Pump) Regulates Fuel Volume & Press
Leaking Injector

What was the code the dealer found?

There are a few tests that can be done with a scan tool to isolate it down and monitor pressure drops (viewing) the pressure sensor PIDs
Low Side vs High Side pressure will isolate which side the issue is on.
If still seeing Low Pressure (readings) on the Low Side, it's going to be the pressure sensor, but it also needs CONFIRMED with a gauge pressure test.

Are your dome lights working correctly when the driver's door is opened, I am looking for is the LP Fuel Pump - Prime triggering with the PCM Wake circuit.

If you replaced the LP (In-Tank) Pump
The Fuel Pressure Sensor is mounted on top of the tank, next to the pump.
This is the feedback sensor for the Fuel Pump Control Module to regulate LP Pump pressure.
I have a hunch if the LP pump was diagnosed as bad (Low Press) it did not have an actual fuel pressure test done with a gauge to ensure the (PID) reading was correct.
as the Fuel Pressure reading comes from that sensor.

If it's on the HP Pump Side:
The Fuel Pressure Regulator (Part of the HP Pump) would be my first choice of issue
Fuel Rail Pressure Sensor
Leaking Fuel Injector - Pressure drop on the fuel rail

 

[airline tech]

Test Example: When I was playing with the scan tool
Note: The Pressure Reading comes from the Fuel Pressure Sensor, if this fails the test (note this is an automated) test that can be monitored for 24hrs
An actual gauge test can be tapped in between the HP Fuel Supply Line & HP Pump to compare readings.

After 15-Minutes the spec is greater than 45 PSI

 

[airline tech]

Ok, Not the best snap shots - but at least provides a ref of normal pressure readings
Note: shot 3 for each line only adds the Low Side Fuel Press

Cold Start: From Overnight (Rest)
Door was opened and the LP Pump Primed


KOEO (Key On Eng Off) Readings

Just after engine start (Cooling Fan) and RPMs Higher Speed @ Idle

After Eng Running for 10-Minutes, RPMs and Cooling Fan - Settled Down @ Idle

 

[airline tech]

There are a few tests for a leaking injector.
This is the best one as it will isolate the injector.
It's an automated test and it runs through each injector
Pressurizes the Fuel Rail (Reads Fuel Rail Press) to a specified target
Each Injector is pulsed (On & Off) in a cycle, and it measures the time in (ms) it takes each injector for the Fuel Rail Press to drop to the test value (specified target) (I do not remember) that value off hand without getting into my notes.

Relative Injector Flow Test
Test is done in the Firing Order
The results need to be near equal
Normal Range = 140 +/- 15ms
The arrows provide the Min/Max Range, and the scale will turn red if out of range.

Lower Result (faster time) shows a leaking injector
Higher Result (longer time) shows a clogged injector

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