engine misfiring ?

hello,

Many things make hesitation and high fuel consumption, as a first step you must read the fault codes by using scan tool, problem like no spark or defected fuel injector in a certain cylinder, low cylinder compression, vacuum leak, rich mixture or leak mixture, defected oxygen sensor.

check our guide how to read fault codes and procedure how to fix miss fire problem.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

https://www.2carpros.com/articles/vibration-noise


https://www.2carpros.com/articles/engine-hesitates

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

https://www.2carpros.com/articles/how-to-test-an-ignition-system

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/how-to-test-engine-compression

Read the fault codes and send to us to help you what's the problem on your engine.

Thank you

The code with an scanner is P0171 but it has several causes. I replaced the Mass Air Flow sensor, the Oxygen sensor, the gas filter and the Idle Air Control valve, but the problem did not decrease. The mechanic told that another cause could be the intake manifold (Or maybe the gasket at the intake). What's your opinion?

The vehicle shakes when it's idle and has high gas consumption when running. I want to know which is the normal spark advance. Does is has to remain constant (fixed) ? or has to varies according to the speed of the truck? Which should the normal reading for spark advance?

The spark advance should be fourteen to twenty degrees at hot idle, but I have never looked at this parameter when troubleshooting a fuel mileage issue because a misfire or cam/crank synchronization codes would be set. I pay attention to the long fuel trim and short fuel trims, along with the fuel system status-closed or open loop (should be closed when warmed up). The fuel trims should be at 0-7 percent, now this is my spec not the factory one, but I have 28 years in Ford dealerships and this is my norm. The PCV elbow is known to collapse and suck a hole in it, also spray the intake to head area while monitoring the o2s11 sensor, if it spikes up then bingo! you've found the leak. These are just a few things to look at that are most common.

hello,

Refer to diagnostic procedure as described (check table below) fault code p0171 related to system too lean, it means too much air entering the system or not enough fuel quantity and pressure. you already changed the fuel pressure, and mass air flow.

Check for vacuum leaks as described the link below.

https://youtu.be/xN5pcM-5bso

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If no leak found check the fuel pressure you must read about 39 PSI (check the table below).

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

If the pump pressure within specification and no vacuum leak check for exhaust leak and the EGR. check the link below.

https://www.2carpros.com/articles/evap-system-code-repair

https://www.2carpros.com/articles/smog-test-inspection-information

https://youtu.be/DqUCbbKdWf4

Hope these helps let us know what happens with you.

Thank you.