Runs rough

1997 FORD F-150
150,000 MILES • V8 • 4WD • AUTOMATIC
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TIM SMITH2
  • MEMBER
  • 1 POST
I have taken my truck to two different mechanics and they cannot figure out what's causing the problem. The truck starts up running really rough but after it warms up the problem seems to go away and then the truck runs fine I've changed the ignition wires the spark plugs fuel injector. anybody have any thoughts?
Apr 29, 2021 at 5:48 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,246 POSTS
Hi,

Do you have a live data scan tool or access to one? I have two things I would link you to check. First, what are the short-term fuel trims when this is happening. Second, what does the engine coolant temp sensor (ECT) indicate?

A rich or lean fuel mixture can cause this. High fuel pressure or a vacuum leak can take it one way or the other. Also, the ECT can not be accurate which can cause an improper fuel mixture.

If you don't have a live data scan tool, then I need you to check fuel pressure and for engine vacuum leaks. Here are two links that explain how this is done:

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

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

Let me know if this helps or if you have other question's. Also, let me know if there are any diagnostic trouble codes.

Take care,

Joe

Apr 30, 2021 at 1:50 PM
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