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Truck misfires at 45, 55 and 65 MPH?

Tiny
RUBENGR541
  • MEMBER
  • 2003 FORD F-250
  • 6.0L
  • V8
  • TURBO
  • 4WD
  • AUTOMATIC
  • 220,000 MILES
Truck starts to run rough at 45, 55 and 65 MPH it misfires and starts to sputter and jerk once I get past or under those speeds it runs fine check engine light isn't on just changed oil and all the filters with one Motorcraft filters.
Tuesday, February 20th, 2024 AT 1:27 PM

17 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

If there is a misfire, by design, the check engine light should be flashing when it happens. Since there is no CEL, I have to question other things. Could it be related to a transmission issue in a specific gear? Also, have you tried scanning the can-bus to see if there are any codes related to the issue?

Here is a link that explains how to check all modules for codes:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Let me know.

Joe
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Tuesday, February 20th, 2024 AT 8:23 PM
Tiny
RUBENGR541
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I scanned it and there’s no codes. The transmission shifts fine, and everything works fine on the transmission. I replaced the blue spring upgrade on it I also replaced the fuel filters I upgraded the oil cooler EGR cooler and hpop.
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Tuesday, February 20th, 2024 AT 8:57 PM
Tiny
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Hi,

This is an odd one. Have you checked to make sure the fuel pressure is within spec? Also, do you have access to a live data scan tool? If you do, could you let me know what the short-term fuel trims are at idle and at operating temperature?

Joe
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Wednesday, February 21st, 2024 AT 6:37 PM
Tiny
RUBENGR541
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I have a fuel gauge connected at the fuel regulator and I have 65 PSI.
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Wednesday, February 21st, 2024 AT 9:41 PM
Tiny
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Is that on the regulated side of the regulator? I ask because it is high. I attached the manufacturer's fuel pressure specifications below.

Let me know.

Joe

See pic below.
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Thursday, February 22nd, 2024 AT 7:50 PM
Tiny
RUBENGR541
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I have an adjustable fuel regulator turned it down to 60 PSI the truck still misfires and sputters at 45, 55 and 65 MPH.
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Thursday, February 22nd, 2024 AT 8:50 PM
Tiny
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The operating pressure is 55 PSI max. Are you able to turn it down so that it runs at 50 PSI? Also, is there any change when you lowered it?

Joe
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Friday, February 23rd, 2024 AT 8:04 PM
Tiny
RUBENGR541
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I lowered it to 50 PSI and there’s no changed.
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Friday, February 23rd, 2024 AT 8:34 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Is there any smoke from the exhaust when this happens? Have you inspected the injector pressure regulator valves (IPR)? They can cause an erratic pressure changes.

I attached a few tests below. Take a look through them and let me know if you are comfortable performing them. Note: These diagnostics are based on a technical service bulletin related to a few different symptoms. One symptom is a misfire based on engine RPM speed.

Let me know.

Joe

See pics below.
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Friday, February 23rd, 2024 AT 9:52 PM
Tiny
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The ICP and IPR valve was replaced about 5 months ago.
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Friday, February 23rd, 2024 AT 9:57 PM
Tiny
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At this point, the only thing I would try is driving the vehicle while you have a live data scan tool attached and have a helper watch what happens when you notice the misfire.

I wish I had a better answer.

Let me know.

Joe
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Saturday, February 24th, 2024 AT 7:38 PM
Tiny
RUBENGR541
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I did everything seems to be working right.
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Saturday, February 24th, 2024 AT 9:37 PM
Tiny
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Has the problem been resolved?

Joe
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Sunday, February 25th, 2024 AT 6:30 PM
Tiny
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No it hasn’t.
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Sunday, February 25th, 2024 AT 6:36 PM
Tiny
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Hi,

When you said everything seemed to be working right, I assumed it was resolved. After I sent you the last message, I realized you likely meant while you were testing things appeared right.

Just to review, does it do this every time at the speeds you mentioned?

Joe
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Sunday, February 25th, 2024 AT 6:43 PM
Tiny
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Yes, it does it every time at the speeds I mentioned and smells like unburnt diesel at start up.
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Sunday, February 25th, 2024 AT 6:58 PM
Tiny
JACOBANDNICKOLAS
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Hi,

I feel bad asking so many questions, but not being there makes it a bit more difficult. I hope you understand.

When you checked the fuel pressure, how quickly did it drop off when the system was turned off? The idea that you smell raw fuel when starting may indicate an injector is leaking.

Let me know.

Joe
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Sunday, February 25th, 2024 AT 8:13 PM

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