Truck misfires at 45, 55 and 65 MPH?

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

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.

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

I have a fuel gauge connected at the fuel regulator and i have 65 PSI.

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.

I have an adjustable fuel regulator turned it down to 60 PSI the truck still misfires and sputters at 45,55 and 65 MPH.

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

I lowered it to 50 PSI and there’s no changed.

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.

The ICP and IPR valve was replaced about 5 months ago.

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

I did everything seems to be working right.

Has the problem been resolved?


Joe

No it hasn’t.

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

Yes, it does it every time at the speeds I mentioned and smells like unburnt diesel at start up.

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